Therefore, similarly to the hygiene hypothesis that suggests that a preventive effect on allergic and autoimmune responses results from constant exposure to various benign infectious agents, we may postulate that any protective effect of infections on cancer development would require a constant or frequent enhancement of cancer immunosurveillance through repeated exposure to infectious agents triggering activation of appropriate immune responses, including IFN-γ-producing NK cells. The gene discussed is IFNG; the disease is infection.