Macrophages release melanocyte dendrite extension factor in response to ultra-violet ray

Mammalian melanocytes in epidermis extend their dendrites in response to UV ray in vivo in addition to proliferation and pigmentation. We found that cultured macrophages exert a factor in response to UV irradiation and that this factor induces the extension of dendrites of melanocyte. We designated this factor as dendrite extension factor (DEF) and characterized it as a protein. Our results indicate that the molecular weight of DEF is 30,000-100,000 and that it is heat-labile. Macrophages release DEF through transcription and translation. DEF seems to be a novel factor that enhances melanogenesis by UV irradiation.