Melanosomes in Phagocytic Vacuoles in Langerhans Cells

~Ihe nature of Langerhans cells is disputed. ~fhey have been considered effete melanocytes (1, 2), postmelanin-synthetic cells (3), melanocyte precursors (4), intraepidermal nerve endings (5, 6), or postdivisional stages of previously melanogenic melanocytes (7). Under the electron microscope, melanocytes and Langerhans cells are distinguished by highly characteristic cytoplasmic or-ganelles: melanosomes in the melanocytes, and disc-shaped bodies in the Langerhans cells. Any postulated relationship between the two types of cells must remain hypothetical as long as there is no evidence that a cell can turn from synthesis of one type of organelle to that of the other. Since removal of the stratum corneum of the epidermis by Scotch tape stripping has been shown to increase epidermal cell turnover and to cause characteristic subcellular changes (8), and since melanocytes and keratinocytes form a symbiosis (9), it seemed possible that the events after stripping might provide a better opportunity to observe the proposed melanocyte-Langerhans cell conversion. MATERIALS AND METHODS Specimens of normal adult Ncgro and Caucasian skin were obtained from the flexor surface of the forearm at various intervals after Scotch tape stripping (10). Control sections wcrc takcn from a corresponding unstripped area. Specimens were immediately fixed in OsO4 for 120 rain and embedded in Maraglas 655. Staining was carried cut with 1% phosphotungstic acid at the absolute ethanol stage of dehydration and with lcad citrate (11) after ultra-thin sectioning. Sections were examined with an RCA EMU-3F or EMU-3G microscope. RESULTS Cells containing both mclanosomes and Langer-hans cell granules have not been found previously in normal integument, and the present study did not reveal such cells in control sections. However, the number of typical Langerhans cells seen in the epidermis of human skin obtained 18 and 24 hr after keratin layer stripping appears to be significantly increased as compared to the number found in normal control skin. Fig. 1 shows two Langerhans cells in juxtaposi-tion to a middle level prickle cell 24 hr after stripping. These Langerhans cells characteristically exhibit absence of tonofilaments and desmo-somes, in contrast to surrounding keratinocytes. They have an indented or convoluted nucleus in addition to their distinctive organelles. Melano-somes are present in both Langerhans cells, although the upper cell contains fewer granules. Higher magnification of one of these Langerhans cells (Fig. 2) reveals typical Langerhans cell granules. They appear rod-shaped with rounded ends and often have vesicles continuous with their outer limiting membrane. The rod-shaped structure contains an …