Fig. 2.
F4/80-immunoreactive macrophages (amorphous cells in red) were mainly detected in the lamina propria of the mucosa in control tissue. Tissue sections were counterstained with 4′,6-diamidino-2-phenylindole (nuclei in blue). Four and twenty-four hours after the third daily intracolonic treatment with Zym, an accumulation of macrophages at the bottom of the crypts and in the submucosa in the distal colorectum was evident (boxed area), which resolved by day 6. The isotype control antibody, rat κ monoclonal IgG2b (1:1,000, Abcam, Cambridge, MA), showed no staining, indicating that the immunostaining with F4/80 antibody was not due to nonspecific binding of immunoglobulins to Fc receptors expressed on immune cells.