The role of secretory IgM on cGVHD has not been defined yet, however, it was reported that both IgG and IgM were frequently found in the basal epidermis in both acute and chronic GVHD patient biopsies, and their number was positively related to the degree of epidermal necrosis observed in histologic section (39). Here, CD40LG is linked to chronic graft versus host disease.