Interleukin‐7 in the skin of Schistosoma mansoni ‐infected mice is associated with a decrease in interferon‐ γ production and leads to an aggravation of the disease

The effect of recombinant interleukin‐7 (rIL‐7) on the course of murine schistosomiasis and the development of the accompanying immune response were investigated. We demonstrated that IL‐7 expression could be detected in the skin of infected mice from 1 to 21 days following infection. We here report that intradermal injection of exogenous human IL‐7, prior to the penetration of the parasite into the skin, leads to a more severe liver pathology and an increased number of surviving adult parasites. In addition, injection of rIL‐7 alters parasite migration (estimation of burdens of young larvae in lungs and liver). Administration of rIL‐7 led to a decrease of IL‐12 and interferon‐ γ ‐ (IFN‐ γ ) specific messengers RNA in skin and, more markedly, in skin‐draining lymph nodes. The number of B220 expressing cells was increased, and T‐cell number was reduced, in IL‐7‐treated infected mice. In addition, levels of IFN‐ γ and IL‐4 in sera were significantly reduced, whereas there was a shift from a Th1 to a Th2 type associated humoral response towards the egg antigens. Our experimental observations illustrate that the exogenous administration of rIL‐7 affects both the development of the host’s immune response and the behaviour of the parasite within the infected host. The early and specific production of IL‐7 in the host skin, following infection with Schistosoma mansoni , raises fascinating questions concerning the relationships between the parasite and its host at the very beginning of their interaction.