IDO2 and infection: Currently, infection of susceptible C3H/HeN mice with R. conorii is one of the best available animal models to mimic the salient manifestations of human rickettsial infections, as exemplified by its ability to recapitulate the expression of tumor necrosis factor-α (TNF-α), interferon-γ (INF-γ), chemokine (C-C motif) ligand 5 (ccl5/RANTES), indoleamine-2,3-dioxygenase (Ido), and inducible nitric oxide synthase (iNOS) as observed in human patients with MSF [17,18].