Autoimmunity is a malfunction of the immune system. In autoimmune diseases, the body loses tolerance to the body’s own structures. As a result, chronic inflammation occurs.
What is autoimmunity?
The body loses tolerance to the body’s own structures in autoimmune diseases. One autoimmune disease is multiple sclerosis, for example. Autoimmunity is the body’s inability to recognize its tissue structures as the body’s own. The immune system reacts incorrectly and attacks its own tissue. The result is chronic inflammation. Various tissues can be affected by the attacks of the immune system. Known autoimmune diseases are multiple sclerosis, Hashimoto’s thyroiditis or lupus erythematosus.
Function and task
The immune system can be divided into specific and nonspecific defenses. The main cells of the specific defense are the B and T lymphocytes. They mature in the bone marrow and thymus. In the lymphatic tissues of the spleen, lymph nodes and mucosa-associated lymphoid tissue (MALT), they are supposed to attack and render harmless anything foreign. Each lymphocyte is responsible for a different foreign structure. The foreign structures are also called antigens. Each B lymphocyte carries a receptor on its surface. Upon contact with the specific antigen, the B lymphocyte transforms into a plasma cell and produces antibodies against the foreign substance. These bind to the antigen and eliminate it. T lymphocytes also have similar recognition mechanisms. When a pathogen enters a cell, the cell presents part of the pathogen on its surface. The T lymphocytes recognize this so-called antigen presentation. They are activated by this and differentiate. The resulting T killer cells destroy the diseased cell, T helper cells attract other immune cells for support, and regulatory T cells prevent excessive immune reactions. The imprinting organs actually ensure that lymphocytes imprinted on the body’s own structures do not enter the systemic circulation. Such lymphocytes should change their blueprint for the receptor. If this does not succeed, they are eliminated with the help of apoptosis. In a healthy body, therefore, only lymphocytes that are tolerant to the body’s own structures circulate. In autoimmune diseases, this tolerance is lost. The body’s own antigens are not recognized by the lymphocytes. They react to these substances as if they were foreign substances. However, the exact mechanism of autoimmunity has not yet been adequately clarified. Two different causes are being discussed: First, it is possible that there are foreign antigens that resemble the body’s own antigens. Thus, the antibodies produced during an immune response also unintentionally damage the body’s own antigens. On the other hand, it is conceivable that autoreactive cells, i.e. cells that also react to their own tissue, are not eliminated during lymphocyte imprinting but are retained. However, why the immune system is now directed against components of the thyroid gland in one person and against components of the pancreas in another is not known.
Diseases and disorders
A well-known autoimmune disease is multiple sclerosis (MS). Here, the immune system reacts to the sheathing of nerve fibers. The insulating layers of the nerve fibers, the myelin sheaths, are destroyed in the process. The disease is characterized by lesions of the axons. These are found throughout the central nervous system, but are often located in the optic nerve and brainstem regions. In the majority of patients, the disease begins between the ages of twenty and forty. Early symptoms of MS include visual disturbances, gait unsteadiness, numbness or tingling in the arms and legs, and dizziness. The disease often progresses in relapses. Initially, the symptoms disappear completely. As the disease progresses, disabilities often persist. Often, the relapsing course turns into a progressive stage. Multiple sclerosis is not curable. Another autoimmune disease is lupus erythematosus (LE). This systemic disease belongs to the group of collagenoses. It is characterized by a high titer of autoantibodies. These are directed against the DNA. Lupus can be divided into different subtypes. Systemic LE mostly affects women between the ages of twenty and forty.The autoantibodies and the resulting immune complexes cause tissue damage and thus give rise to the typical dermatological clinical picture. This form progresses in episodes and is characterized by the so-called butterfly erythema on the face. There are also joint diseases, pleurisy, pericarditis and kidney damage. The nervous system is also involved. The subacute cutaneous form is much milder. Here, red scaly skin manifestations are found on sun-exposed areas of the body. The disease cannot be cured. Severe cases require high doses of cortisone or chemotherapy. The chronic inflammatory bowel diseases ulcerative colitis and Crohn’s disease are also autoimmune diseases. In both diseases, inflammation of the intestine occurs. In Crohn’s disease, inflammation can occur throughout the entire digestive tract. The small intestine, the large intestine and the esophagus are preferentially affected. In ulcerative colitis, the colon is almost exclusively affected. Patients of both diseases suffer from abdominal pain, diarrhea, fever, weight loss, loss of appetite, nausea and vomiting. In about half of all patients, there are also manifestations outside the intestine. In Graves’ disease, antibodies are directed against thyroid tissue. The antibodies produced attack the TSH receptors of the thyroid gland. TSH, thyroid-stimulating hormone, is produced in the pituitary gland and stimulates the thyroid gland to produce thyroid hormones. The action of antibodies on the receptor is similar to the action of TSH. This results in an overproduction of the thyroid hormones T3 and T4. Hyperthyroidism results, with a classic symptom triad of rapid heartbeat, goiter, and bulging eyeballs (exophthalmos).
