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Autoimmunity is when the body's natural defences (the immune system) mistakenly attacks the body's own tissue. "Auto" is derived from the Greek auto, meaning self, and autoimmune means attacking self.

There are a large number of diseases that are believed to be autoimmune. These include Multiple Sclerosis (MS), Addison's Disease, Angiitis, Alopecia Areata, Ankylosing Spondylitis, Antiphospholipid Syndrome, Autism, Autoimmune Haemolytic Anaemia, Autoimmune Hepatitis, Behcet's Syndrome, Berger's disease, Bullous Pemphigoid, Cardiomyopathy, Coeliac Disease, Chronic Fatigue Syndrome (CFS, CFIDS), Chronic Inflammatory Polyneuropathy, Churg-Strauss Syndrome, CREST Syndrome, Crohn's Disease, Dermatomyositis, Fibromyalgia, Giant Cell Arteritis, Grave's Disease, Guillain Barre Syndrome, Hashimoto's Thyroiditis, Idiopathic Pulmonary Fibrosis, Idiopathic Thrombocytopenia Purpura (ITP), Type 1 Diabetes, Lichen Planus, Ménière's Disease, Mixed Connective Tissue Disease, Myasthenia Gravis, Polyarteritis Nodosa, Polymyalgia Rheumatica, Polymyositis, Primary Biliary Cirrhosis, Psoriasis, Raynaud's Disease, Reiter's Syndrome, Relapsing Polychondritis, Rheumatic Fever, Rheumatoid Arthritis (RA), Sarcoidosis, Scleroderma, Sjögren's Syndrome, Stiff-Man Syndrome, Systemic Lupus Erythematosus (SLE), Ulcerative Colitis, Uveitis, Vitiligo and Wegener's Granulomatosis.

The cause of most autoimmune diseases is unknown but most seem to arise out of a combination of a genetic susceptibility (as demonstrated by twin and other family studies) and environmental factors, perhaps infection, although no one has a clear idea what these are. In a few autoimmune diseases, such as System Lupus Erythematosus, a genetic mutation has been identified, although having this gene does not guarantee that the individual will develop Lupus. Certain genetic mutations to a self-identifing protein, the Major Histocompatibility Complex (MHC), have been linked to a propensity to develop autoimmune diseases.

Many autoimmune diseases are only guessed to be autoimmune because there appears to be an excess of immune system activity but no pathogen involved.

Some autoimmune diseases are more common in women than men (Rheumatoid Arthritis and System Lupus Erythematosus), some are equally common in both sexes (Ulcerative Colitis, Lichen Planus) and some are more common in men than women (Reiter's Syndrome, Autism). The Relapsing-Remitting and Secondary Progressive forms of Multiple Sclerosis are nearly twice as common in women than in men but the Primary Progressive form is equally common in men as women.

Some autoimmune diseases are associated with others, for example Vitiligo and Lichen Planus are often found in individuals with another autoimmune diseases. More recent studies have shown a familial trend across many autoimmune diseases - people with one autoimmune are more likely to have family members with another one. A syndrome known as Multiple Autoimmune Syndrome (MAS) is defined as a person having three or more autoimmune diseases.

Hypersensitivity and allergic diseases such as asthma, migraine and eczema are sometimes considered to be autoimmune diseases. These generally result from an inappropriate immune response to a harmless substance such as pollen. However it appears that the etiology and pathogenesis of these complaints is quite different to that of the autoimmune diseases.

The immune mechanisms differ from one autoimmune disease to another. In many, including multiple sclerosis, it appears that the specific immune system (T-cells and B-cells) are targetting protein segments (antigens) derived from the body's own tissue. In MS, it appears that these antigens are derived from myelin, the insulating sheath to nerve fibres (neurons) in the central nervous system.

Autoimmunity links:
autoimmune disease
American Autoimmune Related Diseases Association

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