Differential effects of pure human alpha and gamma interferons on fibroblast cell growth and the cell cycle.

Pure human alpha and recombinant gamma interferons had differential effects on two strains of fetal lung fibroblasts in vitro. Alpha interferon had little effect on long-term cell growth, whereas gamma interferons, both glycosylated and non-glycosylated, were cytotoxic. However, when synchronized cells were studied, alpha interferon prolonged both G1 and S + G2 phases of the cell cycle, whereas gamma interferon only affected the G1 phase.