Detection of TdT-positive cells in the mesenteric lymph nodes of immunodeficient rats: study of their antigenic phenotype.

Terminal deoxynucleotidyl transferase (TdT) containing cells were found in the mesenteric lymph nodes of protein deprived and casein re-fed rats. Double immunofluorescence was used to characterize these TdT+ cells according to their surface antigenic phenotype. TdT+ cells expressing T-cell antigen markers recognized by monoclonal antibodies: W3/13 and OX-19 indicated thymic origin. It was found that these cells represented half the existing TdT+ population in the mesenteric lymph nodes. The rest of them presented the Ia antigen which is coded for by the class II major histocompatibility complex and is recognized by the OX-6 mAb. TdT+ cells presenting the OX-6+ phenotype were ascribed to a bone marrow derived subset. These results indicate that, in some instances, i.e., immunodeficiency due to protein deprivation, TdT+ cells may appear in the mesenteric lymph nodes. Their origin may be attributed either to trafficking of immature cells from the thymus or to cells that leave the bone marrow as a consequence of the damage provoked by protein deprivation.