The presence of infectious virus but not conventional antigen can exacerbate graft-versus-host reactions

Previous reports have demonstrated that the introduction of virus (MCMV, HSV-1) concurrent with a graft-versus-host reaction (GvHR) limited to a class I MHC disparity can result in the enhancement of GvHR-associated phenotypic (changes in CD4/CD8 ratio) and functional (inability to produce secondary antibody responses) alterations including the augmentation of in situ natural killer (NK) and donor anti-host cytotoxic T-cell activity. In the present study, we investigated whether immunogens other than infectious virus may be capable of enhancing GvHR. Mice receiving donor cells and the T-dependent antigen dinitrophenyl-bovine serum albumin (DNP-BSA) did not display exacerbated GvHR as evidenced by the absence of phenotypic alterations and the absence of elevated NK activity and the lack of donor anti-host cytotoxic activity. Furthermore, these recipients produced normal levels of IgM and IgG anti-DNP antibody. In addition, mice which received ultraviolet light (UV)-inactivated virus (even at 100 x dosage) together with donor cells also did not exhibit exacerbated GvHR. In total, these findings illustrate a novel ability of infectious virus to exacerbate GvH reactions and are consistent with the hypothesis that viral-induced immune responses may be important in the ability of a pathogen to induce the development of severe GvHR.