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What is autoimmunity?
Autoimmunity is a situation where the body's immune system reacts against elements of the body itself (made of "self" molecules) instead of against infectious microbes (made of "foreign" molecules). The clearest examples of autoimmunity are those diseases in which antibodies to "self" molecules, known as "autoantibodies" are found in the bloodstream. These include rheumatoid arthritis, lupus (SLE), thyroid diseases, myasthenia gravis, scleroderma, dermatomyositis, primary biliary cirrhosis, chronic active hepatitis and pernicious anaemia.

Other conditions such as multiple sclerosis, ankylosing spondylitis, Crohn's disease, sarcoidosis, ulcerative colitis, and psoriasis might be called autoimmune, but it is less clear that any true immune response to self is present. In conditions such as multiple sclerosis, Crohn's disease and sarcoidosis abnormal antibodies are present, but it is not certain that they are anti-self. In ankylosing spondylitis, which is dealt with on a separate page, there is no clear evidence of an anti-self reaction as such.

The way doctors divide up these diseases depends to a large extent on which cells of the immune system we think are causing the problem. Scientists are in the middle of a debate about this, particularly when it comes to B cells and T cells. Our research group at UCL is of the view that both B and T cells are essential to the typical autoimmune diseases that show autoantibodies. However, we think it is likely that the order in which these cells are involved is different from that generally recognised up to 1996. The idea is that autoimmnity occurs when a B cell that makes an antibody to self, which should not be allowed to survive, keeps itself alive with the help of quite normal T cells by cheating the signalling system. This is explained in more detail on the page "B cells and T cells in autoimmunity".

The importance of this idea is that it raises the possibility that autoimmunity can be got rid of by removing the key B cells involved. This has led to the use of B cell depletion therapy in rheumatoid arthritis which is currently in trials. A lay explanation of what we think happens in autoimmunity, first put on the web in 1998, before we started B cell depletion treatment is on the page "Rheumatoid Arthritis and Autoimmunity". A more technical discussion of B cells and T cells, written in 2002 is on the page "B cells and T cells in autoimmunity: 2002". Some further comments about previous T cell theories of rheumatoid arthritis are given on a further page. Quite a bit of the material on these pages overlaps, but the hope is that people will be able to find on one or other page the ideas in a form they can follow.