Podcast
Questions and Answers
What is a primary characteristic of innate immunity?
What is a primary characteristic of innate immunity?
- It has a specific response to antigens.
- It is present from birth. (correct)
- It involves memory of past infections.
- It requires prior exposure to pathogens.
Which function is NOT associated with the immune system?
Which function is NOT associated with the immune system?
- Mounting a specific response against non-self antigens.
- Creating new pathogens. (correct)
- Recognition of self from non-self antigens.
- Memory of previously recognized non-self antigens.
What distinguishes adaptive immunity from innate immunity?
What distinguishes adaptive immunity from innate immunity?
- Adaptive immunity does not trigger responses.
- Adaptive immunity is not present at birth. (correct)
- Adaptive immunity has immediate protection.
- Adaptive immunity lacks specificity.
Which type of immunity involves the transfer of antibodies from mother to child?
Which type of immunity involves the transfer of antibodies from mother to child?
How does innate immunity primarily function?
How does innate immunity primarily function?
What is the primary function of epithelial barriers in innate immunity?
What is the primary function of epithelial barriers in innate immunity?
Which cells are primarily responsible for humoral immunity?
Which cells are primarily responsible for humoral immunity?
Which characteristic is true about the memory aspect of the immune response?
Which characteristic is true about the memory aspect of the immune response?
What role does the adaptive immune response play after the innate immune response?
What role does the adaptive immune response play after the innate immune response?
Which component of the immune system is responsible for defense against intracellular microbes?
Which component of the immune system is responsible for defense against intracellular microbes?
Which of the following best describes the nature of adaptive immunity?
Which of the following best describes the nature of adaptive immunity?
What can cause diseases of the immune system?
What can cause diseases of the immune system?
In which organ do T cells primarily develop?
In which organ do T cells primarily develop?
What role do regulatory T lymphocytes play in the immune response?
What role do regulatory T lymphocytes play in the immune response?
Which of the following is NOT a primary lymphoid organ?
Which of the following is NOT a primary lymphoid organ?
What is the primary function of natural killer (NK) cells?
What is the primary function of natural killer (NK) cells?
What is the primary function of B lymphocytes?
What is the primary function of B lymphocytes?
How do Natural Killer (NK) cells recognize abnormal cells?
How do Natural Killer (NK) cells recognize abnormal cells?
Which antibodies are first produced by plasma cells upon activation?
Which antibodies are first produced by plasma cells upon activation?
What markers are commonly used to identify Natural Killer (NK) cells?
What markers are commonly used to identify Natural Killer (NK) cells?
What percentage of human peripheral lymphoid cells do NK cells comprise?
What percentage of human peripheral lymphoid cells do NK cells comprise?
How do inhibitory receptors on NK cells function?
How do inhibitory receptors on NK cells function?
What type of cells do B lymphocytes develop into after stimulation?
What type of cells do B lymphocytes develop into after stimulation?
Which surface molecules do NK cells use to recognize targets?
Which surface molecules do NK cells use to recognize targets?
What is the primary role of opsonins in the immune response?
What is the primary role of opsonins in the immune response?
Which cytokines primarily mediate inflammation and anti-viral defense?
Which cytokines primarily mediate inflammation and anti-viral defense?
Which of the following is NOT a function of macrophages?
Which of the following is NOT a function of macrophages?
Which class of cytokines is primarily responsible for the stimulation of hematopoiesis?
Which class of cytokines is primarily responsible for the stimulation of hematopoiesis?
Which statement about monocytes is true?
Which statement about monocytes is true?
What is the relationship between cytokines and immune cells?
What is the relationship between cytokines and immune cells?
What role does the Major Histocompatibility Complex (MHC) play in the immune system?
What role does the Major Histocompatibility Complex (MHC) play in the immune system?
Which type of cellular communication do cytokines facilitate in the immune system?
Which type of cellular communication do cytokines facilitate in the immune system?
Which of the following statements about MHC class I molecules is correct?
Which of the following statements about MHC class I molecules is correct?
What is the primary function of MHC class II molecules?
What is the primary function of MHC class II molecules?
HLA-B27 is most strongly associated with which of the following conditions?
HLA-B27 is most strongly associated with which of the following conditions?
What distinguishes MHC class II molecules from MHC class I molecules?
What distinguishes MHC class II molecules from MHC class I molecules?
Which of the following is NOT a function associated with MHC molecules?
Which of the following is NOT a function associated with MHC molecules?
The genes encoding MHC molecules are located on which chromosome in humans?
The genes encoding MHC molecules are located on which chromosome in humans?
Which type of MHC molecule is primarily expressed on professional antigen-presenting cells?
Which type of MHC molecule is primarily expressed on professional antigen-presenting cells?
Which of the following is a function of MHC class III molecules?
Which of the following is a function of MHC class III molecules?
Mature B cells constitute 20% to 30% of the circulating peripheral lymphocyte population.
Mature B cells constitute 20% to 30% of the circulating peripheral lymphocyte population.
The primary antibody produced by plasma cells is IgA.
The primary antibody produced by plasma cells is IgA.
Natural Killer (NK) cells are classified as phagocytic lymphocytes.
Natural Killer (NK) cells are classified as phagocytic lymphocytes.
NK cells recognize abnormal cells primarily through a perforin-granzymes system.
NK cells recognize abnormal cells primarily through a perforin-granzymes system.
B cells can function as antigen presenting cells without prior activation.
B cells can function as antigen presenting cells without prior activation.
NK cells bear the markers CD16 and CD56, which are used to identify T lymphocytes.
NK cells bear the markers CD16 and CD56, which are used to identify T lymphocytes.
B-cell receptors (BCR) are composed of IgE and IgD on the surface of B cells.
B-cell receptors (BCR) are composed of IgE and IgD on the surface of B cells.
Natural Killer cells comprise about 10% to 20% of human peripheral lymphoid cells.
Natural Killer cells comprise about 10% to 20% of human peripheral lymphoid cells.
Epithelial barriers serve as mechanical barriers to protect against the entry of microbes.
Epithelial barriers serve as mechanical barriers to protect against the entry of microbes.
Humoral immunity is primarily responsible for defending against intracellular microbes.
Humoral immunity is primarily responsible for defending against intracellular microbes.
CD8+ T cells are also known as helper T cells and play a role in suppressing the immune response.
CD8+ T cells are also known as helper T cells and play a role in suppressing the immune response.
Primary lymphoid organs, such as the thymus and bone marrow, are essential for the maturation of T cells and B cells.
Primary lymphoid organs, such as the thymus and bone marrow, are essential for the maturation of T cells and B cells.
The adaptive immune response provides short-lasting immunity after exposure to an antigen.
The adaptive immune response provides short-lasting immunity after exposure to an antigen.
Natural killer (NK) cells are primarily responsible for the humoral immune response.
