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TITLE:  GM Food: The Risk Assessment of Immune Hypersensitivity
        Reactions Covers More Than Allergenicity
SOURCE: Food, Agriculture & Environment Vol.1(1): 42-45
        by Alexander G. Haslberger
DATE:   April 2003

------------------ archive: http://www.gene.ch/genet.html ------------------


GM Food: The Risk Assessment of Immune Hypersensitivity Reactions Covers
More Than Allergenicity

Alexander G. Haslberger
Institute for Microbiology and Genetics, University of Vienna, Austria
Department of food safety, WHO, Geneva, Switzerland
alexander.haslberger@univie.ac.at

Abstract: Allergenicity of genetically modified food ( GM food ) has become
a public concern and international expert panels e.g. WHO/ FAO have depicted
decision trees for a rigorous assessment and testing for GM foods, especially
where no history of safe use is available. The way to use patient sera for
the assessment of allergenicity is still under discussion in cases of proteins
where stability and protein sequences may not be conclusive or for potential
new allergies. The risk assessment of immune hypersensitivity reactions
induced potentially by GM food needs also to consider effects on other type of
immune responses e.g. activation of specific immune cell populations. The role
of antigen presenting cells of the gut is now understood to direct immune
responses resulting in humoral, cellular or IgE predominant characteristics. For
GM microorganisms potential effects on the immune system need to be
assessed.

 No specific international regulatory systems for GM foods safety or GMO
environmental safety are currently in place. In the field of environmental
safety the Cartagena Protocol on Biosafety may enter into force soon and Codex
Alimentarius principles on human health risk analysis are expected to be adopted
in 2003. The premise of these Codex principles dictates a premarket
assessment, performed on a case-by-case basis and including an evaluation of both
direct effects (from the inserted gene) and unintended effects (that may arise
as a consequence of insertion of the new gene).

The safety assessment of GM foods investigates:
(a) direct health effects (toxicity)
(b) tendency to provoke allergic reactions (allergenicity)
(c) specific components thought to have nutritional or toxic properties
(d) the stability of the inserted gene
(e) nutritional effects associated with the specific genetic modification
(f) any unintended effects which could result from the gene insertion1.

When new foods are developed by natural methods, some of the existing
characteristics of foods can be altered unintentionally, either in a positive or a
negative way. New plants developed through traditional breeding techniques
may not be evaluated rigorously using risk assessment techniques2. In contrast
to traditionally developed foods which are not generally tested for
allergenicity before market introduction, protocols for testing detrimental immune
responses, especially the allergenic potential of GM foods have been established
by international expert panels2.

The Role of the Gut

Immune System and Hypersensitivity Responses

Food allergies and other food sensitivities are individualistic adverse
reactions to foods because they affect only a few people in the population.
Within the different types of reactions involved in adverse reactions to foods
non-immunological intolerances (such as reactions to increased contents of
histamins or intolerances against lactose) and reactions involving components of
the immune system need to be differentiated3. In hypersensitivity reactions
involving elements of the immune-system it became evident that these reactions
are mainly caused by a lack of the induction of a tolerance against
components of the foods in specific individuals. While research has delivered a very
good understanding for the structural specificities of the protein food
components which are often the cause for allergenic reactions, basic mechanisms
underlying the reactions are at the focus of present research: Genetic and
environmental factors are believed to influence antigen presenting cells,
especially dendritic cells and T cell subsets which, using different sets of immune
mediators, differentially regulate both, the synthesis of Immunoglobulin E
which is the basis for humoral, immediate (or real, Type I) allergic
hypersensitivity reactions and cellular reactions involving sensitized or self reactive
T cells (delayed type, hypersensitivity reactions).

Antigen presenting cells belong to the gut associated lymphoid tissue
(GALT). Immature dendritic cells reside in the epithelia also of the gut and have
the potential to sense foreign antigens. Following recognition and uptake of
Ag, mature dendritic cells provide signals which polarize Th0 cells into Th1
or Th2 cells, the basis for humoral or cellular immune-responses as well as
decisions for the production of enhanced IgE4. Systemic immune responses to
soluble oral antigens are most likely induced by gut-conditioned dendritic cells
that function both to initiate the gut-oriented response and to impart the
characteristic features that discriminate it from responses induced
parenterally5. Also the differential stimulation of cytokines effecting immune
responses and activation of the immune system was shown in intestinal epithelial
immune cells using non-pathogenic E. coli and Lactobacilli6.

