Cow's milk allergy: A complex disorder

Adverse reactions to dairy products are predominantly caused either by intolerance to lactose or by allergic reactions to cow's milk proteins. These are distinct disorders that have separate mechanisms of action and require different methods for diagnosis and strategies for avoidance. Cow's milk allergy (CMA) affects approximately 1-3% of infants and 0.1-0.5% of adults, with symptoms ranging from mild irritations to life-threatening anaphylaxis. Fortunately, most infants with CMA spontaneously recover during early childhood. For infants and adults with active CMA, avoidance of milk proteins remains the only effective management strategy. Hypoallergenic cow's milk formulas, in which the milk proteins are extensively hydrolysed, are available for allergic infants. However, there remains a dearth of alternative dairy products suitable for adults with CMA. Attaining a better understanding of the immunological mechanisms of CMA is crucial to developing strategies to prevent allergic sensitization, treatments to induce immune tolerance, improved diagnostics and hypoallergenic products. To date, much has been learned about the complexity of CMA, including the diversity of allergenic epitopes within various milk proteins and the heterogeneity of allergic responses among individuals. At a population level, the dominant immunological mechanisms driving CMA appear to change with age. While the antibody class IgE often mediates reactions in infants, CMA in adults is predominately non-IgE-mediated and, the precise immunological mechanisms remain poorly understood. We have been examining differences between the immune responses of milktolerant and milk-allergic adults in order to better understand non-IgE-mediated CMA. Preliminary indications are that serum titres of milk protein-specific antibodies IgA1,2, IgE and IgG1-4 are not related to allergy symptoms, and that allergic adults may have increased T-helper cell Type 1 (Th1) reactivity to milk proteins. We are using these findings to develop new cell-based assays to measure the allergenic potency of modified milk proteins.