Natural killer (NK) cells are primarily responsible for the humoral immune response.
Both B and T lymphocytes have highly specific receptors for a wide variety of substances known as antigens.
Both B and T lymphocytes have highly specific receptors for a wide variety of substances known as antigens.
Regulatory T lymphocytes express CD4 molecules and assist in enhancing the immune response.
Regulatory T lymphocytes express CD4 molecules and assist in enhancing the immune response.
Circulating monocytes make up approximately 10% of peripheral leukocytes.
Circulating monocytes make up approximately 10% of peripheral leukocytes.
Opsonization is the process by which pathogens are directly destroyed by immune cells without any prior coating.
Opsonization is the process by which pathogens are directly destroyed by immune cells without any prior coating.
Cytokines of Adaptive Immunity are primarily secreted by macrophages and dendritic cells.
Cytokines of Adaptive Immunity are primarily secreted by macrophages and dendritic cells.
Major histocompatibility complex (MHC) molecules are membrane-bound proteins encoded by MHC genes.
Major histocompatibility complex (MHC) molecules are membrane-bound proteins encoded by MHC genes.
Cytokines can stimulate hematopoiesis, increasing leukocyte numbers during immune responses.
Cytokines can stimulate hematopoiesis, increasing leukocyte numbers during immune responses.
Acute phase reactants include cytokines like IL-4 and IL-17.
Acute phase reactants include cytokines like IL-4 and IL-17.
Macrophages are the only cells capable of secreting acute phase reactants.
Macrophages are the only cells capable of secreting acute phase reactants.
Innate immunity provides immediate protection but lacks specificity.
Innate immunity provides immediate protection but lacks specificity.
Opsonins are produced exclusively by phagocytic cells.
Opsonins are produced exclusively by phagocytic cells.
The adaptive immune system develops memory cells upon first exposure to an antigen.
The adaptive immune system develops memory cells upon first exposure to an antigen.
Passive immunity can only be acquired through artificial means.
Passive immunity can only be acquired through artificial means.
Antibody formation is a major function of innate immunity.
Antibody formation is a major function of innate immunity.
Memory is a characteristic feature of innate immunity.
Memory is a characteristic feature of innate immunity.
Adaptive immunity can be categorized into active and passive types.
Adaptive immunity can be categorized into active and passive types.
A primary characteristic of innate immunity is its ability to recognize self from non-self antigens.
A primary characteristic of innate immunity is its ability to recognize self from non-self antigens.
HLA class I molecules are expressed on all nucleated cells and platelets except erythrocytes and trophoblasts.
HLA class I molecules are expressed on all nucleated cells and platelets except erythrocytes and trophoblasts.
CD4+ T cells recognize antigens in the context of self-class I molecules.
CD4+ T cells recognize antigens in the context of self-class I molecules.
Cell-mediated reactions are a specific function of the adaptive immune response.
Cell-mediated reactions are a specific function of the adaptive immune response.
HLA-D consists of three sub-regions: HLA-DP, HLA-DQ, and HLA-DR, which are associated with class II MHC molecules.
HLA-D consists of three sub-regions: HLA-DP, HLA-DQ, and HLA-DR, which are associated with class II MHC molecules.
The genes encoding Class III MHC molecules have apparent roles in the immune system.
The genes encoding Class III MHC molecules have apparent roles in the immune system.
The HLA complex is primarily located on the long arm of chromosome 6 in humans.
The HLA complex is primarily located on the long arm of chromosome 6 in humans.
MHC class II molecules interact with CD8+ T lymphocytes during antigen presentation.
MHC class II molecules interact with CD8+ T lymphocytes during antigen presentation.
HLA-B27 is associated with autoimmune diseases such as ankylosing spondylitis.
HLA-B27 is associated with autoimmune diseases such as ankylosing spondylitis.
The major histocompatibility complex (MHC) plays no role in organ/tissue transplantation.
The major histocompatibility complex (MHC) plays no role in organ/tissue transplantation.
What is the role of defensins in innate immunity?
What is the role of defensins in innate immunity?
How does the adaptive immune system enhance the body's defense compared to the innate immune system?
How does the adaptive immune system enhance the body's defense compared to the innate immune system?
Identify the primary function of CD8+ T cells in cellular immunity.
Identify the primary function of CD8+ T cells in cellular immunity.
What distinguishes primary lymphoid organs from secondary lymphoid organs in the immune system?
What distinguishes primary lymphoid organs from secondary lymphoid organs in the immune system?
Explain the role of regulatory T lymphocytes in the immune response.
Explain the role of regulatory T lymphocytes in the immune response.
What is the main characteristic of humoral immunity?
What is the main characteristic of humoral immunity?
Describe the two main components of adaptive immunity.
Describe the two main components of adaptive immunity.
How do secondary lymphoid organs facilitate the generation of adaptive immunity?
How do secondary lymphoid organs facilitate the generation of adaptive immunity?
What is the first antibody produced by plasma cells upon activation?
What is the first antibody produced by plasma cells upon activation?
Explain the role of CD16 in the function of Natural Killer (NK) cells.
Explain the role of CD16 in the function of Natural Killer (NK) cells.
Describe how NK cells differentiate between normal and abnormal cells.
Describe how NK cells differentiate between normal and abnormal cells.
What happens to B cells after they are stimulated by an antigen?
What happens to B cells after they are stimulated by an antigen?
Identify the primary locations where mature B cells are distributed in the body.
Identify the primary locations where mature B cells are distributed in the body.
Outline the method by which NK cells induce apoptosis in target cells lacking MHC molecules.
Outline the method by which NK cells induce apoptosis in target cells lacking MHC molecules.
What distinguishes the B-cell receptor (BCR) components on mature B cells?
What distinguishes the B-cell receptor (BCR) components on mature B cells?
How do Natural Killer cells comprise a certain percentage of the human peripheral lymphoid cell population?
How do Natural Killer cells comprise a certain percentage of the human peripheral lymphoid cell population?
Describe the immediate role of innate immunity in response to pathogens.
Describe the immediate role of innate immunity in response to pathogens.
What are the key characteristics that differentiate innate immunity from adaptive immunity?
What are the key characteristics that differentiate innate immunity from adaptive immunity?
Explain the term 'memory' in the context of adaptive immunity and its absence in innate immunity.
Explain the term 'memory' in the context of adaptive immunity and its absence in innate immunity.
How does innate immunity trigger the adaptive immune response?
How does innate immunity trigger the adaptive immune response?
Discuss the importance of recognizing self from non-self antigens in the immune system.
Discuss the importance of recognizing self from non-self antigens in the immune system.
In the context of immunity, what does the term 'cell-mediated reactions' refer to?
In the context of immunity, what does the term 'cell-mediated reactions' refer to?
Identify and explain the significance of one major dysfunction that can occur in the immune system.
Identify and explain the significance of one major dysfunction that can occur in the immune system.
