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What are the primary components of innate immunity?
Which type of immunity is responsible for defense against intracellular microbes?
What is the CD4:CD8 ratio in T-lymphocytes?
Which T-helper cell subset produces IL-4, IL-5, and IL-13?
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What do CD4 molecules bind to?
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What is the main function of phagocytic cells in innate immunity?
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What is the role of the CD3 complex in T-lymphocytes?
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What type of immunity is characterized by its ability to recognize nonmicrobial substances?
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Which cells mediate humoral immunity?
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Which cytokine is synthesized and secreted by TH1 cells?
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What percentage of peripheral blood lymphocytes do natural killer cells (NK cells) make up?
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Which of the following is a receptor used to identify NK cells?
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What is the primary role of natural killer cells?
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Class I MHC molecules are present on which of the following?
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What type of antigens do class II MHC molecules present?
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Which of the following statements about CD8+ T cells is true?
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The genes encoding MHC molecules are clustered on which chromosome segment?
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NK cells secrete which cytokine to aid in immune response?
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What type of maturation do CD4+ T cells undergo with class II MHC?
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Which categories are MHC gene products classified into?
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What is the primary function of CD8+ T cells?
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What is required for complete activation of T cells?
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Which immunoglobulin constitutes 95% of plasma immunoglobulins after B-cell activation?
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Which role is NOT associated with macrophages in the immune response?
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Where are B-lymphocytes primarily found in the spleen?
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Which immunoglobulin is primarily found as a monomer on the surface of B-cells?
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What do dendritic cells and Langerhan's cells have in common?
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What happens to T cells in the absence of the second signal for activation?
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What role do follicular dendritic cells serve in the germinal centers?
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What is the function of CD21 on B cells?
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What characterizes the immediate phase of a Type I hypersensitivity reaction?
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What is a common consequence of a Type II hypersensitivity reaction?
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In which hypersensitivity reaction is cell-mediated immunity primarily involved?
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What type of hypersensitivity is characterized by the deposition of immune complexes in tissues?
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Which of the following is an example of Type II hypersensitivity?
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Which cells are primarily involved in the delayed-type hypersensitivity of Type IV hypersensitivity reactions?
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What mechanism is associated with antibody-dependent cellular cytotoxicity (ADCC)?
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What time frame characterizes the late phase of a Type I hypersensitivity reaction?
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Which of the following conditions is associated with Type III hypersensitivity?
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Which statement regarding Type I hypersensitivity is correct?
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What characterizes the late phase of a Type I hypersensitivity reaction?
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Which of the following is a mechanism of Type II hypersensitivity reactions?
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What type of hypersensitivity reaction is mediated by antigen-activated T lymphocytes?
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Which condition is commonly associated with Type III hypersensitivity reactions?
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Which of the following best describes the role of antibody-mediated cellular dysfunction in Type II hypersensitivity?
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How do antigen-antibody complexes primarily cause damage in Type III hypersensitivity?
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What duration characterizes the immediate phase of a Type I hypersensitivity reaction?
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What is a common example of an autoimmune condition associated with Type II hypersensitivity?
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What main role do T-lymphocytes serve in the adaptive immune response?
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What is the primary function of T-helper-2 (TH2) cells?
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Which of the following describes the CD4+ T cells' interaction with MHC molecules?
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How does somatic rearrangement affect TCR diversity?
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What characterizes innate immunity?
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What is a major characteristic of B lymphocytes in humoral immunity?
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Which statement about T-cell receptors (TCR) is accurate?
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What defines the adaptive immune response's ability to recognize antigens?
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What is the primary identifying marker for natural killer (NK) cells?
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How do NK cells recognize target cells?
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What type of antigens do class I MHC molecules typically present?
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Which of the following molecules do CD4+ T helper cells recognize?
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Which part of the immune system does CD16 belong to?
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Which class of MHC molecules is expressed on all nucleated cells?
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What mechanisms are implicated in hypersensitivity reactions?
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What is one function of the Main Histocompatibility Complex (MHC)?
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What is the primary role of CD8+ T cells?
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Which molecules do B cells express that are critical for their function?
