[Activated monocytes involved in allograft rejection of rats: spontaneous plaque-forming cell as a new monocyte effector].

Spontaneous plaque-forming cell, SPFC, is a new hemolytic effector of monocytes, which is generated 6 to 7 days after antigen unstimulation or stimulation in man. SPFC is also detected in rats. A significant concomitant response of the SPFC, in number of SPFC at the peak response around the rejection day, and histoincompatibility of allogeneic combinations in skin or heart allograft transplantation of rats was found. Peak number of SPFC (28,850 + 1,343/10(6) on day 6 in H-1 incompatible combination (ACI-Lewis) was higher than that (11,606 + 4,235/10(6)) on day 10 in H-1 compatible combination (F344-Lewis) (p less than 0.05, Student'st-test). The day of peak SPFC response in each experimental group was also concordant with the day of rejection. The OX42 monoclonal antibody against CR3 of leukocyte-adhesion molecules inhibited hemolysis of the SPFC. Since the erythrocyte is a ligand of CR3, it is likely that hemolysis of SPFC is mediated by the CR3 adhesion molecules. In conclusion, SPFC may be an immunologic indicator of allograft rejection in rats.