MPO and graft versus host disease: PGE2: prostaglandin E2; PMNs: polymorphonuclear leukocytes; MPO: myeloperoxidase; GVHD: graft-vs-host disease; BDMC: bone-marrow derived dendritic cells; THP-1: human THP-1 macrophages; RAW 264.7: mouse macrophage cell line; n.d.: not defined.