The hemorrhagic fevers caused by Lassa (LASV) and Ebola (EBOV) viruses are important problems of public health in Africa. The immune responses and the pathogenesis associated with these diseases are unknown. NK cells are at the crossroads between the innate and adaptive immune responses through their abilities to secrete cytokines and kill the infected cells. The interactions between NK cells and dendritic cells (DC) or macrophages potentiate the immune responses. This project aims to understand the role of NK cells in the control of viral replication and in the induction of immune responses during LASV and EBOV infection.An in vitro model of coculture of human NK cells with autologous DC or macrophages has been set up. Cell activation, cytokine production, proliferation and NK cell-mediated killing were analyzed after the infection with LASV or EBOV. In addition, NK cell functions in response to LASV were compared with those induced during Mopeia virus (MOPV) infection, closely related to LASV but not pathogenic for humans.Here, we show that LASV- or MOPV-infected macrophages, but not DC, induce the activation of NK cells and the increase of their cytotoxic capacity. This process involves cell contact and type I IFN. However, these cells are neither able to kill the infected cells nor produce IFN-γ. NK cells are activated and are able to kill the infected cells when stimulated by mutated LASV-infected macrophages and DC. Surprisingly, the type I IFN which are secreted in high amounts in response to these viruses are not involved in NK cell activation. EBOV infection does not lead to NK cell activation in the presence of DC. EBOV-infected macrophages induce low NK cell activation without cytokine production or cytotoxicity.These results allow to better understand the immune responses and the mechanisms of pathogenesis associated with Lassa and Ebola hemorrhagic fevers.
