Passage of ingested protein into the blood during gastrointestinal hypersensitivity reactions: experiments in the...

Preruminant calves given a series of feeds of heated soya bean flour (HSF) frequently develop gastrointestinal hypersensitivity to soya bean antigens. The permeability of the intestinal mucosa of calves undergoing hypersensitivity reactions to ingested HSF has been assessed by feeding them milk and quantitating the leakage of beta-lactoglobulin into the blood. Maternal beta-lactoglobulin did not evoke an antibody response in calves. Therefore its detection in the serum was not influenced by immunological mechanisms that normally remove or exclude antigens from the circulation. In sensitized calves ingestion of HSF caused a dramatic increase in the permeability of the intestine to beta-lactoglobulin. The change was transitory and after 24 hr permeability had almost returned to normal. The mucosal barrier was not permanently damaged regardless of the number or the severity of the reactions experienced. Indomethacin was ineffective in counteracting permeability changes. A progressive increase in the sensitivity of the gut to soya bean antigens was accompanied by a rise in the titre of serum antibodies to soya bean proteins. Absorbed beta-lactoglobulin was present in the serum in its monomeric form only, and quickly disappeared from the circulation. In an enzyme immunoassay used to measure its concentration absorbed beta-lactoglobulin was indistinguishable from the native protein. These results suggest that measurement of intestinal permeability to macromolecules might be useful in the diagnosis of certain forms of food allergy in man.