HLA-II genes such as HLA-DMA and HLA-DRB5 are highly expressed in skin ECs as compared to ECs from brain, trachea, and thyroid, which could explain the higher incidence rate of dermal vasculitis in acute graft-versus-host disease 36, systemic sclerosis 37, and cutaneous leukocytoclastic vasculitis 38. Here, HLA-DMA is linked to acute graft versus host disease.