Figure 4. Increased apoptosis of lung macrophages is associated with clearance of Y. pestis yopK.

Tissue sections from 6, 24, and 72 HPI with 1×10⁴ CFU of WT (A) or 1×10⁶ CFU of yopK (B) were stained by immunohistochemistry with antibodies to cleaved caspase-3. Apoptotic macrophages (A–B) were the most prominent positively staining cells; images are representative and shown at 40× magnification with 100× inset. C) Apoptotic macrophages were counted in 10 non-overlapping fields on blinded slides at 40× magnification. Data shown are the mean number of caspase-3-positive macrophages per field of each mouse, averaged over 6 mice per group *p<0.05, ns not significant, evaluated by unpaired Student's t-test. Data were collected from two independent experiments.