ImmunoglobulinSubklassen

Immunoglobulin subclasses, also known as isotypes, represent distinct classes of antibodies that differ in their heavy chains. In humans, there are five main immunoglobulin subclasses: IgG, IgA, IgM, IgE, and IgD. Each subclass has a unique structure and is primarily produced in response to specific types of antigens and plays a specialized role in the immune response.

IgG is the most abundant antibody in serum and is crucial for neutralizing toxins, opsonizing pathogens for phagocytosis, and mediating antibody-dependent cell-mediated cytotoxicity (ADCC). It is divided into four subclasses: IgG1, IgG2, IgG3, and IgG4, each with slightly different effector functions.

IgA is the predominant antibody found in mucosal secretions, such as saliva, tears, and breast milk, as well as in the bloodstream. It plays a vital role in mucosal immunity by preventing pathogens from adhering to and invading epithelial surfaces. IgA also exists in two subclasses, IgA1 and IgA2.

IgM is the first antibody produced during a primary immune response and is a potent activator of the complement system. It exists as a monomer in serum and as a pentamer on the surface of B cells, where it acts as a B cell receptor.

IgE is present in very low concentrations in serum but is important for defense against parasitic infections and is also involved in allergic reactions. It binds to mast cells and basophils, triggering the release of histamine and other inflammatory mediators upon antigen binding.

IgD is found on the surface of naive B lymphocytes and is thought to play a role in B cell activation and differentiation, though its precise function is still being investigated. The distinct properties of each immunoglobulin subclass allow the immune system to mount a diverse and effective defense against a wide range of threats.