Recombinant human interferon gamma suppresses HTLV-III replication in vitro

Effect of human interferon gamma (rINF gamma) on HTLV-III replication was evaluated quantitatively via a novel infection system using HTLV-I-carrying MT-4 cells. Treatment of HTLV-III-infected MT-4 cells with different concentrations (I-1,000 U/ml) of rINF gamma, which did not affect the growth or viability of uninfected cells, significantly blocked the appearance of immunofluorescent antigens of HTLV-III and the virus-induced cytopathic effect in a dose-dependent manner. A plaque assay was applied to measure the exact amount of viral particles released from HTLV-III-infected MT-4 cultures either untreated or treated with rINF gamma after infection. The number of plaques per dish decreased with increasing drug concentrations. About 50% and 80% of HTLV-III replication were inhibited by the addition of 100 and 1,000 U/ml of rINF gamma, respectively. The effects of INF were observed by day 5 of incubation with the chemical. However, longer treatment of cells with rINF gamma permitted a gradual increase in viral replication. Re-addition of fresh INF into cultures did not change this pattern significantly.