Allergen-specific Immunoglobulin G4 (sIgG4) (sIgG4)

Allergen-specific Immunoglobulin G4 (sIgG4) antibodies are a specialized subclass of IgG that play a pivotal role in the induction of immune tolerance to allergens [NIH, 2021; NIH, 2016]. They are primarily produced in response to chronic allergen exposure or allergen immunotherapy (AIT), where they act as "blocking antibodies" by competing with IgE for allergen binding [Frontiers in Immunology, 2021; NIH, 2025]. This competition prevents the cross-linking of high-affinity IgE receptors (FcεRI) on mast cells and basophils, thereby inhibiting the release of inflammatory mediators such as histamine [NIH, 2016; MDPI, 2021]. Furthermore, sIgG4 can bind to the inhibitory receptor FcγRIIb, which provides a negative signal to suppress allergic inflammation and IgE-facilitated antigen presentation [NIH, 2016; NIH, 2025]. A unique structural feature of IgG4 is its ability to undergo "Fab-arm exchange," resulting in bispecific, functionally monovalent antibodies that do not form large, pro-inflammatory immune complexes [Frontiers in Immunology, 2021; NIH, 2025]. While sIgG4 is generally considered protective in the context of allergy, its overproduction is a hallmark of IgG4-related disease, a systemic fibro-inflammatory condition, and it has been implicated in the pathogenesis of eosinophilic esophagitis and immune evasion in certain cancers [NIH, 2025; Frontiers in Immunology, 2021].

Other names

Blocking antibodiesAntigen-specific IgG4Polyclonal IgG4Immunoglobulin G4

Induction of allergen-specific IgG4 antibodies that compete with IgE for allergen binding and activate the inhibitory receptor FcγRIIb to suppress effector cell activation [NIH, 2016; Frontiers in Immunology, 2021].