IgGvastaaineet

IgGvastaaineet, or IgG antibodies, are the most abundant class of antibodies in human serum and extracellular fluid, forming a central component of the humoral immune response. They are produced by plasma cells derived from B lymphocytes after exposure to antigens and are crucial for long-term protection against pathogens.

IgG molecules are Y-shaped tetramers composed of two identical heavy gamma chains and two light chains. In humans there are four IgG subclasses—IgG1, IgG2, IgG3 and IgG4—each with distinct hinge regions and Fc regions that influence interaction with immune effector mechanisms and antigen specificity.

IgG mediates protection through multiple mechanisms: neutralization of toxins and viruses, opsonization to promote phagocytosis, activation of the classical complement pathway (notably by IgG1 and IgG3), and antibody-dependent cellular cytotoxicity via Fc receptors on natural killer cells and other effector cells. IgG is also capable of crossing the placenta through the neonatal Fc receptor (FcRn), providing passive immunity to the fetus and newborn.

The presence and level of IgG rise during a secondary immune response and can indicate prior infection or successful vaccination when measuring specific pathogen-directed IgG titers. Clinically, total IgG and IgG subclass levels are assessed to diagnose humoral immunodeficiencies or dysgammaglobulinemias, and abnormal patterns may reflect autoimmune disease or chronic infection. Subclasses contribute differently: IgG1 and IgG3 are potent in neutralization and Fc-mediated functions, IgG2 responds mainly to polysaccharide antigens, and IgG4 is associated with tolerance in certain contexts.