Allergens of Agricultural Products

Henry Stevens.

Allergy is a comparatively new term of medical origin. Its modern, everyday meaning, however, is told in an old saying, "What is one man's food is another man's poison." Freely applied, as proverbs usually are, this one can be fitted to all the familiar and widely varied symptoms called allergy.

Continual sneezing and smarting eyes torment the victims of hay fever. Their distress is seasonal; it lasts from the beginning to the end of the blooming period of one or more species of trees, grasses, or weeds. Air-borne pollens from those plants act as poisons in the air passages and eyes of people who are allergic to them. Pollen hay fever or, worse, pollen asthma, is the result. But for most persons the same pollens are entirely harmless and can be neither seen nor sensed in the air they breathe.

Food allergy may be recognized by a brief but annoying outbreak of hives a familiar penalty of overindulgence when wild strawberries are bearing in abundance. Far more serious and persistent disorders of the skin, the air passages, the digestive system, and other organs, however, may signify allergy caused by food. One or several usually wholesome ingredients of a varied diet may be, in fact, another man's poison.

Allergy, regarded as disease to be identified and treated, is a medical problem requiring the special knowledge and skills of a physician. However, most allergens the substances that provoke allergy are found among products and byproducts of farming. Thus, agriculture has a stake in problems involving the identity of allergens as minor, but important, components of farm products. I give one example.

Among the hundreds of farm products examined and cataloged by allergists in their search for and evaluation of allergens, cottonseed proved to be especially impressive. Clinical evidence derived from testing allergic subjects with extracts of the cottonseed kernel or cottonseed press cake demonstrated the presence of an allergen of exceptional potency. The allergen was presumed to be a protein, but extracts diluted beyond the limit of chemical detection of the compounds still exhibited the capacity to induce allergic reactions. Lacking knowledge of the chemical and physical properties of allergenic components, or any means other than clinical tests to detect them, the allergists concluded that complete avoidance of all cottonseed products should be advised when the allergic persons showed positive reactions to test with cottonseed extract. Because derivatives of cottonseed were presumed to carry the seed allergen, particular emphasis was given to strict avoidance of foods containing refined, edible cottonseed oil and hydrogenated shortenings. Also recommended was avoidance of mattresses and other furnishings containing cotton linters. Two products, edible cottonseed oil and cotton linters, which account for the major industrial value of cottonseed, thus were recognized by clinicians as probable or actual sources of the cottonseed allergen.

The clinical evidence against cottonseed oil and the cotton linters appeared incontestable. No identifying chemical or physical properties of the allergen were known. No one had isolated an allergen. No one knew whether an allergen would retain its activity if purified. Therefore, the presence or absence of the allergen could not be proved by chemical analysis of the edible oil and linters. Moreover, medical consensus supported the conviction that a clinically significant quantity of cottonseed allergen would be determinable by clinical evidence alone.

To test the conclusions of the clinicians required first the isolation and chemical characterization of cottonseed allergen. The objective involved chemical fractionation of the cottonseed kernel to find a component of unknown chemical and physical properties and recognizable, therefore, only by its biologic activity as an allergen.

All the previously known proteins of cottonseed were separated, purified, and evaluated for allergenic activity. Together, the proteins comprised the major nitrogenous substance of the cottonseed. But none exhibited sufficient allergenic activity to account for the potency attributed to the crude extracts employed by clinicians in assembling their evidence or in reaching their conclusions.

Fractionation was then directed to the components of cottonseed that can be extracted with water alone. That approach was successful. The principal allergen of the cottonseed was identified with a minor protein component combined with a complex carbohydrate. This protein component of cottonseed had not been previously recognized. Moreover, it differed significantly from all proteins previously classified and named. This unusual component had both allergenic specificity and potency of a degree to account for the allergenic properties of the crude seed-extract.

Isolation of the principal allergenic Component of the cottonseed made possible the first comprehensive examination of an industrial oilseed and its Commercial derivatives. The results proved conclusively that the principal allergen of cottonseed is a natural proteose of the seed embryo. In relation to other components of the seed, the proportion of this protein would be insignificant except for its exceptional allergenic properties. This allergenic component of the seed embryo is not a component of the linters or hulls of cottonseed. The allergen of the seed embryo is stable under conditions employed in the milling of cottonseed for recovery of the oil, meal, and edible flour. Both cottonseed meal and edible cottonseed flour contain significant amounts of the allergen. However, the conventional industrial refining excludes the allergen from edible cottonseed oil, which is also the source of hydrogenated shortenings and other edible fats.

The findings have led to revision of firmly established clinical opinion on the management of cottonseed allergy. No justification remains for avoidance of foods containing edible cottonseed oil or hydrogenated cottonseed oil, regardless of clinical sensitiveness to cottonseed allergen. Among the edible products of cottonseed, only the flour need be excluded from the diet to avoid the cottonseed allergen. Cotton linters of all grades are free from the cottonseed allergen. Accordingly, substitution of other filling for mattresses and upholstered furnishings is not essential when one tries to avoid exposure to cottonseed allergen.

Investigations prompted by the significance of allergens to the utilization of agricultural products have continually produced evidence of immediate value to processors and consumers of farm products, and of collateral importance, also, to clinicians whose first concern is relief of allergic symptoms.

HENRY STEVENS heads the research on allergens of agricultural products for the Bureau of Agricultural and Industrial Chemistry. Dr. Stevens found his chief interest in chemical reasons for disease while a student of agricultural chemistry at the University of Wisconsin.