What role do antibodies play in the immune response and how does their formation occur?
What role do antibodies play in the immune response and how does their formation occur?
What are two key functions of macrophages?
What are two key functions of macrophages?
How does opsonization enhance the immune response?
How does opsonization enhance the immune response?
Identify a major function of cytokines in the immune system.
Identify a major function of cytokines in the immune system.
What cytokines are mainly produced by CD4+ T lymphocytes?
What cytokines are mainly produced by CD4+ T lymphocytes?
What are colony-stimulating factors characterized by in terms of their function?
What are colony-stimulating factors characterized by in terms of their function?
Explain the significance of Major Histocompatibility Complex (MHC) in the immune system.
Explain the significance of Major Histocompatibility Complex (MHC) in the immune system.
What types of cytokines are produced rapidly in response to microbes?
What types of cytokines are produced rapidly in response to microbes?
Differentiate between the roles of opsonins and cytokines in the immune response.
Differentiate between the roles of opsonins and cytokines in the immune response.
What are the primary functions of MHC class I molecules?
What are the primary functions of MHC class I molecules?
How are MHC class II molecules primarily expressed and what is their function?
How are MHC class II molecules primarily expressed and what is their function?
Describe the genes that encode the human major histocompatibility complex and their significance.
Describe the genes that encode the human major histocompatibility complex and their significance.
What is the main distinguishing feature of MHC class III molecules?
What is the main distinguishing feature of MHC class III molecules?
Explain the relationship between HLA and autoimmune diseases.
Explain the relationship between HLA and autoimmune diseases.
Why are MHC molecules critical in organ/tissue transplantation?
Why are MHC molecules critical in organ/tissue transplantation?
What is the role of CD4+ T cells in relation to MHC class II molecules?
What is the role of CD4+ T cells in relation to MHC class II molecules?
Describe the differences in antigen presentation between MHC class I and class II molecules.
Describe the differences in antigen presentation between MHC class I and class II molecules.
Match the components of the immune system with their primary functions:
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What is a critical feature of Type I hypersensitivity reactions?
What is a critical feature of Type I hypersensitivity reactions?
What is a characteristic feature of the late-phase reaction in type I hypersensitivity?
What is a characteristic feature of the late-phase reaction in type I hypersensitivity?
Which type of antigens can trigger hypersensitivity reactions?
Which type of antigens can trigger hypersensitivity reactions?
Which of the following is an example of systemic type I hypersensitivity reaction?
Which of the following is an example of systemic type I hypersensitivity reaction?
What percentage of the population is typically affected by Type I hypersensitivity reactions?
What percentage of the population is typically affected by Type I hypersensitivity reactions?
Which immunoglobulin is primarily involved in the mediation of Type I hypersensitivity reactions?
Which immunoglobulin is primarily involved in the mediation of Type I hypersensitivity reactions?
What mediators are primarily released in the late-phase reaction of type I hypersensitivity?
What mediators are primarily released in the late-phase reaction of type I hypersensitivity?
What role do HLA genes play in hypersensitivity reactions?
What role do HLA genes play in hypersensitivity reactions?
Which type of antibodies is predominantly involved in type II hypersensitivity reactions?
Which type of antibodies is predominantly involved in type II hypersensitivity reactions?
What is a common effect of the antigen-antibody reaction in type II hypersensitivity?
What is a common effect of the antigen-antibody reaction in type II hypersensitivity?
Which of the following best describes the sensitization phase of hypersensitivity reactions?
Which of the following best describes the sensitization phase of hypersensitivity reactions?
Which characteristic distinguishes Type II hypersensitivity reactions from Type I?
Which characteristic distinguishes Type II hypersensitivity reactions from Type I?
What type of hypersensitivity reaction is characterized by smooth muscle spasms and glandular secretions?
What type of hypersensitivity reaction is characterized by smooth muscle spasms and glandular secretions?
What is the main consequence of the interaction between allergens and sensitized mast cells in Type I hypersensitivity?
What is the main consequence of the interaction between allergens and sensitized mast cells in Type I hypersensitivity?
Which of the following cell types is typically infiltrated during a type I hypersensitivity reaction?
Which of the following cell types is typically infiltrated during a type I hypersensitivity reaction?
What role do inflammatory mediators play in the context of a localized type I hypersensitivity reaction like hay fever?
What role do inflammatory mediators play in the context of a localized type I hypersensitivity reaction like hay fever?
What is the role of IL-4 in the sensitization phase of hypersensitivity reactions?
What is the role of IL-4 in the sensitization phase of hypersensitivity reactions?
Which of the following best describes the immediate phase response in a hypersensitivity reaction?
Which of the following best describes the immediate phase response in a hypersensitivity reaction?
Which cell type is primarily responsible for the release of mediators during a re-exposure to the allergen?
Which cell type is primarily responsible for the release of mediators during a re-exposure to the allergen?
What is the effect of cross-linking IgE on the surface of mast cells?
What is the effect of cross-linking IgE on the surface of mast cells?
Which cytokine is primarily responsible for eosinophil activation during the sensitization phase?
Which cytokine is primarily responsible for eosinophil activation during the sensitization phase?
During the sensitization process, what is the role of antigen-presenting cells (APCs)?
During the sensitization process, what is the role of antigen-presenting cells (APCs)?
What is the function of TH2 cells in the allergic response?
What is the function of TH2 cells in the allergic response?
Which of the following components released from mast cells is primarily responsible for increased vascular permeability?
Which of the following components released from mast cells is primarily responsible for increased vascular permeability?
Which mechanism involves antibody-dependent lysis of target cells through complement activation?
Which mechanism involves antibody-dependent lysis of target cells through complement activation?
What type of hypersensitivity reaction is characterized by antibody-mediated destruction of cells?
What type of hypersensitivity reaction is characterized by antibody-mediated destruction of cells?
In which scenario do antibodies cause dysfunction without directly injuring the cell?
In which scenario do antibodies cause dysfunction without directly injuring the cell?
What is the primary role of opsonization in phagocytosis?
What is the primary role of opsonization in phagocytosis?
Which example illustrates a type II hypersensitivity reaction involving blood cells?
Which example illustrates a type II hypersensitivity reaction involving blood cells?
In antibody-dependent cellular cytotoxicity, what is the role of the antibody?
In antibody-dependent cellular cytotoxicity, what is the role of the antibody?
What is a consequence of autoantibodies binding to cell surface receptors in antibody-mediated dysfunction?
What is a consequence of autoantibodies binding to cell surface receptors in antibody-mediated dysfunction?
Which of the following conditions does NOT represent a type II hypersensitivity reaction?
Which of the following conditions does NOT represent a type II hypersensitivity reaction?
What is a crucial requirement for the development of hypersensitivity reactions?
What is a crucial requirement for the development of hypersensitivity reactions?
