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The Immune System and Breast Milk

By Melissa Kotlen Nagin, About.com

Updated: February 21, 2008

About.com Health's Disease and Condition content is reviewed by Meredith Shur, MD

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.

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