Allergy from Peanuts

We always see that Americans are allergic to peanuts, but Chinese do not. Are peanuts still picking people?

Why do we always see reports of peanut allergies in Americans, but not reports of allergies in Chinese people?

Why do we always see reports of peanut allergies in Americans, but not reports of allergies in Chinese people?

Let us start with the summary: Because Chinese people eat peanuts less frequently and geographically than foreign countries, and the content of allergens in peanuts produced in China is less than that in foreign countries, the proportion of peanut allergies in China is relatively small. But the absolute number is not necessarily small.

 

1. Hygiene Hypothesis for Peanut Allergies

On the issue of differences between China and the United States. In 1989, Strachan first proposed the hygiene hypothesis in a landmark article to explain the inverse relationship between family size and/or hygiene and susceptibility to allergic diseases. 

The subjects of this study are from the same European First World country, and in this group of Caucasians, it can be observed that there are iconic differences between different social groups. 

It is especially worth noting that people with lower socioeconomic levels and larger families will have a lower risk of allergic diseases.

 

Currently, the commonly used mechanism to explain the difference in the prevalence of these diseases is based on the assumption that "the population of the lower socioeconomic level in the research group has the highest overall microbial exposure". 

In addition, the hypothesis also proposes that the increased exposure to microbes, especially the increased exposure to pathogens, in the lower affluent populations can divert the immune system's attention to non-pathogenic environmental allergens, thereby reducing the degree of allergies.

 

A study completed 13 years ago also came to basically consistent conclusions. The study evaluated the indigenous Indian population (the Métis) whose living conditions in northern Canada are equivalent to those of third world countries. 

Gerrard et al. reported that although the serum IgE level of the neighboring white population was lower than that of the Métis population, allergic diseases rarely occurred in the Métis population. 

In contrast, severe viral and bacterial infections and parasitic infections are more common among Indians. Therefore, Gerrard et al. put forward a foreseeable view, “Relatively speaking, atopic diseases are the price paid by some members of the white population to avoid viral, bacterial and parasitic diseases”.

 

Allergic diseases are polygenic diseases

It is known that allergic diseases are polygenic diseases, and genetic changes cannot be used to explain the prevalence of allergic diseases. People pay more attention to the influence of environmental factors on the incidence of allergic diseases, especially in the early life. 

Since the first few years after birth are the peak period of immune system development, it is particularly vulnerable to allergic symptoms caused by environmental factors, and the environmental factors that inhibit or promote the occurrence of allergic diseases are very complex. 

Known risk factors for allergic diseases include early feeding, food, infections, allergens, air pollution and cigarettes. 

The role of infection in the pathogenesis of allergic diseases is very complex, which is related to the types of exposed microorganisms, exposure time, dose and clinical phenotype of allergic diseases.

 

The same is true for allergen exposure, which may not all induce allergic diseases, and is closely related to the allergen dose. Early high-level cat allergen exposure can prevent the occurrence of asthma, while low-level exposure promotes the occurrence of asthma.

The author's in vitro studies have shown that high-level dust mite stimulation can promote cord blood lymphocytes to reduce the expression of inducible costimulatory factor (ICOS) on T cells, increase the expression of T2bet, and promote the development of T cells to Th1. 

Further clarifying the factors that cause or inhibit the occurrence of allergic diseases will be able to recommend feasible interventions to the community.

 

From Th1/Th2 to Th/Toll-like receptors, from classic "hygiene hypothesis" to "new hygienic hypothesis". 

The classic "hygiene hypothesis" believes that in places with a high degree of industrialization, the lifestyle is relatively clean, exposure to infectious pathogens is reduced, a large number of antibiotics and vaccination are used to reduce the development of Th1 function of the body, and the body's immune function is weakened to a non-allergic response. Tilt, leading to asthma.

 

The imbalance of Th1 and Th2 functions is the basis of the classic "hygiene hypothesis", but with the deepening of understanding of allergic diseases, people have found that early intestinal parasite infection can increase Th2 response and also reduce the occurrence of allergic diseases. 

Studies have also shown that the role of interferon 2γ (IFN2γ) in the immune pathology of asthma may be more pronounced than its role in down-regulating Th2 cytokines. Therefore, the hygienic hypothesis based on Th1/Th2 cannot explain the entire mechanism of allergic diseases.

