Immunity and Immune System Functions

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Questions and Answers

What defines the primary function of opsonins in the immune system?

Coating pathogens to enhance their phagocytosis. (correct)

Facilitating the repair of tissues after an immune response.

Stimulating the production of antibodies in B cells.

Targeting pathogens for destruction by T lymphocytes.

Which of the following cytokines is primarily involved in the promotion of lymphocyte proliferation and differentiation?

IL-1

TNF

IFN-γ

IL-2 (correct)

What role do macrophages primarily serve in the immune response?

Functioning as antigen-presenting cells. (correct)

Increasing the production of red blood cells.

Secreting only acute phase reactants.

Producing antibodies against specific antigens.

Which of these cytokines is classified as a cytokine of innate immunity?

IL-12 Signup and view all the answers

What is the main function of cytokines classified as Colony-Stimulating Factors?

Stimulating blood cell formation from bone marrow. Signup and view all the answers

Which of the following statements best describes monocytes?

They are immature macrophages circulating in peripheral blood. Signup and view all the answers

Which of the following best describes acute phase reactants produced by macrophages?

Substances that promote healing and tissue regeneration. Signup and view all the answers

How are Major Histocompatibility Complex (MHC) proteins primarily classified?

By their function in antigen presentation to T cells. Signup and view all the answers

What characterizes the innate immune system?

It lacks specificity. Signup and view all the answers

Which function is not a primary role of the immune system?

Regulating metabolic processes. Signup and view all the answers

What feature distinguishes adaptive immunity from innate immunity?

Specificity to particular pathogens. Signup and view all the answers

Which of the following statements about the adaptive immune response is true?

It involves a previous contact with antigens. Signup and view all the answers

Which component is involved in the active adaptive immunity?

Immunization. Signup and view all the answers

What role do epithelial cells play in innate immunity?

They act as mechanical barriers and produce antimicrobial molecules. Signup and view all the answers

What is the primary distinction between natural passive immunity and artificial passive immunity?

Artificial passive immunity involves the transfer of antibodies externally. Signup and view all the answers

What is an accurate description of antibody formation in the immune system?

Is an integral part of the adaptive immune response. Signup and view all the answers

Which of the following best describes the characteristics of adaptive immunity?

Acquired over time with memory formation and specificity. Signup and view all the answers

What component primarily mediates humoral immunity?

B lymphocytes and antibodies. Signup and view all the answers

Which of the following is a characteristic of the innate immune response?

It acts as the body's first line of defense. Signup and view all the answers

Which cell type is responsible for suppressing immune responses?

Regulatory T lymphocytes. Signup and view all the answers

What is the primary function of CD8+ T cells?

To destroy host cells that harbor microbes or tumors. Signup and view all the answers

Which statement about the organs of the immune system is accurate?

Secondary lymphoid organs concentrate antigens and promote adaptive immunity. Signup and view all the answers

Which type of immunity primarily targets intracellular pathogens?

Cell-mediated immunity. Signup and view all the answers

What feature differentiates adaptive immunity from innate immunity?

Ability to remember previous exposures to antigens. Signup and view all the answers

What percentage of circulating peripheral lymphocyte population do mature B cells constitute?

10% to 20% Signup and view all the answers

Which of the following is NOT a primary function of B cells?

Activation of T cells Signup and view all the answers

What are the common markers used to identify natural killer cells?

CD16 and CD56 Signup and view all the answers

Which antibody is initially produced by plasma cells upon stimulation?

IgM Signup and view all the answers

How do natural killer cells primarily recognize abnormal cells?

Through activating and inhibitory receptors Signup and view all the answers

Which type of lymphocyte is characterized as non-phagocytic and has azurophilic granules?

Natural killer cells Signup and view all the answers

What role do inhibitory receptors play in the functioning of natural killer cells?

They prevent destruction of normal host cells. Signup and view all the answers

What is the function of the perforin-granzymes system in natural killer cells?

To induce apoptosis in target cells Signup and view all the answers

What is the primary role of Class I MHC molecules in the immune response?

