Heterogeneity of human anti-pig natural antibodies cross-reactive with the Gal(alpha1,3)Galactose epitope.

Background: The cell surface carbohydrate moiety, Gal(alpha1,3)Galactose (alphaGal), 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 alphaGal conjugated to bovine serum albumin.

Methods: A screen of 95 human serum samples by this method demonstrated marked variability in the alphaGal reactivity of unrelated donors. The percentage of alphaGal-reactive NAb relative to total immunoglobulin was determined for 10 donors.

Results: alphaGal-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 alphaGal-reactive IgM suggests that xenoreactive NAbs may be the product of germ-line genes. Two-dimensional gel analysis of affinity-purified alphaGal-reactive NAb from two donors provided evidence suggesting that IgM from this subpopulation of NAb were restricted in protein charge heterogeneity.