IgG3

**Semantic type:** Amino Acid, Peptide, or Protein|Immunologic Factor

**Definition:** 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.

**Synonyms:** - Immunoglobulin G Subclass 3 - Immunoglobulin G3