In addition to control of A. phagocytophilum infection, IFNγ production in the murine HGA model is a major contributor to inflammatory tissue injury since histopathologic lesions in Ifng knockout mice are completely abrogated despite a marked increase in the pathogen load, implying that most histopathologic injury that belies disease is immune-mediated (Martin et al., 2000). The gene discussed is IFNG; the disease is human granulocytic anaplasmosis.