α-Galactosyl antibody redistributes α-galactosyl at the surface of pig blood and endothelial cells

The interaction of antibodies with cell surface antigens may induce redistribution of immune complexes, followed by antigen depletion, with increased resistance to injurious effect of antibody and complement (antigenic modulation). Human natural antibodies to Gal alpha 1,3Gal beta 1,4GlcNAc-R (alpha Gal) epitopes expressed at the surface of pig cells are a major obstacle to xenotransplantation. Recent studies have shown that these antibodies do not modulate alpha Gal, but the morphological consequences of the antigen-antibody interaction are unknown. Pig blood and endothelial cells, were exposed to baboon alpha-Gal antibodies, and studied by immunofluorescence and phase contrast microscopy, flow cytometry, and inhibition enzyme-linked immunosorbent assay. In cells studied at 4 degrees C or fixed, alpha Gal was diffusely expressed at the surface. After cross-linking at 37 degrees C, antigenic modulation did not occur, but granular redistribution of alpha Gal immune complexes was seen in all cell types. In other systems a similar redistribution is known to induce perturbation of the plasma membrane/cytoskeletal structure with changes in adhesive properties, gene regulation, and T cell activation, which could be important if pig xenografts will be made to survive for prolonged periods.