Human preformed IgG combining with membrane-bound porcine serotransferrin lyse porcine endothelial cells through antibody-dependent cellular cytotoxicity

Preformed antibodies are involved in xenograft rejection. The purpose of th is work was to characterize porcine xenoantigens recognized by human prefor med IgG (hplgG), and to investigate the role of hplgG in xenogeneic rejecti on. IgG eluted from porcine livers perfused with human plasma, human sera a nd total human IgG were immunoblotted on porcine aortic endothelial cell ex tracts. The amino acid sequence of a 76-kDa antigen constantly revealed was 100 % homologous with porcine serotransferrin (psTf). hplgG from human ser a, human IgG1 and IgG2 and F(ab')(2)gamma specifically bound to psTf. Neutr alization by psTf abolished that binding. Although alpha 1,3-linked galacto se residues (Gal alpha 1,3Gal) is the dominant epitope recognized by prefor med antibodies in the swine-to-human combination, the analysis of carbohydr ate composition of psTf showed that the molecule was devoid of Gal alpha 1, 3Gal moieties and that preformed anti-psTf IgG bound to epitopes localized on the peptide core of the molecule. Purified human anti-psTf IgG antibodie s were able to bind to psTf linked to its receptor on porcine endothelial c ells, and to kill those cells through antibody-dependent cellular cytotoxic ity.