Complement activation

Definition

Complement activation refers to a crucial part of the immune response where a series of proteins, known as complement proteins, are triggered to help eliminate pathogens. This process enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells, promote inflammation, and attack the pathogen's cell membrane. Complement activation can lead to various immunological disorders when it is overactive or misdirected, contributing to hypersensitivities and autoimmune diseases.

5 Must Know Facts For Your Next Test

1. Complement activation can occur through three main pathways: the classical pathway, the lectin pathway, and the alternative pathway, each triggered by different mechanisms.
2. Once activated, complement proteins can form a membrane attack complex (MAC) that punctures the cell membrane of pathogens, leading to their lysis.
3. Inappropriate complement activation can contribute to chronic inflammatory diseases and conditions like systemic lupus erythematosus (SLE).
4. Certain immunological disorders are associated with deficiencies in specific complement proteins, making individuals more susceptible to infections.
5. Complement activation plays a role in mediating hypersensitivity reactions, where an exaggerated immune response leads to tissue damage and inflammation.

Review Questions

• How does complement activation enhance the immune response against pathogens?
  • Complement activation enhances the immune response by promoting opsonization, which tags pathogens for destruction by phagocytic cells. It also facilitates inflammation through the release of anaphylatoxins that attract immune cells to the site of infection. Additionally, the formation of the membrane attack complex (MAC) directly disrupts the integrity of pathogen cell membranes, leading to their death. This multi-faceted approach makes complement activation vital for effective immune defense.
• What role does complement activation play in autoimmune diseases and hypersensitivity reactions?
  • In autoimmune diseases, improper complement activation can cause damage to healthy tissues as the immune system mistakenly targets them. This misfiring can lead to chronic inflammation and tissue injury. In hypersensitivity reactions, such as anaphylaxis, excessive complement activation contributes to severe symptoms by amplifying the inflammatory response and promoting vasodilation and increased vascular permeability. Understanding these roles is crucial for developing therapeutic strategies targeting these conditions.
• Evaluate how deficiencies or dysregulation in complement activation can lead to specific health issues.
  • Deficiencies or dysregulation in complement activation can result in increased susceptibility to infections due to the immune system's impaired ability to clear pathogens effectively. For example, individuals lacking certain complement components may experience recurrent bacterial infections. Conversely, overactivation of complement can contribute to autoimmunity and chronic inflammatory conditions like rheumatoid arthritis or lupus. Analyzing these aspects helps in understanding the delicate balance required for proper immune function and highlights potential therapeutic interventions for related disorders.

Related terms

Anaphylaxis: A severe, potentially life-threatening allergic reaction that occurs rapidly after exposure to an allergen, often involving complement activation.

Autoimmunity: A condition arising from an abnormal immune response where the immune system mistakenly attacks the body's own tissues, often linked to dysregulation of complement activation.

Inflammation: A biological response of body tissues to harmful stimuli, which can be influenced by complement activation, leading to increased blood flow and immune cell recruitment.