LATE-TERM FETAL THYMECTOMY DOES NOT PREVENT THE DEVELOPMENT OF GUT-HOMING T-CELLS AFTER BIRTH

Tissue-specific circulation of T cells is a critical element in the in tegration of systemic immune responses. Current models of T-cell migra tion suggest that homing specificities of T cells for tissues such as gut and skin are generated outside the thymus as a result of activatio n of virgin T cells by antigen in lymph nodes. We have used the sheep fetus (which is immunologically virgin and contains no memory or effec tor T-cell subsets) to examine the migration of Cr-51-labelled T cells in vivo. We report that gut-homing T cells are not present in the fet us and that gut-homing T cells from postnatal lambs home normally to f etal gut. Fetal thymectomy performed immediately prior to birth failed to prevent the development of gut-homing T cells in postnatal life. G ut-homing specificities on T cells are thus acquired extrathymically.