Benzoquinone activation of Cryptococcus neoformans capsular polysaccharide for construction of an immunoaffinity column

Abstract

p-benzoquinone was used as a two-step coupling reagent for preparation of an immunoaffinity absorbent in which the capsular polysaccharide of Cryptococcus neoformans was linked to an agarose gel. Cryptococcal polysaccharide is a difficult subject for chemical modification because it contains immunogenic O-acetyl groups which are sensitive to alkaline hydrolysis. The polysaccharide was activated by treatment with benzoquinone. The 'activated' polysaccharide was reactive with amino groups on AH-Sepharose. A pH of 8-9 was optimal for activation of the polysaccharide. Once activated, the polysaccharide was reactive with a model substrate, L-alanine-4-nitroanilide, over a pH range of 6-10. Since the O-acetyl groups are hydrolyzed at pH above 8.0, an activation pH of 8.0 and a coupling pH of 7.5 were used to prepare the conjugated gel. The polysaccharide immunoaffinity column was used successfully for isolation of rabbit antibodies to cryptococcal polysaccharide.