Phagocytosis of Melanin Particles by Human Epidermal Cells in vitro

Abstract

It is now quite generally accepted that oniy melanocytes, the specialized cells of melanin synthesis, are capable of synthesizing this polymeric pigment. It is also evident that this pigment, after its formation in the melanoeytes of the epidermis, normally finds its way into the epidermal cells Where it may persist during their outward migration and exfoliation. The precise mechanism by Which the pigment particles (the melanized melanosomes) are transferred in vivo from the donor to the receptor cells is not entirely clear. It has been variously proposed that the pigment particles are first liberated into the intercellular space and then phagoeytized by the epidermal cells (1), or that the melanoeytes actively inject the particles into the epidermal cells (2). More recent electron microscopic studies of epidermal cells show that the resident pigment particles are frequently enclosed by a membrane which has been interpreted as the wall of the deiidrite of the melanoeyte (3, 4), implying a phagoeytosis of a portion of the dendritie process. The transfer of pigment particles by melanoeytes to epidermal cells has been directly observed in mixed cell culture by several workers, and in some instances studied by time lapse einemicrography (5, 7). We report here on the ease of human epidermal cells in cultures, to which partially purified melanin particles were added.