How Breast Milk protects New Borns

This article talks about how breast milk benefits the infants much more than artificial milk.
The breast milk supplied to the infants is free of bacteria, unlike artificial milk that can get contaminated easily. Along with that, the breast milk contains 5 different kinds of antibodies IgG, IgA, IgM, IgD and IgE. Also, immune cells are abundant in breast milk - they consist of white blood cells, or leukocytes, that fight infection themselves and activate other defense mechanisms.

Breast-fed babies produce higher levels of antibodies in response to immunizations. Also, certain hormones in milk (such as cortisol) and smaller proteins (including epidermal growth factor, nerve growth factor, insulinlike growth factor and somatomedin C) act to close up the leaky mucosal lining of the newborn, making it relatively impermeable to unwanted pathogens and other potentially harmful agents.

Recent clinical studies have demonstrated that the breast-fed infant has a lower risk of acquiring urinary tract infections. Finally, some evidence also suggests that an unknown factor in human milk may cause breast-fed infants to produce more fibronectin on their own than do bottle-fed babies. Researchers do not yet know how the mother's immune system knows to make antibodies against only pathogenic and not normal bacteria, but whatever the process may be, it favors the establishment of "good bacteria" in a baby's gut.