Science Magazine – May 5, 2023 issue: The immune system protects us from cancer and infection using a powerful armamentarium that is kept in check by an array of regulatory processes. When they fail, the immune system can start attacking the host in a process known as autoimmunity. This special issue highlights recent advances in our understanding of autoimmune diseases and the regulation of immune tolerance. See the special section beginning on page 468.

When a delicate balancing act goes wrong

Antibodies that target self-antigens are an important component of certain autoimmune diseases and are sometimes used as a clinical marker for these syndromes. ILLUSTRATION: STEPHAN SCHMITZ/FOLIOART

A cardinal feature of the immune system is its ability to distinguish self from nonself. Although many early immunologists thought that its powerful defenses could rarely, if ever, be turned against the host, pioneering research on autoimmune diseases beginning in the early 1900s has documented a different reality. More than 80 different autoimmune disorders have now been described that may affect up to 5% of the population.