IL-6 has both pro- and anti-inflammatory effects [1], but pro-inflammatory effects seem to dominate early after allotransplantation as indicated by the correlation between the capacity of IL-6 to induce STAT3 phosphorylation in CD4+ T cells on day +22 post-transplant and the later development of acute GVHD [20]. Here, CD4 is linked to acute graft versus host disease.