The effect of Interleukin-13 on Leishmania major-induced infection in rats. (c2005)

Abstract

Interleukin-13 is a relatively new cytokine with continuously growmg importance to medical research and medical practice. IL-13 has been shown to be involved in suppressing the immune responses in some cases, while promoting it in others. We investigated the effects of recombinant IL-13 (rIL-13) on the host response to Leishmania mrgor in rats. IL-13 treatment started 1 hour pre-infection and was maintained daily for 8 days post-infection. Acquired resistance against L mrg'or is a typical T helper (Th) 1 dominated immune response, whereas Th2 cytokines are thought to worsen leishmaniasis. Although IL-13 has been described as a Th2 cytokine with deactivating antiinflammatory activities, we found that treatment with IL-13 increased the levels of IL-l~; a major pro-inflammatory cytokine. Consequently, IL-13 increased pain perception in rats as assessed by the hot plate tests. Furthermore, IL-13 has been reported to down-regulate IL-12; a key cytokine in the propagation of the Thl immune response, and therefore promoting a Th2 response. In contrast, we found that IL-13 increased IL-12p70 production, but had no effect on the levels of IL-4; a major Th2 cytokine. Further analysis included quantification of L. mqjor parasites from paws (infection site), liver and blood of rats using real-time peR. The tests revealed that 99.99% of the injected parasites were cleared in both IL-13 treated and non-treated rats at day 30 post-infection, suggesting that both groups followed the Thl healing pathway.