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What is the immune system?

The immune system is the body’s means of protection against ‘foreign’ substances such as bacteria and viruses. It is composed of two major parts. One component involves the production of antibodies, proteins that recognise ‘foreign’ substances and cause them to be removed from the body. The other component involves specialised blood cells called T lymphocytes that can attack and kill ‘foreign’ substances directly. Antibodies and T lymphocytes become protective only after they are exposed to a "foreign" substance for the first time. This is the reason that we use vaccinations: to allow our immune system to recognise weakened or inactivated forms of bacteria and viruses that can cause disease, so that we will be protected if we actually come in contact with them.

What are autoimmune disorders?

Normally the immune system recognises the tissues in the body that are not ‘foreign’ and does not attack them. Autoimmune disorders are diseases caused by the body producing an immune response against its own tissues. The cause of autoimmune diseases is unknown, but it appears that there is a genetic predisposition to develop autoimmune disease in many cases (i.e. they are passed down through families). In a few types of autoimmune disease (such as rheumatic fever), a bacteria or virus triggers an immune response, and the antibodies or T-cells attack normal cells because they have some part of their structure that resembles a part of the infecting germ.

Autoimmune disorders fall into two general types: those that damage many organs (‘systemic’), and those where only a single organ or tissue is directly damaged by the autoimmune process (‘localised’).

Some of the most common types of autoimmune disorders
Systemic Autoimmune Diseases Localised Autoimmune Diseases
Rheumatoid arthritis (joints) Type 1 Diabetes Mellitus (pancreas islets)
Lupus [systemic lupus erythematosus] (skin, joints, kidneys, heart, brain, red blood cells, other) Hashimoto's thyroiditis, Graves' disease (thyroid)
Scleroderma (skin, intestine, lung, kidney) Coeliac disease, Crohn's disease, ulcerative colitis (GI tract)
Sjögren’s syndrome (salivary glands, tear glands, joints) Multiple sclerosis, Guillain-Barré syndrome (brain)
Goodpasture's syndrome (lungs, kidneys) Addison's disease (adrenal)
Granulomatosis with polyangiitis (sinuses, lungs, kidneys) Primary biliary sclerosis, sclerosing cholangitis, autoimmune hepatitis (liver)

In some cases, a person may have more than one autoimmune disease; for example, persons with Addison's disease often have type 1 diabetes, while persons with sclerosing cholangitis often have ulcerative colitis.

In some cases, the antibodies may not be directed at a specific tissue or organ; for example, antiphospholipid antibodies can react with the clotting proteins in the blood or with surface proteins on blood cells, leading to formation of blood clots within the blood vessels (thrombosis).

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Last Review Date: December 18, 2016

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