Heterogeneity of human anti-pig natural antibodies cross-reactive with the Gal(alpha 1,3)galactose epitope

Background. The cell surface carbohydrate moiety, Gal(alpha 1,3)Galactose (alpha Gal), has been implicated as the major determinant recognized by more than 80% of human anti-porcine natural antibodies (NAb). An ELISA system was developed for the detection of this subpopulation of porcine cell-reactive NAb using synthetic alpha Gal conjugated to bovine serum albumin. Methods. A screen of 95 human serum samples by this method demonstrated marked variability in the alpha Gal reactivity of unrelated donors. The percentage of alpha Gal-reactive NAb relative to total immunoglobulin was determined for 10 donors. Results. alpha Gal-reactive NAb comprised 1.0-2.4% of total serum IgG, whereas the range was from 3.9% to 8.0% for IgM. Conclusions. The higher level of alpha Gal-reactive IgM suggests that xenoreactive NAbs may be the product of germ-line genes. Two-dimensional gel analysis of affinity-purified alpha Gal-reactive NAb from two donors provided evidence suggesting that IgM from this subpopulation of NAb were restricted in protein charge heterogeneity.