They interact with CD8+ T lymphocytes during antigen presentation. Signup and view all the answers

Which of the following correctly describes Class II MHC molecules?

They are primarily found on professional antigen presenting cells. Signup and view all the answers

Which chromosome contains the genes for human MHC molecules?

Chromosome 6 Signup and view all the answers

What is the significance of HLA in tissue transplantation?

It is critical for the recognition of transplanted tissues by the immune system. Signup and view all the answers

Which of the following diseases is strongly associated with HLA-B27?

Ankylosing Spondylitis Signup and view all the answers

What role do Class III MHC molecules play in the immune system?

They encode components of the complement system. Signup and view all the answers

Which of the following characteristics applies to MHC Class II molecules?

They are encoded in the HLA-D region. Signup and view all the answers

What is a key function of CD4+ T cells in the immune system?

To function as helper cells in the immune response. Signup and view all the answers

Study Notes

Immunity

Immunity refers to the body's defense against diseases.
The immune system comprises cells and molecules that combat pathogenic microbes.
The immune response is a coordinated reaction to infectious agents.

Key Functions of the Immune System

Distinguishing 'self' from 'non-self' antigens.
Launching a specific response against non-self antigens.
Remembering previously encountered non-self antigens.
Antibody formation.
Cell-mediated reactions.

Types of Immunity

Innate (Natural/Native) Immunity:
- First line of defense.
- Present at birth.
- Immediate initial protection against pathogens.
- Independent of prior antigen exposure.
- Lacks specificity, but highly effective.
- Triggers the adaptive immune response.
- No memory.
Adaptive Immunity:
- Acquired through exposure.
- Second line of defense.
- Takes more time to develop, but is more potent.
- Requires prior antigen exposure.
- Recognizes both microbial and non-microbial substances.
- Offers long-lasting protection with memory.
- Specific.

Components of Innate Immunity

Epithelial Barriers: Skin, gastrointestinal and respiratory tracts act as mechanical barriers. Also produce antimicrobial molecules like defensins.
Humoral: Complement system.
Cellular: Neutrophils, macrophages, and natural killer (NK) cells.

Components of Adaptive Immunity

Humoral Immunity: Protects against extracellular microbes and toxins.
- Mediated by B lymphocytes and secreted antibodies (immunoglobulins).
Cell-mediated (Cellular) Immunity: Defends against intracellular microbes and cancers.
- Mediated by T lymphocytes.
Both B and T cells express highly specific receptors for diverse substances called antigens.

Organs of the Immune System

Primary Lymphoid Organs:
- Thymus: Site of T cell development.
- Bone marrow: Site of production of all other blood cells, including naïve B cells.
Secondary Lymphoid Organs: Sites where adaptive immune responses occur.
- Lymph nodes.
- Spleen.
- Mucosal and cutaneous lymphoid tissues.

Immune System Cells

Lymphocytes:
- T lymphocytes (T cells):
  - Originate in bone marrow, mature in thymus.
  - Involved in cell-mediated immunity.
  - Subsets:
    - CD4+ T cells (Helper T cells): Recognize antigens presented by MHC Class II molecules.
    - CD8+ T cells (Cytotoxic T cells): Recognize antigens presented by MHC Class I molecules and directly kill infected or cancerous cells.
    - Regulatory T cells: Suppress the immune response.
- B lymphocytes (B cells):
  - Originate and mature in bone marrow.
  - Involved in humoral immunity.
  - Produce antibodies.
Monocytes, Macrophages, and Dendritic Cells:
- Phagocytize pathogens.
- Present antigens to T cells.
- Secrete cytokines.
Mast Cells and Basophils:
- Release histamine and other inflammatory mediators.
Neutrophils and Eosinophils:
- Involved in phagocytosis and killing of pathogens.

Antibodies (Immunoglobulins)

Five main classes: IgM, IgG, IgA, IgE, and IgD.
Functions:
- Neutralize pathogens.
- Opsonize pathogens for phagocytosis.
- Activate complement.
Structure:
- Two heavy chains and two light chains.
- Variable region: Recognizes specific antigens.
- Constant region: Determines the isotype of the antibody.

