Interleukin-10: an important immunoregulatory cytokine with major impact on psoriasis.

Interleukin (IL)-10 is a pluripotent cytokine with effects on numerous cell populations, in particular circulating and resident immune cells as well as epithelial cells. With its potent immunoregulatory capacities its main biological function seems to be the limitation and termination of inflammatory responses. Thus its low level expression found in psoriasis may have pathophysiological relevance for this immune disease. Remarkably, induction of IL-10 expression was found by conventional antipsoriatic therapies, supporting the hypothesis that IL-10 may be a key cytokine in psoriasis and that application of this cytokine itself may have therapeutic effects. In first clinical trials in patients with established psoriasis IL-10 showed moderate antipsoriatic effects and was well tolerated. Moreover, long term application in psoriatic patients remission showed that IL-10 therapy decreases the incidence of relapse and prolongs the disease free interval. The immunological effects observed during these clinical studies together with in vitro observations suggests that IL-10 exerts its antipsoriatic activity by effects on different cell populations including antigen presenting cells and T-cells (lasting type 1/ type 2 cytokine balance shift), but not through direct effects on keratinocytes. In conclusion IL-10 seems to have major importance in psoriasis. Further investigations, in particular multicenter, placebo-controlled, double blind trials are required to fully determine whether IL-10 application will become a successful antipsoriatic therapy.