Modulation of the gastrointestinal tract of infants by human milk, interfaces and interactions. An evolutionary perspective

Human milk contains agents that affect the growth, development and function s of the epithelium, immune system or nervous system of the gastrointestina l tract. Some human and animal studies indicate that human milk affects the growth of intestinal villi, the development of intestinal disaccharidases, the permeability of the gastrointestinal tract and resistance to certain i nflammatory/immune-mediated diseases. Moreover, one cytokine in human milk, interleukin (IL)-10, protects infant mice genetically deficient in IL-10 a gainst an enterocolitis that resembles necrotizing enterocolitis (NEC) in h uman premature infants, There are seven overlapping evolutionary strategies regarding the relationships between the functions of the mammary gland and the infant's gastrointestinal tract as follows: I) certain immunologic age nts in human milk compensate directly for developmental delays in those sam e agents in the recipient infant; 2) other agents in human milk do not comp ensate directly for developmental delays in the production of those same ag ents, but nevertheless protect the recipient; 3) agents in human milk enhan ce functions that are poorly expressed in the recipient; 4) agents in human milk change the physiologic state of the intestines from one adapted to in trauterine life to one suited to extrauterine life; 5) some agents in human milk prevent inflammation in the recipient's gastrointestinal tract; 6) su rvival of human milk agents in the gastrointestinal tract is enhanced becau se of delayed production of pancreatic proteases and gastric acid by newbor n infants, antiproteases and inhibitors of gastric acid production in human milk, inherent resistance of some human milk agents to proteolysis, and pr otective binding of other factors in human milk; and 7) growth factors in h uman milk aid in establishing a commensal enteric microflora.