Antibody classes are essential players in our immune system, each with unique roles in defending against pathogens. Understanding these classes—IgG, IgM, IgA, IgE, and IgD—helps us grasp how our body responds to infections and maintains health.
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IgG
- The most abundant antibody in serum, constituting about 75-80% of total immunoglobulins.
- Provides the majority of antibody-based immunity against invading pathogens.
- Capable of crossing the placenta, providing passive immunity to the fetus.
- Has four subclasses (IgG1, IgG2, IgG3, IgG4) that vary in function and ability to activate complement.
- Plays a critical role in opsonization, enhancing phagocytosis of pathogens.
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IgM
- The first antibody produced in response to an infection, primarily found in the bloodstream.
- Exists as a pentamer, allowing it to effectively bind multiple antigens simultaneously.
- Strongly activates the complement system, leading to enhanced pathogen clearance.
- Serves as a B cell receptor (BCR) on immature B cells, initiating the adaptive immune response.
- Provides early defense before IgG levels rise during an immune response.
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IgA
- Predominantly found in mucosal areas, such as the gut, respiratory tract, and saliva, as well as in breast milk.
- Exists mainly as a dimer (two IgA molecules linked), which is effective in neutralizing pathogens at mucosal surfaces.
- Plays a crucial role in mucosal immunity, protecting against infections in epithelial tissues.
- Provides passive immunity to infants through breast milk, aiding in their early defense against pathogens.
- Involved in immune exclusion, preventing pathogen adherence and invasion.
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IgE
- Involved in allergic reactions and responses to parasitic infections.
- Binds to allergens and triggers histamine release from mast cells and basophils, leading to inflammation.
- Present in very low concentrations in serum but plays a significant role in hypersensitivity reactions.
- Provides defense against helminthic (worm) infections by promoting eosinophil activation.
- Its role in allergy makes it a target for therapeutic interventions in allergic diseases.
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IgD
- Primarily found on the surface of B cells as a receptor, playing a role in B cell activation and differentiation.
- Present in low concentrations in serum, with a less well-defined function compared to other antibody classes.
- May play a role in respiratory immune defense, although its exact function remains less understood.
- Involved in the initiation of immune responses, particularly in the early stages of B cell activation.
- Its presence on B cells suggests a role in the regulation of B cell maturation and function.