Human Immunoglobulin G (IgG)

Human Immunoglobulin G is the predominant antibody class in serum and extracellular fluids, comprising about 75% of circulating immunoglobulins. It consists of two γ heavy chains and two light chains (κ or λ), forming a Y-shaped (H₂L₂) molecule of ~150 kDa. The molecule has a Fab domain for antigen binding and an Fc domain for effector function with immune cells and complement components. There are four subclasses (IgG1, IgG2, IgG3, IgG4), each with distinct biological activities and hinge region flexibility. IgG is crucial for pathogen neutralization, opsonization, activation of phagocytic and cytotoxic cells, and complement activation. Clinically, IgG deficiency is treated with replacement therapy (IVIg), and monoclonal antibodies of the IgG class are used to target cancer, autoimmune disorders, and infections. Elevated or dysfunctional IgG plays roles in hypersensitivity reactions and autoimmune pathology.

Other names

Immunoglobulin GIgG antibodygamma globulin

Replacement of deficient antibodies (passive immunity in immunodeficiencies); Modulation of immune system (blocking antibody-mediated attack, anti-inflammatory effects, regulation of cytokines); Neutralization of pathogenic antigens (via monoclonal antibodies); Inhibition of complement activation and self reactivity; Promotion of apoptosis or immune tolerance via Fc receptor pathways