Programmed cell death pathways activated during infection with either type A F. tularensis strain KU49 or LVS. Strain KU49 has been described previously (Wickstrum,et al., 2007). Arrows indicate the expression of cleaved caspase-1, detected by immunoperoxidase techniques (Bokhari,et al., 2008) (antibody from Santa Cruz), in marginal zone macrophages. Bar, 100 μm.