T lymphocytes in human milk: Their role in immune system maturation through maternal microchimerism

Breastfeeding promotes the trafficking of immune cells and soluble factors from the mother to the neonate during lactation, resulting in maternal microchimerism. Human milk is abundant in T lymphocytes, but little is known about their priming and actions in neonatal mucosal tissues and their role in conferring immune tolerance in early life. This review summarises recent findings on the characteristics of human milk T cells compared to their counterparts in maternal and neonatal blood. We discuss how bioactive components of human milk, such as cytokines, hormones, and miRNA, may modulate the immune suppressive function of this cell subset. We shed light on the presence and possible functions of regulatory T cells (Tregs) in the breastfeeding triad of mother, human milk, and neonate, and how this subset of T lymphocytes may contribute to the prevention of immune pathologies, such as allergies and autoimmune diseases, later in life through human milk-induced maternal microchimerism in the newborn.