α1,3Galactosyltransferase knockout pigs produce the natural anti‐Gal antibody and simulate the evolutionary appearance of this antibody in primates

Abstract

Anti-Gal is the most abundant natural antibody in humans and Old World primates (apes and Old World monkeys). Its ligand, the α-gal epitope (Galα1-3Galβ1-4GlcNAc-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 α1,3galactosyltransferase (α1,3GT) gene in ancestral Old World primates, as recent as 20-28 million years ago. Since anti-Gal has been a "forbidden" autoantibody for >140 million years of evolution in mammals producing α-gal epitopes it was of interest to determine whether ancestral Old World primates could produce anti-Gal once α-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 α-gal epitopes. This question was studied by evaluating anti-Gal prodution in α1,3GT knockout (GT-KO) pigs recently generated from wild-type pigs in which the α-gal epitope is a major self-antigen. Anti-Gal antibody activity in pig sera was assessed by ELISA, flow cytometry and complement mediated cytolysis and compared to that in human sera. 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. Pigs and probably other mammals producing α-gal epitopes carry immunoglobulin genes encoding anti-Gal as an autoantibody. Once the α-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 α1,3GT gene in ancestral Old World primates enabled the immediate production of anti-Gal, possibly as a protective antibody against detrimental microbial agents carrying α-gal epitopes.