Effect of rifamycin SV on the in vitro induced immune response

Mouse peritoneal cells producing antibodies against sheep red cells were used to study the effect of Rifamycin SV on an in vitro induced immunological response by the localized hemolysis technique. At a concentration of 100 μg/ml, Rifamycin SV has a greater inhibiting effect on lymphocytes than on macrophages. Lymphocytes are still clearly inhibited by 10 μg/ml, but the same concentration acting on macrophages causes an increase in the number of plaque-forming cells. One thousand μg/ml Rifamycin SV completely suppresses antibody production, whereas 1 μg/ml has no detectable action. The effect of Rifamycin SV on incorporation of radioactive amino-acids and uridine was also studied. We found that it has a weak effect on protein synthesis but inhibits synthesis of RNA; this inhibition is stronger in the absence of antigen. Furthermore, protein synthesis by these cells seems to be controlled by long-lived ribonucleic acids.