Leukocytes in the intestinal epithelium: an unusual immunological compartment.

Antigens which penetrate the mucosal epithelium of the intestine stimulate B lymphocytes to produce local IgA that minimizes antigen uptake across the epithelium(1). Yet in the intestinal epithelium there are as many lymphocyte-like cells as in the spleen. Some are lymphocytes(2) but because the cells are heterogeneous a more precise term for them would be intraepithelial leukocytes (IEL). They are directly in line with macromolecules in transit across the epithelium(2,3) and increase in number in many enteric inflammatory processes(3,4). Here Peter Ernst and his colleagues review the diverse properties of IEL that have been uncovered by isolation procedures which separate IEL from lamina proprial cells, their potential role as effectors of cell-mediated immunity and their contribution to the prevention and pathogenesis of enteric disease.