Immunohistological characterisation of intraepithelial lymphocytes of the human gastrointestinal tract.

Intraepithelial lymphocytes (IEL) of the normal human stomach, small intestine, and large intestine have been characterised in tissue sections by a double marker immunofluorescent technique. A panel of reagents was used in combination, including antisera to T lymphocyte antigen (HuTLA), Ia-like (p28, 33) antigens and immunoglobulin subclasses, as well as a mouse monoclonal antibody to a human leucocyte antigen (HLe-1). In stomach and proximal small intestine over 95% of IEL were T lymphocytes (HLe-1+, HuTLA+). The proportion was slightly lower in the colon and rectum (85--95%). IEL rarely expressed Ia-like antigens. B lymphocytes were not seen within the epithelium of any of the tissues examined. The functions of IEL must be assessed in the light of the finding that they are predominantly T cells.