Similar to IFN-γ, studies using KO mouse models deficient in either TNF-α or p55 TNF-α receptor have defined a central function for this cytokine in many intracellular bacterial infections such as M. tuberculosis [29], Salmonella [22], Chlamydia [23], Brucella [24], L. monocytogenes [25], and F. tularensis [26], and in viral infections such as HSV [27] and HIV [28]. This evidence concerns the gene TNF and viral infectious disease.