Figure 6. Murine norovirus infection promotes bacteria-induced TNF-α production and lethality in mice via Nod1 and Nod2.

(A and B) WT, and Nod1^−/−Nod2^−/− mice were injected i.p. with PBS (n=5) or poly I:C (200 μg/mouse, n=10) and then infected with E. coli 3 × 10⁸ CFU/mouse i. p. 24 h after poly I:C administration. Lethality was monitored for 5 days after infection (A). At 3 h post-infection, the levels of TNF-α in serum were assessed by ELISA (n=5 or 10) (B). (C and D) WT, and Nod1^−/−Nod2^−/− mice were injected with PBS or poly I:C (200 μg/mouse) i.p. and then infected with P. aeruginosa 2.5 × 10⁷ CFU/mouse i. n. 24 h after poly I:C administration. Lethality was monitored for 5 days after infection (n=10–11) (C). At 3 hrpost-infection, the level of TNF-α in lung homogenates was assessed by ELISA (n=6) (D) (E–I) WT, Nod1^−/−Nod2^−/−, and Rip2^−/− mice were mock-infected or infected orally with MNV-1 (1 × 10⁷ PFU/mouse) and then infected with E. coli 3 × 10⁸ CFU/mouse i. p. 24 h after the MNV-1 infection. Lethality was monitored for 5 days after E. coli infection (n=9–10) (E). Bacterial loads in lung (F) and blood (G) samples were determined at 8 h post-infection by plating (n=7–8). The short black horizontal lines show the mean values for the groups. Each symbol represents one animal. N.S. denotes not significant. At 3 h post-infection, serum TNF-α levels were assessed by ELISA (n=9–10). N.S. denotes not significant (H). 1 h before E. coli infection, WT mice were injected i.p. with control rat IgG or anti-TNF-α rat IgG and lethality was monitored for 5 days after infection (n=10) (I). Data are expressed as mean ± S.D. Results are representative of 2 or 3 independent experiments.