DERMAL ENDOTHELIAL-CELLS AND KERATINOCYTES PRODUCE IL-7 IN-VIVO AFTERHUMAN SCHISTOSOMA-MANSONI PERCUTANEOUS INFECTION

The parasite Schistosoma mansoni infects its definitive mammalian host through an obligatory cutaneous penetration. In this work, we studied early immune response following migration of larvae through human ski n, the first immunocompetent organ encountered by the parasite, For th is purpose we used an experimental model of severe combined immunodefi cient mice engrafted with human skin and injected with autologous PBL, Six days after percutaneous infection, we observed an infiltration of lymphocytes within the human skin, predominantly composed of CD4(+) T f cells. Moreover, among the cytokines potentially present in the infe cted skin, immunohistochemistry analysis revealed an in vivo expressio n of IL-7 in the epidermal layers and strikingly at the level of vascu lar endothelium. Using an in vitro coculture system, we showed that th e S. mansoni larvae-directly trigger IL-7 production by human dermal m icrovascular endothelial cells but not by keratinocytes, Finally, meas urements of IL-7 concentrations in plasma of 187 S, mansoni-infected i ndividuals showed that the youngest, which are also the most infected, displayed the highest IL-7 levels, Together, these findings describe dermal endothelial cells as a novel source of IL-7, a cytokine particu larly important in schistosomiasis.