immunoglobin antibodies Flashcards
(17 cards)
Q: Describe the general structure of an antibody. What are the roles of the Fab and Fc regions?
A: An antibody is Y-shaped with two heavy chains and two light chains. The Fab region binds antigens, while the Fc region mediates effector functions like complement activation and binding to Fc receptors on immune cells.
Q: What is the significance of the variable and constant regions in an antibody?
A: The variable region (VH and VL) determines antigen specificity by binding antigens. The constant region (CH and CL) defines the antibody isotype and mediates interactions with immune cells and complements the immune response.
Q: How are the different classes of immunoglobulins structurally different?
A: Each class has distinct heavy chains (e.g., IgG - γ, IgA - α, IgM - μ, IgE - ε, IgD - δ). IgA can form dimers, IgM forms pentamers, and IgG, IgE, and IgD are monomers. Their structures correspond to specific functions.
Q: Which immunoglobulin isotypes can cross the placenta, and why is this important?
A: IgG is the only isotype that can cross the placenta. It provides passive immunity to the fetus, protecting against infections during early life.
Q: Why is IgG considered the most versatile antibody class?
A: IgG is abundant in blood and extracellular fluid, crosses the placenta, activates complement, and participates in opsonization and neutralization, making it critical in both innate and adaptive immunity.
Q: What structural feature allows IgA to function effectively at mucosal surfaces?
A: Secretory IgA is a dimer linked by a J chain and protected by a secretory component, which shields it from enzymatic degradation, enabling effective mucosal immunity.
Q: Discuss the role of secretory IgA in immune defense within the gastrointestinal and respiratory tracts.
A: Secretory IgA binds pathogens and toxins at mucosal surfaces, preventing them from adhering to epithelial cells and neutralizing them before they can cause infection.
Q: Why is IgM more effective in forming antigen-antibody complexes compared to IgG?
A: IgM is a pentamer, providing 10 antigen-binding sites, allowing it to form larger complexes and activate complement more efficiently, especially in the early immune response.
Q: How does IgE binding to mast cells and basophils contribute to allergic reactions?
A: IgE binds to FcεRI receptors on mast cells and basophils. Upon allergen exposure, cross-linking of IgE triggers the release of histamine and other mediators, causing allergic symptoms.
Q: What is the primary role of IgD in the immune system?
A: IgD is mainly found on naive B cells, where it acts as a B cell receptor (BCR). It helps activate B cells during the initial stages of the immune response.
Q: Why is measuring IgE levels clinically relevant in diagnosing allergies?
A: Elevated IgE levels are indicative of allergic diseases like asthma, hay fever, or food allergies. IgE mediates hypersensitivity reactions by triggering mast cell degranulation.
Q: Why do newborns have temporary passive immunity after birth?
A: Newborns receive IgG from their mother via the placenta. This protects them against infections temporarily until their own immune system matures and maternal IgG declines.
IgG
general function
where in the body its found
structure
A: IgG provides long-term immunity, neutralizes pathogens, opsonizes antigens for phagocytosis, activates the classical complement pathway, and crosses the placenta to protect the fetus.
A: Found in the bloodstream, extracellular fluid, and tissues. It also crosses the placenta into the fetal circulation.
A: IgG is a monomer with two heavy chains (γ) and two light chains, forming a Y-shaped structure with one antigen-binding site per arm.
IgM
general function
where in the body its found
structure
A: IgM is the first antibody produced in a primary immune response, excellent at forming antigen-antibody complexes, and strongly activates the classical complement pathway.
A: Found in the blood and lymphatic fluid; rarely found in tissues due to its large size.
A: IgM is a pentamer, consisting of five antibody units linked by a J chain, with 10 antigen-binding sites, making it very effective in agglutination and complement activation.
IgE
general function
where in the body its found
structure
A: IgE is involved in allergic reactions and defends against parasites by binding to mast cells and basophils, triggering histamine release.
A: Found in low concentrations in the blood but binds to mast cells and basophils in tissues like the skin, lungs, and mucosal surfaces.
A: IgE is a monomer, similar to IgG, with two heavy chains (ε) and two light chains. Its Fc region binds strongly to FcεRI receptors on mast cells and basophils.
IgA
general function
where in the body its found
structure
A: IgA protects mucosal surfaces by neutralizing pathogens and preventing their adhesion to epithelial cells. It also contributes to immune exclusion in the gut and respiratory tracts.
A: Found in mucosal secretions (e.g., saliva, tears, breast milk, and respiratory/gastrointestinal secretions). Some IgA circulates in the blood.
A: IgA is typically a dimer linked by a J chain and has a secretory component in mucosal secretions. It can also exist as a monomer in the bloodstream.
IgD
general function
where in the body its found
structure
A: IgD acts as a receptor on naive B cells, playing a role in B cell activation and signaling during the early immune response.
A: Primarily found on the surface of immature and naive B cells; very low concentrations are present in the blood.
A: IgD is a monomer with two heavy chains (δ) and two light chains, similar to IgG, but with a unique hinge region that contributes to its flexibility.
