In Vitro Characterization of Human Intestinal Intraepithelial Lymphocytes

Enriched populations of human intestinal and colonic intraepithelial lymphocytes were isolated separate from lamina propria lymphocytes. These populations, and peripheral blood mononuclear cells, were characterized for membrane features, lymphocyte subsets, and proliferative potential to the nonspecific mitogenic lectins phytohemagglutinin, concanavalin A, and pokeweed mitogen. All three populations were predominantly T lymphocytes as measured by sheep red blood cell rosettes and monoclonal antibodies. Peripheral blood mononuclear cells had a T4: T8 ratio of 2.15 while intraepithelial lymphocytes were enriched for T8 + cells with a T4: T8 ratio of 0.06–0.14. Peripheral blood mononuclear cells and lamina propria lymphocytes registered vigorous proliferative responses to phytohemagglutinin, concanavalin A, and pokeweed mitogen. Intraepithelial lymphocytes, in contrast, failed to respond to the lectins. Control experiments with peripheral blood mononuclear cells indicated that the isolation reagents and procedures had no adverse effect on lectin-stimulated proliferation or on T-cell subset proportions. Viability of the intraepithelial lymphocytes after separation (88%) and after 3 days in culture with lectin (77%–85%) was confirmed by trypan blue dye exclusion, by light microscopy, by electron microscopy, and by ability to affect pokeweed mitogen-induced immunoglobulin synthesis when added to autologous and heterologous peripheral blood mononuclear cells. The failure of intraepithelial lymphocytes to respond to lectins was not due to failure of lectin binding, macrophage depletion, or absence of T-cell growth factor in culture. The possibility that the T-cell subset proportions (T4: T8 ratio) affect the proliferative response of isolated intraepithelial lymphocytes is discussed.