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How do T cells undergo complete activation?
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Which immunoglobulin is mainly found in traces in the serum?
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What is a key characteristic of dendritic cells?
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What happens to T cells that do not receive a second signal during activation?
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Which function is NOT associated with macrophages?
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Where do B-lymphocytes primarily reside in the lymph nodes?
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Which statement accurately describes innate immunity?
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What is the primary function of T-lymphocytes?
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Which T-cell subset predominantly binds to class II MHC molecules?
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Which cytokine is NOT produced by TH1 cells?
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Which cell type is primarily responsible for humoral immunity?
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What type of immunity arises from prior exposure to microbes?
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What role does somatic rearrangement play in T-cell receptors?
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Which of the following describes the CD4:CD8 ratio in T-cells?
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What is the initial time frame for the immediate phase of a Type I hypersensitivity reaction?
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Which mechanism is NOT involved in Type II hypersensitivity reactions?
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What type of immune response is primarily associated with Type IV hypersensitivity?
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Which condition is an example of a Type III hypersensitivity reaction?
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What characterizes the late phase of a Type I hypersensitivity reaction?
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Which of the following describes the mechanism of tissue damage in Type III hypersensitivity?
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What type of antibodies are primarily involved in Type II hypersensitivity reactions?
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In Type IV hypersensitivity, sensitized T cells mainly respond to which type of antigens?
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What is the main identifying marker for natural killer cells?
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Which class of MHC molecules presents endogenous antigens?
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Which statement best describes the activator and inhibitor receptors of NK cells?
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What is the primary function of class II MHC molecules?
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Which cytokine do natural killer cells primarily secrete?
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What primary role does CD8 perform in T cell activation?
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Which of the following genes encode components of the complement system?
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Where are class I MHC molecules commonly expressed?
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What are the primary functions of CD8+ T cells?
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What is the role of B-cells after antigen stimulation?
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What is required for the complete activation of T cells?
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Which statement accurately describes roles of macrophages?
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What molecule does CD40 on B-cells interact with?
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Where are B-lymphocytes primarily located in lymph nodes?
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Which differences exist between dendritic cells and Langerhan's cells?
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What is the consequence for T cells if they do not receive the second signal for activation?
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Study Notes
Immune Response Types
-
Innate Immunity: Pre-existing defenses that recognize microbes and protect against infections.
- Components:
- Epithelial barriers, e.g., skin
- Phagocytic cells: neutrophils, macrophages
- Natural killer (NK) cells
- Complement system proteins
- Components:
-
Adaptive (Acquired) Immunity: Activated by microbes and can recognize non-microbial substances (antigens).
- Types:
- Cell-Mediated Immunity: Targets intracellular microbes; mediated by T lymphocytes (thymus-derived)
- Humoral Immunity: Targets extracellular microbes and their toxins; mediated by B lymphocytes (bone marrow-derived) and secreted antibodies.
- Types:
Immune Cells
-
T Lymphocytes (T Cells): 60-70% of circulating lymphocytes.
-
T Cell Receptor (TCR): Recognizes specific antigens; composed of α and β polypeptide chains
- Variable region: Binds to antigen
- Constant region: Links to CD3 complex
- CD3 Complex: Involves in signal transduction for TCR activation.
- Somatic Rearrangement: TCR gene rearrangements create diversity.
-
CD4 and CD8 Coreceptors:
- CD4: Present in about 60% of T cells; binds to class II MHC molecules on antigen-presenting cells.
- CD8: Present in about 30% of T cells; binds to class I MHC molecules.
-
T Helper (TH) Cells:
- TH1: Secrete IL-2 and IFN-γ; involved in delayed hypersensitivity, macrophage activation.
- TH2: Secrete IL-4, IL-5, and IL-13; aid in antibody production and eosinophil activation.
- CD8+ Cytotoxic T Cells: Kill other cells, primarily in cell-mediated immunity.
-
T Cell Activation: Requires two signals:
- Engagement of TCR by appropriate MHC-antigen complex with CD4 or CD8 coreceptors.
- Interaction of CD28 on T cells with CD80 or CD86 on antigen-presenting cells.
