FIG 4.

Tlr7^−/− mice are more resistant to plague and express reduced serum IFN-β levels. Groups of 5 to 8 WT and Tlr7^−/− mice (A to C) or WT and MyD88^−/− mice (D) were challenged by intranasal infection with 1 × 10⁶ CFU Y. pestis KIM D27 (T3SS⁺ pgm negative) and monitored for survival over 14 days (n = 15 per strain, collected in 3 independent trials) (A) or euthanized on day 5 (B and C) or day 3 (D) postinfection, blood was collected, and serum was analyzed for IFN-β (B and D) or TNF-α (C) by an ELISA (n = 10 per strain, collected in 2 independent trials). X indicates that the animal died prior to analysis, and bars indicate the medians. Data were analyzed by a Mantel-Cox log rank test (A) or by Student's t test (B to D). *, P < 0.05.