Human allograft vein failure: Immunohistochemical arguments supporting the involvement of an immune-mediated mechanism

The aim of this study was to search for signs suggestive of an ongoing immune-mediated reaction in failed human cryopreserved venous allografts. In 15 samples, the authors analyzed: (1) the pattern of morphological changes; (2) the density, distribution, and phenotype of leukocytic infiltrate; and (3) the expression of class II major histocompatibility complex (MHC) antigens and inducible adhesion molecules. Two groups of samples could be recognized. In samples explanted before 3 months after grafting, the structure of the vessel wall was preserved. A dense leukocytic infiltrate was present within the intima and around the numerous vasa vasorum located in medial and adventitial layers. Class II MHC antigens and cytokine-dependent molecules were induced on endothelial cells lining the vasa vasorum and on residual smooth muscle cells. In samples explanted after 3 months of evolution, the vessel wall has lost its normal structure and contained few vasa vasorum. A few leukocytes were detected around capillary vessels located in the peripheral connective tissue surrounding the graft. Class H MHC antigens and adhesion molecules were induced on endothelial cells lining the peripheral capillary vessels. These results suggest the involvement of an immune-mediated mechanism at the early stage of the evolution of failed human venous allografts.