Suppression of Friend leukemia virus by Bacillus Calmette-Guérin and a streptococcal preparation, OK-432.

OK-432, a streptococcal preparation, and BCG effectively inhibited splenomegaly in Friend leukemia virus (FLV)-infected mice. Divided drug dosage resulted in stronger inhibition than single administration. When the second dose was fixed at the 3rd pre-infection day, the best timing for the first dose was approximately 30 days before infection. The optimal dosages were 100--600 KE/kg for OK-432 and 25--100 mg/kg for BCG. Transfer of peritoneal exudate cells (PEC) from immunomodulator-treated mice, but not PEC from untreated mice, conferred resistance against FLV which was highest when PEC were transferred 1 day before FLV infection. The transfer of PEC on the day of or one day after infection had no protective effect. Inactivation also occurred when FLV was incubated in the presence of PEC from immunomodulator-treated mice, however, no significant effect was observed for PEC from untreated mice.