Altered threshold for the induction of graft-versus-host immunodeficiency following murine cytomegalovirus infection. Host and donor contributions.

Acute murine cytomegalovirus (MCMV) infection enhances the ability of parental spleen cells to induce graft-vs.-host immunodeficiency (GVHID) in F1 hybrid mice when the two processes occur simultaneously in the recipient. The present study assessed GVHID as the ability of spleen cells to generate in vitro cytotoxic T lymphocyte responses to trinitrophenyl-modified syngeneic cells. The results indicate that MCMV infection not only reduces the number of parental spleen cells required to induce GVHID, but accelerates the onset of GVHID, which occurs as early as 3 days after cell and virus challenge. To determine whether MCMV infection exerts this synergistic effect primarily through the donor or the host component, we examined the effect of MCMV infection of either donor mice or recipient mice at 3, 10, and 17 days prior to spleen cell transfer. Two weeks after cell transfer, splenocytes were tested for their ability to generate CTL. When donor mice were infected with MCMV three days prior to cell transfer, the ability of donor cells to induce GVHID was reduced. In contrast, MCMV infection of the recipients three days prior to cell transfer increased their susceptibility to GVHID induction. Infection of either donor or host mice 10 days or 17 days prior to parental spleen cell transfer had little effect on the ability to induce or resist GVHID when compared with sham-infected mice. Thus, acute MCMV infection can modulate the severity of GVHID depending on whether it is the donor or the host that is infected. The ability of acute MCMV to alter the course and severity of GVHID may be relevant for human bone marrow transplants in which preceding CMV infection has been associated with chronic GVH. In this setting, CMV may lower the threshold necessary to induce a GVH reaction.