What is an autoimmune disease?

What is an autoimmune disease?

The term autoimmune disease encompasses a multitude of chronic conditions, including: rheumatoid arthritis, systemic lupus erythematosus (SLE), type 1 diabetes, multiple sclerosis, ankylosing spondylitis, Crohn's disease, Hashimoto's thyroiditis, Biermer's anemia, Guillain-Barre syndrome, Basedow's disease, Sjögren's syndrome, and more.

Physiopathology

A healthy immune system guards the body against infection and disease. When it detects an "invading" bacteria or virus, it sends out protective cells to attack it. Normally, the immune system can distinguish between foreign cells and your body's own cells, but in the case of autoimmune disease it mistakes parts of your body, such as skin or joints for example, as foreign and sends out autoantibodies to attack it. This self-attack has various consequences depending on its location in the body. Indeed, the immune dysfunction leads to a persistent inflammatory reaction that leads to the chronic nature of the disease.

For example, in multiple sclerosis, it is the myelin sheath (the protective layer of neurons that guarantees the rapid transmission of nerve impulses) that is targeted by the immune system. Self-reactive T-lymphocytes (a type of white blood cell) will progressively destroy this sheath and alter nerve transmission, which has various but above all damaging consequences on the neurological system. In the same way for type 1 diabetes, it is the self-destruction of the beta cells of the pancreatic islets (which secrete insulin) that causes insulin dependence. For rheumatoid arthritis, this time the self-attack is directed at the membranes surrounding the joints, causing joint pain which spreads to the tendons and ligaments and even to the cartilage and bones.

A distinction can be made between organ-specific autoimmune diseases (affecting a single organ in particular) and non-organ-specific diseases (affecting several organs).

Epidemiology

There are more than 80 diseases that can be classified as autoimmune disease. They affect more than 24 million people in the US and 5 to 8% of the world's population.

Moreover, autoimmune diseases tend to affect women more than men (8 out of 10 sufferers are women). This is a trend, but it does not concern all autoimmune conditions, for example type 1 diabetes has the same prevalence (number of cases) in men as in women.

In recent years, the age of onset of a majority of autoimmune diseases has risen, with increasingly younger patients being diagnosed. However, overall, the age of onset varies greatly depending on the pathology.

Clinical expression

Generally speaking, autoimmune diseases evolve through flare-ups and remissions. They can affect many organs, so the clinical symptoms vary widely. Depending on the organ(s) affected, the inflammation may be perceptible to the patient. Locally, the inflammation may be red, painful or swollen. At the systemic level, the inflammation may result in a change in overall health, extreme fatigue, significant weight loss or even fever. Sometimes it is mainly blood tests that are indicative, as the clinical symptoms are not very telling.

The clinical manifestations of these pathologies are more or less evocative of an illness. In lupus, a butterfly-shaped rash across the cheeks appears in lupus sufferers and is very characteristic of the disease. Type 1 diabetics only feel the consequences of the self-destruction of the liver (and not the destruction itself), which manifests itself in hypoglycemia. Antiphospholipid syndrome (APS) is characterized by repeated miscarriages (in the first three months of pregnancy) due to inflammation and blockage of the blood vessels connecting mother and child. Conversely, in the face of a symptomatology which is not very revealing and which may be reminiscent of other digestive disorders, the diagnosis of Biermer's disease is made through blood tests. In fact, it is a form of anemia whose pernicious course is confirmed by a vitamin B12 deficiency (essential for neurological functioning).

Diagnosis

Diagnosis of an autoimmune disease is specific to the particular disease and is confirmed by key clinical features. It requires both clinical and biological arguments. Usually several tests are conducted:

• Functional testing of the affected organ(s),
• Blood tests to:
• identify the inflammatory syndrome,
• perform an immunological assessment (search for autoantibodies)
• The search for other complications, especially those related to vital functions, is systematic.

What causes autoimmune diseases?

The term "multifactorial diseases" is used because it is difficult to identify a single origin for each autoimmune condition. Therefore, a single factor is unlikely to be sufficient to trigger an autoimmune disease. It is the accumulation of multiple factors that leads to the development of this type of disease.

Genetic factors

Genetics seem to be able to explain about 30% of autoimmune diseases but is not sufficient to affirm that they are hereditary diseases. Genetics seem to be able to explain about 30% of autoimmune diseases but is not sufficient to affirm that they are hereditary diseases. Many cases arise without prior family history, so transmission to the offspring is inconsistent and unpredictable. Furthermore, it has been found that the presence of certain genes (in particular the association of several genes) favors the occurrence of certain auto-immune diseases.

These include HLA genes (which code the HLA proteins on the surface of cells that allow the immune system to distinguish between "foreign" and "native"), some versions of which are thought to be associated with the occurrence of different autoimmune diseases. The association with other non-HLA genes is discussed but with less importance.

