immunoglobuliinide

Immunoglobuliinide, or antibodies, are glycoprotein molecules produced mainly by plasma cells derived from B lymphocytes. They recognize and help neutralize foreign substances such as pathogens, toxins, and abnormal cells. In circulation and in body fluids they occur as soluble proteins, and on the surface of B cells they function as antigen receptors.

A typical immunoglobulin molecule is a Y-shaped heterotetramer composed of two identical heavy chains and two identical light chains held together by disulfide bonds. The antigen-binding fragment (Fab) is located at the tips of the arms, while the crystallizable fragment (Fc) forms the stem. The variable regions of the heavy and light chains create a unique antigen-binding site, and the constant region of the heavy chain defines the immunoglobulin class.

There are five conventional isotypes in humans: IgA, IgD, IgE, IgG, and IgM. Light chains come in two types, kappa and lambda. Diversity is generated by V(D)J recombination during B-cell development, followed by somatic hypermutation and class switch recombination, which can change the antibody isotype while preserving antigen specificity.

Functions of immunoglobuliinide include neutralization of toxins and pathogens, agglutination of antigens, opsonization to promote phagocytosis, and activation of the complement system (particularly by IgM and certain IgG subclasses). IgG antibodies can also mediate antibody-dependent cellular cytotoxicity, and IgG is transferred across the placenta to provide neonatal protection. IgA is prevalent in mucosal secretions, contributing to local immunity.

Clinically, immunoglobuliinide are measured in serology to assess immune status. Deficiencies or dysregulation can lead to immunodeficiencies or autoimmunity, and therapeutic approaches include intravenous or subcutaneous immunoglobulin (IVIG/SCIG) and monoclonal antibody therapies.