Hypersensitivity reaction

Hypersensitivity reaction - Type III

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What is Hypersensitivity reaction - Type III?

Hypersensitivity means that the body responds to a particular substance (called allergens) in an exaggerated fashion, where it does not happen in normal circumstances. There are 4 types of hypersensitivity reaction, type I, II, III and IV. They are different in terms of the disease manifestation and pathological processes. However, only type III hypersensitivity reaction will be discussed here.

In type III hypersensitivity, soluble antibodies bind to antigens to form immune complexes in the blood. These complexes travel through the blood stream and get deposited in various organs. Hence this can occur in many parts of the body. Generally, common sites of deposition include:

skin

kidney

joints

blood vessels

lungs

One example of a Type III hypersensitivity is serum sickness, a condition that may develop when a patient is injected with a large amount of antitoxin that was produced in an animal. The image below is that of serum sickness:

Who gets Hypersensitivity reaction - Type III?

The cases of different diseases vary widely. Certain diseases can be common, such as rheumatoid arthritis. Diseases such as systemic lupus erythematosus can have the figure of 1.8-7.6 cases per 100,000 per year.

Note that systemic lupus erythromatosus is a disease of mixed hypersensitivity - type II and III hypersensitivity reaction occur in this disease.

Predisposing Factors

Depending on the manifestations of different type III hypersensitivity diseases, there are different risk factors as well.

There are some gender differences between diseases of type II hypersensitivity. Some diseases are more common in women such as rheumatoid arthritis.

As different diseases are included in type III hypersensitivity, ethnicity and geographical location can have impact on the disease cases.

Progression

Type III hypersensitivity reaction is induced by antigen-antibody complexes. By the various biochemical mechanisms, the end result are tissue damage to the body.

The antigens can either be from the body itself or from outside the body (for example, bacteria or microorganisms that infect the body).

It must be remembered that the formation of antigen-antibody complex in the circulation does not indicate the presence of type III hypersensitivity diseases. It is the capability of these complexes to mount a reaction leading to tissue damage that is the cause of diseases themselves.

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