Overview
This lecture covers the structure, function, and key features of Immunoglobulin A (IgA), emphasizing its role in mucosal immunity and its unique dimeric form.
Immunoglobulins Overview
- Immunoglobulins (antibodies) are Y-shaped proteins made by B cells that identify and neutralize foreign antigens.
- The variable region (FAB) binds to antigens; the constant region (FC) determines the antibody class.
- Five major classes: IgA, IgE, IgD, IgM, and IgG.
IgA Structure and Forms
- IgA is typically secreted as a dimer, meaning two IgA molecules are joined by a J-chain.
- In blood, IgA can exist as a monomer, but most is secreted as a dimer.
Distribution and Function of IgA
- IgA is primarily found in body secretions: tears, saliva, mucus, and breast milk (especially colostrum).
- Provides immunity at mucosal membranes, including the mouth, GI tract, and airways.
- Secreted IgA neutralizes pathogens, preventing them from attaching to mucosal surfaces.
Production Sites and Clinical Relevance
- Peyer’s patches in the intestines are a major source of IgA.
- IgA lines the GI epithelium, protecting against pathogens, especially parasites like Giardia.
- Selective IgA deficiency can lead to recurrent infections, particularly with Giardia.
Key Terms & Definitions
- Immunoglobulin (antibody) — A protein made by B cells that binds antigens to neutralize them.
- FAB (Fragment Antigen Binding) — The part of the antibody that binds antigens.
- FC (Fragment Crystallizable) — The antibody region that interacts with immune cells and determines class.
- Dimer — Two antibody molecules joined together.
- J-chain — The protein that links two IgA molecules into a dimer.
- Secretions — Body fluids produced by mucous membranes (e.g., saliva, mucus, tears, breast milk).
- Peyer’s patches — Lymphoid tissue in the intestines that produces IgA.
Action Items / Next Steps
- Review the different immunoglobulin classes and their functions for test preparation.
- Watch the dedicated video on selective IgA deficiency for further understanding.
- Recall key associations of IgA with mucosal immunity and protection of infants via breast milk.