Summary:Despite contemporary typing procedures for bone marrow transplantation (BMT), graft-versus-host disease (GVHD) continues to be a major complication of transplants performed between MHC-matched donors and recipients. Although GVHD can be alleviated by T cell depletion, this procedure increases the risk of graft failure and leukemic relapse and therefore is not a solution to the GVHD problem. The high degree of variation in the intensity of GVHD observed in different patients suggests that multiple non-MHC genetic factors influence GVHD severity. We hypothesize that, in addition to minor histocompatibility antigen disparities, polymorphisms in genes encoding immunologic effector molecules may be important factors influencing GVHD development. This study aims to explore this hypothesis by identifying non-MHC genes that influence the outcome of BMT in a murine model. In this model, B10.D2 donor leukocytes cause acute GVHD in (C57BL/6 × DBA/2)F1 (B6D2F1) recipients, whereas DBA/2 donor leukocytes do not. To date, a locus on chromosome 1 has been identified as influencing the severity of GVHD in this model. Our current study shows that a locus on chromosome 2 acts independently of the chromosome 1 locus to also influence GVHD severity in this model. The region of chromosome 2 implicated in our study contains genes encoding ␤ 2 -microglobulin, the minor histocompatibility antigen H-3 and the pro-inflammatory cytokine IL-1.