- Absence of the second signal: T cells undergo apoptosis or become unresponsive (anergic), preventing autoimmune reactions.
-
T Cell Receptor (TCR): Recognizes specific antigens; composed of α and β polypeptide chains
-
B Lymphocytes (B Cells): 10-20% of circulating lymphocytes.
- B Cell Receptor (BCR): Monomeric IgM; serves as an antigen receptor on B cells.
- Somatic Rearrangement: Immunoglobulin gene rearrangements result in unique antigen specificity.
- Other B Cell Molecules: CD19, CD20, CD21 (complement receptor, EBV binding), CD40 (interacts with CD154 on activated T cells)
-
Differentiation:
- Plasma Cells: Secrete antibodies (IgG, IgM, IgA, IgE).
-
Macrophages: Role in immune response:
- Antigen presentation to T cells via class II MHC molecules.
- Cytokine production to influence other immune cells (T cells, B cells, endothelial cells, fibroblasts).
- Secretion of toxic metabolites and enzymes to kill tumor cells.
- Effector cells in delayed hypersensitivity reactions.
-
Dendritic Cells and Langerhan's Cells: Dendritic cell processes and high expression of class II MHC molecules.
- Dendritic Cells: Found in lymphoid tissue.
- Langerhan's Cells: Found in the epidermis.
- Efficient Antigen Presentation: Low phagocytic activity.
- Follicular Dendritic Cells: Found in germinal centers; express antibodies on their surface and have Fc receptors.
-
Natural Killer (NK) Cells: 10-15% of peripheral blood lymphocytes; not express TCR or immunoglobulin.
- Larger Than Small Lymphocytes: Contains azurophilic granules (large granular lymphocytes).
- Part of Innate Immunity: Kill tumor and virally infected cells without prior sensitization.
- Identification: CD16 (Fc receptor for IgG-coated cells) and CD56.
-
Receptors:
- Activators: Recognize ill-defined molecules on abnormal cells.
- Inhibitors: Recognize class I MHC on normal cells.
- Secrete IFN-γ:
- Antibody-Dependent Cell Mediated Cytotoxicity (ADCC): NK cells kill antibody-coated cells via CD16.
Major Histocompatibility Complex (MHC)
- Function: Present peptide fragments of foreign proteins to T cells.
- MHC Gene Location: Clustered on chromosome 6 (Human Leukocyte Antigen - HLA).
-
MHC Molecules:
-
Class I:
- Expressed on all nucleated cells and platelets.
- Encoded by HLA-A, HLA-B, and HLA-C loci.
- Present endogenous antigens (e.g., viral proteins) to CD8+ cytotoxic T cells.
-
Class II:
- Encoded by HLA-DP, HLA-DQ, and HLA-DR regions.
- Present exogenous antigens (e.g., extracellular microbes) to CD4+ helper T cells.
- Class III: Encode components of the complement system.
-
Class I:
Hypersensitivity Reactions (Types)
-
Type I (Immediate) Hypersensitivity: Rapid immune reaction within minutes of antigen-antibody binding to mast cells in previously sensitized individuals.
-
Phases:
- Immediate Phase: Vasodilatation and exudation (5-30 minutes, subsiding in 60 minutes).
- Late Phase: Leukocyte influx (2-4 hours, lasting for days)
- Examples: Anaphylaxis, bronchial asthma, allergic rhinitis.
-
Phases:
-
Type II Hypersensitivity: Antibodies against antigens on cell surfaces or extracellular matrix.
-
Mechanisms of Destruction:
- Opsonization and Fc receptor-mediated phagocytosis.
- Antibody-dependent cellular cytotoxicity (ADCC).
- Antibody-mediated cellular dysfunction.
-
Examples:
- Transfusion reactions
- Autoimmune hemolytic anemia
- Drug reactions
- Myasthenia gravis
- Grave's disease
- Glomerulonephritis
- Organ rejection
-
Mechanisms of Destruction:
-
Type III Hypersensitivity: Immune complex (antigen-antibody) deposition in tissues causing inflammation and damage.
