An autoimmune disease is a condition in which the immune system attacks the body’s own healthy tissues, causing injury or abnormal organ function. The category includes more than 80 recognized diseases affecting almost any part of the body. Some primarily involve a particular organ, while others affect several organ systems. Many are chronic conditions whose severity and course vary considerably. Autoimmune diseases are not contagious, although infections may contribute to their development in susceptible individuals. (niehs.nih.gov)
Biological basis
Autoimmune disease involves autoimmunity: immune responses directed against components of the body itself. These responses can involve T cells and immune-mediated reactions against a person’s own tissues. The resulting disease is therefore not simply an unusually strong response to an external infection, but a response directed at inappropriate targets within the body. (research.nih.gov)
One important mechanism involves autoantibodies, which are antibodies that recognize the body’s own components. Antibodies are immune proteins; their targets are called antigens. In autoimmune disease, immune recognition can contribute to tissue destruction, altered organ growth, or disruption of normal function. However, autoantibodies can also occur in healthy people, so their presence alone does not establish an autoimmune disease. (medlineplus.gov)
Autoimmune effects are not limited to tissue destruction. In Graves’ disease, thyroid-stimulating antibodies imitate the action of thyroid-stimulating hormone, causing excessive thyroid hormone production. In myasthenia gravis, antibodies commonly interfere with acetylcholine receptors or other proteins involved in communication between nerves and muscles, producing muscle weakness. These examples illustrate how immune responses can change physiological signaling rather than merely destroy an organ. (niddk.nih.gov)
Organ-specific and systemic diseases
Autoimmune diseases are often described as organ-specific or systemic, according to the distribution of their principal targets. Organ-specific conditions predominantly involve a particular organ or tissue; systemic conditions can affect multiple organs throughout the body. This distinction describes patterns of involvement rather than the severity of disease. (magazine.medlineplus.gov)
In type 1 diabetes, the immune system destroys insulin-producing cells in the pancreas. The resulting deficiency of insulin impairs regulation of blood glucose. Graves’ disease primarily affects the thyroid, although it can also involve tissues around the eyes. (niddk.nih.gov)
Systemic diseases include systemic lupus erythematosus, which may affect the skin, joints, kidneys, lungs, heart, blood cells, and nervous system. Rheumatoid arthritis principally causes inflammation of joint linings but can also produce disease outside the joints. Consequently, a prominent symptom in one tissue does not necessarily indicate that the condition is confined to that tissue. (niams.nih.gov)
Causes and susceptibility
Most autoimmune diseases do not have a single established cause. Evidence supports interactions between inherited susceptibility, immune processes, and environmental exposures. Certain genes increase susceptibility, and autoimmune diseases often cluster in families. Infections involving viruses or bacteria, some medicines, and particular environmental chemicals may contribute to disease development, but the relevant factors differ between conditions. (niehs.nih.gov)
Age, sex, and ancestry are associated with differences in susceptibility to particular diseases. Many autoimmune conditions occur more frequently in women than in men, but this pattern is not identical across the category. People with one autoimmune disease also have an increased likelihood of developing another. These associations do not imply that an individual with a particular background will necessarily develop disease. (medlineplus.gov)
Clinical manifestations and course
Symptoms depend on the affected tissues. Common manifestations include fatigue, fever, joint pain, muscle discomfort, and rashes. Many conditions cause inflammation, with pain, swelling, redness, or warmth in affected areas. These findings are nonspecific and occur in numerous other illnesses, which can complicate recognition of an autoimmune disorder. (medlineplus.gov)
Symptoms may fluctuate through periods of increased activity, called flares, and periods of reduced symptoms, called remission. Remission describes improvement and does not necessarily mean that the underlying condition has been cured. Most autoimmune diseases are chronic, although many can be controlled with treatment. (medlineplus.gov)
Diagnosis
Diagnosis combines symptoms, examination findings, medical and family history, and disease-specific investigations. Tests may assess autoantibodies, blood-cell counts, inflammation, or organ function. Imaging and biopsy may provide additional evidence when relevant to the suspected condition. There is no single test that reliably identifies all autoimmune diseases. (medlineplus.gov)
Antinuclear antibody testing is useful in evaluating certain disorders, particularly lupus, but positive results also occur in healthy people and in other conditions. Conversely, a negative autoantibody result does not exclude every autoimmune disease. Laboratory findings therefore require interpretation alongside clinical evidence rather than being treated as independent proof of disease. (medlineplus.gov)
Treatment and complications
Treatment differs by disease and organ involvement. Its objectives include controlling the autoimmune process, reducing symptoms, and preserving function. Therapies include corticosteroids and other immunosuppressive medicines; some conditions are treated with targeted agents that inhibit inflammatory mediators such as particular cytokines. Replacement treatments, including insulin or thyroid hormone, address substances no longer produced adequately because of organ damage. (medlineplus.gov)
Complications arise both from the disease and from its treatment. Their nature depends on the organs involved and the medicines used. Immune-suppressing therapies can increase susceptibility to infectious disease, while persistent autoimmune activity may impair affected organs. Long-term outcomes vary substantially between conditions and between individuals with the same diagnosis. (medlineplus.gov)