Human lymphocyte adhesion to xenogeneic porcine endothelial cells: modulation by human TNF-α and involvement of VLA-4 and LFA-1

Abstract

Considering that in the allogeneic situation the adhesion of recipient lymphocytes to donor endothelial cells initiates the cellular rejection, we questioned the possible occurrence of a similar process in the xenogeneic situation. The adhesion of human peripheral blood lymphocytes (PBL) to porcine aortic endothelial cells (PAEC) was thus studied in an in vitro porcine-to-human xenogeneic model. It was found that 25.9% of human PBL adhered to resting PAEC. Furthermore, this adhesion increased significantly when the PAEC were stimulated by the human cytokine TNF-α (tumor necrosis factor-α). The effect of human TNF-α was concentration- and time-dependent and was maximal (from 25.9% to 35.6%) with 100 U/ml during 6 h. Moreover, blocking experiments with monoclonal antibody (mAb) demonstrated the role of the PBL adhesion molecules LFA-1 and especially VLA-4. Indeed, an anti-CDl 1a mAb decreased PBL adhesion to resting PAEC by 17.1% and to TNF-α stimulated PAEC by 16.9%, whereas an anti-CD49d mAb decreased dramatically PBL adhesion to resting PAEC by 53.1% and to TNF-α stimulated PAEC by 41.0%. Finally, phenotypic analysis of the adherent PBL showed that 50.5% of adherent cells to resting PAEC were NK (natural killer) cells, whereas 50.7% of adherent cells to TNF-α stimulated PAEC were T lymphocytes, showing the preferential adhesion of NK cells to resting PAEC, and that the stimulation of the PAEC with human TNF-α affects predominantly T lymphocyte adhesion. These results indicate that human PBL could bind to xenogeneic PAEC and that this interaction could be a first step of xenogeneic cellular rejection.