Immunohistochemical staining for macrophages with F4/80 antibody: Macrophages in healthy colonic mucosa (control) and at day 3 of DSS ingestion are localized predominantly in the lamina propria. Positive staining for macrophages in the submucosa was initially found at day 6 and increased at day 8 of DSS ingestion. 2.5% DSS-induced colitis. Findings from inflamed colons of 5%DSS-induced colitis were similar. Original magnification × 20.