Natural Killer Cells (NK cells)

Non-phagocytic lymphocytes.
Larger than T and B cells, containing azurophillic granules.
Lack markers for T or B cells.
Identified by CD16 and CD56 markers.
Kill virus-infected cells and tumor cells without prior exposure.
Recognize abnormal cells through:
- Antibody-dependent cellular cytotoxicity (ADCC): NK cells bind to IgG-coated target cells through CD16.
- Perforin-granzymes system: NK cells release perforins (create pores in target cell membranes) and granzymes (induce apoptosis).

Monocytes and Macrophages

Monocytes are immature macrophages, circulating in the blood.
Function as:
- Antigen recognition.
- Phagocytosis.
- Secretion of cytokines:
  - Cytokines.
  - Wound Healing proteins (e.g., collagenase, elastase, fibroblast growth factor, angiogenesis factor).
  - Acute phase reactants (e.g., fibronectin, microglobulin, complement components).
- Antigen presentation.

Soluble Mediators of Immunity

Soluble molecules that regulate innate immunity and effector cell behavior.
Opsonins:
- Coats microbes for phagocytosis.
- Examples: Immunoglobulins and complement proteins.
Cytokines:
- Short-acting soluble proteins.
- Secreted by hematopoietic and non-hematopoietic cells.
- Immune system messenger molecules.
- Types:
  - Innate Immunity Cytokines: TNF, IL-1, IL-12, chemokines.
  - Adaptive Immunity Cytokines: IL-2, IL-4, IL-5, IL-17, IFN-.
  - Colony-Stimulating Factors: stimulate hematopoiesis and increase leukocyte numbers.
Proteins of the Complement System:
- Part of the innate immune system.
- A series of proteins that work together to eliminate pathogens.
- Functions:
  - Opsonize pathogens.
  - Attract phagocytes.
  - Form membrane attack complexes (MACs) to lyse pathogens
  - Initiate inflammation.

Major Histocompatibility Complex (MHC)

Membrane-bound proteins encoded by the MHC gene.
Serve as peptide display molecules for recognition by T lymphocytes.
Critical for inducing T-cell immunity.
In humans, MHC genes are located on the short arm of chromosome 6.
Also called the human leukocyte antigen (HLA) complex.

Importance of the MHC

Organ/tissue transplantation: MHC compatibility is crucial for successful transplant outcomes.
Autoimmune diseases: Certain HLA alleles are linked to autoimmune diseases.

Classification of MHC Molecules

MHC Class I Molecules:
- Expressed on all nucleated cells and platelets, except erythrocytes and trophoblasts.
- Encoded by HLA-A, HLA-B, and HLA-C loci.
- Function:
  - Important for responses to intracellular infections, tumors, and allografts.
  - Interact with CD8+ T lymphocytes during antigen presentation for cytotoxic reactions.
MHC Class II Molecules:
- Expressed only on professional antigen-presenting cells (B cells, macrophages, dendritic cells, and activated T cells).
- Encoded by HLA-DP, HLA-DQ, and HLA-DR.
- Function:
  - Involved in antigen processing and presentation.
  - Interact with CD4+ T cells (helper cells) for immune responses.
MHC Class III Molecules:
- Encoded by genes that express complement system components, cytokines, and some proteins with unknown immune functions.

HLA and Disease Association

Certain HLA alleles are associated with specific diseases:
- Inflammatory Diseases: Ankylosing spondylitis is strongly linked to HLA-B27.
- Autoimmune Diseases: Autoimmune endocrinopathies are associated with HLA-DR alleles.
- Inherited Errors of Metabolism: Specific HLA alleles are often linked to metabolic disorders.

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Description

Explore the intricate workings of the immune system with this quiz. Learn about the key functions of immunity, including the distinctions between innate and adaptive immunity. Test your understanding of how the body defends against diseases and the mechanisms involved.