The IRG protein-based resistance mechanism in mice and its relation to virulence in Toxoplasma gondii

► Up to 18 IRG proteins defend mice against Toxoplasma gondii and two Chlamydia species, but not against several other organisms. ► IRG proteins disrupt the T. gondii parasitophorous vacuole. ► The IRG resistance system is absent from man, from several other mammals and from birds. ► Three specialised IRG family members (IRGM proteins) act as regulators of the activity of the others. ► IRG proteins in mice are inactivated by kinases secreted by virulent strains of T. gondii.