Introduction The normal count for intraepithelial lymphocytes (IELs)/100 enterocytes in the colon has been defined at 20. Normal eosinophil counts are harder to identify. In the caecum, eosinophils are more numerous and up to 40/high power fields (HPF) is suggested to be normal. Irritable Bowel Syndrome (IBS), by definition is not associated with pathology by microscopy but colonic innate immune disorder is implicated in some patients. The aim of this study was to define cell counts in a normal group of subjects and to compare these in subjects with IBS to ascertain if these may be used as biomarkers.

Methods Colonoscopy with biopsies was performed in 742 subjects (mean age 51 years, 45% male) and biopsies taken from ileum (TI), caecum, transverse (TC), sigmoid colon (SC) and rectum (R) with a completed validated questionnaire of GI symptoms from a random population sample in Stockholm. Ethical approval, Karolinska Instititet. A case control study was performed comparing 90 normal subjects and 100 subjects with IBS, subtyped,(defined by Rome III criteria) to count IELs/100 enterocytes and eosinophils/5 HPF at each site in biopsies stained by H&E. Sections were examined by two observers. For each section the number of IELs/100 enterocytes was counted, and the number of eosinophils counted in five non-overlapping HPF.

Results Of 90 control subjects, mean age 52 years, (SD11.4) 53.3% men. Of 100 IBS patients, mean age 46 years (SD13.7) 39% men. In IBS subjects, 17 were classified IBS-C (35% men), 30 with IBS-D (30% men), 13 with IBS-M (15% men), 40 with unsubtyped IBS (58% men). Lin's concordance results for inter-observer variability were 0.94 for IELs and 0.99 for eosinophils. Histopathology in controls and IBS was normal. Cell counts were compared in normal subjects categorised by gender, BMI, age and medications and no significant differences were observed between any categories. Eosinophil counts were highest in the caecum regardless of diagnosis (p<0.05) (Abstract 048).

Conclusion This study has defined normal cell counts for IELs and eosinophils in the TI and colon. No significant differences were found with medication, BMI, age or gender or comparing normal subjects with IBS patients.