IMMUNOLOGY OF THE DEVELOPING GASTROINTESTINAL

TRACT: ROLE OF PROTECTIVE NUTRIENTS

W. Allan Walker, M.D.

Conrad Taff Professor of Nutrition

Professor of Pediatrics

Director, Division of Nutrition

Harvard Medical School

The human neonate at birth has an immature mucosal immune system in the gastrointestinal tract. The gut lacks polymeric IgA (pIgA) antibodies, overreacts to inflammatory stimuli and has increased permeability to dietary food antigens and pathologic bacteria. This immaturity makes the neonate more susceptible to intestinal infections, inflammation, and food allergy. Breast milk provides passive and active protection of the newborn gut in the post partum period. This problem includes the presence of IgA antibodies, cytokines, growth factors, and protective nutrients. A major factor in the maturation of the human gut’s mucosal immune system is the initial colonization by bacteria. Oligosaccharides in breast milk, also known as prebiotics, help determine the nature of bacterial flora which appropriately stimulates the immune system and inhibit excessive inflammation. Other protective nutrients in breast milk include nucleotides, amino acids such as glutamine, arginine and ornithine, proteins such as lactoferrin and fatty acids such as omega-3 fatty acids also promote active development of the mature immune system. These protective nutrients can be provided to infants in the second six months of life as dietary supplements to assure ongoing normal immune function and to help prevent disease. In this lecture, I will review intestinal immune functions and immaturities in newborn gut immunity as well as consider clinical studies to suggest protective affects of supplemental nutrients in the second six months of life.