Mice also exhibit a substantial increase in the plasma IFNγ level with infection, and the lack of A. phagocytophilum growth restriction in immunocompromised mouse strains is consistent with an important role for acquired immunity in controlling bacterial burdens and complete bacterial killing (Martin et al., 2000; Von Loewenich et al., 2004; Birkner et al., 2008). Here, IFNG is linked to infection.