Specificities of human IgM and IgG anticarbohydrate xenoantibodies found in the sera of diabetic patients grafted with fetal pig islets

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Abstract
Serum samples were collected from four diabetic patients who had received intraportal injections of pig fetal islet‐like cell clusters (ICC). The binding of IgM and IgG antibodies to glycosphingolipid antigens prepared from different pig organs and separated on thin layer plates was investigated in pre‐ and posttransplant serum samples. Both IgM and IgG antibodies in the pretransplant serum samples bind to several glycolipid fractions from the tri‐, tetra‐ and pentasaccharide regions but also to compounds with longer carbohydrate chains. In the posttransplant serum samples stronger binding, compared to the pretransplant samples, was noted for both Ig‐classes. Strong binding was seen in the pentasaccharide region known to contain the “linear blood group B” structure Galαl‐3Galβl‐4GlcNAcβl‐3Galβl‐4Glcβl‐lCer. There was no convincing evidence of the I recognition of new specificities. Adsorption of a patient serum to a Synsorbcolumn with Galαl‐3Gal specificity did not grossly change the binding pattern of the IgG antibodies in the effluate. However, the eluate from the column showed strong binding to the “linear B” compound but also to glycolipids with longer carbohydrate chains presumably with the same terminal epitope. Identification of these are in progress.The human natural anti‐pig antibodies against carbohydrate antigens expressed on pig cells seem to detect a rather limitted number of epitopes. The “linear B” structure appears to be one major target. However, other structures may also be targets for xenoreactive antibodies. Immunisation with pig cells does not seem to initiate antibody production against new carbohydrate epitopes but leads to an increased production against the existing ones.