Intraepithelial lymphocytes: bystanders or causative factors in functional gastrointestinal disorders?

Intraepithelial lymphocytes(IELs)are immune cells located in the epithelium of the mucosal layer of the gastrointestinal tract that typically show a CD3-positive phenotype.They are T lymphocytes that are involved in the primary immune response to several luminal antigens,such as food proteins and infectious agents.For this reason,their increase may be pathogenetic in several diseases,the most important being celiac disease.However,an increase above 25 IELs/100 enterocytes in the duodenum,which is considered the cutoff value for celiac disease,may occur in several conditions,such as nonceliac gluten sensitivity,food allergy,Helicobacter pylori(H.pylori)infection,gastroenteritis,and even irritable bowel syndrome(IBS).Therefore,the generic term“microscopic enteritis”or“duodenal lymphocytosis”has been proposed for this condition.