Distribution of melanocytes in the skin of psoriasis patients

Psoriasis is a chronic immune-mediated inflammatory disease with predominant damage to the skin and joints. Despite fundamental studies of its pathogenesis, the cause of the development of the T-cell response has not been determined. More recently, a new concept has been proposed for the formation of psoriatic inflammation, where a significant role in the pathogenesis is assigned to melanocytes. Evaluation of the content of these cells and their relationship with other participants of inflammation will allow expanding the understanding of the pathogenesis of psoriasis and the targets of targeted therapy.

Aim: study of the quantity, distribution and proliferative activity of melanocytes.

Materials and methods. The study included 20 patients with plaque psoriasis: men — 18 (90 %), women — 2 (10 %). The severity of the disease was assessed by the index of the area and severity of PASI psoriatic lesions. In the histological specimens, the thickness of the epidermis, the length of the basement membrane in the visual field, and pathological changes in the epidermis and dermis were determined. For immunohistochemical detection of melanocytes, the MelanA marker was used, the cell proliferative activity was Ki67, and the cytotoxic T-lymphocytes, CD8. Used a dual visualization system. Differences were considered significant at p < 0.05.

Results. The number of MelanA⁺  cells in the affected skin of patients with psoriasis — 54 (44–64)/1.4 mm2 was 2.4 times higher than in unaffected skin — 24 (22–30)/1.4 mm² (p < 0.05), and 2 times higher than in the skin of healthy individuals — 27 (25–32)/1.4 mm² (p < 0.05). The content of MelanA⁺ cells per 1 mm of the basement membrane in patients with psoriasis in the affected skin is 11 [7–13] cells/mm, unaffected — 12 [11–14] cells/mm and in healthy individuals — 12 [9–13] cells/mm did not significantly differ (p > 0.05). In the affected skin of patients with psoriasis, multiple contacts of CD8⁺ and MelanA⁺ cells were detected — 10 [8–13]/1.4 mm².

Conclusions. In the affected skin of patients with psoriasis, the absolute number of melanocytes is significantly higher than in unaffected skin and the skin of healthy individuals, while the ratio of melanocytes to basal keratinocytes did not differ. In the skin of all the studied groups, no melanocytes in the proliferation stage were detected. Multiple contacts of MelanA⁺ and CD8⁺ cells are observed in the affected skin of patients with psoriasis.

Conflict of interest: the authors state that there is no potential conflict of interest requiring disclosure in this article.