Which type of hypersensitivity reaction is primarily mediated by IgE antibodies?
Which type of hypersensitivity reaction is primarily mediated by IgE antibodies?
What percentage of the population is estimated to experience Type I hypersensitivity reactions?
What percentage of the population is estimated to experience Type I hypersensitivity reactions?
Which statement correctly describes the nature of antigens involved in hypersensitivity reactions?
Which statement correctly describes the nature of antigens involved in hypersensitivity reactions?
Which feature distinguishes Type IV hypersensitivity from Types I, II, and III?
Which feature distinguishes Type IV hypersensitivity from Types I, II, and III?
Genetic susceptibility to hypersensitivity diseases often involves which type of genes?
Genetic susceptibility to hypersensitivity diseases often involves which type of genes?
Which of the following best describes the timing of a Type I hypersensitivity reaction?
Which of the following best describes the timing of a Type I hypersensitivity reaction?
What role do mast cells play in Type I hypersensitivity reactions?
What role do mast cells play in Type I hypersensitivity reactions?
What is the primary role of TH2 cells once activated by sensitizing antigens?
What is the primary role of TH2 cells once activated by sensitizing antigens?
Which type of antibody is produced as a result of B cell activation by IL-4 from TH2 cells?
Which type of antibody is produced as a result of B cell activation by IL-4 from TH2 cells?
What triggers the immediate phase response upon re-exposure to an allergen?
What triggers the immediate phase response upon re-exposure to an allergen?
Which of the following describes a characteristic of mast cells in allergic reactions?
Which of the following describes a characteristic of mast cells in allergic reactions?
What is the general time frame for the development of the immediate phase response after re-exposure to an allergen?
What is the general time frame for the development of the immediate phase response after re-exposure to an allergen?
What types of allergic reactions can be seen in genetically susceptible individuals?
What types of allergic reactions can be seen in genetically susceptible individuals?
Which cytokine released by TH2 cells primarily activates eosinophils?
Which cytokine released by TH2 cells primarily activates eosinophils?
What is a consequence of mast cell degranulation during a type I hypersensitivity reaction?
What is a consequence of mast cell degranulation during a type I hypersensitivity reaction?
What is the role of IgG and IgM in type II hypersensitivity reactions?
What is the role of IgG and IgM in type II hypersensitivity reactions?
Which mechanism leads to the phagocytosis of cells coated with antibodies?
Which mechanism leads to the phagocytosis of cells coated with antibodies?
In which condition do antibodies act as agonists, stimulating the target cell's activity?
In which condition do antibodies act as agonists, stimulating the target cell's activity?
What type of hypersensitivity reaction is characterized by cell lysis due to antibody binding to cell surface antigens?
What type of hypersensitivity reaction is characterized by cell lysis due to antibody binding to cell surface antigens?
Which mechanism illustrates antibody-dependent cellular cytotoxicity (ADCC)?
Which mechanism illustrates antibody-dependent cellular cytotoxicity (ADCC)?
What is a common cause of hemolytic anemia related to type II hypersensitivity?
What is a common cause of hemolytic anemia related to type II hypersensitivity?
Which of the following correctly describes the consequences of antibody-mediated cellular dysfunction?
Which of the following correctly describes the consequences of antibody-mediated cellular dysfunction?
How do opsonized cells become targets for macrophages?
How do opsonized cells become targets for macrophages?
What is a primary characteristic of the late-phase reaction in a type I hypersensitivity response?
What is a primary characteristic of the late-phase reaction in a type I hypersensitivity response?
Which type of hypersensitivity reaction is characterized by the presence of antibodies targeting specific antigens on cell surfaces?
Which type of hypersensitivity reaction is characterized by the presence of antibodies targeting specific antigens on cell surfaces?
What type of cell is primarily involved in the immediate hypersensitivity reactions such as hay fever and asthma?
What type of cell is primarily involved in the immediate hypersensitivity reactions such as hay fever and asthma?
What clinical condition may result from systemic type I hypersensitivity reactions?
What clinical condition may result from systemic type I hypersensitivity reactions?
Which mediators are typically released during the late-phase reaction of type I hypersensitivity?
Which mediators are typically released during the late-phase reaction of type I hypersensitivity?
In an antibody-mediated type II hypersensitivity reaction, which of the following effects is NOT a consequence of the antigen-antibody reaction?
In an antibody-mediated type II hypersensitivity reaction, which of the following effects is NOT a consequence of the antigen-antibody reaction?
Which cells are primarily involved in the infiltration seen during late-phase type I hypersensitivity reactions?
Which cells are primarily involved in the infiltration seen during late-phase type I hypersensitivity reactions?
Which antibody is most commonly associated with IgG-dependent type II hypersensitivity reactions?
Which antibody is most commonly associated with IgG-dependent type II hypersensitivity reactions?
Study Notes
Immunity: Protection Against Disease
- Immunity: The body's defense mechanism against pathogens.
- Immune System: Consists of cells (leukocytes) & molecules that combat microbes.
- Immune Response: Collaborative reaction of cells & molecules to pathogens.
Functions of the Immune System
- Recognizes "self" from "non-self" antigens (foreign substances).
- Mounts a specific response to non-self antigens.
- Retains memory of previously encountered non-self antigens.
- Produces antibodies (immunoglobulins, Ig).
- Orchestrates cell-mediated reactions.
Types of Immunity
-
Innate Immunity (Natural/Native): First line of defense.
- Present at birth.
- Immediate protection against invaders.
- Lacks specificity; highly effective.
- Triggers adaptive immunity.
- No memory response.
-
Adaptive Immunity: Second Line of defense.
- Acquired over time through exposure.
- Slower to develop, but more powerful.
- Requires prior antigen exposure.
- Highly specific to targets.
- Long-lasting protection (memory).
Components of Innate Immunity
- Epithelial Barriers: Skin, gastrointestinal & respiratory tracts act as physical & chemical barriers (defensins).
- Humoral: Complement system (proteins that help in destruction of pathogens).
- Cellular: Includes:
- Neutrophils
- Macrophages
- Natural Killer (NK) cells.
Components of Adaptive Immunity
-
Humoral Immunity: Protects against extracellular microbes & toxins.
- Mediated by B lymphocytes (bone marrow-derived).
- Produces antibodies (Ig).
-
Cell-mediated (Cellular) Immunity: Defends against intracellular microbes & cancer.
- Mediated by T lymphocytes (thymus-derived).
Major Organs of the Immune System
-
Primary Lymphoid Organs:
- Thymus: Site of T cell development.
- Bone Marrow: Produces all blood cells, including naïve B cells.
-
Secondary Lymphoid Organs: Where adaptive immune responses occur.
- Lymph Nodes
- Spleen
- Mucosal & Cutaneous Lymphoid Tissues
Cells of the Immune System
- Lymphocytes:
- T Lymphocytes:
- CD4+ T cells (Helper T cells): Activate other immune cells.
