B10.Q/J mice fail to genetically complement Tyk2-deficient mice. (a) T cell blasts from wild-type, B10.Q/J, Tyk2–/–, B10.Q/Ai × Tyk2–/– F1, and B10.Q/J × Tyk2–/– F1 mice were assayed for IL-12-induced phosphorylation of Stat4. (b) IFN-γ levels were determined in sera obtained 4 days after T. gondii infection in parental strains, B10.Q/Ai × Tyk2–/– F1, and B10.Q/J × Tyk2–/– F1 mice. (c) The percentage of infected peritoneal cells of the same mice described in b were determined on day 5 postinfection. Results shown are representative of one of two experiments. In each experiment, three to four age- and sex-matched mice were used.