(k) autoimmune diseases

The idea

An autoimmune disease occurs when the immune system fails to distinguish self from non-self and mounts an immune response against the body's own tissues. Self-tolerance normally prevents this, so autoimmunity reflects a breakdown in that recognition. The immune attack may involve antibodies directed at self antigens or T cells attacking self cells, and the resulting damage produces the symptoms. Examples include type 1 diabetes, in which beta cells of the pancreas are destroyed so insulin production falls, and rheumatoid arthritis, in which the immune system attacks joint tissues causing inflammation. A question may ask for the definition, a named example, the mechanism of self-recognition failure, or the consequence for a specific tissue, so identify which is being tested.

What earns the marks

• Definition: an autoimmune disease is one in which the immune system attacks the body's own tissues because self is not distinguished from non-self.
• Mechanism: self-tolerance breaks down, so self antigens are treated as foreign and provoke an immune response.
• The response may involve antibodies against self antigens or T cells attacking self cells, leading to tissue damage and symptoms.
• A valid named example with its consequence, such as type 1 diabetes where pancreatic beta cells are destroyed and insulin production is reduced.
• A second valid example such as rheumatoid arthritis, where immune attack on joint tissues causes inflammation.
• The symptoms arise from damage to the specific tissue targeted, so linking the affected tissue to the resulting effect is essential.

Common mistakes and how to put them right

• Confusing autoimmune disease with immunodeficiency.

  Put it right by noting that autoimmunity is an overactive misdirected response against self, not a failure to respond to pathogens.

• Describing an autoimmune disease as caused by a pathogen directly attacking tissue.

  Put it right by identifying the immune system itself as the agent of damage.

• Giving an example without its mechanism or consequence.

  Put it right by stating which tissue is attacked and what effect follows, such as beta cell destruction reducing insulin production.

Exam tips

• Check whether the question asks for a definition, a mechanism or an example, and answer that specific demand.
• When using an example, always pair it with the tissue attacked and the resulting effect.
• Eliminate options that describe immunodeficiency or pathogen-driven damage rather than immune attack on self.