Leucocytes in human milk and lymphocyte subsets in cow's milk-allergic infants

The breast-fed infant ingests an average of 108 leucocytes per day, with breast-feeding often continuing for several months. The precise role of human milk leucocytes is still unresolved. Breast-feeding has been recommended for infants at high risk of allergy to prevent or delay the development of food allergies and atopic eczema. However, studies dealing with distinct immunologic factors in the mother's milk, and their effect on health status or development of allergies in the infant, are scarce. We evaluated the relationship between the cellular composition of human milk and the development of cow's milk allergy (CMA) in the breast-fed infant. Leucocyte subsets in the breast-fed infants were also measured. The study population comprised 61 breast-feeding mothers and their infants. Thirty-nine mothers each had a cow's milk-allergic infant, 10 had an infant with atopic dermatitis without CMA, and 12 mothers had a healthy infant. Leucocyte subsets in mothers' milk were counted using a light microscope and confirmed by flow cytometry. In infants, peripheral blood lymphocyte subsets were determined by flow cytometry and were correlated with the health status of the breast-fed infant and leucocyte composition of the mother's milk. Human milk was found to be a non-homogenous morphological entity. In the milk of mothers of infants with CMA, the proportion of macrophages was significantly smaller than in the mothers with infants without CMA (p = 0.036, t-test). Mothers with high proportions of neutrophils in their milk (> 20%) had significantly more often infants with CMA than did those with low proportions of neutrophils (p = 0.02; Fischer's exact test). Eosinophils comprising > 1% of milk cells were only detected in the mothers who had infants with CMA. Furthermore, the proportions of CD4+ T cells were positively correlated with the proportion of milk macrophages and negatively with the percentage of milk neutrophils and eosinophils. The proportions of total B cells and those expressing CD23, a low-affinity immunoglobulin E (IgE) receptor, were positively correlated with the proportions of neutrophils and eosinophils in mother's milk and negatively with the percentage of milk macrophages. To conclude, the composition of breast milk in some mothers is abnormal and correlates with a diagnosis of CMA in a breast-fed infant. This may provide a new and interesting insight into the development of food allergies.