Antigenic cross-reactions among human intestinal brush-border enzymes revealed by the immunoblotting method and rabbit anti-enzyme sera.

Antibodies against 3 purified human small intestinal brush-border hydrolases (sucrase-isomaltase, maltase-glucoamylase and neutral aminopeptidase) were produced in rabbits. By double immunodiffusion and crossed immunoelectrophoresis the antisera appeared to be monospecific. However, with the immunoblotting method antibodies reacting with many brush-border proteins were detected. In one case, the cross-reactions were due to the presence of anti-A antibodies. In other cases absorption of the antisera with absorbants with blood group A and H activities did not eliminate these reactions. As the main brush-border proteins are glycosylated and share common lectin reactivities, it is possible that these antibodies are directed against carbohydrate antigens. The use of such antibodies for immunocytochemical methods and for immunoassays must be undertaken with caution. These principles are applicable to other antigen systems.