IFNG and viral infectious disease: The profound susceptibility of IFN-γ-deficient mice to a wide range of protozoan parasites, including Toxoplasma gondii[3], [4], Cryptosporidium parvum[5], Leishmania major[6] and Trypanosoma cruzi[7], has given rise to the widely-held view that type II interferon (IFN-γ) is responsible for controlling protozoan infections, in contrast to type I interferons (IFN-α/β) which are primarily associated with control of viral infections.