Otkjaer et al. [22] determined IL-19 and IL-20 in nonlesional and lesional psoriatic skin after 28 days of treatment using topical calcipotriol ointment for mild cases and oral cyclosporine for moderate and severe cases. They found that in patients treated with calcipotriol, IL-19 and IL-20 mRNA expression levels in lesional psoriatic skin were reduced after 14 days, but the reduction became statistically significant only after 28 days. So the timing for mRNA expression analysis could affect the degree of significance. This is further supported by studies demonstrating a decrease of IL-18 levels after narrowband UVB therapy together with other parameters' characteristics for the T helper 1 (Th1) response [23] . Apart from stimulating the Th1 response, IL-18 can regulate the Th2 response depending on the local cytokine network. IL-12 enhances IFN-γ production induced by IL-18, whereas IL-18 alone induces IL-4 and IL-13 production [24] .