Immunoglobulin G subclass 4 antibody (IgG4)

Immunoglobulin G subclass 4 antibody (IgG4) is one of the four subclasses of immunoglobulin G found in human serum. It is produced by plasma B cells and represents a minor fraction of total serum IgG. Structurally, it consists of two γ heavy chains and two light chains (κ or λ), forming a Y-shaped molecule with antigen-binding sites at each arm. Unique among the subclasses, IgG4 exhibits functional monovalency due to its ability to undergo Fab-arm exchange—where half-molecules swap between antibodies—resulting in bispecific antibodies that can bind two different antigens. This property makes it generally immunologically inert, as it does not efficiently activate complement or trigger immune effector functions through Fcγ receptors. Biologically, IgG4 plays a role in modulating immune responses, often associated with chronic antigen exposure and tolerance rather than acute inflammation. Elevated levels are characteristic of certain autoimmune conditions collectively termed "IgG4-related diseases," which include disorders such as autoimmune pancreatitis and sclerosing cholangitis. Measurement of serum IgG4 serves as a biomarker for these diseases. While therapies affecting B cell activity more broadly can influence overall immunoglobulin production patterns, IgG4 is not considered a direct therapeutic target like a receptor or enzyme. The term "Immunoglobulin G subclass 4 antibody" (abbreviation: IgG4) describes a specific molecular entity.

Other names

IgG4Immunoglobulin G4IgG subclass 4