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
http://www.fao.org/waicent/faoinfo/economics/esnbiotech/six.htm
For antiidiotope antibodies see: S.Kawaguchi, Int. Archives of Allergy &
Immunity, Vol. 106, p. 372, 1995