Interleukin-2 production by mitogen-stimulated intestinal mucosal leukocytes from cattle

Leukocytes isolated from intraepithelium, lamina propria, and aggregated lymphatic follicles of the small intestine of healthy adult cattle were tested for their ability to produce interleukin 2 (IL-2) by in vitro stimulation of cells with mitogens. Supernatants from interepithelial leukocytes, lamina propria leukocytes, and cultures stimulated with concanavalin A (conA), phytohemagglutinin, and pokeweed mitogen contained growth factors with the capacity to maintain proliferation of a bovine IL-2-dependent lymphoblastoid cell line. Interleukin-2 activity was demonstrated in supernatants of all 3 conA-stimulated leukocyte populations as early as 20 hours after initiation of culture, reached peak values at 30 to 50 hours, and decreased by 72 hours. Although quantitative variations of IL-2 production were observed between various cell types and among cattle, conA was the most potent in inducing IL-2 activity in all 3 leukocyte populations. Supplementation of culture medium with 2-mercaptoethanol or phorbol myristrate acetate neither induced IL-2 production nor enhanced mitogen-induced IL-2 production. Addition of indomethacin to conA-stimulated cultures enhanced IL-2 production. Although depletion of adherent cells did not affect IL-2 production, total elimination of Ia-positive accessory cells inhibited its production by all 3 cell populations. Lymphocytes responsible for IL-2 production in aggregated lymphatic follicle population were presumptive T cells because they were nylon wool-nonadherent, B26A positive (monoclonal antibody directed against pan T cells), pIg45A negative (antibody directed against pan B cells), and considered peanut agglutination-positive.