 

New Hygiene Hypothesis

The "New Hygiene Hypothesis" is based on the theory of regulatory T cells (CD4+CD25+T cells, Tr). It is believed that due to superior sanitary conditions, the lack of microbial exposure reduces the surface of microbes such as lipopolysaccharide (LPS) and CpG dinucleotides. 

There is the possibility that pathogen-related molecular patterns (PAMPs) stimulate immune body regulatory cells through Toll-like receptors, resulting in the loss of T cell balance regulation during the development of Th1 and Th2 responses. 

The author's preliminary study also showed abnormal Tr function in children during acute asthma attacks. The treatment of allergic diseases by acting on Tr intervention is currently a research hotspot.

 

2. Peanut allergens

In North America and Europe, 1% and 0.5% of children and adults are allergic to peanuts. Hyperallergic patients can induce allergic reactions by ingesting 100 ug of peanut protein. In the United States, 100 to 200 patients die of peanut allergy every year. 

China is the world's largest producer, consumer and exporter of peanuts, but the peanuts produced in the country are mainly for oil, and only about 30% are directly eaten. 

70% to 80% of peanuts in developed countries such as the United States and Europe are eaten directly. In the United States and Japan, nearly 94% of households eat peanut butter.

 

With the widespread consumption of peanut food, the number of people allergic to peanuts is increasing. 

In the past 10 years, the number of peanut allergy cases in Western countries has increased from 1 stewed 1,000 to 1 stewed 200. 

At present, about 0.5% to 1% of people in the United States, Britain and France are allergic to peanuts. In the Isle of Wight in the United Kingdom, it has even reached 1 .5%. 

In some Asian countries and regions, peanut products are also one of the main allergens that cause food allergies in children. 

Allergy researchers from the Chinese Academy of Medical Sciences found that about 4% of patients were allergic to peanuts. 

Ye Shitai's research shows that oil crops such as peanuts are highly allergenic, which usually cause severe allergic reactions and even lead to fatal shock.

 

In other words, there are many people in China who are allergic to peanuts. One of the reasons may be that it is really not that common for Chinese people to eat peanut butter.

 

Peanut sensitization refers to the adverse immune response mediated by IgE produced by the human body to peanut antigen material, which belongs to type I allergy. 

When allergic patients eat peanuts, the body becomes more responsive to antigens and induces IgE reactions.

When peanut allergens are consumed again, the existing IgE will directly recognize and bind these substances, thereby inducing cells to release histamine, Vasoactive substances such as serotonin cause the body to lose function in a certain tissue, organ, or even the whole body.

 

The peanut allergic reaction may be caused by the main sensitizing components (Arah1, Arah2, Arah3) or secondary sensitizing components (Arah4, Arah5, Arah6, Arah7, Arah8). 

But they are all proteins. Among them, the recognition rate of the first seven kinds of protein allergic patients' serum exceeds 50%, so it is the main peanut allergenic protein. 

Peanut allergy serology is different in different countries, and the recognition rate of Ara h 1 in different European populations is 35%.

 

The main allergenic proteins in China are Ara h1, Ara h1 subunits and three Ara h 3 polypeptides, and Ara h1 and Ara h1 subunits are the most sensitizing. 

The difference of Ara h 1 among different peanut varieties is extremely significant (p<0.01), and the difference of 37.5kD polypeptide in Ara h 3 is significant (p<0.05). 

And the relative content of Ara h1 and Arah 3 are lower than foreign peanut varieties, which is another reason why the incidence of peanut allergy in China is lower than that in foreign countries.

 

Liu Enmei, Yang Xiqiang. Research progress and prospects of allergic diseases [J]. Journal of Applied Clinical Pediatrics, 2007, 22(21): 1603-1604.

 

Wang Tong, Liang Xuanqiang, Li Ling. Research progress on peanut allergens [J]. Chinese Journal of Oil Crops, 2007, 29(3): 353-358.

 

Cong Yanjun, Lou Fei, Xue Wentong, et al. Identification of Chinese Peanut Allergenic Protein [J]. Food Science, 2007, 28(10): 109-112.