Because T. gondii infects mice, this natural host–pathogen combination provides a model to understand (1) how the host can sense infection; (2) the events that lead to the production of cytokines (IL-12 and IL-1 family members) that promote the production of IFN-γ; and (3) the IFN-γ–mediated pathways that allow infected cells to limit parasite replication. The gene discussed is IFNG; the disease is infection.