Cow's milk-specific immunoglobulin G4 (Cow's milk-specific IgG4)

Cow's milk-specific immunoglobulin G4 (IgG4) is a specialized subclass of antibodies that recognize and bind to proteins found in cow's milk, such as casein, alpha-lactalbumin, and beta-lactoglobulin. In the context of food allergy, it is primarily recognized as a "blocking antibody" that promotes immune tolerance by competing with IgE for allergen binding and signaling through the inhibitory receptor FcγRIIb. This interaction prevents the activation of mast cells and basophils, which would otherwise trigger an allergic response. Elevated levels of milk-specific IgG4 are frequently used as a biomarker for the successful outcome of oral immunotherapy or the natural resolution of milk allergy in children. However, recent clinical evidence has also linked high titers of these antibodies to the local inflammatory response in Eosinophilic Esophagitis (EoE), indicating a complex role in different disease states. Structurally, IgG4 is unique due to its ability to undergo Fab-arm exchange, which results in functional monovalency and a reduced capacity to form large immune complexes or activate the complement system.

Other names

Milk-specific IgG4Anti-cow's milk IgG4sIgG4 to cow's milk proteinsCasein-specific IgG4Beta-lactoglobulin-specific IgG4Alpha-lactalbumin-specific IgG4

Cow's milk-specific IgG4 acts as a blocking antibody by competing with allergen-specific IgE for binding to milk proteins, thereby preventing IgE-mediated cross-linking on effector cells. It also binds to the inhibitory receptor FcγRIIb on mast cells and basophils, which actively suppresses the signaling pathways required for degranulation and the release of inflammatory mediators.