Increased interleukin-7 levels in the sera of psoriatic patients: lack of correlations with interleukin-6 levels and disease intensity

Interleukin (IL)-7 is a multifunctional cytokine which is involved in the regulation of keratinocyte-T lymphocyte interactions; the latter is an important factor in the pathogenesis of psoriasis. In vitro, IL-7 is able to induce release of cytokines, including IL-6; IL-6 expression is known to be enhanced in psoriatic patients. Serum levels of IL-7 and IL-6 were measured by ELISA in 40 psoriatic patients and compared with cytokine levels in 18 healthy individuals. Serum levels of IL-7 were also evaluated in 24 psoriatic patients during the remission of the disease after effective treatment. The IL-7 and IL-6 serum levels were significantly higher in psoriatic patients than in healthy subjects and the IL-7 serum levels did not significantly decrease after treatment. Serum levels of IL-7 did not correlate with PASI scores; however, a significant positive relationship was observed between IL-6 levels and PASI scores. There was no correlation between increased levels of IL-7 and IL-6 in the sera of psoriatic patients, suggesting the lack of a direct link between these two cytokines in the psoriatic process. In conclusion, increased IL-7 serum levels suggest that IL-7, like IL-6, may be involved in the pathogenesis of psoriasis, but in contrast with IL-6, serum IL-7 levels could not be used as a marker of disease activity in psoriatic patients.