Host resistance to Toxoplasma gondii: model for studying the selective induction of cell-mediated immunity by intracellular parasites.

Cell-mediated immunity (CMI) provides a major host defense against infectious disease and malignancy. Nevertheless, the mechanisms underlying the induction of CMI remain poorly understood and this lack of knowledge remains an important impasse in the design of rationally based vaccines and immunotherapies. Toxoplasma gondii is an intracellular pathogen that, as part of its normal life cycle, induces a potent CMI response leading to host resistance. Studies on the interaction of this parasite with the immune system therefore provide a unique approach for identifying events that selectively lead to the triggering of host-protective CMI. In addition, this knowledge may provide new strategies for immunotherapy of opportunistic infections in immunodeficient hosts.