Endogenous factors 

Endogenous factors refer to the internal components of the body, such as hormones. It is important to know that hormones have an influence in the development of autoimmune conditions, especially in women, in whom they occur more frequently. The association of the occurrence of autoimmune disease with prolactin levels and sex hormones (estrogens) seems to be consistent.

Exogenous (environmental) factors

Stress has been identified as a contributing factor. An emotional shock or a significant or traumatic event can trigger an autoimmune disease. The intervention of a psychological aspect has been pinpointed but remains poorly understood.

Many causal links have been established between exposure to infectious agents and the occurrence of a fair number of autoimmune diseases. For example, previous infections with the Epstein Barr virus or the human cytomegalovirus have been identified as factors contributing to the development of autoimmune disease. This phenomenon is thoughts to be due to a similarity between the make-up of these viruses and certain human proteins.

Also, the environment (UV rays, smoking or exposure to chemicals) plays a major role in the development of autoimmune disease. For example, exposure to second-hand smoke is a common factor among patients with lupus or rheumatoid arthritis. Sun exposure, and therefore UV exposure, triggers the onset of lupus flare-ups; these patients are considered to be "photosensitive".

Occupational exposure to chemicals such as silica particles has been strongly correlated with an increased risk of developing systemic sclerosis (scleroderma), systemic lupus and rheumatoid arthritis.

There is also evidence of an increase in the prevalence (number of cases) of autoimmune diseases in industrialized countries: this would support the hygiene hypothesis that states that hygiene and the exponential use of antibiotics reduce our exposure to infectious agents and thus reduce the learning capacity of our immune system.

Medicine-related factors

Certain medicines can cause immune tolerance to be disrupted. For example, some cancer drugs have been shown to induce autoimmunity, such as immune checkpoint inhibitors (e.g. nivolumab or atezolizumab) used to stimulate the immune defense system. It has been reported that patients treated with these drugs have more frequently developed certain autoimmune conditions (vitiligo, thyroiditis), although it remains to be proven that these patients did not already have other predisposing factors for these diseases.

In addition, more specifically for lupus, certain medications have been identified which are likely to contribute to the development of the disease; they are said to cause what is known as “drug-induced lupus”.

How are autoimmune diseases treated? 

Today there is still no cure for an autoimmune disease, although it is possible to slow down its progression. The challenge in developing this type of treatment lies in finding a balance between limiting the immune system (autoimmunity) and not diminishing its natural defenses against bacteria and infection.

Therapeutic management is unique to each disease, and includes two types of medication: treatment for flare-ups and symptoms, and background treatment specific to the type of autoimmune condition.

Symptom management and treatment of flare-ups

As a first-line treatment, low-dose corticosteroids are often prescribed to alleviate pain due to inflammation, for their potency and rapid action.

Analgesics and non-steroidal anti-inflammatory drugs (NSAIDs) may be prescribed to reduce pain and limit discomfort due to inflammation (especially of the joints).

Non-therapeutic solutions are also recommended, such as physical therapy or occupational therapy, which are part of the non-medicinal treatment of certain pathologies. Regular physical activity is also important to avoid weakening muscles, stiffening joints, to reduce mobility issues or simply to fight against the underlying fatigue caused by the disease.

In addition, therapeutic patient education programs are important and should be implemented for each condition in order to involve the patient as much as possible in the management of his or her illness. The significance of the social and psychological aspects of chronic illnesses must also be taken into account. This is why psychological support is recommended, especially for pathologies whose flare-ups are triggered by stress, for example.

Background treatment: immunosuppressants & biotherapy

Depending on the extent or severity of organ damage, immunosuppressive drugs to inhibit or control autoimmunity may be used (cyclophosphamide, methotrexate, azathioprine, cyclosporine or higher doses of corticosteroids). These drugs have the particularity of suppressing the body's natural immune response and, as a result, expose a patient to an increased risk of infection.

Since the early 2000s, progress in biotechnology has led to the development of targeted biotherapies. These are molecules designed to specifically block an effector of the inflammatory process inherent to autoimmune disease. In general, they are used when the disease has reached a high stage of severity or when it does not respond to immunosuppressants.

They include anti-TNF-alpha drugs, which inhibit the action of TNF-alpha, a factor involved in tumor necrosis and a mediator of inflammation. They are part of the therapeutic strategy for the treatment of rheumatoid arthritis and ankylosing spondylitis.

Therapeutic plasma exchange (plasmapheresis) and immunoglobulins

Therapeutic plasma exchange (TPE) consists of taking blood from a patient, filtering out the proteins responsible for or involved in the pathology (autoantibodies for example), then reinjecting this filtered blood. This technique is used, for example, in Guillain-Barre syndrome.

Immunoglobulins (antibodies) from donated blood can be injected into a patient to treat autoimmune disease. They may alter or neutralize the autoantibodies.

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