Cellular components of breast secrets and postnatal immunity of the offender

Mammary secretions contain viable maternal cells that are mainly lymphocytes, macrophages, neutrophils and epithelial cells. Their biological functions in the neonate, though not yet clearly established, are strongly suggested by experimental data. This paper reviews current knowledge of the cellular components of mammary secretions: their nature, in vitro properties, and demonstrated in vivo effects in the neonate, and discusses possible future experimental approaches. It is thought that the main role of the cellular components from mammary secretions is to interact with the development of local immunity in the newborn, and to modulate active immunization of the neonatal intestine during this critical period when the development of adapted responses to antigens (protection/tolerance/alimentary allergy) is of crucial importance for the future of the young.