Common and distinct characteristics between murine and human plasmacytoid dendritic cells (pDCs) and their putative roles during allogeneic hematopoietic cell transplantation based upon affecting innate and adaptive immune responses. Ab = antibody, Ag = antigen, GvHD = graft-versus-host disease, HSC = hematopoietic stem cell, IFN = interferon, Mo/Mϕ =monocyte/macrophage, NK = natural killer, TLR = toll-like receptor, TNF = tumor necrosis factor, Treg = T-regulatory cell.