- Th1 Cells: Promote cell-mediated immunity.
- Th2 Cells: Promote humoral immunity.
- CD8+ T cells (Cytotoxic T cells): Destroy infected cells.
- Regulatory T cells: Suppress immune responses.
- CD4+ T cells (Helper T cells): Activate other immune cells.
- B Lymphocytes:
- Produce antibodies.
- Act as antigen-presenting cells.
- Natural Killer (NK) Cells: Kill infected or cancerous cells without prior sensitization.
- T Lymphocytes:
- Monocytes and Macrophages: Phagocytose pathogens, present antigens, and release inflammatory mediators.
- Mast Cells and Basophils: Release histamine and other inflammatory mediators.
- Neutrophils and Eosinophils: Phagocytose pathogens and release enzymes to kill them.
Soluble Mediators of Immunity
- Opsonins: Coat pathogens to enhance phagocytosis.
- Cytokines: Signaling molecules that regulate immune responses.
- Innate Immunity Cytokines: TNF, IL-1, IL-12, chemokines.
- Adaptive Immunity Cytokines: IL-2, IL-4, IL-5, IL-17, IFN-γ.
- Colony-Stimulating Factors: Stimulate hematopoiesis (blood cell production).
- Complement System Proteins: A cascade of proteins that leads to lysis of pathogens, inflammation, and opsonization.
Major Histocompatibility Complex (MHC)
- Function: Present peptides from pathogens to T cells for recognition.
- MHC Genes: Encode MHC molecules, located on chromosome 6.
- Human Leukocyte Antigen (HLA) System: The human MHC system.
- Class I MHC Molecules: Expressed on all nucleated cells. Present peptides to CD8+ T cells.
- Class II MHC Molecules: Expressed on antigen-presenting cells. Present peptides to CD4+ T cells.
- Class III MHC Molecules: Encode complement proteins, cytokines, and other proteins.
HLA and Disease Association
- Certain HLA alleles are linked to specific diseases:
- Inflammatory Diseases: Ankylosing spondylitis.
- Autoimmune Diseases: Autoimmune endocrinopathies.
- Inherited Metabolic Errors: Various genetic conditions.
Immunity
- Immunity protects the body against diseases.
- The immune system comprises cells and molecules that defend against pathogens.
- The immune response is a coordinated reaction to infectious agents.
Immune System Functions
- Recognizes self from non-self antigens.
- Mounts a specific response to non-self antigens.
- Retains memory of previously encountered non-self antigens.
- Produces antibodies.
- Facilitates cell-mediated reactions.
Types of Immunity
- Innate Immunity: Present at birth and provides immediate initial protection.
- Does not require prior exposure to foreign antigens.
- Lacks specificity but is highly effective.
- Triggers the adaptive immune response.
- Adaptive Immunity: Acquired through exposure to antigens.
- Slower to develop but more powerful than innate immunity.
- Highly specific and provides long-lasting protection (memory).
Innate Immunity Components
- Epithelial barriers act as mechanical barriers and produce antimicrobial molecules (defensins).
- Humoral component: Complement.
- Cellular component: Neutrophils, macrophages, and natural killer (NK) cells.
Adaptive Immunity Components
- Humoral Immunity: Protects against extracellular microbes and toxins.
- Mediated by B lymphocytes and their antibodies (immunoglobulins, Ig).
- Cell-mediated Immunity: Responsible for defense against intracellular microbes and cancers.
- Mediated by T lymphocytes.
Organs of the Immune System
- Primary lymphoid organs:
- Thymus: T cell development.
- Bone marrow: Production of all blood cells, including naïve B cells.
- Secondary lymphoid organs:
- Lymph nodes, spleen, and mucosal/cutaneous lymphoid tissues: Sites of adaptive immune responses.
Immune System Cells
- Lymphocytes:
- T lymphocytes (T cells):
- CD4+ T cells (helper T cells):
- Express CD4 molecule.
- Assist other immune cells (B cells, macrophages) in fighting infection.
- Secrete cytokines that regulate the immune response.
- CD8+ T cells (cytotoxic/killer T cells):
- Express CD8 molecule.
- Directly destroy infected or cancerous cells.
- Regulatory T cells:
- Suppress immune responses to prevent overreaction.
- CD4+ T cells (helper T cells):
- B lymphocytes (B cells):
- Mature in the bone marrow.
- Produce antibodies (IgM, IgG, IgD, IgA, IgE) upon activation by antigen.
- Function as antigen-presenting cells.
- Natural Killer (NK) cells:
- Large granular lymphocytes.
- Kill virus-infected cells and tumor cells without prior sensitization.
- Use ADCC (Antibody-dependent cellular cytotoxicity) and perforin-granzymes system.
- T lymphocytes (T cells):
- Monocytes and Macrophages:
- Immature macrophages in circulation.
- Phagocytose pathogens.
- Secrete cytokines and proteins involved in wound healing.
- Present antigens to T cells.
Soluble Mediators of Immunity
- Opsonins:
- Coat pathogens to enhance phagocytosis.
- Include immunoglobulins and complements.
- Cytokines:
- Short-acting soluble proteins secreted by immune cells.
- Mediate communication between immune cells.
- Classified based on their functions (innate immunity, adaptive immunity, colony-stimulating factors).
- Complement System:
- Group of proteins that activate a cascade of reactions leading to pathogen destruction.
Major Histocompatibility Complex (MHC)
- Membrane-bound proteins encoded by MHC genes.
- Present peptides to T cells.
- Critical for T-cell immunity.
- In humans, MHC genes are located on chromosome 6 and called HLA (human leukocyte antigen) complex.
MHC Molecules
- Class I MHC: Expressed on all nucleated cells and platelets.
- Involved in the immune response to intracellular infections, tumors, and allografts.
- Interact with CD8+ T lymphocytes during antigen presentation.
- Class II MHC: Expressed on antigen-presenting cells (B lymphocytes, macrophages, dendritic cells) and activated T cells.
- Involved in antigen processing and presentation.
- Recognized by CD4+ T lymphocytes (helper cells).
- Class III MHC:
- Encode components of the complement system, cytokines, and other proteins.
HLA and Disease Association
- Certain HLA alleles are associated with specific diseases.
- Inflammatory diseases (e.g., ankylosing spondylitis linked to HLA-B27).
- Autoimmune diseases (e.g., autoimmune endocrinopathies linked to DR locus alleles).
- Inherited errors of metabolism.
Immunity
- Immunity is the body's defense system against infectious agents.
Immune System
- The immune system is a collection of cells and molecules responsible for defending the body.
- Key functions include:
- Recognizing self from non-self antigens.
- Mounting a specific response to non-self antigens.
- Remembering previously recognized non-self antigens.
- Antibody formation.
