What are autoantibodies?
Our body’s own defence system continuously produces the so-called antibodies, small proteins that support the immune cells in their defence against pathogens and cancer cells. Unfortunately, this system is not infallible and some people produce antibodies that make our own body cells feel foreign and threatening. This leads to the immune cells destroying these cells, resulting in diseases such as rheumatoid arthritis or diabetes mellitus type 1. These antibodies, which are directed against the body’s own cells, are called autoantibodies.
These autoantibodies exist
There are a large number of known autoantibodies. The following is an overview of typical autoantibodies and the diseases associated with them:
- Acetylcholine receptor antibody (AChR-Ak) in myasthenia gravis
- Antimitochondrial antibodies (AMA) in primary biliary cirrhosis
- Antinuclear antibodies (ANA) in a variety of diseases (e.g. lupus erythematosus, scleroderma)
- Double-stranded DNA antibodies (anti-dsDNA) in systemic lupus erythematosus and other collagenoses
- Antiphospholipid antibodies (aPL) in antiphospholipid syndrome
- Anti-Neutrophil Cytoplasmic Antibodies (c-ANCA) in Wegener’s disease
- Anti-Neutrophil Perinuclear Antibodies (pANCA) in microscopic polyangiitis and other diseases
- Rheumatoid factor (RF) in rheumatoid arthritis
- Antithyroglobulin (Anti-Tg)
- Thyeroperoxidase antibody (TPO-AK) and TSH receptor autoantibodies in autoimmune thyroid diseases.
These symptoms cause autoantibodies
Autoantibodies can trigger a variety of diseases almost everywhere in our body and therefore have a wide range of symptoms. What they all have in common is that functional tissue is destroyed by our body’s own immune system. In any case, this leads to a functional limitation of the affected body region.
In joints, for example, this leads to a painful restriction of movement (e.g. in rheumatoid arthritis), in organs to reduced performance (e.g. reduced thyroid hormone production in Hashimoto’s thyroiditis or reduced insulin production by the pancreas in diabetes mellitus type I) or to muscle weakness as in myasthenia gravis. Such autoimmune diseases are often accompanied by general fatigue, tiredness and weakness.
Many patients show relative anaemia. Some diseases can also be seen from the outside of the body, such as the painful, inflamed joints in rheumatism or the skin changes in lupus erythematosus. Other diseases manifest themselves through organ deterioration or even organ failure.
It can therefore be seen that the many different autoantibodies are the cause of many diseases, which, depending on the damaged tissue, show up with very different symptoms. The so-called rheumatoid factor (RF) is probably one of the best known autoantibodies. It is used in the diagnosis of rheumatoid arthritis, a chronic inflammatory disease of the joints and often also of the internal organs.
Painful inflammation of the small finger joints is typical, accompanied by severe morning stiffness. Many patients also suffer damage to the internal organs, such as inflammation of the pleura or pericardium. If rheumatoid arthritis is suspected, several parameters can be determined with a blood test, including the rheumatoid factor.
If the rheumatoid factor shows up in high concentrations, this can be an indication of rheumatoid arthritis. Unfortunately, the rheumatoid factor does not show a particularly high specificity, which means that it can also be elevated in many healthy people or in chronic infections. It is often only detectable in the course of the disease.
Therefore, the additional determination of the anti-CCP antibody, which has a higher specificity, can be helpful. However, the physical symptoms of a patient are decisive for the diagnosis of rheumatoid arthritis. For example, a positive rheumatoid factor without joint complaints is not considered rheumatoid arthritis.
The following article may also be of interest to you at this point: RheumatismThe antinuclear antibodies, also known as ANA, can be elevated in many autoimmune diseases, but they are typical mainly for the group of collagenoses. Collagenoses is a collective term for autoimmune diseases that mainly affect the connective tissue and are more common in women. Known representatives of this group are lupus erythematosus, scleroderma or Sjögren’s syndrome.
In all these diseases, antinuclear antibodies can typically be detected in the blood, so they are not specific to a disease. However, more complex laboratory procedures can be used to differentiate the autoantibodies even more clearly from each other and to find typical patterns for the individual diseases. It is important to note that a positive ANA should not lead to a therapy without physical symptoms.
On the other hand, suspected collagenosis with typical symptoms should not be rejected because of negative autoantibodies. Thus, a positive ANA blood test may give an indication of disease, but it can never lead to a diagnosis on its own. Antineutrophil cytoplasmic antibodies, or ANCA for short, are typically elevated in diseases of the vasculitis group.