-
Examples:
- Systemic lupus erythematosus
- Polyarteritis nodosa
- Poststreptococcal glomerulonephritis
- Serum sickness.
-
Examples:
-
Type IV (Cell-Mediated) Hypersensitivity: Initiated by antigen-activated T lymphocytes.
-
Mechanisms:
- Delayed type hypersensitivity (CD4+ T cells): Defense against intracellular pathogens (e.g., mycobacteria, fungi, parasites).
- Direct cell cytotoxicity (CD8+ T cells): Graft rejection.
-
Examples:
- Contact dermatitis
- Tuberculin reaction
- Transplant rejection
- Tumor immunity.
-
Mechanisms:
The Immune Response
- Innate immunity comprises defenses present before infection. It includes epithelial barriers, phagocytic cells, NK cells, and complement system proteins.
- Adaptive immunity is stimulated by infection and can recognize microbes and nonmicrobial substances (antigens).
- Cell-mediated immunity protects against intracellular microbes and is mediated by T lymphocytes.
- Humoral immunity protects against extracellular microbes and toxins and is mediated by B lymphocytes and antibodies.
Cells of the Immune System
-
T-lymphocytes
- 60-70% of circulating lymphocytes.
- Found in lymph nodes and spleen.
- Contain a T cell receptor (TCR) composed of α and β chains with variable and constant regions.
- Express CD4 or CD8 as coreceptors.
- CD4+ T cells bind to class II MHC molecules and include TH1 (IL-2 and IFN-γ) and TH2 (IL-4, IL-5, and IL-13) subsets.
- CD8+ T cells bind to class I MHC molecules and mainly function as cytotoxic cells.
- T cell activation requires TCR engagement with MHC-antigen complex and CD28 interaction with CD80/CD86.
-
B-lymphocytes
- 10-20% of circulating lymphocytes.
- Found in lymph nodes and spleen.
- Transform into plasma cells secreting antibodies.
- Express a B cell receptor (BCR) composed of monomeric IgM.
- Express CD19, CD20, CD21, and CD40.
-
Macrophages
- Present antigens to T cells via class II MHC molecules.
- Produce cytokines influencing other immune cells.
- Secrete toxic metabolites and enzymes.
- Important effector cells in delayed hypersensitivity.
-
Dendritic and Langerhans' cells
- Have dendritic processes and high class II MHC expression.
- Found in lymphoid tissue (dendritic) and epidermis (Langerhans).
- Efficient antigen presenters with poor phagocytic activity.
- Follicular dendritic cells in germinal centers trap antibodies.
-
Natural killer cells (NK cells)
- 10-15% of peripheral blood lymphocytes.
- Lack TCR and immunoglobulin.
- Larger than lymphocytes and contain azurophilic granules.
- Kill tumor and virally infected cells without prior sensitization.
- Express CD16 and CD56.
- Possess activating receptors and inhibitory receptors that recognize class I MHC.
Major Histocompatibility Complex (MHC)
-
MHC molecules bind peptide fragments of foreign proteins for presentation to T cells.
-
Located on chromosome 6 and classified into class I, class II, and class III.
-
Class I MHC
- Expressed on all nucleated cells and platelets.
- Bind peptides derived from intracellular proteins (e.g., viral antigens).
- Recognized by CD8+ cytotoxic T cells (class I MHC-restricted).
-
Class II MHC
- Encoded by HLA-DP, HLA-DQ, and HLA-DR.
- Present exogenous antigens (e.g., extracellular microbes).
- Recognized by CD4+ helper T cells (class II MHC-restricted).
Hypersensitivity Reactions
-
Type I (immediate) hypersensitivity: Rapid reaction (minutes) triggered by antigen-antibody binding to mast cells.
- Immediate phase (5-30 min): Vasodilatation and exudation due to vasoactive amine release.
- Late phase (2-4 hours): Influx of leukocytes (bronchial asthma, allergic rhinitis).
-
Type II hypersensitivity: Antibody-mediated against cell surface or extracellular matrix antigens.
- Mechanisms: Opsonization and phagocytosis, antibody-dependent cell cytotoxicity (ADCC), antibody-mediated cellular dysfunction.