- Cell-mediated reactions.
Immune System Diseases
- Failure or derangement of the immune system results in diseases of the immune system.
Types of Immunity
- There are two main categories: innate and adaptive.
- Innate immunity is present at birth, providing immediate protection.
- Adaptive immunity is acquired and takes longer to develop.
Innate Immunity
-
Features:
- First line of defense.
- Present at birth.
- Immediate initial protection.
- Does not rely on prior contact with foreign antigens.
- Lacks specificity, but highly effective.
- Triggers adaptive immune response.
- No memory.
-
Components:
- Epithelial barriers: Skin and gastrointestinal/ respiratory tracts act as physical barriers and produce antimicrobial molecules like defensins.
- Humoral: Includes complement.
- Cellular: Consists of neutrophils, macrophages, and natural killer (NK) cells.
Adaptive Immunity
-
Features:
- Acquired in nature.
- Second line of defense.
- More powerful and takes longer to develop than innate immunity.
- Requires prior exposure to antigens.
- Recognizes microbial and non-microbial substances.
- Long-lasting protection (memory).
- Specific.
-
Components:
- Humoral immunity: Mediated by B lymphocytes and their antibodies.
- Cell-mediated (or cellular) immunity: Responsible for defense against intracellular microbes and cancers. Mediated by T lymphocytes.
Organs of the Immune System
-
Primary lymphoid organs: Where immune cells develop.
- Thymus: Development of T cells.
- Bone Marrow: Production of all other blood cells, including naïve B cells.
-
Secondary lymphoid organs: Where adaptive immune responses occur.
- Lymph nodes: Filter lymph and house lymphocytes.
- Spleen: Filters blood and houses lymphocytes.
- Mucosal and cutaneous lymphoid tissues: Immune responses in the lining of the gut and skin.
Immune System Cells
-
Lymphocytes:
- T lymphocytes (T cells):
- CD4+ T cells: Helper T cells that activate other immune cells.
- CD8+ T cells: Cytotoxic (killer) T cells that destroy infected cells.
- Regulatory T cells: Suppress the immune response.
- B lymphocytes (B cells):
- Develop in bone marrow.
- Produce antibodies.
- Function as Antigen Presenting Cells (APCs).
- Natural Killer Cells (NK cells):
- Non-phagocytic lymphocytes.
- Kill virus-infected and tumor cells.
- Recognize abnormal cells via:
- Antibody-dependent cellular cytotoxicity (ADCC).
- Perforin-granzyme system.
- T lymphocytes (T cells):
-
Monocytes and Macrophages:
- Monocytes are immature macrophages.
- Functions:
- Antigen recognition.
- Phagocytosis.
- Secretion of cytokines, collagenase, elastase, fibroblast growth factor, angiogenesis factor, etc.
- Antigen presentation.
-
Mast cells and basophils: Involved in allergic reactions and inflammation.
-
Neutrophils and eosinophils: Phagocytic cells that fight infections.
Soluble Mediators of Immunity
-
Opsonins: Molecules that coat pathogens, enhancing phagocytosis.
-
Cytokines:
- Short-acting soluble proteins that mediate communication between cells.
- Innate immunity cytokines: Produced by macrophages, dendritic cells, and NK cells.
- Adaptive immunity cytokines: Produced by CD4+ T lymphocytes.
- Colony-Stimulating Factors: Stimulate hematopoiesis.
-
Proteins of the complement system: A system of proteins that helps eliminate pathogens.
Major Histocompatibility Complex (MHC)
- MHC genes: Located on chromosome 6 in humans.
- MHC proteins: Membrane-bound proteins that display peptide fragments for recognition by T cells.
- Human MHC: Called HLA (human leukocyte antigen).
Importance of MHC
- Organ/Tissue transplantation: MHC compatibility is crucial for transplant success.
- Autoimmune diseases: Certain HLA alleles are associated with autoimmune diseases.
Classification of MHC Molecules
-
Class I MHC:
- Expressed by all nucleated cells.
- Encoded by HLA-A, HLA-B, and HLA-C genes.
- Involved in immune response against intracellular infections, cancers, and allografts.
- Interact with CD8+ T lymphocytes during antigen presentation.
-
Class II MHC:
- Expressed by professional antigen-presenting cells (APCs) and activated T cells.
- Encoded by HLA-DP, HLA-DQ, and HLA-DR genes.
- Involved in antigen processing and presentation.
- Interact with CD4+ T lymphocytes.
-
Class III MHC:
- Encode components of the complement system, cytokines, and other proteins.
HLA and Disease Association
- Some diseases are associated with specific HLA alleles:
- Inflammatory diseases: Ankylosing spondylitis is strongly associated with HLA-B27.
- Autoimmune diseases: Autoimmune endocrinopathies are associated with DR alleles.
- Inherited errors of metabolism: Specific HLA alleles can be associated with certain metabolic disorders.
Immunity
- Definition: Protection against diseases.
- Immune System: Collection of cells and molecules responsible for defending the body against pathogens.
- Immune Response: Coordinated reaction of cells and molecules to infectious agents.
- Immune System Functions:
- Recognition of self from non-self antigens.
- Mounting specific response to non-self antigens.
- Memory of recognized non-self antigens.
- Antibody formation.
- Cell-mediated reactions.
- Immune System Diseases: Result from failure or derangement of the immune system.
Types of Immunity
- Innate (Natural/Native) Immunity:
- General Features:
- First line of defense.
- Present at birth.
- Provides immediate initial protection.
- Does not depend on prior contact with foreign antigens.
- Lacks specificity, but highly effective.
- Triggers adaptive immune response.
- No memory.
- Major Components:
- Epithelial Barriers: Act as mechanical barriers.
- Humoral: Comprised by complement.
- Cellular: Includes neutrophils, macrophages, and NK cells.
- General Features:
- Adaptive (Specific) Immunity:
- General Features:
- Acquired in nature.
- Second line of defense.
- Takes more time to develop.
- More powerful than innate immunity.
- Prior exposure to antigen is required.
- Recognizes microbial and non-microbial substances.
- Long-lasting protection (memory).
- Specific.
- Two Main Components:
- Humoral Immunity: Protects against extracellular microbes and their toxins. Mediated by B lymphocytes and antibodies.
- Cell-mediated Immunity: Defense against intracellular microbes and cancers. Mediated by T lymphocytes.
- General Features:
Organs of the Immune System
- Primary Lymphoid Organs:
- Thymus: T cell development.
- Bone Marrow: Production of all other blood cells, including naive B cells.
- Secondary Lymphoid Organs:
- Lymph Nodes: Adaptive immune responses.
- Spleen: Adaptive immune responses.
- Mucosal and Cutaneous Lymphoid Tissues: Adaptive immune responses.
Immune System Cells
- Lymphocytes:
- T Lymphocytes:
- CD4+ T Cells: Helper T cells.
