Role of Lymphocyte Subpopulations in The Immunopathogenesis of Psoriasis and The Effect of Narrow Band UVB Phototherapy on The Immunological Profile of Psoriasis Patients.

Psoriasis is one of the most common chronic, inflammatory, T-cell-mediated autoimmune diseases. Narrow-band UVB (NB-UVB) therapy is widely used in the treatment of psoriasis; however, its mechanism of action is still not well understood. The objective of this study was to investigate the circulating T-lymphocyte subpopulations in psoriasis patients before and after NB-UVB, to get insights into the mechanism of NB-UVB in the treatment of psoriasis. The severity of psoriasis was assessed by means of the Psoriasis Area and Severity Index (PASI-score). The percentage of CD4+ T helper, CD8+ T cells, CD4+ CD25+T reg cells and CD4+ CD161+ T h17 cells were determined in the peripheral blood mononuclear cells in 40 untreated psoriasis patients with moderate-to-severe disease (PASI-score ?12) and in 30 age and sex matched healthy controls using flow cytometry. Psoriasis patients were treated with NB-UVB therapy three times / week for 8 weeks. Disease severity (PASI-score) and T cells frequencies in the blood were evaluated on enrolment (W0) and at 8 (W8) weeks. Compared with healthy controls, psoriasis patients with active disease had significantly higher proportion of peripheral CD4+Th, CD8+ T cells, and CD4+CD161+Th17 with lower proportion of CD4+CD25+Treg cells. Patients demonstrating marked improvement after NB-UVB phototherapy with significantly reduced circulating Th1and Th17 and CD8+ cytotoxic T cell levels while increasing Treg cell levels with a highly statistically significant difference after therapy (P < 0.001). In conclusion, our data indicated that the overexpression of CD4+Th, CD8+ T cells and CD4+CD161+Th17 cells together with the decreased frequency of Treg cells may play an important role in the pathogenesis of psoriasis. NB-UVB phototherapy is an effective and safe treatment for psoriasis acts through the inhibition of CD4+Th and CD4+CD161+Th17 cell immune response as well as the promotion of Treg cell immune response.