Patients suffering from non-IgE-mediated cow's milk protein intolerance cannot be diagnosed based on IgG subclass or IgA responses to milk allergens

Background: Cow's milk is one of the most common causes of food allergy. In two-thirds of patients, adverse symptoms following milk ingestion are caused by IgE-mediated allergic reactions, whereas for one-third, the mechanisms are unknown. Aim of this study was to investigate whether patients suffering from non-IgE-mediated cow's milk protein intolerance can be distinguished from persons without cow's milk protein intolerance based on serological measurement of IgG and IgA specific for purified cow's milk antigens. Methods: We determined IgG 1-4 subclass and IgA antibody levels to purified recombinant αS1-casein, αS2-casein, β-casein, κ-casein, α-lactalbumin, and β-lactoglobulin in four patient groups by ELISA: Patients with IgE-mediated cow's milk allergy (CMA, n = 25), patients with non-IgE-mediated cow's milk protein intolerance (CMPI, n = 19), patients with gastrointestinal symptoms not associated with cow's milk ingestion (GI, n = 15) and control persons without gastrointestinal problems (C, n = 26). Cow's milk-specific IgE levels were determined by ImmunoCAP. Results: Only CMA patients had IgE antibodies to cow's milk. Cow's milk allergic patients mounted the highest IgG 1 and IgG 4 antibody levels to αS1-casein, αS2-casein, β-casein, κ-casein, and α-lactalbumin. No elevated levels of IgG 4, IgA, and complement-binding IgG subclasses (IgG 1, IgG 2, IgG 3) to purified cow's milk allergens were found within the CMPI patients compared to persons without cow's milk protein intolerance (GI and C groups). Conclusion: Cow's milk protein intolerant patients cannot be distinguished from persons without cow's milk protein intolerance on the basis of IgG subclass or IgA reactivity to cow's milk allergens. © 2011 John Wiley & Sons A/S.