Extracorporeal (''ex vivo'') connection of pig kidneys to humans .2. The anti-pig antibody response

Pig kidneys were extracorporeally ''ex vivo'' connected to the circulation of two volunteer male dialysis patients (Breimer et al., this issue). The patients were pretreated by daily plasmapheresis for 3 consecutive days, which reduced the anti-pig lymphocytotoxic titer from 8 to 2 in the first patient and from 8 to 1 in the second patient. The anti-pig hemagglutinating titers were reduced from 32 to 4 in the first patient and from 2 to 1 in the second patient. No drugs, except heparin, were given. The perfusion lasted for 65 min in patient 1 and the experiment was terminated due to increased vascular resistance in the pig kidney. Ultrastructural investigation showed a picture similar to a hyperacute vascular rejection. Immunohistochemical studies showed a weak staining of IgM antibodies, but no IgG in the small arteries and glomeruli. The pig kidney of patient 2 was perfused for 15 min and the experiment terminated due to serious side effects of the patient. Light and electron microscopical investigation showed virtually no structural changes of the kidney tissue and immunostaining for human antibodies was negative. In both patients, serum samples collected 2-5 weeks postperfusion showed a strong anti-pig antibody titer rise (up to 512) which thereafter declined but stabilized on a higher level than before the experiment. The antibody response in the two patients was different. In patient 1, the major anti-pig antibodies directed to carbohydrate antigens were of IgG (IgG1 and IgG2 subclasses) type, while the IgM response was less prominent and virtually no IgA antibodies were produced. Despite the short duration of the perfusion in patient 2, a humoral immune response was seen that was mainly confined to the IgA immunoglobulin class (IgA1 subclass). Blood group glycospingolipid fractions, prepared from the contralateral kidney of the donor pigs, were used for immunostaining with patient serum samples. In both patients, the antibodies produced after the perfusion, mainly recognized the Gal alpha 1-3Gal epitope both as part of the ''linear B'' pentasaccharide but also on more complex carbohydrate structures. Patient 1 was HLA-immunized before the experiment due to a kidney allograft and had a panel reactivity of 85% before the perfusion. No change in the panel reactivity of HLA-antibodies was found after the perfusion experiments. Patient 2 had no HLA antibodies before and remained negative after the perfusion. Patient serum samples collected before and after the perfusion were tested for reactivity against human endothelial cell lines. No antibodies were generated.