Flagellin-dependent variation in caspase 1 processing in L. monocytogenes-infected macrophages is dependent on Ipaf. A, LPS-primed WT macrophages were infected with WT, flaA, flgK, or ΔLLO L. monocytogenes at MOI 6. IL-1β secretion from supernatants was assessed 4 h post infection. *, p < 0.05. B, WT macrophages were infected at MOI 6 for 4 h then proteins precipitated from supernatants and combined with cell lysates. Samples were Western blotted then probed for the p10 fragment of caspase 1. U, Uninfected; and **, nonspecific band. L. monocytogenes infected Ipaf−/− macrophages were analyzed for (C) IL-1β secretion and (D) caspase 1 processing as in A and B above. Error bars, SD. Representative of three experiments. E, LPS-primed WT macrophages were infected with WT, flaA, flgK, or ΔLLO L. monocytogenes at MOI 1, 3, 6, or 12. IL-1β secretion from supernatants was assessed 4 h post infection.