Not all food are allergenic, and not all allergenic
foods are equally allergenic. In other words, foods vary in clinical allergy significance. Generally speaking,
all food proteins are potentially allergenic for some people. Among all foods, 8 foods accounts for 90% of food
allergies: milk, wheat, peanuts, tree nuts, eggs, fish,
crustacea, and soy (1).
Soy proteins tend to be
less immunologically reactive than many other food proteins.
Immunology of food allergy
Type I food allergy
consists of 3 steps (2,3,4,5). First there is a sensitization starting with
food antigens moving across the intestinal barrier. An immature gut, or
infection will worsen the process. Antibody responses are triggered (IgG and
IgA) leading to an allergic response.
Food antigens activate antigen-specific
B cells and helper T cells that direct B cells to differentiate into
IgE-producing plasma cells. IgE is then quickly bound by high-affinity IgE
receptors mainly on the surface of mast cells. Mast cells contain large amounts
of histamine which is a main inducer of symptoms of allergy. Following this
insult, a large number of mast cells armed with IgE antibodies is present in
circulation and tissues.
After sensitization, allergen
or multivalent allergen fragments are again absorbed after ingestion. IgE
antibodies on mast cells bind the allergen so that the allergen cross-links at
least 2 receptor-bound IgE molecules. This sends a signal causing the mast cell
to release histamine and other inflammatory mediators (degranulation). Timing
and magnitude of the release is defined by allergen dose and a number of poorly
understood host factors. At the end, clinical symptoms ensure when histamine
and other inflammatory mediators stimulate the wide variety of allergic
symptoms in other cells and organs.
Soy allergy
The first allergic
reactions to soy in humans were described in 1934 (2,6). Anti-soy IgE
antibodies have been identified but allergen specificity patterns are variable and
complex. As many as 28 soy proteins bind to IgE from soy-allergic patients (2,7).
Soy is also an aeroallergen,
although the pathologies and allergen reactivity profiles are different for ingestion
versus inhalation, where soy hull antigens not present in soy protein isolates
seem to dominate (2,8).
Among the
various food allergies, soy is less allergenic than egg, milk, wheat and peanut
(2). This means that a greater soy dose is necessary to cause the same reaction
as the other foods, the reaction is less severe.
The prevalence of soy allergy was only found to be
1.2% in in a cohort of 505 children
(9), and 0.4 in 243 children fed soy protein formulate during the first 6
months (10). European cohorts observed a prevalence from 0-0.7% in children subject
to double-blind placebo-controlled challenge (11). Soy allergy is less common than
cow’s milk allergy (CMA), but 10% to 14% of patients with CMA also present with
soy protein allergy (12,13,14).
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References
1. Food and
Agriculture Organization of the United Nations (1995) Report of the FAO
Technical Consultation on Food Allergies. Rome, Italy.
2. Christopher T. Cordle. Soy Protein Allergy:
Incidence and Relative Severity. J. Nutr. 134: 1213S–1219S, 2004.
3. Sicherer,
S. H. (2002) Food allergy. Lancet 360: 701–710.
4. Sampson,
H. A. (2003) Food allergy. J. Allergy Clin. Immunol. 111: S540–S547.
5. Sicherer,
S. H., Monoz-Furlong, A., Murphy, R., Wood, R. A. & Sampson, H. A. (2003)
Pediatric food allergy. Pediatrics 111: 1591–1680.
6. Duke, W.
W. (1934) Soybean as a possible important source of allergy.
J. Allergy 5:
300–302.
7. Awazuhara,
H., Kawai, H. & Maruchi, N. (1997) Major allergens in soybean and clinical
significance of IgG4 antibodies investigated by IgE- and IgG4-immunoblotting
with sera from soybean-sensitive patients. Clin. Exp. Allergy
27: 325–332.
8. Codina, R., Lockey, R. F.,
Fernandez-Caldas, E. & Rama, R. (1997). Purification and characterization
of a soybean hull allergen responsible for the Barcelona asthma outbreaks. II.
Purification and sequencing of the Gly m 2 allergen. Clin. Exp. Allergy 27:
424–430.
9. Bruno G,
Giampietro PG, Del Guercio MJ, et al. Soy allergy is not common in atopic children: a multicenter study. Pediatr
Allergy Immunol. 1997;8(4):190–3.
10. Osterballe M, Hansen TK, Mortz CG, et al.
The prevalence of food hypersensitivity in an unselected population of children
and adults. Pediatr Allergy Immunol. 2005;16(7):567–73.
11. Roehr CC, Edenharter G, Reimann S, et al.
Food allergy and non-allergic food hypersensitivity in children and
adolescents. Clin Exp Allergy. 2004;34(10):1534–41.
12. Bhatia J, Greer F. American Academy of
Pediatrics Committee on Nutrition. Use of soy protein-based formulas in infant
feeding. Pediatrics. 2008;121(5):1062–8.
13. Klemola T, Vanto T, Juntunen-Backman K, et
al. Allergy to soy formula and to extensively hydrolyzed whey formula in
infants with cow’s milk allergy: a prospective, randomized study with a
follow-up to the age of 2 years. J Pediatr. 2002;140(2):219–24.
14. Zeiger RS, Sampson HA, Bock SA, et al. Soy
allergy in infant and children with IgE-associated cow’s milk allergy. J Pediatr. 1999;134 (5):614 –622.
