IDO1 and infection: Because T. gondii preferentially infects CD11b+ cells (e.g., monocytes) and spreads throughout various tissues from the primary sites of infection in vivo (37), GRA15 might play a role in parasite proliferation in human liver tissue, where newly arrived monocytes infected with GRA15-intact T. gondii might produce IL-1β and inhibit IDO1 expression in an iNOS-dependent fashion.