Role of sex and early interferon production in the susceptibility of mice to encephalomyocarditis virus.

Adult female Swiss mice showed a greater resistance to intraperitoneal (i.p.) infection with encephalomyocarditis virus (EMCV) than male mice. This difference was not observed in weanling mice, in castrated adult mice or in adult mice injected intracerebrally. Administration of antibody to mouse interferon alpha/beta enhanced the virulence of EMCV for both sexes and no difference was then observed in susceptibility between male and female mice. Six h after EMCV infection, serum interferon titres were higher in adult female mice than in male mice. There was a close correlation between the early serum interferon titre (at 6 h) and survival of EMCV-infected mice. No differences in serum interferon titres were observed between male or female weanling mice or castrated adult mice. Potent preparations of exogenous interferon provided the same degree of protection against EMCV infection in male and female mice. We conclude that the more marked early interferon response of female mice to i.p. EMCV infection is one of the important factors underlying the differential susceptibility to EMCV. It is possible that the interferon system is also involved in the reported greater prevalence of picornavirus infections of men compared with women.