The immunologic properties of breast milk are what truly set it apart from any other form of infant sustenance. The body of a newborn baby is very vulnerable and it does not have inborn defense mechanisms to protect itself from the environment outside of the womb.
Breast milk contains 90% phagocytes, which engulf and absorb pathogens; release IgA; produce complement, lactoferrin, and lysozyme; and likely protect the breast tissue. Breast milk carries 10% lymphocytes, or T-cells and B-cells, which identify and eliminate antigens -- this is called mediated immunity. Most importantly, breast milk contains immunoglobulins, or proteins generated by plasma cells in response to immunogens.
