Reduction of COX-2 expression after celecoxib-treatment. A) Tumour sections of untreated (n = 7) and celecoxib treated mice (n = 8) were immunohistochemically double-stained for the presence of Gr-1 (red) and COX-2 expression (blue). No expression of COX-2 was found in tumour sections from mice with dietary celecoxib. Gr-1+ cells were reduced in tumour sections of mice treated with celecoxib [magnification 200× left and 400× right]. B) PGE2 levels were measured in peritoneal washings of untreated (n = 7) versus celecoxib treated mice (n = 8) (p = 0.0061). NO was detected using Greiss reagent.