Melanocyte-lymphocyte interaction in human graft-versus-host disease

Pigmentary disorders in chronic human GvHD comprise reticular or diffuse hyper- and hypopigmentation and seem to result from an interaction between lymphocytes and melanocytes. This interaction could be visualized by standard microscopy with a specific staining for melanin. The main ultrastructural findings were, in hyperpigmented areas: broad contact between melanocytes and lymphocytes, numerous and packed melanosomes, presence of cytoplasmic lipid droplets; in hypopigmented areas: disintegrating melanocytes with large intercellular spaces, small melanosomes, numerous lipid droplets, vacuolated organelles, as well as condensed and convoluted nuclei. Different hypotheses to explain the dysfunction of melanocytes are presented.