GM-CSF confers resistance to influenza by enhancing innate immune mechanisms that depend on alveolar macrophages. Pulmonary delivery of this cytokine has the potential to reduce the morbidity and mortality due to influenza virus.

Avirulent strains of Salmonella typhimurium are being considered as antigen delivery vectors. During its intracellular stage in the host, S. typhimurium resides within a membrane-bound compartment and is not an efficient inducer of class I-restricted immune responses. Viral epitopes were successfully delivered to the host-cell cytosol by using the type III protein secretion system of S. typhimurium. This resulted in class I-restricted immune responses that protected vaccinated animals against lethal infection. This approach may allow the efficient use of S. typhimurium as an antigen delivery system to control infections by pathogens that require this type of immune response for protection.

We studied the role of NK cells in regulating human CD8+ T cell effector function against mononuclear phagocytes infected with the intracellular pathogen Mycobacterium tuberculosis. Depletion of NK cells from PBMC of healthy tuberculin reactors reduced the frequency of M. tuberculosis-responsive CD8+IFN-γ+ cells and decreased their capacity to lyse M. tuberculosis-infected monocytes. The frequency of CD8+IFN-γ+cells was restored by soluble factors produced by activated NK cells and was dependent on IFN-γ, IL-15, and IL-18. M. tuberculosis-activated NK cells produced IFN-γ, activated NK cells stimulated infected monocytes to produce IL-15 and IL-18, and production of IL-15 and IL-18 were inhibited by anti-IFN-γ. These findings suggest that NK cells maintain the frequency of M. tuberculosis-responsive CD8+IFN-γ+ T cells by producing IFN-γ, which elicits secretion of IL-15 and IL-18 by monocytes. These monokines in turn favor expansion of Tc1 CD8+ T cells. The capacity of NK cells to prime CD8+ T cells to lyse M. tuberculosis-infected target cells required cell-cell contact between NK cells and infected monocytes and depended on interactions between the CD40 ligand on NK cells and CD40 on infected monocytes. NK cells link the innate and the adaptive immune responses by optimizing the capacity of CD8+ T cells to produce IFN-γ and to lyse infected cells, functions that are critical for protective immunity against M. tuberculosis and other intracellular pathogens.