Interleukin-7 in the skin of Schistosoma mansoni-infected mice is associated with a decrease in interferon-gamma 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-gamma-(IFN-gamma) 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-gamma 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 observation 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.