The surgically resected specimen was fixed in 10% buffered formalin, processed through graded ethanol, and embedded in paraffin blocks. A 3-μm section including both normal colonic mucosa and cancerous tissue was used. Deparaffinized sections were created, and the slide was boiled for 10 min. To quench endogenous peroxidase activity, the slide was immersed in mixed methanol and H2O2 for 25 min at room temperature. PGE2 expression was examined using rabbit anti-human PGE2 antibody (Abcam, Cambridge, UK) and VECTASTAIN Elite ABC Rabbit IgG Kit (Vector Laboratories, Burlingame, CA, USA). The slide was blocked by blocking serum for 20 min at room temperature and incubated with a primary antibody (rabbit anti-human PGE2 antibody; Abcam, Cambridge, UK) (1:100) overnight at 4 °C. After overnight incubation, the slide was incubated with a secondary antibody (biotinylated goat anti-rabbit antibody) for 30 min at room temperature and incubated with Reagent A and B mixed for 20 min at room temperature. It was then incubated with Histofine (Nichirei Biosciences Inc., Tokyo, Japan) for 14 min. Finally, the slide was stained with Meyer’s hematoxylin (Wako Pure Chemical Industries, Osaka, Japan) for 3 min.
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