immunoglobulinsuperfamiljen

Immunoglobulins, or antibodies, are glycoprotein molecules produced predominantly by plasma cells derived from B lymphocytes. They are key effectors of the adaptive immune response, recognizing specific antigens and mediating their neutralization and clearance.

Each immunoglobulin molecule is Y-shaped, with two identical heavy chains and two identical light chains held together by disulfide bonds. The variable domains at the tips form the antigen-binding site, while the constant domains determine the antibody class and effector functions. There are five main classes in humans: IgG, IgA, IgM, IgD, and IgE. IgG is the most abundant in serum and can cross the placenta. IgA predominates in mucosal areas and secretions. IgM is produced early in responses and exists mainly as a pentamer. IgD serves largely as a B cell receptor, and IgE is involved in responses to parasites and allergic reactions.

Diversity is generated by VDJ recombination, junctional diversity, and somatic hypermutation; B cells can switch isotypes through class switch recombination, altering effector function without changing antigen specificity.

Functions include antigen binding, neutralization of pathogens and toxins, opsonization to promote phagocytosis, activation of the complement system by the classical pathway, and engagement of Fc receptors to mediate cytotoxicity and inflammatory responses. Secretory IgA provides mucosal protection, and IgG is the primary isotype in systemic immunity.

Clinical aspects: Serum immunoglobulin levels are measured to diagnose immunodeficiencies or monitor therapy. Primary and secondary immunodeficiencies may involve reduced Ig levels. Immunoglobulin replacement therapy using intravenous or subcutaneous immunoglobulin products supports deficient individuals. Therapeutic monoclonal antibodies are engineered immunoglobulins used to treat a range of diseases.