RNA in the peripheries of various populations of lymph node cells (LNC) has been evaluated by measuring the electrophoretic mobilities of cells, before and after treatment with active or inactivated ribonucleases. Three different populations of LNC were studied: (1) "resting" normal age control LNC; (2) "syngeneic" LNC from irradiated (C3H x C57BL)Fi or C3H mice four to six days following transplantation of syngeneic spleen cells; such cells were progeny of lymphopoietic progenitor cells of the spleen; and (3) "allogeneic"LNC from irradiated (C3H X C57BL)Fl mice four to six days after grafting C3H (parental) spleen cells; such cells were progeny of lymphopoietic progenitor cells, but also alloantigen-sensitive cells of the spleen which proliferate in response to the host's doantigens ( a "graft-versus-host" immunological reaction). Whereas the normal LNC had no detectable peripheral RNA, the allogeneic and syngeneic LNC did, i.e., ribonuclease reduced their mean electrophoretic mobilities by 13.6 and 9.2 per cent, respectively. Since both allogeneic and syngeneic LNC had peripheral RNA, no specific correlation could be made with immunological activity. 3H-uridine and '*-thymidine incorporation into lymph nodes was greatest in allogeneic, intermediate in syngeneic and least in age control lymph nodes, indicating a "population shift" in the spleen cell chimeras toward relatively immature, rapidly proliferating cells, which had a relatively high rate of RNA synthesis. Thus, rapidly proliferating lymphoid cells do have RNA in their peripheries, but its relation to specific immunological function has yet to be ascertained.
( Bennett , '69).
MATERIALS AND METHOD
Mice. Adult C3H/He, C3H/St and (C3H/St X C57BL/Ha)Fi mice of both sexes were obtained from the West Seneca Animal Production Unit of Roswell Park Memorial Institute (RPMI) and (C3H/He X C57BL/lO)R mice were obtained from Battelle Memorial Institute, Columbus, Ohio. The mice were housed 5-6 per cage throughout the experiments, and were fed Rockland lab chow and water ad libitum.
Transplantation procedure. The irradiation of mice and preparation of spleen cells for intravenous infusion have been