Autoantibodies are a group of (immune ) that mistakenly target and damage specific tissues or organs of the body. In many instances they may not be ‘pathogenic’, that is cause disease, but a sign of damage that is occurring or may be going to occur. One or more autoantibodies may be produced by a person’s when it fails to distinguish between ‘self’ and ‘non-self’ proteins. Usually the immune system is able to discriminate by recognising foreign substances (‘non-self’) and ignoring the body’s own cells (‘self’), yet not overreact to non-threatening substances such as foods, dust and pollen, or beneficial microorganisms.
It creates antibodies only when it perceives what it has been exposed to as a threat (‘non-self’). When the immune system ceases to recognise one or more of the body’s normal constituents as ‘self’, it may produce autoantibodies that attack its own cells, tissues, and/or organs, causing and damage. The causes of this inappropriate action are varied and are not well understood, often resulting in a chronic autoimmune disorder.
While there is not a direct link, it is thought that many cases of autoantibody production are due to a genetic predisposition combined with an environmental trigger (such as a viral illness or a prolonged exposure to certain toxic chemicals, for example, in cigarette smoke, or benzene). Some families have been shown to have a high prevalence of autoimmune conditions, however, individual family members may have different autoimmune disorders or may never develop an autoimmune condition.
Researchers believe that there may also be a hormonal component to the cause as many of the autoimmune conditions are more common in women of childbearing age.
The type of autoimmune disorder or disease that occurs and the amount of destruction done to the body depends on which systems or organs are targeted by the autoantibodies. Disorders caused by autoantibodies that primarily affect a single organ, such as the thyroid in Graves’ disease or Hashimoto’s thyroiditis, are often the easiest to diagnose as they frequently present with organ-related symptoms.
Disorders due to autoantibodies (affects multiple organs or systems) can be much more elusive. Although the associated autoimmune disorders are rare, the and they cause are relatively common and may include: arthritis-type joint pain, fatigue, fever, rashes, cold or allergy-type symptoms, weight loss and muscular weakness. Additional complications may include vasculitis (inflammation of blood vessels) and anaemia.
Signs and symptoms
Signs and symptoms will vary from person to person. They can vary over time and/or with organ involvement, often tapering off and then flaring up unexpectedly. To complicate the situation, some may have more than one autoantibody, have more than one autoimmune disorder, and/or have an autoimmune disorder without a detectable level of an autoantibody. This may make it difficult for the doctor to identify the prime cause and arrive at a diagnosis.
The diagnosis of autoimmune disorders starts with a complete medical history and a thorough physical examination. The doctor may request one or more diagnostic studies that will help to identify a specific disease. These studies may include:
- blood tests to detect autoantibodies, inflammation, and organ involvement/damage.
- x-rays and other imaging scans to detect changes in bones, joints, and organs.
- to look for pathologic changes in tissue specimens.
As a rule, information is required from multiple sources (rather than a single laboratory test) to accurately diagnose disorders associated with systemic autoantibodies.
Why are autoantibody tests done?
Autoantibody tests are used to help diagnose autoimmune disorders. In a few cases, they are used to help evaluate the severity of the condition, monitor remissions, flares and relapses of the disorder and to monitor the effectiveness of treatment.
Autoantibody tests may be ordered when a patient presents with chronic, progressive arthritic symptoms, fever, fatigue, muscle weakness, and/or a rash that can not readily be explained. One test initially ordered is the antinuclear antibody (ANA) test, a marker of the autoimmune process that is positive with a variety of autoimmune diseases. It may be positive in systemic lupus erythematosus, Sjögren’s syndrome, rheumatoid arthritis, autoimmune hepatitis, primary biliary cirrhosis, alcohol-related liver disease, and hepatitis B. It is frequently followed up with other specific autoantibody tests, such as anti-double strand DNA (anti-dsDNA), anti-Sjögren’s syndrome A (anti-SS-A) (Ro), anti-Sjögren’s syndrome B (anti-SS-B) (La) and anti-ribonucleic protein (anti-RNP). In addition, other tests associated with arthritis and inflammation, such as an rheumatoid factor (RF), an erythrocyte sedimentation rate (ESR), a C-reactive protein (CRP), and/or complement levels (C3, C4), may also be performed.
A single autoantibody test is not diagnostic, but it adds weight to the doctor’s determination as to whether a particular autoimmune disorder is likely or unlikely to be present. Each autoantibody result should be considered individually and as part of the group. Some systemic disorders, such as systemic lupus erythematosus (SLE) may be more likely if several autoantibodies are present, while others, such as mixed connective tissue disease (MCTD) may be more likely if a single autoantibody (anti-RNP - ribonucleic protein) is the only one present. Those who have more than one autoimmune disorder may have several detectable autoantibodies.
Whether a particular autoantibody will be present is both very individual and a matter of statistics. Each will be present in a certain percentage of people who have a particular autoimmune disorder. For instance, 60 to 80% of those with SLE will have a positive anti-double strand DNA (anti-dsDNA) test, but only about 25-30% will have a positive anti-RNP. Some individuals who do have an autoimmune disorder will have negative autoantibody test results, but at a later date – as the disorder progresses - the autoantibodies may develop. A small percentage of the general population may have one or more autoantibodies present in their blood with no associated symptoms. Autoantibodies are more commonly found in older people.
Common autoantibodies and disease associations
Listed below are just some of the more common autoantibodies that are used to identify a variety of systemic autoimmune disorders. These disorders cause inflammatory, arthritis-type symptoms. This table, Autoantibodies and related disorders (pdf), identifies whether each autoantibody test is generally positive or negative with several of these disorders.
- Anti-nuclear antibody (ANA)
- Anti-neutrophil cytoplasmic antibody (ANCA)
- Anti-double strand DNA (anti-dsDNA)
- Anti-Sjögren’s syndrome A (anti-SS-A) (Ro)
- Anti-Sjögren’s syndrome B (anti-SS-B) (La)
- Rheumatoid factor (RF)
- Anti-ribonucleic protein (anti-RNP)
- Anti-Smith (Anti-SM)
- Antiscleroderma antibody (anti-SCL-70)
- Cardiolipin autoantibodies
- Tissue transglutaminase autoantibodies (anti-TTG)
Organ specific autoantibodies
On this site:
Tests: ANA, ESR, rheumatoid factor, FBC, CRP, complement levels, HLA-B27, AMA, SMA, thyroid antibodies, diabetes autoantibodies
Conditions: Autoimmune disorders, systemic lupus erythematosus, rheumatoid arthritis, Sjögren’s syndrome
On the web:
Better Health Channel: autoimmune disorders
Patient UK.: Plasma Autoantibodies Disease Associations
American Autoimmune Related Diseases Association: Patient Information
Last Review Date: July 20, 2014