- CD8+ T Cells: Cytotoxic/Killer T cells.
- Regulatory T Cells: Suppress the immune response.
- B Lymphocytes:
- Development: Mature in bone marrow.
- Distribution: Peripheral blood, lymph nodes, spleen, and mucosa-associated lymphoid tissues.
- Function: Produce antibodies, antigen presenting cells.
- Natural Killer (NK) Cells:
- Function: Kill virus-infected cells and tumor cells without prior exposure.
- Mechanisms:
- Antibody-dependent cellular cytotoxicity (ADCC): NK cells lyse IgG-coated target cells.
- Perforin-granzymes system: NK cells cause apoptosis of target cells.
- T Lymphocytes:
- Monocytes, Macrophages, and Dendritic Cells:
- Monocytes: Immature macrophages.
- Macrophages: Antigen recognition, phagocytosis, cytokine secretion, antigen presentation.
- Mast Cells and Basophils:
- Neutrophils and Eosinophils:
Soluble Mediators of Immunity
- Opsonins: Enhance phagocytosis by coating pathogens.
- Cytokines:
- Functions: Messenger molecules of the immune system, mediate communication between cells.
- Classification:
- Cytokines of Innate Immunity: Produced rapidly by macrophages, dendritic cells, and NK cells.
- Cytokines of Adaptive Immunity: Produced by CD4+ T cells.
- Colony-Stimulating Factors: Stimulate hematopoiesis.
- Complement System: A group of serum proteins that act in concert to bring about the destruction of foreign cells.
Major Histocompatibility Complex (MHC)
- Definition: Membrane-bound proteins encoded by MHC genes.
- Function: Peptide display molecules for recognition by T lymphocytes.
- Location: Chromosome 6 (short arm).
- Human MHC: Called Human Leukocyte Antigen (HLA) complex.
- Importance:
- Organ/tissue transplantation.
- Disease association, including inflammatory and autoimmune diseases.
MHC Classification
- Class I MHC Molecules:
- Expression: All nucleated cells and platelets.
- Encoding Genes: HLA-A, HLA-B, and HLA-C.
- Functions: Interact with CD8+ T lymphocytes, involved in cytotoxic reactions.
- Class II MHC Molecules:
- Encoding Genes: HLA-DP, HLADQ, and HLA-DR.
- Expression: Professional antigen-presenting cells (B cells, macrophages, dendritic cells).
- Functions: Interact with CD4+ T lymphocytes, involved in helper T cell responses.
- Class III MHC Molecules:
- Encoding Genes: Genes encoding components of the complement system, cytokines and other proteins.
Hypersensitivity Reactions
- A type of immune response causing tissue injury, disease, or even death in a sensitized individual.
- Also known as an exaggerated response to an antigen.
- Key features:
- Priming/Sensitization: Prior exposure to the allergen is required for sensitization to occur.
- Genetic Susceptibility: Predisposition to hypersensitivity may be inherited, especially involving HLA genes.
- Complex Interaction: Genetic predisposition and exposure play a critical role in developing hypersensitivity towards specific allergens.
- Antigen Origin: Allergens can be endogenous or exogenous.
- Exogenous Allergens: Commonly found in dust, pollens, foods, drugs, microbes, chemicals, and blood products.
- Endogenous Allergens: Self antigens.
Classification of Hypersensitivity Reactions
- Type I (Immediate Hypersensitivity): Commonly called allergic or atopic disorders, elicited by allergens from the environment.
- Type II Hypersensitivity (Antibody-Mediated Disorder): Antibodies directed against specific antigens fixed on cell surfaces, causing lysis of target cells.
- Type III Hypersensitivity (Immune Complex-Mediated Disorders): Immune complexes formed between antigens and antibodies deposit in tissues, triggering inflammation.
- Type IV Hypersensitivity (Cell-Mediated or Delayed Type): T cell-mediated immune response, delayed reaction (24-72 hours).
Type I (Immediate) Hypersensitivity Reactions
- Characteristics:
- Affects 10-20% of the population.
- Rapid reaction occurring within 5-10 minutes.
- Mediated by IgE antibody.
- Elevated serum IgE levels in atopic individuals.
- Occurs in genetically susceptible individuals previously sensitized to the antigen (atopic).
- Allergens: Many allergens (e.g., house dust mites, pollens, animal danders, molds) are harmless for most people.
- Examples: Bronchial asthma, hay fever, food allergies.
Mechanisms of Type I Hypersensitivity Reactions
- Initial Exposure to Antigen (Sensitization):
- Exposure: Inhalation, ingestion, or injection of the allergen.
- Presentation: Allergen presented to T cells by antigen-presenting cells (APCs - macrophages).
- TH2 Cell Activation: In genetically susceptible people, allergens activate TH2 cells, which secrete cytokines like IL-4, IL-5, and IL-13.
- IgE Antibody Production: IL-4 from TH2 cells stimulates B cells to produce IgE antibodies.
- IL-5 activates eosinophils.
- IL-13 triggers mucus production by epithelial cells.
- Mast Cell Sensitization by IgE:
- Mast Cells are concentrated near blood vessels, nerves, and subepithelial tissues.
- Mast cells have Fc receptors with high affinity for IgE.
- IgE antibodies attach to mast cells and basophils - this sensitization takes time to develop.
- First exposure to the allergen does not cause a reaction.
- Re-exposure to Antigen:
- Allergen cross-links IgE molecules on the surface of mast cells or basophils, activating degranulation.
- Mediators Release: Mast cells/basophils release mediators like histamine, cytokines, prostaglandins, and leukotrienes, causing immediate allergic symptoms.
- Immediate Phase Response:
- Occurs within 5-30 minutes after exposure, subsides in 60 minutes.
- Pre-formed mediators (histamine, proteases, chemotactic factors) are released.
- Characterized by vasodilation, increased vascular permeability, smooth muscle spasm, and glandular secretions.
- Late-Phase Reaction:
- Develops 2-8 hours after exposure, lasting for several days.
- Release of secondary mediators from mast cells (prostaglandins, leukotrienes, cytokines, platelet-activating factor (PAF)).
- Characterized by tissue infiltration with eosinophils, neutrophils, basophils, monocytes, and TH2 cells.
- Mucosal epithelial cell damage can occur.
Examples of Type I Hypersensitivity
- Localized Type I Hypersensitivity:
- Hay Fever: Acute inflammation of the nasal & conjunctival mucosae with sneezing, hypersecretion, and runny nose - triggered by pollen or food allergens.
- Extrinsic Asthma: Wheezing & acute respiratory distress due to bronchospasm and increased mucus secretion, triggered by house dust or animal dander.
- Systemic Type I Hypersensitivity:
- Anaphylaxis: Hypotension, widespread urticaria, and dyspnea - can be fatal, often triggered by drugs like penicillin in sensitive individuals.
