INFLUENCE OF BONE-MARROW AND SPLEEN MICROENVIRONMENTS ON THE PRODUCTION OF THYMIC PROGENITORS

Previous experiments indicated that in lethally irradiated mice the thymic repopulation differed depending on the origin of the restorative cell suspension: BM-derived cells repopulated the thymus more rapidly than spleen-derived ones. It was assumed that this difference expressed the respective influences of the BM and spleen HIM on the production of thymic progenitors or precursors. The purpose of the present experiments was to determine the delay necessary for BM or spleen CFU engrafted into a new HIM to repopulate the thymus at a rate characteristic of their new HIM. It was confirmed that BM and spleen HIM act differenty on the differentiation process of thymic progenitors and precursors. In addition, it was shown that when BM or spleen cells are transferred into a new HIM, the rates at which thymic progenitors are produced remain characteristic of their original HIM during the first 9 days following their transplantation. This experimental finding might be explained either by a refractory state of the transplanted cells which have been conditioned in their original HIM, or by a transitory damage induced by radiation to the recipient HIM. © 1979.