Allergy-related diseases affect nearly one quarter of the world’s population and are listed by the World Health Organization as one of the three major diseases to be controlled in the 21st century. Among them, adverse reactions to food have attracted much attention. About 30% of adults have experienced adverse reactions to food at least once in their lifetime, and 20% to 65% of patients have allergic bowel syndrome and indigestion to food allergies.
What is a food allergy?
An allergic reaction is an abnormal immune response that is inherent to a foreign substance, such as food. Any food that causes an allergic reaction is called an allergen.
With age and long-term consumption of a certain food, the allergenicity of that food will also change. When the immune system produces a large amount of antibodies to a certain food, it causes inflammation or allergies in different places.
Many unexplained chronic and recurrent symptoms are linked to food allergies.
Most people experience inexplicable allergic symptoms such as skin rash, diarrhea, headache, indigestion, flatulence, nasal congestion and nasal fluid. If you take into account some common minor discomfort symptoms: such as occasional anxiety, joint stiffness, edema, and dark circles, at least a quarter of the world’s population is affected by food allergies.
What factors will promote an allergic reaction?
Heavy metal poisoning, food additives, partial eclipse, stress, genetics, long-term infections, inflammation, drugs, environmental pollutants and toxins (such as toxins released from styrofoam food utensils) can promote an allergic reaction.
At present, the only effective treatment method is to avoid eating allergic foods, and it is particularly important to patients to detect which food is allergic to him/her. The study of food allergens is an important basis for the research and development of detection reagents and allergy mechanisms. The current detection methods of food allergens and the research progress of common allergens are summarized below.
First, the detection method of food allergens
(1) Double-blind food challenge test
(2) Skin prick test (SPT)
(3) In vitro 8IgE detection
- a. Radio allergosorbent test (RAST)
- b. Cap (CAP) Allergen Detection System
- Other reagents and methods
(4) Biological resonance technology
Second, research progress on common food allergens
Because all kinds of allergen detection reagents use recombinant or extracted allergens and allergens play an important role in the treatment of allergic diseases, it is of great significance to study allergens. Food allergens are generally proteins or glycoproteins with a relative molecular mass of 10,000 to 70,000. They can be divided into major allergens and minor allergens. Most allergic patients are sensitive to major allergens.
(1) Crustaceans and their products
As seafood has become more and more popular, reports of allergic reactions to such foods have gradually increased. Among them, shrimp allergens have attracted much attention. It is reported that 0.6% to 2.8% of patients with allergic diseases are allergic to shrimp. At least 13 IgE-binding proteins have been detected in shrimp, but tropomyosin has been identified as the only major allergen, with a relative molecular mass between 34,000 and 39,000. It is reported that tropomyosin is an important antigen of invertebrates such as shrimp, crab, oyster, and squid, and has a highly conserved amino acid sequence.
(2) Eggs and their products
Eggs are one of the most common causes of food allergic reactions in children, with a positive rate of 35% in food allergies in children and 12% in adults. The major allergens of the protein are oval mucin Galdl (relative molecular mass 28000), ovalbumin Gald2 (relative molecular mass 44000), oval transferrin Gald3 (relative molecular mass 77000), and lysozyme Gald4 (relative molecular mass) 14000); the main allergen for egg yolk is Ot yolk protein (relative molecular mass 70,000). According to reports, egg allergy is more likely to cause allergies than egg yolk, and ovalbumin is the main allergen.
(3) Milk and dairy products
Milk allergy rates among children under 2 years of age range from 1.6% to 2.8%, and 50% to 9% of children become tolerant before the age of 6 years. The main allergens of milk are casein (Bosd8, relative molecular mass is 20,000 to 30,000), Bosd5 (relative molecular mass is 18000), Ot. Lactalbumin (Bosd4, relative molecular weight is 14000), bovine serum albumin (Bosd6, relative molecular weight is 67000), and bovine immunoglobulins, among which casein is the most immunogenic and antigenic. Milk antigens are relatively stable and retain their immunogenicity after routine processing.
(4) Peanuts and Products
Due to the severity and high incidence of peanut allergic reactions, this allergen has caused widespread concern in medical institutions. Peanut allergies account for 10% to 47% of food-induced allergic reactions. The main peanut allergens are Arah1 (relative molecular mass is 63500), Arah2 (relative molecular mass is 17000), and other related antigens are Arah3 (relative molecular mass is 60,000) and Arah4 (relative molecular mass is 14000). The secondary antigens are Arah6, Arah7 and actin. ELISA inhibition test confirmed that Arah2 was the main antigen that caused cross-reaction of peanut with hazelnut and almond. Different food processing methods have different effects on peanut antigens. It is reported that baking will increase Amhl content and make IgE antibody-binding epitopes more easily bind to antibodies. Although peanut and legumes have cross-reactive proteins, clinical cross-reactivity is rare. Peanut allergy is more common in individuals who are allergic to eggs, milk, walnuts, etc., but it has not been found to have cross-reactive proteins with walnuts. In most cases, peanut allergy persists and turn worsen. In recent years, various technologies such as immunoelectrophoresis, ELISA, PCR, and biosensors have been applied to the study of food allergens, which has greatly improved people’s understanding of food allergens. However, the cross-reactivity of food allergens and different treatments on its allergenicity and the allergenicity of genetically modified foods need to be further explored.
In summary, in recent years, the incidence of food allergies has been increasing, and the detection of allergens is of great significance for the prevention and treatment of diseases. With the development of immunology, food allergen detection technology has made great progress, but there are also shortcomings: (1) because food allergens are (glyco) proteins, some of these (glyco) proteins are stable, and some are not stable, which limits the sensitivity of the test; (2) Some nut foods and seafood have cross-reactions, so the food allergen detection is not specific and further improvements are needed in the future. There are also methods for detecting food allergens such as blood IGG test, histamine release test, and basophil granulocyte activation test. No method can detect all food allergens, so combination should be used in clinical practice when necessary.
The development of molecular biology and immunology has made people have a better understanding of the structure and immunogenicity of food allergens. The development of bioinformatics has provided a strong support for the study of allergens. The recognition of T-lymphocyte and B-lymphocyte epitopes and the assessment of allergenicity and cross-reactivity are complementary to traditional laboratory techniques. Now the cross-reactivity of food proteins is available, and the allergenicity of genetically modified foods based on their genetic sequences is evaluated. It is believed that in the near future, human beings will have a deeper understanding of food allergens, which will provide a good platform for future research on food allergy mechanisms and research and development of allergen detection reagents.