Plasma and scales levels of interleukin 18 in comparison with other possible clinical and laboratory biomarkers of psoriasis activity

The aim of the study was to assess plasma and scales levels of interleukin (IL) 18 collected from psoriatic patients with different disease activity. IL-18 concentrations were measured using an enzyme immunoassay in the plasma and scales of 34 patients with chronic plaque type psoriasis. IL-18 levels were analysed with respect to plasma-transforming growth factor β₁ (TGF-β₁), the disease duration and the duration of the present relapse, and psoriasis area and severity index (PASI). Plasma IL-18 concentration varied from 90 to 1300 pg ml^-1 and means (368.2±42.4 pg ml^-1) were significantly elevated in comparison with healthy controls (205.9±31.8 pg ml^-1). The presence of IL-18 was also demonstrated in scales from skin lesions. Treatment caused a significant decrease of plasma IL-18 concentration to 250.2±13.8 pg ml^-1. There was a significant correlation between plasma IL-18 levels and PASI values (r=0.554). There was no correlation between IL-18 concentration in scales and PASI, between IL-18 concentrations in plasma and scales, and between plasma IL-18 and the disease duration or duration of present relapse. Plasma TGF-β₁ concentration demonstrated a significant correlation with PASI (r=0.353), but not with IL-18 levels in plasma (r=0.063) and scales (0.141). The sum of plasma levels of IL-18 and TGF-β₁ divided by the optimal coefficient demonstrated a statistically significant correlation with the highest r-value. The findings confirm an association between plasma IL-18 concentration and psoriasis severity. Moreover, it was shown that combined measurement of IL-18 and TGF-β₁ in plasma can be considered as a possible biomarker of psoriasis activity.