Why are natural killer cells important for defense against Aspergillus?

There is growing evidence that natural killer (NK) cells play an important role in the host response to Aspergillus spp. In vitro data clearly demonstrate that both murine and human NK cells are able to damage Aspergillus. NK cells exert direct antifungal activity via cytotoxic molecules such as perforin, and NK cell-derived cytokines and interferons modulate proliferation and activation of a variety of immune cells in order to fight the fungus. However, in turn, Aspergillus is able to exhibit immunosuppressive effects on NK cells. Antibody-mediated depletion of NK cells in neutropenic mice infected with A. fumigatus further impairs clearance of the pathogen from the lungs and results in a higher mortality as compared to animals with NK cells. Clinical data on the impact of NK cells in the antifungal host response are less clear, as different arms of the human immune system are involved, which interact and overlap in a complex network. Future studies must better characterize the interaction of NK cells and Aspergillus and to clarify the benefit and potential risks of using NK cells as adoptive immunotherapy in patients suffering from invasive aspergillosis, which may be a significant step toward decreasing morbidity and mortality of these patients.