Capture of anti‐(Galα1‐3Gal) antibodies by immobilized Galα1‐3Gal oligomers derived from carrageenan

An immobilized Galα1‐3Gal‐bearing affinity ligand was prepared as a possible prophylactic binding site of human anti‐(Galα1‐3Gal) antibodies for the prevention of hyperacute rejection of pig xenografts. λ‐Carrageenan, a natural polysaccharide known to possess alternately α1‐3 and β1‐4‐linked D‐galactopyranose sulphate residues, was selectively degraded by acetolysis and subsequently deacetylated to obtain λ‐carrageenan oligosaccharides. The resulting syrup was ultrafiltered to remove higher polymers and chromatographed on Sephadex G‐15 to produce a series of sized oligosaccharide fractions. An immuno‐dot‐blot method was established on the basis of the competition between the λ‐carrageenan oligosaccharides in solution and bovine thyroglobulin (BTG), a glycoprotein known to express the Galα1‐3Gal marker, as the solid‐phase antigen. Increasing amounts of λ‐carrageenan fractions added to normal human plasma resulted in a progressive decrease in Galα1‐3Gal‐specific human IgM and IgG binding to BTG. Complete inhibition of Galα1‐3Gal‐specific human immunoglobulin was attained at concentrations less than 0.6 mg of carbohydrate/ml of human plasma with the more active fractions. These bioactive λ‐carrageenan oligosaccharides were immobilized on hydrazide‐modified microporous nylon membranes, yielding capacities between 2.18 and 2.86 mg/ml of membrane. A subsequent decrease in the human anti‐(Galα1‐3Gal) antibody level in normal human plasma was demonstrated and proved with the established immuno‐dot‐blot procedure.