Functional characterization of Con A-responsive Lyt2-positive mouse small intestinal intraepithelial lymphocytes.

The surface phenotypes of resting vs Con A-stimulated intraepithelial lymphocytes (IEL) from mouse small intestine were directly determined by immunofluorescence with double labelling. Both Thy 1.2+, Lyt 2+ and Thy 1.2+ Lyt 2- IEL underwent blastogenesis and expressed interleukin-2 (IL-2) receptors. The Lyt 2+ subsets of IEL (which represent 80% of the total cells) were isolated by panning and shown to proliferate in response to Con A and IL-2, although the frequency of responsive precursors was dramatically lower than that seen in the splenic Lyt 2+ T-cell population (1 in 500 vs 1 in 8, respectively). Con A-stimulated Lyt 2+ IEL produced lymphokines supporting the growth of the interleukin-3 (IL-3)-dependent cell line DA-1, and of the FDC-P2 cell line that proliferates in response to both IL-3 and GM-CSF. The results therefore support the possibility that Lyt 2+ IEL act as inducers of local cell-mediated immune reactions by producing haematopoietic lymphokines.