Purpose: The exact etiology and pathogenesis of IBD is not well defined. In particular, colonic immune responses and the importance of specific pro-inflammatory cells remain controversial. However, the ubiquitous presence of eosinophils (EOS) in the gut submucosa together with hypotheses implicating EOS as potential regulators of the immune tissue microenvironment, suggest these cells may play a role in IBD patients. We tested the hypothesis that tissue biopsies from ulcerative colitis (UC) and Crohn's disease (CD) patients would display more robust EOS infiltrate associated with degranulation when compared to controls.
Methods: To validate our hypothesis, we used a novel anti-eosinophil peroxidase (EPO) mouse monoclonal antibody capable of reliably detecting both tissue EOS and evidence of released EPO using formalin-fixed paraffin-embedded tissues by immunohistochemistry. We assessed for tissue infiltration of EOS and the release of secondary granule proteins (i.e., degranulation) in colon biopsies from clinically-defined UC and CD pts compared to normal controls. Specifically, the extent of the EOS infiltration and the level of EOS activation (defined by degranulation) were tested as metrics of inflammation. All data are presented as mean ± SD.
Results: 5 patients with UC (mean age 42 ± 19 yrs, F80%), 5 patients with CD (mean age 44 ± 15 yrs, F50%), and 5 healthy patients (mean age 63 ± 12 yrs, F80%) were studied. The groups were not statistically different in terms of age or gender. This novel IHC assay confirmed that EOS are increased in IBD patients (i.e., relative to “normal” controls) and, these infiltrates are associated with significant levels of EOS degranulation. Interestingly, CD was associated with an intense and diffuse massive release of EOS granule protein compared to UC which was much more focal and patchy and less intense. UC patients also had a unique vascular ring pattern.
Conclusion: Our new anti-EPO monoclonal antibody-based assay demonstrates that IBD is associated with increased EOS and extensive degranulation. These results suggest that EOS activation may be an important component of immune/inflammatory responses in the colon of IBD patients, CD more than UC, and may have future implications in understanding the pathogenesis and treatment of these diseases.