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)Galact ose (alpha Gal), has been implicated as the major determinant recogniz ed 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 bov ine 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 t o total immunoglobulin was determined for 10 donors. Results. alpha Ga l-reactive NAb comprised 1.0-2.4% of total serum IgG, whereas the rang e was from 3.9% to 8.0% for IgM. Conclusions. The higher level of alph a 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 th at IgM from this subpopulation of NAb were restricted in protein charg e heterogeneity.