Antibody-Mediated (Type II) Hypersensitivity Reactions
- Definition: Antibodies directed against cell surface antigens cause cell lysis.
- Characteristics:
- Antibodies: Mostly IgG, occasionally IgM.
- Antigens:
- Endogenous Antigens: Self-antigens.
- Exogenous Antigens: Can be adsorbed onto cell surfaces, or modified to alter surface antigens (e.g., drug metabolites).
- Mechanism of Action:
- Complement-Dependent Hypersensitivity:
- Complement activation and lysis of the target cell after opsonization and phagocytosis.
- C3b and IgG/IgM are involved.
- Antibody-Dependent Cellular Cytotoxicity:
- Antibody acts as a bridge between NK cells/macrophages and the target cell.
- Does not involve phagocytosis or complement activation.
- The NK/macrophages release perforin and granzyme to lyse the target cell.
- Antibody-Mediated Cellular Dysfunction:
- Antibody binds to cell surface receptors, disrupting or interfering with their function without causing cell injury or inflammation.
- Complement-Dependent Hypersensitivity:
Mechanisms of Injury in Type II Hypersensitivity Reactions
- Cell Lysis (Antibody-Dependent):
- Antibodies against cell membrane antigens activate complement, leading to cell lysis.
- Examples:
- Transfusion Reaction: ABO or Rh incompatibility leading to lysis of incompatible donor RBCs.
- Hemolytic Anemia:
- Penicillin attaches to RBCs.
- IgG antibodies are produced against penicillin.
- Splenic macrophages phagocytose the antibody-coated RBCs.
- Phagocytosis:
- Erythrocytes or platelets coated with autoantibodies (with or without complement) are phagocytosed by macrophages.
Examples of Type II Hypersensitivity Reactions
- Antibodies to Blood Cells:
- Autoimmune Hemolytic Anemia: Antibodies against red blood cells.
- Transfusion Reactions: Reactions against incompatible blood transfusions.
- Hemolytic Disease of the Newborn (Erythroblastosis Fetalis): Mother produces antibodies against fetal red blood cells, leading to destruction of the infant's red blood cells.
- Idiopathic Thrombocytopenic Purpura (ITP): Antibodies against platelets, causing platelet destruction.
- Drug-Induced Cytotoxic Antibodies: Some drugs can bind to cell surfaces and trigger antibody production, leading to cell destruction.
- Antibodies to Tissue Components:
- Antibodies to thyroid epithelial cells: Can cause hypothyroidism (Hashimoto thyroiditis) or hyperthyroidism (Grave's disease).
Hypersensitivity Reactions
- An exaggerated immune response to an antigen, causing tissue damage, disease, or even death.
- Requires prior sensitization to the allergen.
- Almost anything can cause an immune response.
- Inherited susceptibility genes play a role in developing hypersensitivity.
- Exogenous Antigens: Substances from outside the body, including dust, pollen, food, drugs, microbes, chemicals, and some blood products.
- Endogenous Antigens: Self-antigens from within the body.
Classifications of Hypersensitivity Reactions
- Type I (Immediate): Also known as allergic or atopic disorders.
- Type II (Antibody-Mediated): Involves antibodies directed against antigens fixed on cell surfaces.
- Type III (Immune Complex-Mediated): Caused by the formation of immune complexes.
- Type IV (Cell-Mediated or Delayed): Involves T-cell responses.
Type I (Immediate) Hypersensitivity Reactions
- Characteristics:
- Occurs within minutes after allergen exposure.
- Mediated by IgE antibodies.
- Genetic susceptibility: Occurs in individuals with a genetic predisposition and prior sensitization.
- Common examples: Bronchial asthma, hay fever, food allergies.
Mechanism of Type I Hypersensitivity
-
Initial Exposure (Sensitization):
- Exposure to the allergen through inhalation, ingestion, or injection.
- The allergen is presented to T cells by antigen-presenting cells (APCs), like macrophages.
- The T cell differentiates into a TH2 cell.
- TH2 cells release cytokines, IL-4, IL-5, and IL-13.
- IL-4 stimulates B cells to produce IgE antibodies.
- IL-5 activates eosinophils.
- IL-13 stimulates epithelial cells to produce mucus.
- IgE antibodies attach to Fc receptors on mast cells and basophils.
-
Re-exposure to Antigen:
- Allergen cross-links IgE molecules on mast cells or basophils, triggering degranulation.
- Mast cells and basophils release mediators like histamine, cytokines, prostaglandins, and leukotrienes.
Phases of IgE Triggered Reactions
-
Immediate Phase Response:
- Occurs within 5-30 minutes after allergen exposure.
- Releases preformed mediators like histamine, proteases, and chemotactic factors.
- Characterized by vasodilation, vascular leakage, smooth muscle spasm, and glandular secretions.
-
Late-Phase Reaction:
- Develops 2-8 hours after exposure, lasting several days..
- Releases secondary mediators like prostaglandins, leukotrienes, cytokines, and PAF.
- Characterized by tissue infiltration with eosinophils, neutrophils, basophils, monocytes, and TH2 cells.
- Also shows mucosal epithelial cell damage.
Examples of Type I Hypersensitivity
- Localized Type I: Hay fever and extrinsic asthma.
- Systemic Type I (Anaphylactic Reaction): Characterized by hypotension, widespread urticaria, and dyspnea. Can be life-threatening.
Antibody-Mediated (Type II) Hypersensitivity Reactions
- Definition: Antibodies directed against specific antigens on cell surfaces cause lysis of target cells.
- Characteristics:
- Involves IgG and occasionally IgM antibodies.
- Antigens can be endogenous or exogenous, which may be adsorbed on cell surfaces or extracellular matrix.
- Mechanisms of Injury:
- Complement Dependent: Antibody-mediated activation of complement leading to lysis of target cells; often seen in blood transfusions.
- Phagocytosis (Opsonization): Antibodies coat cells, making them targets for phagocytosis by macrophages.
- Antibody-Dependent Cellular Cytotoxicity (ADCC): Antibodies bridge natural killer cells or macrophages to the target cell, leading to cell destruction without phagocytosis or complement activation.
- Antibody-Mediated Cellular Dysfunction: Antibodies block or dysregulate the function of cell surface receptors.
Examples of Type II Hypersensitivity
- Antibodies to Blood Cells: Autoimmune hemolytic anemia, transfusion reactions, hemolytic disease of the newborn (erythroblastosis fetalis), idiopathic thrombocytopenic purpura (ITP), and drug-induced cytotoxic antibodies.
- Antibodies to Tissue Components: Immune reactions involving thyroid, kidneys, and lungs, for example.
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Explore the fascinating world of immunity and the immune system. This quiz covers the functions, types, and mechanisms that protect the body from diseases. Test your knowledge on both innate and adaptive immunity and how they work together to defend against pathogens.
