Our previous studies have shown that the difference between undifferentiated crypt intestinal epithelial cells (lECs) and differentiated tip lECs extend to expression of cytokines and cytokines receptors. These observations suggested different roles for tip and crypt lECs in the cell-to-cell interactions with gastrointestinal (GI) tract lymphoid cells through the cytokine network. We have investigated the potential role of tip and crypt lECs for activation/stimulation of T cells including intraepithelial lymphocytes (lELs) by analyzing expression of B7-1 (CD80) and B7-2 (CD86) costimulatory molecules. Tip and crypt lECs were freshly isolated from mouse small intestine and stained with biotinylated anti-CD80 and anti-CD86 monoclonal antibodies following by FTTC-avidin. Flow cytometry analysis revealed the expression of low and similar levels of CD80 and CD86 molecules on crypt lECs. On the other hand, tip lECs expressed higher levels of both costimulatory molecules than did crypt lECs and similar levels of CD80 and CD86 molecules were detected on these cells. These results indicate that the differentiation of intestinal epithelial cells is associated with an increase in the expression of CD80 and CD86 molecules. To determine functional differences associated with this distribution of costimualtory molecules on lECs, we are currently investigating the role of different Cs.