Engineering immunity in the mammary gland.

The major physiological function of milk is the transport of amino acids, carbohydrates, lipids, and minerals to mammalian offspring. However, milk is also a rich collection of antimicrobial substances, which provide protection against pathogenic infections. These molecules safeguard the integrity of the lactating mammary gland, but also provide protection for the suckling offspring during a time when its immune system is still immature. The protective substances can be classified into two categories: 1) nonspecific defense substances, which provide innate immunity, and 2) molecules such as antibodies, which provide adaptive immunity and are directed against specific pathogens. The antimicrobial potency of milk has not been a target for farm animal breeding in the past, and present day ruminants provide suboptimal levels of antimicrobial substances in milk. Altered breeding regimes, pharmacological intervention, and transgenesis can be utilized to improve the antimicrobial properties of milk. Such alterations of milk composition have implications for human and animal health.