IFN-γ from CD4 T cells is essential for host survival and enhances CD8 T cell function during Mycobacterium tuberculosis infection.

IFN-γ is necessary in both humans and mice for control of Mycobacterium tuberculosis. CD4 T cells are a significant source of IFN-γ during acute infection in mice and are required for control of bacterial growth and host survival. However, several other types of cells can and do produce IFN-γ during the course of the infection. We sought to determine whether IFN-γ from sources other than CD4 T cells was sufficient to control M. tuberculosis infection and whether CD4 T cells had a role in addition to IFN-γ production. To investigate the role of IFN-γ from CD4 T cells, a murine adoptive transfer model was developed in which all cells were capable of producing IFN-γ, with the exception of CD4 T cells. Our data in this system support that CD4 T cells are essential for control of infection, but also that IFN-γ from CD4 T cells is necessary for host survival and optimal long-term control of bacterial burden. In addition, IFN-γ from CD4 T cells was required for a robust CD8 T cell response. IFN-γ from T cells inhibited intracellular replication of M. tuberculosis in macrophages, suggesting IFN-γ may be necessary for intracellular bactericidal activity. Thus, although CD4 T cells play additional roles in the control of M. tuberculosis infection, IFN-γ is a major function by which these cells participate in resistance to tuberculosis.