The average numbers of (A) apoptotic (positive for caspase3, Casp3) and (B) proliferative/regenerative (positive for Ki67) ileal epithelial cells as well as of (C) T lymphocytes (positive for CD3) and (D) B lymphocytes (positive for B220) in the ileal mucosa and lamina propria from six high power fields (HPF, 400× magnification) per mouse were assessed microscopically in immunohistochemically stained small intestinal paraffin sections at day 6 post-infection. The gene discussed is CASP3; the disease is infection.