Colorectal mucus non-invasively collected from patients with inflammatory bowel disease and its suitability for diagnostic cytology.

Colorectal mucus is a key component of the protective gut barrier which is altered in inflammatory bowel disease (IBD). We aimed to cytologically characterize colorectal mucus non-invasively collected from IBD patients using our new sampling technique. Colorectal mucus was self-collected by 58 IBD patients comprising 31 ulcerative colitis (UC) and 27 Crohn's disease (CD) cases. The samples were examined cytologically, and immunocytochemically. Large numbers of well-preserved granulocytes were typically detected (neutrophils undergoing degradation were observed as well). Plasma cells and erythrophagocytosis were present in 18.2% and 29.1% of cases, respectively, predominantly in patients with UC and distal CD. Immunocytochemical visualization of calprotectin in neutrophils, eosinophil-derived neurotoxin in eosinophils and tumour necrosis factor-α in macrophages was also achieved. Correct cytological diagnosis was made in 61.8% of analysed IBD cases. Our new method of colorectal mucus sampling provides highly informative material for cytology. Findings of the presence of plasmocytes and erythrophagocytosis in colorectal mucus are unique and may reflect previously unknown mechanisms of IBD pathogenesis. Immunocytochemical detection of inflammation biomarkers demonstrates the suitability of this material for biomarker quantification. These promising results suggest a potential role for colorectal mucus cytology in the non-invasive diagnosis of IBD.