Autoimmunity
Autoimmunity is where the body's immune system recognises and reacts to 'self' cells. During development there are mechanisms to prevent immune responses against the body's own cells, clonal deletion. When these mechanisms fail it leads to autoimmune disorders. There are many factors that can cause or increase susceptibility to autoimmune diseases such as multiplicity of genes and pre-existing problems in the target organ.
Rheumatoid Arthritis:
An example of an autoimmune disease, rheumatoid arthritis is the inflammation of the synovial membrane found in joints. It is thought that the inflammation is caused by T helper cells which are specific to an antigen found in joints, when they bind this antigen the T cells release lymphokines that lead to swelling in the joint. Macrophages and leukocytes accumulate in the synovial membrane forming a 'pannus'. The local inflammation causes damage to the cartilage and ultimately destroys the joint. Antibodies such as rheumatoid factor also play a role in cartilage damage, they bind through the Fc region on one IgG rheumatoid factor and the Fab on another forming a complex.
The symptoms of rheumatoid arthritis are:
- Joints become stiff particularly early in the morning.
- The joints are also swollen and painful, the swelling is soft due to the inflammation and perhaps fluid.
- Joints also become deformed with progression of the disease.
- People with rheumatoid arthritis also often experience fatigue.
Laboratory tests are used to diagnose rheumatoid arthritis, the main tests are:
- Erythrocyte sedimentation rate, measures how long it takes a sample of blood cells to settle and gives an indication of the level of inflammation. The quicker the cells settle the more severe the inflammation.
- c reactive protein, levels of c reactive protein increase when there is inflammation in the body. This test provides a clearer result as the levels of c reactive protein normally found in the body are very low.
Non-steroidal anti-inflammatory drugs are used to treat the symptoms, to reduce pain and inflammation. To try and prevent bone damage and to reduce the inflammatory reactions Disease Modifying Anti-Rheumatic Drugs (DMARDs) are used the most commonly used DMARD is methotrexate which is taken once a week. These drugs are much slower acting and can take up to three months to show results.
References:
National Rheumatoid Arthritis Society
Immunology, 7th edition, Male D. Brostoff J. Roth D. B. Roitt I. 2006, Elsevier.
Immunobiology: The Immune System in Health and Disease. 5th edition, Janeway C. A. Travers P. Walport M. 2001, Garland Science.
Diagram courtesy of Wikimedia Commons
Image courtesy of Wikimedia Commons