CURRENT CONCEPTS IN MUCOSAL IMMUNITY - III - ONTOGENY AND FUNCTION OFGAMMA-DELTA T-CELLS IN THE INTESTINE

gamma delta T cells are located in the paracellular space between epit helial cells. In the human colon and small intestine, 5-40% of intraep ithelial lymphocytes (IEL) are ya T cells, and in mice an even greater proportion of IEL are gamma delta T cells. The ya T cell receptor rep ertoire in the human intestine undergoes marked changes in V region ge ne usage and junctional diversity during development from fetus to new born to adult, suggesting that gamma delta T cells may mediate qualita tively or quantitatively different functions at various stages of deve lopment. ya IEL have been shown to produce cytokines and growth factor s and to influence epithelial cell proliferation and differentiation, as well as the mucosal development of immunoglobulin A B cells. gamma delta IEL also manifest cytolytic activity. However, the ligands recog nized by intestinal gamma delta T cells and the role they play in inte stinal immune responses, in immune defense to enteric pathogens, and i n the pathogenesis of intestinal disease are thus far largely unknown.