Hydrogen peroxide increases human leukocyte adhesion to porcine aortic endothelial cells via NFκB-dependent up-regulation of VCAM-1

Although a severe shortage of organs in transplantation can be overcome by using xenotransplantation of porcine donor organs, profound immune rejection to xenogeneic antigens remains a main obstacle. To elucidate the role of hydrogen peroxide (H2O2) on xenogeneic immune responses, we investigated its effects on porcine aortic endothelial cells (PAECs). We found that H2O2 can specifically induce vascular cell adhesion molecule-1 (VCAM-1) expression on PAECs, but little on human umbilical vein endothelial cells (HUVECs) and aortic endothelial cells (HAECs). Furthermore, we further confirmed that H2O2 induces activation of NF kappa B in PAECs, but not in HAECs. Interestingly, cell adhesion assay showed that U937, human promonocytic leukocyte, can adhere to PAECs in an H2O2-dependent manner and by using a neutralizing assay with anti-VCAM-1-specific antibodies, we also found that the interaction is mediated primarily by VCAM-1. Finally, we also demonstrated that up-regulation of VCAM-1 expression on PAECs by reactive oxygen species-producing HL-60, human leukemic neutrophil cells, could be significantly diminished by over-expressing an H2O2-removing catalase. In summary, our results suggest that NF kappa B-dependent porcine VCAM-1 expression by H2O2 may promote interaction of human leukocyte to PAECs, and thus may play an important role on inducing xenogeneic immune responses.