Antimitochondrial antibodies (AMAs) are autoantibodies that target the mitochondria, indicating an autoimmune disease such as primary biliary cirrhosis, rheumatoid arthritis, autoimmune hepatitis, systemic lupus erythematosus, or thyroiditis. The presence of AMAs in body fluids implies that the immune system has lost its tolerance for mitochondria, causing inflammation and cirrhosis in the liver. The AMA blood test can diagnose autoimmune hepatitis and primary biliary cirrhosis.
Antimitochondrial antibodies (AMAs) are autoantibodies, or antibodies against the self, that target the mitochondria. A mitochondrion is an organelle, or structure within a cell, that helps produce cellular energy, monitor cell growth, and cause cell death, among other functions. An antibody is a protein called immunoglobulin that works with the immune system to find and disarm damaged cells and foreign objects, such as harmful viruses or bacteria. In a healthy patient, the immune system provides several crucial defense mechanisms for the body, but when the immune system mistakenly targets healthy body tissue, it can cause serious illnesses known as autoimmune diseases. The presence of antimitochondrial antibodies in the blood indicates an autoimmune disease, such as primary biliary cirrhosis (PBC), rheumatoid arthritis, autoimmune hepatitis, systemic lupus erythematosus, or thyroiditis.
An antibody is a protein composed of two heavy polypeptide chains and two light polypeptide chains that form a “Y” shape. The trunk of the “Y” is the constant region, of which there are five classes, or isotypes, that control how the antigen is destroyed and how the immune system should respond. An antigen is the target of the antibody, or the mitochondria in the case of antimitochondrial antibodies. The two arms of the “Y” form the variable regions of the antibody, which include hypervariable regions and antigen binding sites. Antigen binding sites are specially formed, either through random composition or in response to an immune reaction, to recognize a very specific antigen, then bind to and destroy it.
In a healthy body, a mechanism called immune tolerance prevents the body from attacking certain antigens, such as healthy body tissue. Antibodies that fail to recognize themselves and try to attack healthy tissue are removed from the system. Some foreign antigens, or non-self antigens, such as an organ transplant or a fetus in a pregnant woman, require an immune system mechanism called acquired tolerance.
The presence of anti-mitochondrial antibodies in body fluids implies that the immune system has lost its tolerance for mitochondria, or has lost its ability to recognize mitochondria as part of the self. These antibodies then target a protein that sits on an enzyme complex, called pyruvate dehydrogenase-enzyme 2 (PDC-E2) complex, in the inner lining of the mitochondria. Often, the mitochondria in the liver are the most affected.
Autoimmune hepatitis occurs when the immune system attacks the liver, causing inflammation or swelling and cirrhosis in the advanced stages. Cirrhosis refers to scarring of liver tissue, which can lead to decreased liver function. Autoimmune hepatitis has symptoms of dark urine, pale stools, fatigue, loss of appetite, general itching, nausea, and bloating, and usually occurs in young women with a family history of the disease. A positive blood test for antimitochondrial antibodies, among other signs, is often used to diagnose this disease.
The AMA blood test can also be used to diagnose primary biliary cirrhosis (PBC). For unknown causes, PBC irritates the bile ducts in the liver, causing inflammation and then blockage of the bile ducts. This blockage then causes liver cell damage and eventually cirrhosis. This disease mainly occurs in middle-aged women and has symptoms of jaundice, abdominal pain, itching, bloating, fatty stools, and fat collection under the skin.
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