The role of B cells in acute graft-versus-host disease

which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The role of B cells in acute graft-versus-host disease TO THE EDITOR: Mounting evidences implicates B cells in the pathogenesis of chronic graft-versus-host disease (GVHD). The body of evidence includes findings such as correlation between chronic GVHD and antibody production against Y chromosome-encoded minor histo-compatabilty antigens (mHA) generated after sex-mis-matched allogeneic stem cell transplantation (SCT), the clinical response of steroid-refractory chronic GVHD to ritux-imab, and association between high serum B cell-activating factor (BAFF) levels and chronic GVHD [1]. However, the role of B cells in acute GVHD remains controversial. Some studies that showed the association of high B cell count in the grafts in SCT patients with acute GVHD and beneficial effects of rituximab (used for B cell lymphoma treatment before transplantation) in acute GVHD patients, have suggested the possible role of B cells in the development of acute GVHD. Kim et al. reported that the BAFF level/absolute lympho-cyte count (ALC) ratio or that of APRIL (a proliferation-inducing ligand) level/ALC at the time of acute GVHD diagnosis was associated with disease severity [2]. In their study, patients with grade III-IV acute GVHD (6) had higher BAFF level/ALC or APRIL level/ALC ratio than the corresponding ratio observed in patients with grade II acute GVHD (9). These findings suggest that BAFF level/ALC or APRIL lev-el/ALC ratio can help determine the severity of acute GVHD and need to be confirmed in large prospective studies. However, it would be somewhat unreasonable to conclude that B cells may play an important role in the development of acute GVHD on the basis of these findings alone. First, counting the number of B cells should be performed along with measurement of the BAFF or APRIL levels because higher serum BAFF levels may reflect relative B lymphope-nia depending on the period after transplantation. Furthermore, comparison of the findings for patients with and without acute GVHD for the same period after alloge-neic SCT is essential for investigating the relationship between B cells and acute GVHD. BAFF has a complex, dichotomous role in immunity, which is mediated by the differential regulation of T cell-and B cell-dependent immune responses [3]. BAFF, a critical regulator of normal B cell homeostasis in mice and humans, also promotes T cell activation and survival [4]; these T cells play a pivotal role in acute GVHD pathogenesis. However, …