Autoimmunity

Autoimmunity refers to conditions in which the immune system reacts against the body's own tissues, causing injury and dysfunction. These reactions arise from a loss of self-tolerance, allowing autoreactive cells and antibodies to persist. Autoimmune diseases can be organ-specific or systemic.

Causes and mechanisms are multifactorial. Genetic factors, including certain HLA alleles, increase risk. Environmental triggers such as infections, toxins, or hormonal factors can initiate disease in predisposed individuals. Immunological processes include molecular mimicry, bystander activation, epitope spreading, and impaired regulatory T cell function. Autoreactive B cells produce autoantibodies, while autoreactive T cells drive tissue inflammation.

Common autoimmune diseases include type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, autoimmune thyroid disease, and inflammatory bowel disease. Others affect skin, nerves, or the endocrine system. The clinical course ranges from mild to severe and may involve relapses and remissions.

Diagnosis relies on clinical features supported by laboratory tests for autoantibodies and inflammatory markers, along with imaging or biopsy when indicated. Examples include anti-nuclear antibodies, anti-dsDNA, anti-thyroid antibodies, and anti-citrullinated protein antibodies. Disease-specific criteria are used to establish a diagnosis.

Treatment aims to reduce immune activity, relieve symptoms, and prevent organ damage. Options include corticosteroids, conventional disease-modifying antirheumatic drugs, and targeted biologics that inhibit specific immune pathways. Management also addresses organ protection, infection prevention, and comorbidities.

Autoimmune diseases affect millions worldwide, with prevalence influenced by sex, age, and ethnicity. Research seeks to understand genetic and environmental contributions, mechanisms of tolerance loss, and strategies to induce tolerance or prevent relapse.