Stimulation of CD2-activated mucosal T cells by intestinal epithelial cells (IEC) requires LFA-3 and is independent of MHC class II and B7

Previous studies from our laboratory demonstrated that stimulation of lamina propria T cell (LPT) proliferation and cytokine synthesis by ailogeneic intestinal epithelial cells (IEC) is dependent on signaling via the CD2 receptor (GE 112:A1007, 1997). The purpose of this study is to identify the costimulatory molecules expressed by IEC which mediate LPT activation. Methods LPT were purified (97%) from normal mucosa by negative selection. Allogeneic IEC or irradiated Caco-2 epithelial ceils were cultured with lxl0 s LPT and a sub-optimal concentration of a stimulatory pair of anti-CD2 antibodies (Tl12/Tl13). Neutralizing antibody to LFA-3 and MHC class II (L243) and the B7 antagonist, CTLA-4-Ig, were added at culture initiation. Proliferation was measured on day 5. Results Conditioned media from IEC or Caco-2 cultures did not stimulate LPT proliferation, suggesting that direct cell-cell contact was required. The addition of the MHC mAb L243 or CILA-4-Ig did not inhibit the proliferation of LPT induced by IEC and Tll2/Tll 3, each alone, or in combination. In contrast, antibody to LFA-3 inhibited greater than 85% of the LPT response to co-stimulation with IEC and Tll2/Tll~. As a control, L243 and CTLA-4-Ig blocked the proliferation of both blood T ceils and LPT to allogeneic monocytes. Conclusion IEC stimulation of CD2-activated LPT is not mediated by the co-stimulatory molecule BT. In addition, our findings show that the restricting element for allogeneic IEC activation of LPT is not MHC class II. These results suggest that another surface IEC protein activates LPT in a CD2 dependent manner in collaboration with LFA-3. The use of alternate accessory proteins and signaling pathways to regulate intestinal T ceils may explain the unique properties of mucosal immunity.