598 FOOD PROTEIN-INDUCED ENTEROCOLITIS: DETECTION OF ORALLY INGESTED ANTIGEN IN SERUM AND URINE

Abstract

Enhanced macromolecular absorption of food antigens has been suspected in a variety of clinical disorders, but a method for evaluating this in humans has not been established. We developed an ELISA assay to detect ovalbumin in urine and serum. A solid phase sandwich assay using commercial anti-ovalbumin antibodies (aOA) detected as little as 10 ng/ml of ovalbumin. Urine did not interfere with the assay but serum containing aOA reduced assay sensitivity up to 97%. However, serum inhibition did not occur if aOA were not detected in baseline serum. We evaluated ovalbumin absorption in infants <1 year of age undergoing diagnostic food challenges to soy and cow milk protein one month after recovery from enterocolitis. Serum was obtained at 1-hour post ingestion of a standardized oral dose of egg white (.6 gm protein/kg) and urine collected for 12 hours. Ovalbumin was detected in the serum in 14 of 15 infants and in the urine in 8 of 10 infants. The mean serum 1-hour concentration was 105 ng/ml (range 0 to 218, n=15). The mean 12-hour urinary excretion was 5.0 × 10^-4percent of ingested dose (range 0-2100, n=6). No correlation between ovalbumin absorption and age, total serum immunoglobulins or clinical response to challenge could be demonstrated. Thus by evaluating both serum and urine after a standardized egg white ingestion, we were able to detect absorption of ovalbumin antigen in all infants. This should allow quantitative studies to evaluate the clinical importance of macromolecular protein absorption.

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