Current concepts in mucosal immunity. III. Ontogeny and function of gamma delta T cells in the intestine.

-gamma delta T cells are located in the paracellular space between epithelial cells. In the human colon and small intestine, 5-40% of intraepithelial lymphocytes (IEL) are gamma delta T cells, and in mice an even greater proportion of IEL are gamma delta T cells. The gamma delta T cell receptor repertoire in the human intestine undergoes marked changes in V region gene usage and junctional diversity during development from fetus to newborn to adult, suggesting that gamma delta T cells may mediate qualitatively or quantitatively different functions at various stages of development. gamma delta IEL have been shown to produce cytokines and growth factors 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 recognized by intestinal gamma delta T cells and the role they play in intestinal immune responses, in immune defense to enteric pathogens, and in the pathogenesis of intestinal disease are thus far largely unknown.