Recent studies suggest that the content of immune components in milk is influenced by the mother's health and also by the infant she feeds. We aimed to evaluate the effect of a child's respiratory tract infection on the cellular composition of breast milk (neutrophils, monocytes, eosinophils, lymphocytes, and their subpopulations). Twenty-six breastfeeding mothers whose children were hospitalized for respiratory tract infections were enrolled in the study. The control group consisted of 23 mothers of healthy children. Regarding the children, baseline laboratory blood tests were performed, and nasal swabs were taken for the presence of RS virus. In the next step, milk samples were collected from the mothers to assess the cellular composition of the milk, including neutrophils, monocytes, eosinophils, lymphocytes, and their subpopulations. Significantly higher percentages of T lymphocytes (helper and cytotoxic lymphocytes) were observed in the milk of the studied mothers. There was a significantly higher percentage of milk lymphocytes in the group of affected children with confirmed RSV etiology than in children with excluded RSV etiology. A significant positive correlation was observed between the duration of infection and the percentage of milk NK cells and between milk CD19 lymphocytes and the child's serum leukocytosis. This study may provide evidence of a link between cells in breast milk and disease in the breastfed infant. The severity of the infection, its duration, and the etiological agent of the infection may affect the cellular composition of milk.
Keywords: breastfeeding; cellular composition of milk; human milk; immunomodulation; infection.