Allergen-specific immunoglobulin G4 antibody (IgG4 (when context allows, "allergen-specific IgG4 antibody" is also used))

Allergen-specific immunoglobulin G4 antibody is a subclass of the immunoglobulin G (IgG) family that specifically binds to allergens. It is produced by B cells following repeated or high-dose exposure to an allergen, such as through allergen immunotherapy or chronic environmental exposure[4][6][12]. IgG4 possesses unique structural and functional properties: it is functionally monovalent due to its ability to undergo Fab-arm exchange, which creates bi-specific or functionally monovalent antibodies unable to form large immune complexes or activate complement[2][4][5]. IgG4 antibodies act as blocking antibodies, inhibiting IgE-allergen interactions and downstream degranulation of mast cells and basophils by competitive inhibition and by engaging the inhibitory FcγRIIb on immune cells, contributing to reduced allergic inflammation and clinical tolerance[3][4][6][10]. Serum levels of allergen-specific IgG4 increase during successful allergen immunotherapy, and measurement of these antibodies, or the IgG4/IgE ratio, is used as a biomarker of immunologic tolerance[4][6][12]. Although IgG4 antibodies are generally regarded as anti-inflammatory and associated with tolerance, elevated levels may sometimes be found in specific inflammatory conditions (e.g., IgG4-related disease) and can occasionally reflect ongoing immune activation[7][4]. Experimental monoclonal allergen-specific IgG4 antibodies have shown promise as therapeutics to block immediate allergic reactions, as exemplified by IGNX001 targeting peanut allergens[3][8][10]. IgG4’s role is complex and context-dependent, capable of serving as both protector and, less commonly, participant in pathogenic responses depending on allergen exposure, immune environment, and specific disease context[4][7].

Other names

Allergen-specific IgG4IgG4 blocking antibodyAllergen-specific immunoglobulin G4

Blocks IgE binding to allergen, preventing IgE-mediated mast cell and basophil activation[3][4][10]; Engages inhibitory FcγRIIb on immune cells, leading to downregulation of allergic inflammation[4][6]; Neutralizes allergens directly, reducing free allergen available to trigger reactions[4][6]