Why do hypersensitivity reactions occur?

A hypersensitivity reaction occurs when the body produces an unnecessary and undesirable immune response following exposure to a certain antigen. Many people refer to hypersensitivity as a form of allergy.

What is a hypersensitivity reaction?

Hypersensitivity reactions (HR) are immune responses that are exaggerated or inappropriate against an antigen or allergen.

What is the difference between hypersensitivity reaction and allergic reaction?

Allergy is also known as a ‘hypersensitivity reaction’ or a ‘hypersensitivity response’. This article uses the terms allergy and hypersensitivity interchangeably. An allergy refers to the clinical syndrome while hypersensitivity is a descriptive term for the immunological process.

When does a person manifest a hypersensitivity reaction?

In general, a patient that presents with a type I hypersensitivity usually develops a reaction within one hour after exposure to an antigen. The signs and symptoms exhibited in this type of reaction involve vasoactive mediators that are released by IgE bound mast cells and basophils.

Can you be allergic to something and not have a reaction?

An allergic reaction may not occur the first time you are exposed to an allergy-producing substance (allergen). For example, the first time you are stung by a bee, you may have only pain and redness from the sting.

How many hypersensitivity reactions are there?

The four types of hypersensitivity are: Type I: reaction mediated by IgE antibodies. Type II: cytotoxic reaction mediated by IgG or IgM antibodies. Type III: reaction mediated by immune complexes.

Where do hypersensitivity reactions occur?

Allergic reactions are sensitivities to substances called allergens that come into contact with the skin, nose, eyes, respiratory tract, and gastrointestinal tract. They can be breathed into the lungs, swallowed, or injected.

What is the difference between Type 2 and Type 3 hypersensitivity reactions?

Type 2 hypersensitivity reactions may occur in response to host cells (i.e. autoimmune) or to non-self cells, as occurs in blood transfusion reactions. Type 2 is distinguished from Type 3 by the location of the antigens – in Type 2, the antigens are cell bound, whereas in Type 3 the antigens are soluble.

What is the difference between autoimmunity and hypersensitivity?

On the one hand, there are hypersensitivity diseases, which are characterized by excessive and undesirable reactions, produced by the immune system [4]. On the other hand, autoimmune diseases refer to the failure of the immunological tolerance mechanisms, causing reactions against own cells and tissues [5].

Is asthma a hypersensitivity reaction?

It is a type I hypersensitivity reaction, that is an immediate exaggerated or harmful immune reaction. Interestingly, only 7\% of allergic people develop asthma,43 which can lead us to believe that they present a unique phenotype that distinguishes them from other allergic, but nonasthmatic, individuals.

What is an IgE reaction?

If you have an allergy, your immune system overreacts to an allergen by producing antibodies called Immunoglobulin E (IgE). These antibodies travel to cells that release chemicals, causing an allergic reaction. This reaction usually causes symptoms in the nose, lungs, throat, or on the skin.

Can you have an allergic reaction only once?

First-time exposure may produce only a mild reaction. Repeated exposures may lead to more serious reactions. Once a person has had an exposure or an allergic reaction (is sensitized), even a very limited exposure to a very small amount of allergen can trigger a severe reaction.

What is an immediate hypersensitivity reaction?

Type I, II, and III hypersensitivity reactions are known as immediate hypersensitivity reactions because they occur within 24 hours of exposure to the antigen or allergen. Immediate hypersensitivity reactions are predominantly mediated by IgE, IgM, and IgG antibodies.

What is an example of a Type 4 hypersensitivity?

Type IV hypersensitivities are regulated by T cells and are delayed reactions to antigens associated with cells. Tuberculin reactions, chronic asthma, and contact dermatitis are examples of type IV reactions. Hypersensitivity reactions are categorized into four major types: type I, type II, type III,…

What are Type II hypersensitivity reactions to autoimmune diseases?

Type II hypersensitivity reactions can be seen in immune thrombocytopenia, autoimmune hemolytic anemia, and autoimmune neutropenia.

What are the antigens that trigger hypersensitivity called?

The antigens eliciting an immediate hypersensitivity are called allergens, particularly when they are involved in local allergic reactions. Hapten molecules such as penicillin molecules may be involved when they are bound to larger protein molecules. Foods, feathers, pollen grains, animal dander,…