Decreased PD-1 positive blood follicular helper T cells in patients with psoriasis

Follicular helper T (Tfh) cells are recently characterized subset of helper T cells, which are initially found in the germinal centers of B cell follicles. The major role of Tfh cells is helping B cell activation and antibody production during humoral immunity. Recently, blood Tfh cells were shown to be associated with autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, bullous pemphigoid and psoriasis. There is only one study which investigated Tfh cells in psoriasis patients. Therefore, in this study, we evaluated and analyzed blood Tfh cells in Korean patients with psoriasis. A total of 28 psoriasis patients and 16 healthy controls were enrolled. The frequency and absolute number of CXCR5⁺PD-1⁺ Tfh cells were decreased in patients with psoriasis compared to healthy controls. CD4⁺CXCR5⁺ T cells and CXCR5⁺ICOS⁺ Tfh cells did not show differences. The frequency and absolute number of CXCR5⁺PD-1⁺ Tfh cells in psoriasis patients negatively correlated with erythrocyte sedimentation rate and positively correlated with disease duration. The absolute number of CXCR5⁺ICOS⁺ Tfh cells also showed positive correlation with disease duration. However, the subpopulations of Tfh cells did not correlate with Psoriasis Area and Severity Index. Serum interleukin-21 level was significantly increased in psoriasis patients compared to healthy controls, however, its level did not correlate with clinical and experimental parameters of psoriasis patients. These findings suggest the decreased function of Tfh cells in psoriasis, which could result in attenuated B cell immune responses in the pathogenesis of psoriasis. However, further investigations are necessary to confirm the function of Tfh cells in psoriasis vulgaris.