Gene Tinkering Blues: Allergy

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Gene Tinkering Blues, Vol.2, Issue 3, February 1997
Topic: Allergenicity
by Joe Cummins, PhD, Professor Emeritus of Genetics
University of Western Ontario

Food allergy is one of the important issues in evaluating the impact of genetically engineered foods. Food allergy may effect as many as one third of the earth's population, but the officious estimate of the incidence of food allergy is about 2% of the population. About 5% of children are allergic to one or another food items but many of the children outgrow their allergies. Nevertheless, allergy may pop up unexpectedly in adults who had not previously experienced allergy. The symptoms of food allergy range from migraine headache to death. One major example of food allergy is celiac disease or wheat gluten sensitivity. The disease causes inflammation of the digestive system and the disease has a high incidence among people with mental illness- both schizophrenia and bipolar disorders. Extreme sensitivity to foods containing allergens results in the airways being swollen closed, which requires immediate treatment to save the victim's life.

Food allergy is a concern with genetically engineered crops because novel products may be introduced or the context of a gene pattern may be altered so that gene products are mixed in novel configurations. Introducing new food items such as Kiwi fruit results in 'new' allergies among the population testing the introduction. Peanut allergy is relatively uncommon in African populations who have used the nuts as a food staple, while it is a prevalent allergy in European populations. Presumably the people with genes for peanut allergy have been eliminated from the African gene pool by natural selection. The main food crops have been established for about ten thousand years by selection of both crop genes and people who can tolerate the crops. Plants and animals have carried out biological warfare since they originated. Plants have to avoid being grazed out of existence and achieve that by devices including toxins, allergens, spines and shells. Crop plants are protected by their cultivators and their allergens and toxins have been eliminated by thousands of years of careful selection. Genetic engineering is starting to reintroduce the genes earlier eliminated by crop selection.

Any crop can cause food allergy but a few food items cause most food allergy. These include peanuts, soybeans, wheat, tree nuts, crustaceans, fish, milk, and eggs. The allergens are the substances that promote the allergic response by the IgE components of the immune system. Most allergens are proteins while those related to drug allergy are 'haptens,' or small molecules associated with proteins. Traces of allergen may trigger a response in sensitive people but most allergy requires a fairly large intake. A response may take place minutes to hours after eating an offending food. Avoidance is the only way to prevent food allergy and processed foods must be labeled correctly.

The biotechnology industry and governments prevent labeling gene tinkered crops based on a form of superstition called 'substantial equivalence'. The superstitious belief is that genetically engineered foods need not be tested nor labeled because they are identical in essential detail to the crop from which they originated. The 'dogma' demands that believers ignore the antibiotic tolerance genes from bacteria and the promoter genes from a pararetrovirus present in the crops. Unfortunately the dogmatic superstitious believers form cults that regulate crops and spread the crops worldwide.

Presently more than 160 foods are known to be allergenic (a few foods cause most allergy however) and from that group only a few have been subject to molecular genetic analysis. The reason that molecular genetic analysis is useful is that a 3 dimensional representation of the active area of the allergen (the epitope) can be constructed. The gene sequence specifies a string of amino acids in the protein that will take on a shape that activates the allergic response. The problem is that only a few such epitope maps have been constructed. Nevertheless, it has grown popular to take those few data to judge the gene sequences that will cause an allergic response. The advantage to the proponent of a particular crop is that the data base is so small that most allergens will not be recognized; only those showing the characteristics of the limited data base will be recognized.

Most allergens known are relatively small proteins (10 to 40 kilodaltons). Some but not all allergens are inactivated by heating. Most allergens resist stomach acids and digestive enzymes. New proteins expressed in non edible plant parts are not of concern in food allergy.

Testing for allergenicity requires experiments on humans. A relatively large group must be employed because the factors causing allergy are not well defined. Limited release of genetically engineered foods would be desirable, but has been rejected those promoting the technology. The sera of allergic people can be used to test for reactions in extracts of a crop. Unless the allergenicity of the genes used in genetic engineering is known, the number of sera sources would have to be very large to pick up a new allergen. Another test involves pricking the skin of people with known food allergies to inject traces of the food, which reacts to produce a sensitive response. The method is not well fitted to picking up unexpected allergens.

There is another kind of effect that may be important in genetic engineering. This effect is called the antiidiotope allergen. When an antibody is made against an antigen (allergen) there is an antibody made against the antibody (antiidiotope antibody). Most genetically engineered crops have genes for antibiotic tolerance, which produce enzymes that match an allergenic antibiotic. The enzymes will produce antibodies that are allergens. Thus most genetically engineered crops are likely to be allergenic to people sensitive to antibiotics.

It would be rational to label the food from genetically engineered crops so that the food allergies produced can be related to the crop. However, if the allergen is recognized the producer of the genetic change will face liability. That seems to be the true meaning of "substantial equivalence". The public should continue to demand labeling of genetically engineered crops. Clear evidence of food allergy will be debated and litigated for a decade. During that time gene tinkered crops will be spread pervasively.

References: 6 SPECIAL ISSUES
For antiidiotope antibodies see: S.Kawaguchi, Int. Archives of Allergy & Immunity, Vol. 106, p. 372, 1995