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SUMMARY Biopsy specimens of papules taken from eight patients with polymorphic light eruption were examined by immunoperoxidase techniques employing monoclonal antibodies. In each case, most infiltrating mononuclear cells were T cells. The majority of T cells were T8-positive (cytotoxic/suppressor) in four cases and T4-positive (helper/inducer) in two. In two cases, approximately equal numbers of both T cell subsets were present. In only three cases were rare B cells identified by their reactivity with anti-IgM antibody. M1-positive mononuclear cells (macrophages) represented less than 5% of cells infiltrating the dermis. In five subjects, anti-T6 antibody stained increased numbers of dermal mononuclear cells considered to be Langerhans/indeterminate cells. The pathogenesis of papular polymorphic light eruption may involve injury to upper dermal venules mediated by T cells and Langerhans/indeterminate cells.

Monoclonal anti-T6 antibody, which reacts with the majority of cortical thymocytes but not peripheral T cells, also reacts with human epidermal Langerhans cells, as shown by a four-step immunoperoxidase method and immunoelectron microscopy. To define whether T6-positive cells are also present in normal human dermis, we used these techniques to demonstrate two immunologically distinct populations of histiocyte-like cells in normal human dermis. The first population contains cells devoid of phagolysosomes or Birbeck granules. These cells react with anti-T6 antibody, but not with monoclonal anti-T3 antibody which defines peripheral T cells, and are found predominantly in and around dermal lymphatic vessels. The second is composed of phagolysosome-containing cells which do not react with anti-T6 antibody or anti-T3 antibody. Because to date, Langerhans cells are the only cells in normal human epidermis that react with anti-T6 antibody, these data provide immunological evidence for a specific link between Langerhans cells and a T6-positive dermal mononuclear cell, possibly the so-called indeterminate cell. In addition, application of these techniques should, for the first time, permit the immunological distinction of these T6-positive mononuclear cells from other cells bearing Ia antigens, such as dermal histiocytes and certain lymphocytes, in normal and diseased skin.

The distribution of major histocompatibility antigens HLA-A,B,C (HLA), beta 2-microglobulin (beta 2m), and Ia-like antigens (HLA-DR; Ia) in normal skin was studied in frozen tissue sections by a four-step immunoperoxidase method and an avidin-biotin method employing monoclonal antibodies. HLA and beta 2m were present on the basal and spinous keratinocytes of the epidermis, on the outer root sheath epithelium in the infundibulum of the hair follicle, and on the excretory sebaceous duct epithelium. Ia-positive dendritic cells were found in the epidermis and hair follicles, but they were more frequent in the infundibulum and isthmus of the hair follicle than in its inferior portion or in the epidermis. In the straight eccrine duct, HLA and beta 2m-positivity was most striking in its lower portion. In the superficial duct, there was a less intense staining using the four-step procedure, but when an avidin-biotin method was used, the difference was less apparent. In contrast, the acrosyringial epithelium was markedly Ia-positive with decreasing intensity of staining as the duct penetrated the dermis. No HLA or Ia antigens were identified in eccrine glands and apocrine glands. Eccrine glands were slightly beta 2m-positive. HLA and beta 2m were uniformly present in non-dilated and dilated intradermal apocrine ducts.

SUMMARY Skin biopsies from four patients with lichen planus were studied using monoclonal antibodies directed against T lymphocytes. Anti-T1 and anti-T3 antibodies, which react with all peripheral T cells, stained most cells in the dermal infiltrates. The majority of infiltrating cells also stained with anti-T4 and anti-T4b antibodies, which react with helper/inducer cells, whereas a minority of cells stained with anti-T8 antibody, which reacts with cytotoxic/suppres-sor cells. Surface IgM was not identified on any infiltrating cells, providing evidence against B cell participation. Intraepidermal and dermal cells with long cytoplasmic extensions stained with anti-T6 antibody in all cases, defining them as Langerhans cells or their precursors. T6-positive cells were seen in greater number than in normal control epidermis and dermis. The results indicate that well-developed lesions of lichen planus are characterized by an influx of helper/inducer T lymphocytes and increased numbers of Langerhans cells. These observations support the contention that cellular immunity is important in the pathogenesis of this disorder.