ADHESION AND PENETRATION PROPERTIES OF HUMAN-LYMPHOCYTES ACTING ON ALLOGENEIC VASCULAR ENDOTHELIAL-CELLS

Lymphocyte infiltration through vascular endothelium is one important step in the course of graft rejection. To investigate this process mor e exactly we established a monolayer invasion assay which enabled us t o discriminate between adherent and penetrated cells. Detailed studies of adhesion and penetration kinetics of peripheral blood lymphocytes (PBL) acting on allogeneic human umbilical vein endothelial cells (HUV EC) were carried out by combined phase contrast and reflection interfe rence contrast microscopy. Between 30 and 35% of all PBL attached to H UVEC after 4 hr. Out of these less than 10% penetrated. When HUVEC wer e prestimulated for 2 hr by interferon (IFN)-alpha, -beta, -gamma or i nterleukin (IL)-1, PBL adhesion in the early phase of cellular attachm ent to endothelial cells was accelerated. Overall adhesion however did not increase. Long-term pretreatment of HUVEC for 72 hr with IFN-gamm a or IL-1 also modified PBL-HUVEC interactions. However, a 72-hr pretr eatment with IFN-alpha or -beta did not influence lymphocyte binding b ehaviour. PBL penetration was not only accelerated but also enhanced b y IFN-alpha, -beta, -gamma, irrespective of whether HUVEC were prestim ulated for 2 hr or PBL and cytokines were added simultaneously to HUVE C. On the other hand IL-1 was not able to enhance the amount of penetr ated cells but only accelerated the infiltration process. Upregulation or de novo expression of the adhesion molecules ICAM-1 (intercellular adhesion molecule), ELAM-1 (endothelial leucocyte adhesion molecule) and VCAM-1 (vascular cell adhesion molecule) did not parallel PBL bind ing kinetics. Therefore an ICAM-, ELAM- and VCAM-independent modulatio n in the early phase of lymphocyte attachment to endothelium seems lik ely. The lymphocyte cytoskeleton may have a role in this process.