Complement Activation

Definition

Complement activation refers to the biochemical process in which a series of proteins in the immune system, known as complement proteins, are triggered to respond to pathogens or damaged cells. This process plays a critical role in enhancing the body’s immune response, particularly in hypersensitivity and autoimmune disorders, by marking pathogens for destruction, recruiting immune cells, and promoting inflammation.

5 Must Know Facts For Your Next Test

1. Complement activation can occur via three pathways: the classical pathway, the alternative pathway, and the lectin pathway, each triggered by different stimuli.
2. In hypersensitivity reactions, complement activation can lead to tissue damage and inflammation as immune complexes form and accumulate.
3. Autoimmune disorders may involve excessive or inappropriate complement activation, contributing to damage of host tissues due to persistent inflammation.
4. The anaphylatoxins generated during complement activation (C3a, C4a, C5a) can cause increased vascular permeability and attract immune cells to sites of inflammation.
5. Dysregulation of complement activation is associated with various diseases, including systemic lupus erythematosus (SLE) and rheumatoid arthritis, highlighting its role in pathology.

Review Questions

• How does complement activation contribute to hypersensitivity reactions?
  • Complement activation plays a significant role in hypersensitivity reactions by amplifying the immune response against perceived threats. During these reactions, complement proteins can become activated when antibodies bind to allergens or pathogens. This leads to the formation of immune complexes that activate inflammatory processes and recruit more immune cells, resulting in tissue damage and symptoms such as swelling and redness.
• What is the relationship between complement activation and autoimmune disorders?
  • In autoimmune disorders, complement activation often occurs inappropriately, leading to damage of the body’s own tissues. Autoantibodies can form immune complexes that trigger complement activation, causing an inflammatory response that targets healthy cells. This ongoing cycle of activation and inflammation contributes significantly to the pathology of diseases such as lupus and rheumatoid arthritis.
• Evaluate how dysregulation of complement activation can impact overall health and contribute to disease states.
  • Dysregulation of complement activation can have profound effects on overall health by leading to chronic inflammation and tissue damage. When complement pathways are overactive or misregulated, they can cause excessive inflammation, contributing to the development of autoimmune diseases or chronic inflammatory conditions. Conversely, underactive complement systems can impair the ability to clear infections effectively. Thus, maintaining a balance in complement activation is essential for both preventing disease and ensuring an effective immune response.

Related terms

Anaphylaxis:

A severe and rapid allergic reaction that can be life-threatening, often involving the release of histamine and other mediators from mast cells.

Autoantibodies:

Antibodies produced by the immune system that mistakenly target and attack the body's own tissues, often involved in autoimmune disorders.

Inflammation: A biological response to harmful stimuli, such as pathogens or tissue injury, characterized by redness, swelling, heat, and pain, often mediated by complement activation.