Allergen-specific immunoglobulin G4 (sIgG4)

Allergen-specific immunoglobulin G4 (sIgG4) is a specialized subclass of antibodies characterized by its unique ability to undergo 'Fab-arm exchange' and its critical role in mediating peripheral immune tolerance [PMID: 28212948]. In allergic individuals, sIgG4 functions primarily as a 'blocking antibody' that competes with allergen-specific IgE for binding to allergens, thereby preventing the cross-linking of high-affinity IgE receptors (FcεRI) on the surface of mast cells and basophils [PMID: 30043187]. This competition effectively suppresses the release of inflammatory mediators like histamine, which drive allergic symptoms. The therapeutic induction of sIgG4 is a central goal of allergen immunotherapy (AIT), where repeated exposure to escalating doses of specific allergens shifts the immune profile from a Th2-mediated allergic response to a tolerant state associated with regulatory T cells (Tregs) and sIgG4 production [PMID: 29114316]. Beyond its competitive binding, sIgG4 may also engage the inhibitory receptor FcγRIIb to further dampen immune cell activation. Consequently, monitoring serum sIgG4 levels and the sIgG4/IgE ratio is a standard practice for assessing the immunological efficacy and long-term success of desensitization treatments for conditions such as allergic rhinitis, asthma, and food or venom allergies [PMID: 21957431].

Other names

sIgG4Allergen-specific IgG4Blocking antibodyAntigen-specific IgG4Immunoglobulin heavy constant gamma 4IGHG4

Induction of allergen-specific IgG4 antibodies that function as blocking antibodies to compete with IgE for allergen binding sites, thereby inhibiting IgE-mediated mast cell and basophil degranulation and contributing to the induction of long-term immune tolerance [PMID: 30043187, PMID: 28212948].