Variations in host defence mechanisms and blastogenesis in chickens and mice after rifamycin treatments.

The immunobiological effect of rifamycins on different experimental models has been comparatively studied in chickens and mice using cyclophosphamide as a reference immunosuppressive agent. "In vivo" treatments with rifampicin and rifamycin SV diminished interferon levels in chickens and mice up to two hours after virus challenge. Mitogen induced blastogenesis was significantly depressed by either "in vivo" (5-50 mg/kg) or "in vitro" (5-20 micrograms/ml) drug treatments, although the activation of B lymphocytes was more easily inhibited than that of T lymphocytes. Primary anti-SRBC immune responses suffered a similar immune suppressive action by rifamycin treatments "in vivo". In every case, cyclophosphamide (10-20 micrograms/ml "in vitro" and 25 mg/kg "in vivo") proved to be the most active immunosuppressant. On the other hand, a remarkable parallelism in the effect of rifamycins in chickens and mice was observed in all the experimental systems used.