Background: Increased duodenal intraepithelial lymphocytes is a key histological finding in celiac disease. Available studies suggest a wide normal range (10 - 40 intraepithelial lymphocytes /100 epithelial cells, EC). We assessed the normal range of distal duodenal intraepithelial lymphocytes.
Methods: Biopsies from the normal-looking distal duodenum from individuals referring for endoscopy for reasons other than intestinal pathologies were stained with hematoxylin-eosin and immuno-histochemistry (immunohistochemistry, CD45). At least 1000 cells from the tip and body of the villi were assessed. Villous height to crypt depth ratio was calculated.
Results: Fifty individuals were enrolled. Four were excluded (inadequate biopsies). Mean intraepithelial lymphocyte count was similar in villous tip and body. In the whole villous, upper limit of normal (mean+2SD) was 35 intraepithelial lymphocytes/100EC (95% CI: 31 - 39) in immunohistochemistry and 34 intraepithelial lymphocytes/100EC (95%CI: 29 - 37) in H&E staining. The villous height to crypt depth ratio was 3.9. Hematoxylin-eosin and immunohistochemistry had excellent agreement.
Conclusion: Intraepithelial lymphocyte counts less than 35/100EC in IHC and 34/100EC in hematoxylin-eosin staining can be considered normal. Counts between 36-39 (immunohistochemistry) and 35 - 37 (hematoxylin-eosin) are borderline and more than 39 (immunohistochemistry) and 37 (hematoxylin-eosin) are increased. The hematoxylin-eosin staining method seems adequate for clinical purposes. Regional differences in the normal upper limit for intraepithelial lymphocytes as well as changes over time should be considered when interpreting duodenal biopsies.