FIG 6.

NMII-induced B1a B cell death depends on activation of caspase-1. Protein was extracted from purified B1a B cells at day 1 and day 3 postinfection. (A and B) Analysis of caspase-3 (Casp 3) and PARP-1 cleavage (A) and caspase-1 (Casp 1) cleavage (B) in NMII-infected B1a cells by Western blotting. Lanes U, uninfected cells; lanes I, NMII-infected cells; lanes +, staurosporine-treated uninfected cells as an apoptotic cell positive control. (C) IL-18 levels in infected and uninfected cell supernatants at both 1 day and 3 days postinfection were measured using ELISA. (D) IL-1β levels in infected and uninfected cell supernatants were measured using ELISA. (E) The MTS assay was used to measure cell death at day 3 postinfection with NMII following treatment with or without a caspase-1 inhibitor. *, P < 0.05; **, P < 0.01; ***, P < 0.001. These data indicate that NMII-induced cell death in B1a B cells is dependent on cleavage of caspase-1 and causes secretion of the cytokines IL-1β and IL-18.