Lymphocytes: Intraepithelial

Abstract

Intraepithelial lymphocytes (IEL) are small, round mononuclear immune cells, which reside in the paracellular space between nonimmune epithelial cells. They are found in the skin and within the epithelial layer that lines the intestine, the biliary tract, the oral cavity, the upper respiratory tract and lungs and the reproductive tract. The largest population of IEL resides within the epithelium of the small intestine where they form the first line of immune defence against invading pathogens while preserving the integrity of the mucosal barrier. Key concepts The lymphocytes located in the epithelium are at the frontline between the self and nonself. The T‐cell populations from the small intestine are the most important in number and the most diverse in the body. The T‐cell populations from the epithelium often contain unconventional subpopulation such as CD8aa TCRab+ IEL in the intestine. Introduction of the new concept of agonist selection for self‐specific CD8aa TCRab+ IEL. Important function of IEL during immune response against pathogens.