What is an autoimmune disorder?

An autoimmune disorder is characterized by the body's immune system mistakenly identifying its own healthy cells and tissues as foreign and launching an attack against them. This misdirected immune response can lead to inflammation, tissue damage, and dysfunction of various organs. Examples of autoimmune disorders include rheumatoid arthritis, lupus, and multiple sclerosis, where the immune system plays a pivotal role in the pathology of the disease.

The other options describe different medical conditions. A type of cancer affecting blood cells does not align with the definition of an autoimmune disorder, as it involves uncontrolled cell growth rather than an immune attack on the body’s own tissues. An allergic reaction involves the immune system reacting to external environmental factors rather than an internal attack on self-tissues. A contagious illness affecting the immune system again denotes an external agent causing illness, which is distinct from the nature of autoimmune disorders where the body inadvertently turns against itself.