In this group of autoimmune diseases, the immune system mistakenly attacks our body’s own blood vessels. The diagnostic use of ANCA involves examining the blood for different types of this autoantibody. For example, the autoantibody cANCA is often elevated in so-called granulomatosis with polyangiitis (Wegener’s disease).
This rheumatic disease manifests itself in early stages through unspecific infections of the upper respiratory tract or the middle ear and can lead to life-threatening complications throughout the body. In contrast, the autoantibody pANCA is elevated in the so-called Churg-Strauss syndrome and microscopic polyangiitis. Both are diseases that mainly affect the small blood vessels and, depending on the region of the body, lead to a variety of symptoms up to organ failure.
Finally, atypical ANCA can also be detected. These can occur in many autoimmune diseases outside of vasculitis, such as chronic inflammatory bowel diseases like Crohn’s disease or ulcerative colitis. The antimitochondrial antibody, AMA for short, is typical of the autoimmune disease primary biliary cholangitis (PBC).
This is a chronic inflammation of the small bile ducts located in the liver. In the course of the disease, this leads to a structural remodelling of the liver and finally to so-called cirrhosis of the liver, which is associated with a significant deterioration in organ function and an increased risk of liver cancer. The significance of AMA is relatively good and positive in about 90% of PBC patients.
In addition, typical antinuclear autoantibodies (PBC-specific ANA) can often be detected. Unfortunately, the therapy of primary biliary cholangitis is still difficult today, but with an early diagnosis the progression of the disease can be slowed down. The antiphospholipid antibodies are specific autoantibodies for the antiphospholipid syndrome.
In this autoimmune disease, abnormal blood coagulation occurs, which leads to the recurrent formation of blood clots. These can lead to ulcers on the skin, but can also interrupt the blood supply to the organs and thus damage them (e.g. in the event of a stroke). In order to make a diagnosis of antiphospholipid syndrome, a positive antiphospholipid antibody must be present in the blood in addition to the presence of blood clots.
The anti-acetylcholine receptor antibody (AChR-AK) is elevated in the autoimmune disease myasthenia gravis. In this disease, the autoantibodies block the transmission of excitation between nerve and muscle – the result is an excessively rapid fatigue of the muscles, which require a long period of rest for recovery. Typical initial symptoms are drooping eyelids, double vision, difficulty swallowing and speaking.
In addition to the frequently occurring anti-acetylcholine receptor antibodies, there are other autoantibodies which can trigger the disease. Today, myasthenia gravis is well treatable. The TSH receptor antibody, also known as TRAK, is particularly typical for the thyroid disease Graves’ disease.
In this autoimmune disease, the autoantibodies activate the thyroid cells and stimulate them to produce more hormone. The result is a pronounced hyperthyroidism with symptoms such as palpitations, weight loss and excessive sweating. TSH receptor antibodies are found in over 90% of Graves’ disease patients and are therefore very well suited for the diagnosis of hyperthyroidism.
Another frequently occurring autoantibody is the thyroperoxidase antibody (TPO-AK). The anti-CCP autoantibodies are frequently found in rheumatoid arthritis. This well-known autoimmune disease leads to chronic inflammation of the joints, but it can also affect organs.
The basic diagnosis of rheumatoid arthritis also includes an autoantibody determination in the blood. Here, the anti-CCP antibodies are positive in approx. 60% of patients with rheumatoid arthritis.
These autoantibodies are very specific, which means that almost all patients with a positive anti-CCP are actually suffering from rheumatoid arthritis. This is the advantage over the other typical autoantibody rheumatoid factor. It should be noted that not all rheumatoid arthritis patients must have autoantibodies in their blood.
The double-stranded DNA antibody (anti-dsDNA antibody) belongs to the group of antinuclear antibodies (ANA), which are typically elevated in autoimmune diseases of the connective tissue, the so-called collagenoses. Here, the anti-dsDNA antibody is very specific for lupus erythematosus, an autoimmune disease that can affect connective tissue throughout the body. This can lead to skin changes, joint inflammation and kidney failure.
The anti-dsDNA antibody can not only indicate lupus erythematosus, but also express the disease activity – the higher the autoantibody, the more active the relapsing-remitting disease is at present. The endothelial cell antibodies are typical for the so-called Kawasaki syndrome. This autoimmune disease is caused by a severe inflammation of the medium-sized blood vessels and mainly affects children.
Typical symptoms are high fever, conjunctivitis, bright red lips and tongue, swelling of the lymph nodes in the neck and a rash all over the body. Endothelial cell antibodies can be detected in the blood test.