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Biosafety of Food from Genetically Modifi ed Crops 455
introduce new proteins into food crops, not only from the known sources (such as peanuts
and shellfi sh), but also from plants, bacteria, and viruses whose allergenicity is
unknown. This might lead people to avoid foods that are actually safe. If the indigenous
proteins or the new proteins are from the known sources of allergens, then assessing the
allergens within the genetically modifi ed plants is easier. If the source of the allergenic
protein is known, and is related to the introduced gene from sources that have not been
used as a human food, then one has to rely on criteria with which to assess their potential
allergenicity. Eight commonly allergenic and 160 less allergenic foods have been
identifi ed and scientists can avoid the transfer of genes with known allergenic effect
(Lehrer, 2000).
Food allergies occur in 1 to 2% of adults and 6 to 8% of children (Metcalfe et al., 1996;
Sampson, 1997), although severe allergic reactions (anaphylaxis) to foods are relatively
rare. The introduction of a new gene into a plant, or a change in the expression of an existing
gene, may cause that plant to become allergenic. Therefore, known allergens should
not be introduced into food crops. At present, there is no evidence that genetically modifi
ed foods that are commercially available cause any clinical manifestations of allergenicity,
and assertions to the contrary have not been supported by systematic analysis. The
allergenic risks posed by genetically modifi ed plants are in principle no greater than those
posed by conventionally derived crops or by plants introduced from other parts of the
world. Nevertheless, it is important to consider potential allergenic risks posed by genetically
modifi ed plants and to place them in the context of risks posed by introduced plants
and plants produced by conventional or organic means.
Allergic sensitization to a genetically modifi ed plant, as with a conventionally derived
plant, could also occur via the lungs (perhaps through inhaling pollen or dust created during
milling) or through skin contact (for example, during handling), as well as via the
gastrointestinal tract following ingestion of foods. Occupational allergies to conventional
plants can take the form of either immediate hypersensitivity or delayed hypersensitivity
reactions. The latter occur as a consequence of handling plant materials and generally
express themselves as contact dermatitis. Of immediate hypersensitivity allergies to plants,
those that involve inhalation of particulates are quite common. Those at risk from pollen
include the general population and, in particular, farm workers. Individuals involved in
the harvesting of crops and in food processing that generate dusts are at risk of sensitization
through both inhalation and skin contact. Therefore, in order to adequately assess any
risks, it is important to evaluate the allergenic potential of genetically modifi ed plants
through inhalation and skin contact, as well as via ingestion.
Guidelines for assessing the allergenic risks of genetically modifi ed foods have been
developed by FAO/WHO (2001). This approach includes determining whether the source
of the introduced gene is from an allergenic plant, whether genetically modifi ed foods
react with antibodies in the sera of patients with known allergies, and whether the product
encoded by the new gene has similar chemical and biological properties to known allergens.
It also involves animal models that can be used to screen genetically modifi ed foods
for allergenic reaction. Ongoing research to develop adequate animal models for allergenicity
testing will further increase the assurance of this procedure.
Several protein families that contribute to the defense mechanisms of food plants are
allergens or putative allergens, and some of these proteins have been used in molecular
approaches to increase insect resistance in crop plants (Franck Oberaspach and Keller,
2002). These include a-amylase and trypsin inhibitors, lectins, and pathogenesis-related
proteins. Several “self defense” substances produced by plants may be toxic to mammals,
including humans. Food safety can also be severely infl uenced by invading pathogens and