Phenotypical characterization, distribution and quantification of different mast cell subtypes in transmural biopsies from the gastrointestinal tract of cats with inflammatory bowel disease

In this study subtypes, distribution and number of mast cells were investigated within mucosa and submucosa of the gastrointestinal tract of 24 cats with inflammatory bowel disease (IBD) in comparison to 11 control cats. Paraffin sections of formalin-fixed transmural gastrointestinal biopsies from stomach, duodenum, jejunum, ileum and colon were examined. Mast cells were phenotyped and quantified based on their chymase and tryptase content, by applying a combined enzyme-histochemical and immunohistochemical double-labeling technique and on their heparin content by a metachromatic staining method (kresylecht-violet, MCKEV). Mast cells containing both chymase and tryptase were not found in any of the samples examined. Furthermore, in the stomach neither chymase (MCC) nor tryptase (MCT) bearing mast cells were detected. In cats with lymphocytic–plasmacytic enteritis or enterocolitis elevated numbers of MCT or MCC were identified in comparison to controls mainly located in the inflamed segments. The highest quantity of MCC was found in cats with eosinophilic gastroenterocolitis or enterocolitis in comparison to other IBD forms, but only minor numbers of MCT were detected in these cases. In cats with fibrosing enteropathy (FE) a decrease of MCC and mast cells containing heparin was detected in affected segments, while increased numbers of MCT were detected in all locations. The elevation in the number of MCT was higher in unaffected areas than in fibrotic regions. Regarding all IBD cases higher counts of MCC were found especially in the inflamed locations, whereas in unaffected segments increased numbers of MCT were detected. The clear predominance of MCC and MCT within the mucosa and of MCKEV within the submucosa of all cats examined possibly represents differences of the cytokine milieu within the intestinal layers. In FE, mast cells are possibly pivotal for the containment of the inflammatory process because of their antiinflammatory properties. The results of this study indicate that mast cells and their mediators are involved in the pathogenesis of different IBD forms in cats.