Serum and tissue levels of IL-17 in different clinical subtypes of psoriasis

Serum IL-17 levels and IL-17 mRNA expression have been reported to be higher in psoriatic skin than normal skin. There are very limited data in the literature about difference in the levels of this cytokine in various clinical disease subtypes. We aimed to evaluate whether there is a difference in the level of this cytokine according to clinical subtypes of psoriasis. 70 psoriasis patients (30 plaque psoriasis, 20 guttate psoriasis, and 20 pustular psoriasis) and 50 age- and sex-matched healthy volunteers were included in the study. Serum IL-17 levels were determined by ELISA. Skin biopsies obtained from lesions and non-lesional skin area of 12 patients and healthy individuals (n = 5) were analyzed by quantitative PCR (qPCR) to measure the mRNA levels of IL-17. Statistically, the serum IL-17 levels did not exhibit any difference between the patients and control groups. However, analysis of each subgroup revealed that the IL-17 levels were significantly higher in pustular psoriasis group (10.09 ± 12.6 pg/ml) than controls (4.4 ± 4.1 pg/ml) (p = 0.02). In addition, the IL-17 levels of plaque psoriasis patients with PASI score ≥10 (11.30 ± 6.0 pg/ml) were significantly higher than that of patients with PASI score <10 (3.39 ± 2.6 pg/ml) and controls (p < 0.001). The Pearson correlation analysis showed a positive correlation between the serum IL-17 levels and PASI. Lesional skin samples of psoriasis patients showed significantly higher levels of IL-17 mRNA compared with perilesional skin samples (p = 0.017). Also, in the pustular psoriasis, IL-17 mRNA levels were found to be distinctively high in comparison with other clinical subtypes and healthy controls. Our results indicate that IL-17 and Th17 cells have an important role in pustular psoriasis and severe psoriasis.