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Indicators
The second most abundant immunoglobulin G (IgG) subclass in the circulation of healthy individuals. The IgG2 core hinge sequence contains 12 amino acids and up to four interchain disulfide bonds. This subtype has low affinity for binding both Fc receptors and complement component C1q. The production of this IgG2 is stimulated by exposure to bacterial capsular polysaccharides and other antigenic glycans.
Indicators
Along with the immunoglobulin G4 subclass (IgG4), the IgG3 subtype makes up a minor part of circulating antibodies in healthy individuals. The core hinge sequence contains approximately four times the number of amino acids as the other subclasses; allotypes of IgG3 can have up to 62 hinge residues and up to four interchain disulfide bonds. The increased hinge size for IgG3 increases the separation between the Fc (constant fragment) tail and Fab (antigen binding fragment) arms of antibodies of this subclass. This enhances the relative flexibility of the molecule, which may modulate antigen-binding capacity and immune complex formation, and may increase the affinity for binding to both Fc receptors and complement component C1q.
Indicators
Along with the immunoglobulin G3 subclass (IgG3), the IgG4 subtype makes up a minor part of circulating antibodies in healthy individuals. The IgG4 core hinge sequence contains 12 amino acids and two interchain disulfide bonds.This subtype has moderate affinity for binding Fc receptors and does not bind complement component C1q. The production of IgG4 can be stimulated following repeated or long-term exposure to antigen. Elevated levels are found in various diseases and infections and can be indicative of an fibroinflammatory syndrome known as IgG4-related disease.
