Comparing the sensitizing capacity of raw and processed cow's milk in a murine sensitization model for food allergy

Background: Epidemiological studies show that the consumption of raw milk early in life is protective against the development of allergies later in life. The effect was found to be limited to raw milk consumption and was not observed when this milk was boiled or when pasteurized and homogenized shop milk was consumed. So milk processing seems to abolish the allergy protective effects of raw milk. The components and mechanisms involved are however still unknown. In this study the sensitizing capacity of raw and processed cow's milk was compared in a murine sensitization model for food allergy. Method: C3H/HeOuJ mice were sensitized orally once a week for 5 consecutive weeks with raw milk, heated raw milk (10 min 80°C), shop milk (pasteurized and homogenized), an 80:20 mixture of casein/whey protein (equivalent to the amount in milk; sensitized control) or PBS (non-sensitized control) using cholera toxin as adjuvant. One week after the last sensitization mice were challenged both intradermally and orally with casein/whey. Clinical parameters, such as the acute allergic skin response, anaphylactic shock symptoms and changes in body temperature were assessed upon intradermal challenge and serum specific antibodies and mast cell degranulation were measured upon oral challenge. Activated Th2-, Th1- and regulatory T-cell populations were quantified in spleen using flow cytometry and ex vivo cytokine production was measured after restimulation with casein/whey. Results: Mice sensitized with raw milk did not show any clinical symptoms upon challenge and did hardly produce specific IgE antibodies. Sensitization with the processed milk types on the contrary increased the acute allergic skin response and anaphylactic shock symptoms and caused a drop in body temperature. IgE levels were also significantly increased in these mice. No differences were observed in mucosal mast cell degranulation between groups and also T-cell populations did not differ. The production of Th2 cytokines IL-5 and IL-13 was however significantly reduced in the raw milk group compared to the processed milk groups after ex vivo re-stimulation of splenocytes with casein/whey. Conclusion: In contrast to processed milk, raw milk is hardly able to induce sensitization. Allergic symptoms and IgE levels were reduced and this coincided with reduced Th2 cytokine responses. What it is in raw milk that prevents sensitization needs to be elucidated in future studies.