CASP1 and infection: To determine if the expression pattern of active caspase-1 followed the expression of IL-1β in GC B cells (Fig 2D) we determined active caspase-1 at 7-, 10- and 15-days post A/PR8 infection, observing the number of GC B cells expressing active caspase-1 peak at day 10 (Fig 3C).