What happens to the immune system when you have allergies

What happens to the immune system when you have allergies

 This article incorporates public domain material from the U.S. National Cancer Institute document «Dictionary of Cancer Terms».

This briefing is also available as a PDF

An allergy is an unnecessary immune response to an innocuous substance. Examples of common substances people are allergic to include pollens, dust mites, insect venom and food such as nuts or shellfish. Allergies can range in severity with the most extreme symptoms seen in anaphylaxis. Every year in the UK, the number of allergy cases increases, mainly in children.

This briefing should assist illustrate how allergy develops and possible reasons for increasing prevalence.


Introduction

An allergy is an unnecessary immune response to an innocuous substance (an allergen).

What happens to the immune system when you own allergies

Examples of common substances people are allergic to include pollens, dust mites, insect venom and food such as nuts or shellfish. Allergic reactions can be grouped into two classes. The most common and best understood is mediated by a class of antibody called immunoglobulin E (IgE). Other reactions are non-IgE mediated and typically cause symptoms to appear more slowly, sometimes several hours after exposure. In fact, non-IgE mediated reactions do not necessarily involve antibodies but instead, cell reactions of the immune system. They are much less common and are generally less well-understood. The most common way to diagnose an IgE-mediated allergy is through a blood test to identify allergenspecific IgE or a skin prick test which results in a local inflammatory reaction after istration of the trigger allergen.

Allergies can range in severity from symptoms of mild discomfort to the life-threatening systemic reaction seen in anaphylaxis.

What happens to the immune system when you own allergies

The type of symptoms depends mainly on how the person is exposed to the allergen. Every year in the UK, the number of allergy cases increases by approximately 5%, and half of those are in children. The ‘Hygiene Hypothesis’, the thought that increased exposure to microorganisms correlates with a decreased tendency to develop allergy, is one explanation for the rise in prevalence. This has developed into a new hypothesis called The ‘Old Friends Mechanism’ which links the tendency to develop allergy to an individual’s microbiome (collection of microorganisms living in and on an person’s body).


Mechanism

Allergies are an abnormal immune reaction.

The human immune system is designed to protect the body from potential harm and in people who own allergies the immune system will react to allergens (substances that trigger an immune response).

The immune system will produce immunoglobulin E, IgE, antibodies for each allergen. The antibodies will cause cells in the body to produce histamines. These histamines will act on diverse areas of the body (eyes, throat, nose, gastrointestinal tract, skin or lungs) to produce symptoms of an allergic reaction.

The allergic response is not limited to a certain quantity of exposure. If the body is exposed to the allergen multiple times the immune system will react every time the allergen is present.

The reason why people get allergies is not known. The allergens are not passed below through generations. It is believed if parents own allergies the kid is more likely to be allergic to the same allergens.

What happens to the immune system when you own allergies

Some common symptoms include itchiness, swelling, running nose, watery eyes, coughing, wheezing, trouble breathing, hives, rashes, mucus production, or a more severe reaction anaphylaxis. Allergic responses and the severity vary from person to person.

Many substances can trigger an allergic reaction. Common triggers of a reaction include foods, likes nuts, eggs, milk, gluten, fruit and vegetables; insect bites from bees or wasps (often a severe response occurs); environmental factors such as pollen, dust, mold, plants love grass or trees, animal dander; medications or chemicals.

Some people experience an allergic response to freezing or boiling temperatures exterior, jewelry or sunlight.

What happens to the immune system when you own allergies

There are daily treatments to reduce the severity of the allergic response. Often these treatments include an antihistamine oral pill, nasal spray, or eye drops. Other treatments include an allergy shot, which hold the allergic response to a minimum. For more severe reactions an epinephrine injection is carried around. This injection will be taken if the person is going into anaphylactic shock. The best treatment is avoidance of each allergen.


Key points

  1. The prevalence of allergy in the UK and other developed countries is increasing. The reasons for this are poorly understood but are thought to be linked to changes in human lifestyle that own altered our exposure to the diversity of microbes.
  2. Commonly used diagnostic methods for identifying allergy include skin prick and/or blood tests combined with a detailed patient history. Component resolved diagnostics is capable to provide more detailed and precise diagnostic information and is becoming more relevant in allergy clinics.
  3. Allergies encompass a wide range of conditions varying in prevalence.

    They are characterised as an unnecessary immune response to an innocuous substance (such as pollens, latex, or certain foods). When these substances cause an allergic reaction they are considered an allergen.

  4. Allergy immunotherapy or desensitisation can be used in some cases to eliminate a person’s allergy by reversing their immune response to the triggering allergen.


What is allergy?

Allergy describes a wide range of conditions, some of which are rare and some extremely common.

In healthy individuals, when the immune system registers a substance as a threat, B cells, a type of white blood cell, produce antibodies.

What happens to the immune system when you own allergies

This is a process known as sensitisation and is part of the normal immune response. In allergic individuals, the immune system misidentifies a harmless substance as a threat. Therefore, an allergy is an unnecessary immune response to an innocuous substance (termed an allergen). Allergens are generally proteins (called antigens) found in a non-infectious allergy-causing substance (for example pollens or dust mites), which ultimately trigger the immune system to reply in a way that can be harmful, causing tissue damage and serious disease. These harmful immune responses are termed hypersensitivities and often cause a number of undesirable reactions which can lead to wheezing, coughing, oedema (swelling), or, in extreme circumstances, anaphylaxis.

IgE-mediated allergy is broadly characterised as a Type 1 hypersensitivity. Other hypersensitivity reactions (II, III and IV) are mediated by other antibody classes, immune cells or cellular components. Common IgE-mediated allergies include food allergies, wasp venom and hay fever (see Box 1). Some people may own an inherited tendency towards allergies, a condition known as atopy. Atopic individuals are more prone to asthma, eczema and hay fever (the atopic triad).


References

1) Allergies (2011) reviewed by A.D.A.M. A.D.A.M medical encyclopedia

2) Allergies.(2009) reviewed by Geimeier W J.

What happens to the immune system when you own allergies

Teen Health

3) Sicherer S, Sampson HA. Journal of Allergy and Clinical Immunology 2010 Feb 125 (2 suppl2) S116-25.


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