Immunoglobulin G4 (Allergen-specific) (sIgG4)

Allergen-specific Immunoglobulin G4 (sIgG4) is a unique subclass of IgG that plays a pivotal role in the development of immunological tolerance toward environmental and food allergens. Unlike other IgG subclasses, IgG4 can undergo 'Fab-arm exchange,' resulting in functionally monovalent antibodies that are unable to form large immune complexes or trigger classical complement activation (PMID: 17569858, 21256345). In the context of allergy, sIgG4 serves as a 'blocking antibody' by competing with IgE for allergen binding, thereby inhibiting the activation and degranulation of mast cells and basophils (PMID: 19133944, 25210151). The induction of sIgG4 is a hallmark of successful Allergen Immunotherapy (AIT), where repeated exposure to increasing doses of an allergen shifts the immune response from a Th2-mediated allergic profile to a regulatory T cell (Treg) profile that favors sIgG4 production (PMID: 29505459, 31102146). While sIgG4 itself is not a therapeutic target in the traditional sense of a receptor or enzyme being inhibited, it is the primary effector molecule and clinical biomarker targeted for induction by AIT products. Monitoring sIgG4 levels and the sIgG4/IgE ratio is frequently used to assess the efficacy of desensitization treatments and the achievement of long-term clinical tolerance (PMID: 30206198).

Other names

Allergen-specific IgG4Antigen-specific IgG4Blocking antibodyIgG4 subclass antibodySpecific immunoglobulin G4

Drugs (Allergen Immunotherapy) induce the production of sIgG4, which acts as a 'blocking antibody' by competitively binding to allergen epitopes, thereby preventing allergen-IgE cross-linking on the surface of mast cells and basophils.