FIG 4.

S. Typhimurium curli fibers lead to IL-1β production in BMDMs. (A and B) Curli expression was determined in S. Typhimurium bacteria that were grown under conditions optimal for inflammasome activation (A) or curli expression (B) using S. Typhimurium carrying PcsgBA::gfp on a plasmid. S. Typhimurium carrying a plasmid containing promoterless gfp was used as a negative control. S. Typhimurium carrying a plasmid that constitutively expresses GFP via PtetA::gfp was used as a positive control. (C and D) C57BL/6 macrophages pretreated with LPS (50 ng/ml) were infected at an MOI of 20 with S. Typhimurium grown under conditions that were optimal for either inflammasome activation (C) or curli expression (D). The supernatants were collected 4 h after infection and assayed by ELISA for IL-1β. Shown are average means and SE from three independent experiments. *, P < 0.05; n.s., not significant.