What Is the Main Idea?

Peanut allergy is a leading cause of anaphylaxis and some infants are more at risk of developing it than others. In the brief report “Epitope-Specific IgE at 1 Year of Age Can Predict Peanut Allergy Status at 5 Years”, published in the journal International Archives of Allergy and Immunology, the authors describe how levels of particular types of antibodies in blood samples given by infants at age 1 year can be used to predict whether they will develop peanut allergy by the time they are 5 years old.

What Else Can You Learn?

In this blog post, peanut allergy, anaphylaxis, and efforts to predict the development of severe allergy in children are described. Immune system antibodies, antigens, and epitopes are also discussed.

What Is Peanut Allergy?

Peanut allergy is a type of food allergy (an unusual reaction of the body’s immune system to a specific food). The immune systems of people with peanut allergy mistakenly identify peanut proteins as things that are harmful to the body and need to be removed. Although some allergic reactions to foods are relatively mild, causing symptoms such as a rash or abdominal pain, others are more serious. Severe allergic reactions can cause anaphylaxis, which is potentially life-threatening and should be treated as a medical emergency. In addition to the more usual allergy symptoms such as swelling, an itchy or raised rash, or feeling or being sick, anaphylaxis symptoms can include a fast heartbeat, confusion or anxiety, breathing difficulties, feeling lightheaded or faint, and the person losing consciousness. They can develop suddenly and worsen very quickly. Peanut allergy is the leading cause of anaphylaxis in the USA and ranks second (after milk) in the UK.

Peanut allergy usually develops in early childhood and incidence has increased over recent decades. Estimates of the number of affected children vary between countries, but can be as high as 3% of the population. Some infants are at greater risk of developing peanut allergy than others, including those with family members with food allergies and those with egg allergy and/or eczema. Some health services used to advise that infants should not be exposed to foods containing peanuts because of fears that it could trigger peanut allergy. However, there is now strong evidence that introducing infants at risk of peanut allergy to peanuts as early as age 4–6 months can significantly reduce their risk of developing food allergies in the future.

Why Do Some People Have More Severe Peanut Allergies than Others?

It is now believed that peanut allergy can take several different forms called “endotypes” (an endotype is a subtype of a health condition that differs from other subtypes in the way that changes in the body and its systems cause or are caused by the condition). Evidence to support this comes from the fact that around 20% of infants and young children that have an allergic reaction to peanut will outgrow their allergy, while in others the allergy will persist throughout their lives. The difference is thought to be linked to the specific molecules, called “antibodies” (also known as “immunoglobulins”), that the immune system produces when it comes into contact with peanut proteins.

What Are Antibodies?

Antibodies are glycoproteins (molecules that are made up of protein and carbohydrate chains). They are highly specific, and recognise and bind to “antigens” (this term describes anything that causes the immune system to produce antibodies against it and can include chemicals, molecules on the surfaces of bacteria and viruses, and proteins in food like peanuts). Antibodies are divided into five different classes – IgE, IgG, IgM, IgA, and IgE – based on their characteristics and roles. They all have a Y-shaped structure, and while the bottom part does not change from one antibody to another, the two “arms” do and make up the part of the antibody called the “antigen-binding site”. It is differences in this region that enable different antibodies to bind to specific regions of antigens (called “epitopes”) and not to others. For example, an antibody that binds to an epitope on a peanut protein will not bind to an epitope on protein made by the virus that causes flu. Epitopes can be described as “sequential” or “conformational”. Sequential epitopes are made up of a linear sequence of amino acids (the building blocks of proteins) like beads on a string, while conformational epitopes are made up of amino acids that are only brought close together when the string of amino acids is folded up into a three-dimensional structure.

How Can Different Antibody Types Be Used to Predict Peanut Allergy?

Some recent studies have reported that levels of sequential epitope-specific IgE (ses-IgE) antibodies in infants with persistent food allergies are lower than levels of IgE antibodies against a mixture of both conformational and sequential epitopes during the first year of life. ses-IgEs develop as infants get older, raising the possibility that children who develop a persistent peanut allergy later in life may have distinct epitope-specific profiles in infancy. If this is the case, it may become possible to identify infants who are at risk of developing peanut allergy via a simple blood test.

What Did the Study Show?

The authors monitored the development of ses-IgEs in 74 children who were at risk of developing peanut allergy who had either already been identified as allergic to peanut or were not yet allergic, and who were avoiding peanuts. They analysed blood samples taken when the children were aged 4–11 months, and again at 1 and 2.5 years of age. They used a machine learning strategy (a computer system that uses algorithms and statistical models to analyse patterns of data and draw conclusions from them) to identify prognostic biomarkers (characteristics, such as molecules in your blood, that indicate what is going on in the body) that could predict whether or not a child would have an allergic response to an oral food challenge with peanut at a 5-year visit. The results showed that blood samples from children aged as young as 1 year could be used to accurately predict the outcomes of oral food challenge tests at 5 years of age. If these results can be confirmed by further studies, it may become possible for healthcare professionals to identify infants who are likely to develop persistent peanut allergy in the future, enabling them to start peanut exposure interventions early and, hopefully, prevent severe and permanent peanut allergy from developing.

Note: This post is based on an article that is not open-access; i.e., only the abstract is freely available. Furthermore, the authors of this paper make a declaration about grants, research support, consulting fees, lecture fees, etc. received from pharmaceutical companies. It is normal for authors to declare this in case it might be perceived as a conflict of interest.

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