- Examples: Transfusion reactions, autoimmune hemolytic anemia, drug reactions, myasthenia gravis, Grave's disease, glomerulonephritis, organ rejection.
-
Type III hypersensitivity: Immune complex-mediated.
- Complexes deposit in various organs, primarily blood vessels.
- Examples: Systemic lupus erythematosus, polyarteritis nodosa, poststreptococcal glomerulonephritis, serum sickness.
-
Type IV hypersensitivity (cell-mediated): Initiated by antigen-activated T lymphocytes.
- Delayed type hypersensitivity: Mediated by CD4+ T cells, involved in defense against intracellular pathogens (mycobacteria, fungi, parasites), transplant rejection, tumor immunity.
- Direct cell cytotoxicity: Mediated by CD8+ T cells, mainly encountered in graft rejection.
Immune Response
- Two major types of immune response: innate and adaptive
-
Innate immunity: present at birth, non-specific defense against pathogens
- Components: epithelial barriers, phagocytes (neutrophils and macrophages), natural killer (NK) cells, complement system proteins
-
Adaptive immunity: develops after exposure to pathogens, highly specific
- Two types: cell-mediated and humoral immunity
Cells of the Immune System
-
T-lymphocytes (T cells): key players in cell-mediated immunity, originate in bone marrow and mature in thymus
- T cell receptor (TCR): recognizes specific antigens
- CD4 and CD8: coreceptors on T cells, determine which MHC class they interact with
- CD4+ T cells: helper T cells, promote immune response by secreting cytokines
- CD8+ T cells: cytotoxic T cells, directly kill infected or cancerous cells
-
B-lymphocytes (B cells): key players in humoral immunity, originate in bone marrow
- Antibodies (immunoglobulins): secreted proteins that bind to antigens, neutralizing or eliminating pathogens
- B cell receptor (BCR): recognizes specific antigens
- Plasma cells: mature B cells that secrete antibodies
-
Macrophages: phagocytose foreign material and pathogens, present antigens to T cells
- Produce cytokines: proteins that influence the behavior of other immune cells
- Secrete toxic metabolites and enzymes: for killing tumor cells
-
Dendritic cells: antigen-presenting cells with dendritic processes
- Efficient antigen presentation: activate T cells
- Found in various tissues: lymph nodes, skin (Langerhan's cells)
-
Natural killer (NK) cells: part of innate immunity, kill infected or cancerous cells without prior sensitization
- Don't express TCR or immunoglobulins: use other mechanisms for target recognition
- Secrete IFN-γ: immune-stimulating cytokine
Major Histocompatibility Complex (MHC)
- MHC proteins: expressed on cell surfaces, present antigen fragments to T cells
-
Class I MHC: expressed on all nucleated cells, presents antigens from inside the cell (e.g., viral proteins)
- Recognized by CD8+ T cells
-
Class II MHC: expressed on antigen-presenting cells (macrophages, dendritic cells), presents antigens from outside the cell (e.g., bacterial proteins)
- Recognized by CD4+ T cells
Hypersensitivity Reactions
- Hypersensitivity: exaggerated or inappropriate immune response to an antigen, causing tissue damage
-
Type I (Immediate): mediated by IgE antibodies binding to mast cells, triggering immediate release of histamine and other inflammatory mediators
- Examples: allergies, anaphylaxis
-
Type II (Cytotoxic): mediated by antibodies directed against cell surface antigens, leading to cell lysis or dysfunction
- Examples: transfusion reactions, autoimmune hemolytic anemia
-
Type III (Immune Complex-mediated): mediated by antigen-antibody complexes depositing in tissues, triggering inflammation and tissue damage
- Examples: systemic lupus erythematosus, serum sickness
-
Type IV (Cell-mediated): mediated by T cell activation, leading to delayed tissue damage
- Examples: contact dermatitis, graft rejection, tuberculin skin test
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Description
Explore the fundamental aspects of the immune response, including both innate and adaptive immunity. Understand the key roles of various immune cells such as T lymphocytes and their functions in recognizing specific antigens. This quiz will test your knowledge on immune defenses and cell-mediated processes.