Plasma cells, in nature, produce antibodies closely modeled after the receptors found on their precursor B cells.
Here's a breakdown of how this works:
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Antibody Specificity: Each plasma cell is specialized to produce antibodies that recognize and bind to a specific antigen. This specificity is determined by the B cell receptor (BCR) on the surface of the precursor B cell. When a B cell encounters its corresponding antigen, it gets activated and differentiates into a plasma cell.
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Antibody Production: The plasma cell then becomes a dedicated antibody factory, churning out large quantities of antibodies with the same antigen-binding specificity as the original BCR.
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Antibody Classes (Isotypes): While the antigen-binding region (variable region) remains the same, plasma cells can switch the class (isotype) of antibody they produce. The major antibody isotypes in humans are:
- IgM: Typically the first antibody produced during an immune response. It is very effective at activating complement.
- IgG: The most abundant antibody in serum. It provides long-term immunity and can cross the placenta to protect the fetus.
- IgA: Found in mucosal secretions (e.g., saliva, tears, breast milk). It protects mucosal surfaces from infection.
- IgE: Involved in allergic reactions and defense against parasitic worms.
- IgD: Primarily found on the surface of B cells and its role is not entirely clear.
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Function: Once released into the bloodstream and lymphatic system, these antibodies bind to their target antigen. This binding can neutralize the antigen directly (preventing it from infecting cells), mark the antigen for destruction by other immune cells (opsonization), or trigger the complement system to destroy the antigen.
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Duration of Production: Plasma cells continue to produce antibodies for several days or months, until the infection or threat has been neutralized. Some plasma cells, known as long-lived plasma cells, can persist in the bone marrow and continue to produce antibodies for years, providing long-term immunity.
In essence, plasma cells are crucial effector cells of the humoral immune response, producing and secreting large quantities of antibodies designed to neutralize or eliminate specific antigens. These antibodies are essential for protecting the body against a wide range of pathogens.
