immunoglobuliini

Immunoglobulin, or antibody, is a glycoprotein produced by plasma cells that mediates the humoral component of the adaptive immune response. Immunoglobulins circulate in blood and lymph and bind specifically to antigens, neutralizing pathogens or marking them for attack by other immune cells.

Each molecule has two identical heavy chains and two identical light chains, forming a Y-shaped structure. The variable regions at the tips determine antigen specificity (Fab), while the constant Fc region mediates effector functions via Fc receptors and the complement system.

There are five main human isotypes: IgG, IgA, IgM, IgD, and IgE. IgM is produced early and often forms a pentamer; IgG is the most abundant serum antibody; IgA is prominent in mucosal secretions; IgE participates in allergy and defense against parasites; IgD’s role is less defined. Isotypes can undergo class switch recombination to change effector function without altering antigen specificity.

Antibody diversity arises through V(D)J recombination; class switch recombination changes heavy-chain isotype; somatic hypermutation increases affinity.

Functions include neutralization of toxins and microbes, opsonization to enhance phagocytosis, activation of the classical complement pathway, and antibody-dependent cellular cytotoxicity.

Clinically, immunoglobulin levels are measured to diagnose immunodeficiencies and autoimmune diseases. Therapies include intravenous immunoglobulin (IVIG) for replacement and immunomodulation, and monoclonal antibodies used in a wide range of treatments.