Source: Milk Genomics Consortium
From Mother’s Gut to Milk

In a world filled with harmful bacteria, viruses, and parasites, it seems quite paradoxical that a human infant would be born with an immature and inefficient immune system. That is, of course, until you realize the infant benefits from mom’s immune system hard at work in mucosal surfaces. The process of transferring immunity, also known as passive immunity, begins during pregnancy with the transfer of Immunglobulin G (IgG) cells from maternal to fetal circulation through the placenta. At birth, the mammary gland takes over, providing numerous types of immunogloblulins (antibodies) and other immune factors. But the mammary gland isn’t working alone–the antibodies in milk are derived from antibodies the mother produced in her own gut. This link between the mammaries and the gut, known as the entero-mammary pathway, means that infants are not just ingesting generic antibodies with their milk; they are getting antibodies specific to pathogens in their own environment.