Figure. 1. Host adaptive immunity is required for down-regulation of LEE virulence during C. rodentium infection.

A, B, SPF (A) and GF (B) WT B6 and Rag1^-/- mice (n= 7) were infected orally with 1×10⁹ cfu of C. rodentium and pathogen load in feces (left) and mouse survival (right) were determined over the indicated time. Data points are given as mean ± SD. Results are representative of at least 3 independent experiments. † denotes bacterial loads could not be determined beyond this time due to mouse lethality. **; p<0.01 by Log-rank test. C, Bioluminescent imaging of ler expression in the intestines of GF WT and Rag1^-/- mice infected with the ler-lux C. rodentium reporter strain. Imaging was performed on day 5 and 14 post-infection and the signal was quantified based on the color scale shown. Results are representative of 3 individual mice. D, Expression of ler (left) and bacterial burden (right) in fecal pellets of GF mice infected with the reporter ler-lux C. rodentium strain at the indicated day post-infection (dpi). Results show luminescence of ler-lux (relative light units) and C. rodentium cfu in the same samples. Data expressed as mean ± SD of individual mice (n=3). Results are representative of at least 2 experiments. *, p<0.05; N.S., not significant by Student's t test. See also Figure S1.