BACKGROUND: Anti-Gal is the most abundant natural antibody in humans and Old World primates (apes and Old World monkeys). Its ligand, the alpha-gal epitope (Galalpha1-3Galbeta1-4GlcNAc-R), is abundant in nonprimate mammals, prosimians and New World monkeys whereas it is absent in humans and Old World primates as a result of inactivation of the alpha1,3galactosyltransferase (alpha1,3GT) gene in ancestral Old World primates, as recent as 20-28 million years ago. Since anti-Gal has been a "forbidden" autoantibody for greater than 140 million years of evolution in mammals producing alpha-gal epitopes it was of interest to determine whether ancestral Old World primates could produce anti-Gal once alpha-gal epitopes were eliminated, i.e. did they carry anti-Gal encoding immunoglobulin genes, or did evolutionary selection eliminate these genes that may be detrimental in mammals synthesizing alpha-gal epitopes. This question was studied by evaluating anti-Gal prodution in alpha1,3GT knockout (GT-KO) pigs recently generated from wild-type pigs in which the alpha-gal epitope is a major self-antigen.

METHODS: Anti-Gal antibody activity in pig sera was assessed by ELISA, flow cytometry and complement mediated cytolysis and compared to that in human sera.

RESULTS: The study demonstrates abundant production of the natural anti-Gal antibody in GT-KO pigs at titers even higher than in humans. The fine specificity of GT-KO pig anti-Gal is identical to that of human anti-Gal.

CONCLUSIONS: Pigs and probably other mammals producing alpha-gal epitopes carry immunoglobulin genes encoding anti-Gal as an autoantibody. Once the alpha-gal epitope is eliminated in GT-KO pigs, they produce anti-Gal. These findings strongly suggest that similar to GT-KO pigs, inactivation of the alpha1,3GT gene in ancestral Old World primates enabled the immediate production of anti-Gal, possibly as a protective antibody against detrimental microbial agents carrying alpha-gal epitopes.