ADHESION AND PENETRATION OF HUMAN-LYMPHOCYTES THROUGH ALLOGENEIC ENDOTHELIAL-CELLS IN THE COURSE OF ORGAN REJECTION

Introduction: Cellular rejection mechanisms are characterized by the infiltration of sensitized lymphocytes through the donor endothelium into the transplanted organ. The regulation of cellular adhesion molecules by soluble mediators (cytokines) is thought to play a dominant role in this process. In the present study the kinetics of lymphocyte infiltration were examined using a new established in vitro model and compared to the kinetics of adhesion molecule expression. Materials and Methods: Peripheral blood lymphocytes (PBL) of healthy volunteers were pipetted to allogeneic endothelial cell (EC) monolayers and binding rates evaluated after different incubation times. Adherent PBL could be distinguished from penetrated PBL by means of a combined phase contrast-/reflection interference contrast microscope. Results: 30-35% of all pipetted PBL adhered to unstimulated EC maximally. Out of these cells < 10% penetrated through the endothelium (= maximum penetration). The cytokines alpha-, beta-, gamma-interferon (IFN) or IL-1 did not enhance maximum adhesion, but accelerated this process. However, a 2 hrs prestimulus of EC by these cytokines was necessary to induce acceleration. Maximum penetration was enhanced by alpha-, beta-, gamma-IFN, but not by IL-1, irrespective whether PBL were added together with cytokines to unstimulated EC or to already prestimulated EC. Immunocytochemical and fluorometric analyses of adhesion molecule expression revealed a cytokine induced upregulation or de novo expression of the adhesion antigens ICAM-1, ELAM-1 and VCAM-1 on EC membranes. Interestingly, PBL adhered to EC before upregulation or de novo expression of adhesion molecules was detected. Discussion: The results showed that PBL adhesion and penetration processes were regulated differentially by cytokines. The early phase of PBL attachment to EC seemed not to be influenced by adhesion antigens but by an activation of the lymphocyte cytoskeleton.