Stimulatory cells in the generation of T-cell-mediated cytotoxicity: Potent stimulating activity of a small radioresistant spleen cell population (RSCs)

The combined effects of irradiation followed by cultivation on a total spleen cell population in order to study the evolution of the stimulating potential in the in vitro generation of allogeneic cytotoxic T lymphocytes (CTLs) were tested. Results revealed that, after 3 days and up to at least 7 days of cultivating irradiated (1000 rad) spleen cells, the remaining living cells (radioresistant spleen cells or RSC) have the same potential to generate CTLs as irradiated noncultivated spleen cells. RSC can resist a 5000-rad irradiation and induce a primary cytotoxic response pattern similar to that of total spleen cells; they act in primary as well as in secondary cultures with optimal responder to RSC ratios of about 100, but are still stimulatory at MLC ratios up to 1000 or 5000. They are lysed by specific allogeneic CTLs and readily inhibit the specific lysis of H-2-identical labeled targets by CTLs. RSCs do not express unusual levels of H-2 or Ia antigens and do stimulate purified T cells. Alloantisera anti-H-2 are able to completely block the RSC-induced generation of CTL. This RSC population may prove to be a good model to study non-H-2- or H-2-associated, nonserologically detectable determinants interacting in the generation of T-cell-mediated cytotoxicity.