Immunological mechanisms in aspirin hypersensitivity. Studies on the immunogenicity of free aspirin

Anti-aspiryl antibodies were produced in rabbits and guinea pigs by inoculation of aspirin incorporated in complete or incomplete Freund's adjuvant. These antibodies were readily detected by passive haemagglutination using rabbit erythrocytes incubated with aspirin at alkaline pH. Aspiryl conjugates with ovalbumin, human gamma-globulin, bovine gamma-globulin and rabbit serum were also prepared by incubating the proteins with aspirin at alkaline pH. Aspiryl conjugates prepared by this technique behaved, immunologically, identically with the conjugates prepared from aspirin chloride. By contrast, the molar absorbance at 305 nm of the conjugates prepared from aspirin was about 25 times lower than the molar absorbance of the conjugates prepared from aspirin chloride. Since the absorbance of salicylic acid is about eight times greater than that of aspirin, the conclusion is drawn that the aspiryl/salicylyl ratio is significantly higher in the conjugates prepared by incubating proteins with aspirin at alkaline pH than in the conjugates prepared from aspirin chloride. In parallel experiments, salicylic acid did not induce formation of specific antibodies capable of reacting with aspirin- or salicylic acid-treated red cells. Sera giving positive passive haemagglutination with aspirin-treated erythrocytes did not react with erythrocytes treated with salicylic acid or acetic anhydride.