DIFFERENCES IN THE TISSUE-SPECIFIC HOMING OF ALPHA-BETA AND GAMMA-DELTA T-CELLS TO GUT AND PERIPHERAL LYMPH-NODES

Tissue-selective streaming of T cells is considered to be a critical element in the integration of normal immune responses in intact animals. The results presented in this paper show that while there were major subsets of gut-homing T cells present in intestinal lymph, there were considerable differences in the tissue tropism of T cell populations circulating in lymph draining gut and peripheral lymph nodes. Thus, while CD4(+) cells returned preferentially to their tissue of origin, gamma delta T cells showed a strong migratory preference for peripheral lymph nodes regardless of their tissue of origin. In contrast, although a population of gut-homing CD8(+) cells was present in ileal lymph, CD8(+) T cells from peripheral lymph nodes homed equally well to gut and lymph nodes. There were also considerable differences in the expression of L-selectin on T cells circulating in the two compartments. L-selectin was down-regulated on alpha beta T cells present in ileal lymph but not on gamma delta T cells which expressed the highest levels of L-selectin of all T cell subsets. It is suggested that gut-homing alpha beta T cells which have down-regulated L-selectin are formed in the gut-associated lymphoid tissues in response to gut antigens while the migratory properties of gamma delta T cells are ontogenetically determined, independent of antigen.