The benefits of breastfeeding are so well recognized that pointing out a flaw usually meets with considerable doubt, if not with outright hostility. Yet what holds true for other areas of physiology and medicine holds true here: What is "natural" is not necessarily flawless. Breast milk is a case in point.
Maternal immunoglobulins and leukocytes transferred to the infant by colostrum or milk generally bolster the infant's poorly developed immune response.1 However, in some instances the wisdom of breastfeeding is questionable, as when mother and child are not Rh or ABO blood group compatible or when the mother carries a microorganism, such as the human T-cell lymphotropic virus Type I (HTLV-I). It seems appropriate to question whether the transfer of lymphocytes, especially allotypic lymphocytes, from mother to infant by breast milk, is wise.
Colostrum contains about 10,000 lymphocytes per mm; approximately 2,000 of those are T lymphocytes....