Specific microbes in the gut microflora and sporadic infections are so
thought to be important in allergy prevention. The gastrointestinal microflora
promotes potentially antiallergenic processes such as TH1-type immunity,
suppression of TH2-induced allergic inflammation, induction of oral tolerance and
IgA production. The gut microflora might therefore be a major postnatal
counterregulator of the universal TH2-skewed immune system in fetuses and neonates7.
Because of its role to serve as a barrier to pathogenic bacteria and to
enable an immune surveillance of the antigenic environment the local mucosal
immunity of the gut is of a central importance for health. Antigens, primarily
associated with intestinal microbes and dietary antigens, can stimulate
production of IgA in the intestine resulting in local protective immunity. Because
of its role for a stimulation and regulation of immune responses the gut has
become a favourite system for developments and techniques to interfere with
modified or functional foods or vaccines including DNA vaccines 8,9,10.

GM Food and Hypersensitivity

Molecular biology and biochemistry have significantly increased the
knowledge of the nature of allergens. However, only limited information about
specific properties of food allergens is presently available. The majority of known
plant food allergens belong to seed storage proteins, protease and
amylase-inhibitors, profilins or pathogenesis-related (PR) proteins. Less variety is
found among allergenic proteins derived from animal sources. For allergic
reactions it became clear that plant food allergens belong almost exclusively to
one of two structurally related protein superfamilies, which share remarkable
stability to processes such as heating (being stable to temperatures between
75-95ºC, compared with 45- 50ºC for most proteins), and the extremes of pH
and the proteolytic processing environment found in the digestive tract.

These proteins mainly come from foods or food groups often referred to as
“The Big Eight” which account for more than 90-percent of all Type I allergic
reactions worldwide. These Big Eight are; milk, eggs, fish, crustacean
shellfish, peanuts, soybeans, tree nuts and wheat 11. In response to pathogens,
plants synthesize and accumulate a variety of proteins which are part of a plants
defence system. As plant protection against bacteria, fungi, viruses and
insects is a major challenge to agriculture world-wide, over-expression of such
proteins in transgenic plants has been applied to increase the defense
potential. Some of these proteins which are considered for use in the production of
GMOs to increase the resistance to microbial and insectal attack include
proteins with allergenic potential e.g. chitinases providing protection against
fungal attack or insecticidal proteins including protease inhibitors12 .

Risk Assessment of Allergenicity

An assessment of the potential allergenicity of GM foods typically follows
the generally well known decision-tree process which depends from the source
of the genes transferred as outlined by international expert panels 3, 13, 14,
15. The most difficult assessment occurs when genes are obtained from
sources with no history of allergenicity, such as viruses, bacteria or non food
plants. The likelyhood that the proteins derived from such sources of DNA will
be allergens is not very high, since most proteins in nature are not
allergens. The key features of the allergenicity assessment for such foods than again
involves a comparison of the amino acid sequence of the introduced protein
with the amino acid sequences of known allergens and the digestive stability of
the introduced protein.

While the combination of these two criteria provides reasonable assurance
that the introduced protein has limited allergenic potential, the ideal
approaches to the application of these two criteria have been debated, and the
desirability of adding other criteria for the allergenicity assessment of such
products and additional testing has been advocated 14. The development of
additional criteria and additional tests to use in the assessment of the
allergenicity of GM foods would be advantageous in cases where the gene is obtained
from sources with no history of allergenicity. The level of expression of the
introduced protein and the functional category of the introduced protein could
be used as additional criteria.

In addition, the development of suitable animal models for the prediction of
the allergenic potential of the introduced proteins is anticipated in the
future. While several animal models appear to be promising , none has been
sufficiently validated for its routine use in the assessment of the allergenicity
of GM foods. It must also be realised that the absence of sequence
similarity with allergenic protein-epitopes and a missing stability against digestion
does not necessarily prove for a missing allergenicity as examples are known
which contradict to the general rules: Highly homologous sequences with
allergens in case of allergen-isoforms have been shown without any allergenicity.

Furthermore, proteins with a low stability have been shown to exhibit a
significant potency to induce allergenicity or to sensitize for allergic
reactions17-19. The use of patients sera for the testing of allergenicity is
therefore recommended20 .There is also some discussion if the generally agreed system
is sensitive enough to detect upcoming new allergies in time. It is likely
that the first manifestations of a new allergy will occur in pre-existing
adult allergic individuals and could occur as a consequence of cross-reactivity.
A screening programme may be desirable to predict such cross-reactivities by
employing patients sera, however, the number of sera that would need to be
screened may need to be much larger than that hitherto recommended in
international documents 21.

