Expansion and activation of NK cell populations in a gammaherpesvirus infection.

NK cells are an important component of the innate immune response to many virus infections. In particular, they play a major role in control of alpha and beta herpesvirus infections in humans and mice and there is evidence for a protective role in Epstein-Barr virus infection. MHV-68 has been widely used to study gammaherpesvirus pathogenesis and provides a tractable means of investigating the role of NK cells in gammaherpesvirus infections. We have shown that, following MHV-68 infection of mice, the NK cell population is expanded and activated and capable of cytotoxic killing in vitro. However, depletion of NK cells prior to MHV-68 infection did not affect viral loads in vivo. To investigate the possibility that MHV-68 was downregulating NK cell activity in vivo and evading the NK cell response, we infected NK cell-depleted mice with the related virus, MHV-76, which lacks a 9.5 kb region of the genome known to be involved in modulating the host immune response. Infection of NK cell-depleted mice with MHV-76 did not result in increased viral loads indicating that genes within this region do not encode products which modulate NK cell activity.