Interaction of Baboon Anti-α-Galactosyl Antibody with Pig Tissues

Abstract

As barriers to xenotransplantation are surmounted, such as suppression of hyperacute rejection allowing improved graft survival, it becomes important to define longer-term host-xenograft interactions. To this end we have prepared in baboons high titer anti-α-Galactosyl (αGal) and anti-porcine aortic endothelial cell antibodies, similar to human natural xenoantibodies and reactive with epitopes of thyroglobulin, laminin, and heparan sulfate proteoglycans. When injected into pigs with a protocol similar to that used in the rat to show the nephritogenic potential of heterologous anti-laminin and anti-heparan sulfate proteoglycan antibodies, baboon immunoglobulins bound first to renal vascular endothelium, and later to interstitial cells, especially fibroblasts and macrophages, and to antigens in basement membranes and extracellular matrix, where they colocalized with laminin- and heparan sulfate proteoglycan-antibodies, and with bound Griffonia simplicifolia B4. A similar binding was observed in other organs. The pigs did not develop an acute complement-dependent inflammation, but rather chronic lesions of the basement membranes and the extracellular matrix. Incubation of renal fibroblasts with baboon anti-α-Galactosyl antibodies resulted in increased synthesis of transforming growth factor-β and collagen, suggesting a possible basis for the fibrotic response. The results demonstrate that in this experimental model a consequence of αGal antibody interaction with porcine tissues, is immunoreactivity with αGal on matrix molecules and interstitial cells, priming mechanisms leading to fibrosis resembling that in chronic allograft rejection. The possibility that similar lesions may develop in long-surviving pig xenografts is discussed. As barriers to xenotransplantation are surmounted, such as suppression of hyperacute rejection allowing improved graft survival, it becomes important to define longer-term host-xenograft interactions. To this end we have prepared in baboons high titer anti-α-Galactosyl (αGal) and anti-porcine aortic endothelial cell antibodies, similar to human natural xenoantibodies and reactive with epitopes of thyroglobulin, laminin, and heparan sulfate proteoglycans. When injected into pigs with a protocol similar to that used in the rat to show the nephritogenic potential of heterologous anti-laminin and anti-heparan sulfate proteoglycan antibodies, baboon immunoglobulins bound first to renal vascular endothelium, and later to interstitial cells, especially fibroblasts and macrophages, and to antigens in basement membranes and extracellular matrix, where they colocalized with laminin- and heparan sulfate proteoglycan-antibodies, and with bound Griffonia simplicifolia B4. A similar binding was observed in other organs. The pigs did not develop an acute complement-dependent inflammation, but rather chronic lesions of the basement membranes and the extracellular matrix. Incubation of renal fibroblasts with baboon anti-α-Galactosyl antibodies resulted in increased synthesis of transforming growth factor-β and collagen, suggesting a possible basis for the fibrotic response. The results demonstrate that in this experimental model a consequence of αGal antibody interaction with porcine tissues, is immunoreactivity with αGal on matrix molecules and interstitial cells, priming mechanisms leading to fibrosis resembling that in chronic allograft rejection. The possibility that similar lesions may develop in long-surviving pig xenografts is discussed. For several reasons the pig is the donor animal of choice for human xenotransplantation. Therefore, close study of the mechanisms of porcine xenograft rejection is crucial. The most relevant information has been derived from the pig-to-baboon model. After transplantation, pig kidneys and hearts, and, less rapidly, lungs and livers are hyperacutely rejected. This phenomenon is initiated by binding of baboon natural IgM to the vascular endothelium of the graft, by local activation of complement, and additional cytotoxic T lymphocytes injury induced by host's natural killer cells, (CTL), and polymorphonucleus leukocytes (PMNs).1Platt JL Antibodies in graft rejection.in: Bach FH Auchincloss Jr, H Transplantation Immunology. Wiley-Liss & Sons, New York1995: 113-129Google Scholar An IgG response occurs after a first xenograft, or when hyperacute rejection is prevented by depletion of xenoantibodies and complement.2Bach FH Winkler H Ferran C Hancock WW Robson SC Delayed xenograft rejection.Immunol Today. 1996; 17: 379-383Abstract Full Text PDF PubMed Scopus (322) Google Scholar, 3Platt JL McGregor CGA Acute vascular rejection.Xenotransplantation. 1998; 5: 169-175Crossref PubMed Scopus (112) Google Scholar, 4McCurry KR Parker W Cotterell AH Weidner BC Linn SS Daniels LJ Holzhnecht ZE Byrne GW Diamond LE Logan JS Platt JL Humoral responses in pig-to-baboon cardiac transplantation: implications for the pathogenesis and treatment of acute vascular rejection and for accommodation.Hum Immunol. 1997; 58: 91-105Crossref PubMed Scopus (83) Google Scholar In the latter conditions IgG may contribute to activate endothelial cells and cooperate with IgM in the development of the acute vascular rejection (or delayed xenograft rejection) that follows.2Bach FH Winkler H Ferran C Hancock WW Robson SC Delayed xenograft rejection.Immunol Today. 1996; 17: 379-383Abstract Full Text PDF PubMed Scopus (322) Google Scholar, 3Platt JL McGregor CGA Acute vascular rejection.Xenotransplantation. 1998; 5: 169-175Crossref PubMed Scopus (112) Google Scholar The of human and baboon IgM and IgG is the (αGal) AH of human anti-porcine for in Google Scholar, IgM antibodies in human with PubMed Scopus Google Scholar, The and the natural A WW and of and antigens in Google Scholar on and on pig endothelial The and the natural A WW and of and antigens in Google Scholar The and of xenograft rejection not of the antibodies that with endothelium and injury to other cells and extracellular To such additional information we have prepared in baboons antibodies to and to porcine aortic endothelial cells baboon and baboon similar to human and reactive with epitopes of and heparan sulfate injected antibodies into pigs and the The results show that the baboon antibodies with αGal first to endothelium, and and later to αGal epitopes on fibroblasts and and to the extracellular matrix, especially to and heparan sulfate and that the pigs develop basement and Incubation of pig fibroblasts with antibodies increased synthesis of transforming growth and collagen, suggesting a basis for the fibrotic response. 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