The role of cytokines in graft-versus-host reactions and disease.

CD4+ and CD8+ T lymphocytes are responsible for the initiation of graft-versus-host disease (GVHD) which limits the efficacy of human allogeneic bone marrow transplantation. Activated T cells are a rich source of cytokines in vitro, and many of these same molecules are also found in graft-versus-host reactions (GVHR) and GVHD. However, T cells are not the only source of these soluble mediators. Cytokines control the actions of many cell types both in vitro and in vivo, so these soluble factors can easily influence the actions of both the engrafted hematopoietic cells and the host's cells. The complex manner in which cells and cytokines interact in GVHR and GVHD is reviewed here. We speculate that cytokine cascades play major roles in many aspects of GVHR and GVHD.