A partial characterization of suppressor cells in rat fetal liver cells

Rat fetal liver cells (FLC) obtained at 18–20 days gestation suppressed mixed lymphocyte reactions(MLR) of adult lymph node cells. The suppression was not strain specific: both syngeneic and allogeneic FLC were capable of suppressing the MLR. The same suppressor activity was observed with fetal spleen cells but not with fetal thymus cells. Removal of phagocytic cells from FLC failed to inhibit the suppressor activity. The suppressor cells were separated into two different types by BSA density gradient: one is radiosensitive, the other radioresistant. A stronger suppressor activity was observed in radiosensitive cells. The suppressor cells belonged to the fraction agglutinated with peanut agglutinin. The data suggest that the suppressor cells in rat FLC may be a proliferating blastoid-type cell rather than mature lymphocytes or mature macrophages.