Risk Assessment of Cell Mediated Reactions and Microbial Impact on the
Immune System

Although the well characterised interactions which lead to allergic
immediate hypersensitivities may comprise the fare most important food derived
hypersensitivity problems, the role of other type of responses, and their relevance
for food hypersensitivity in general and for the safety assessment for foods
from GM organisms specifically remain more unclear. Adverse food reactions
are discussed and also need to be taken in mind in the assessment of
GM-foods22. Such reactions could comprise delayed type hypersensitivity reactions
which have been characterised to develop slowly, reaching a peak at approximately
48 hours and then slowly subsiding over 72-96 hours. They are known to
involve cell mediated responses without important IgE involvement. Also reactions
to cow milk, soy proteins, eggs etc known in infants and children, Celiac
disease and Crohns disease show missing tolerance and mislead activation of T
cells23.

Potential immune-stimulatory or immune-modulatory effects of GM
microorganisms (GMMs) used as or in foods are a specific area of a risk assessment which
evaluates immune responses to GM organisms. GMMs may establish themselves
within the GI tract and exert influences on the immune system via interactions
with the gut immune system. Even non-viable microorganisms are known to retain
functional properties (i.e. cell adhesion, binding of chemicals,
immunomodulating activities), which can have direct or indirect effects on both
microflora- and host associated functions24. Gut-associated lymphoid tissue (GALT)
has important interactions with the immune system and it is well established
that microbial stimuli are the main antigenic forces in the development and
maintenance of GALT and acquired immunity24. Stimulation of antigen presenting,
dendritic cells influencing immune type responses was shown for bacterial
cell walls before25 Potential safety relevant consequences from rare, but
possible uptake of recombinant DNA from GM food by cells of the immune system
remain to be investigated 26-28.

Conclusions

In general, it seems that the present discussion on GM food safety,
especially in the field of hypersensitivity reactions does not so much point towards
a significantly increased safety problem of GM foods compared with
conventional foods, but it reflects increased regulatory demands as well as perceived
needs for a higher safety level. Conventional foods often have not been
subject of hypersensitivity assessment. Public awareness as well as genuine
scientific considerations in the field of GM foods has resulted in general
guidelines being elaborated for allergenicity assessment of such foods. These
internationally agreed guidelines are specifically important for foods which are
traded globally. Standards established for the assessment of GM foods may then
turn out to be a paragon for the testing of conventional foods. The detailed
analysis of immune mechanisms involved in the stimulation of different type of
immune responses has revealed complex ways and some of these ways are still
poorly understood, such as pathways resulting in cell mediated
hypersensitivity reactions to food.

An improved investigation of activation pathways including antigen
presenting- and T cells will not only contribute to a better understanding of these
reactions but may also result in improved testing methods for allergenicity,
where the possibilities for testing, especially of whole foods, in animal
models are still limited.


References

1 Codex, 2001. Consideration of proposed draft general principles for the
risk analysis of foods derived from modern methods of biotechnology.
http://www.who.int/fsf/ GMfood/bt01_05e.pdf

2 WHO, 2002. 20 Questions on GM Foods. http:// www.who.int/ fsf/
GMfood/q&a.pdf 3 IFT. 2001. Food Allergies and other Food sensitivities, expert panel on
food safety and nutrition: Institute of food technologists.
http://www.ift.org/publications/sss/allergens.pdf

4 Lambrecht B.N. 2001. Allergen uptake and presentation by dendritic cells :
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5 Alpan O., Rudomen G., Matzinger P. 2001. The role of dendritic cells, B
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6 Haller D., Bode C., Hammes W.P., Pfeifer A.M., Schiffrin E.J., Blum S.
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11Institute of food research, 2002. Food allergy.http://www.ifr.bbsrc.
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12 Bindslev-Jensen C., Ebner C., Madsen C., Mäkinen-Kiljunen S., Peltre G.,
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13 Metcalfe, D.D., Astwood, J.D., Townsend, R., Sampson,H.A., Taylor, S.L.,
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14 WHO/FAO 2000. Second Joint WHO/FAO Expert Consultation on Foods Derived
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16 IFT 2000. Expert Report on Biotechnology and Foods:Human Food safety
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17 Ferreira F., Hirtenlehner K., Jilek A., Godnik-Cvar J., Breiteneder H.,
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18 Heiss S., Fischer S., Muller W D., Weber B., Hirschwehr R., Spitzauer S.,
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20 Valenta R.2002. p. comm.

21 Warner J. 2002. p. comm.

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23 Janeway C.A.2001.Immunobiology, New York : Garland; Edinburgh : Churchill
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24 WHO/FAO expert consultation, 2001.Safety assessment of foods derived from
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25 Haslberger A.G., Kohl G., Felnerova D., Mayr U.B., Fuerst- Ladani S.,
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26 Schubbert, R., Renz, D., Schmidt, B. and Dorfler, W.1997. Foreign (M13)
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27 Hohlweg, U. and Doerfler, W. 2001. On the fate of plant or other foreign
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28 Einspanier, R., Klotz, A., Kraft, J., Aulrich, K., Poser, R.,Schwägele,
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