Cyclosporin A inhibits keratinocyte cytokine gene expression

The immunosuppressive peptide cyclosporin A (CyA) is an extremely effective therapy for severe recalcitrant psoriasis, although its mechanism of action is unknown. In this study, we examined the effect of CyA on keratinocyte growth and cytokine expression, and showed that CyA inhibits the growth of murine and human keratinocytes (KC) and KC cell lines. In addition, CyA inhibits the expression of cytokine genes in a dose-dependent fashion. After 2 days' incubation with 20 microM CyA, interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta), and interleukin 8 (IL-8) mRNA were decreased by 4-fold, 3.3-fold and 3.3-fold, respectively, in COLO-16, a keratinocyte cell line. IL-1 biological activity recovered from COLO-16 culture supernatants decreased to one-fifth of that of controls. In the murine KC cell line PAM 212, 10 microM CyA treatment for 2 days downregulated IL-1 alpha, tumour necrosis factor-alpha (TNF-alpha) and IL-1 receptor by 60%, but had no effect on the message for interleukin 3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), ornithine decarboxylase and beta-actin. Cells cultured for 5 days in the presence of CyA required much lower concentrations (2 microM) to achieve the same degree of inhibition of IL-1 alpha. Similar tissue concentrations of CyA have been reported in psoriatics undergoing CyA therapy.(ABSTRACT TRUNCATED AT 250 WORDS)