ADHESION MOLECULES INVOLVED IN THE BINDING AND SUBSEQUENT ENGULFMENT OF THYMOCYTES BY A RAT THYMIC EPITHELIAL-CELL LINE

A rat thymic epithelial cell (TEC) line (R-TNC.1) was established from a long-term TEC culture. Based on its ultrastructure, phenotype and c ytokeratin profile, this line was characterized as a type of cortical TEC. R-TNC.1 cells had nursing activity which was manifested by the bi nding and subsequent engulfment of thymocytes. The role of adhesion mo lecules involved in these processes was studied extensively using a co culture of resting thymocytes and unstimulated or interferon-gamma (IF N-gamma)-stimulated R-TNC.1 cells. It was found that a number of adhes ion molecules, such as CD2, CD4, CD8, LFA-1, CD18, ICAM-1 and Thy-1, w as partly involved in the nursing activity. The effect of monoclonal a ntibodies (mAb) to these molecules depended on the incubation time and stimulation of R-TNC.1 cells. The inhibitory effect of mAb to CD2, LF A-1, CD18 and ICAM-1 on thymocyte engulfment was higher than their eff ect on thymocyte binding to the R-TNC.1 line. In addition, a LFA-1/CD1 8-dependent/ICAM-1-independent adhesion pathway was identified when un stimulated R-TNC.1 cells with minimal expression of ICAM-1 were used. The combination of inhibitory mAb did not completely abrogate the nurs ing activity of the R-TNC.1 line, suggesting the possible involvement of some other adhesion molecules.