Membrane Attack Complex

Definition

The membrane attack complex (MAC) is a structure formed on the surface of pathogen cells, primarily by the complement system, that creates pores in the membrane, leading to cell lysis and death. This complex plays a crucial role in the innate immune response, providing a means for the body to directly eliminate invading microorganisms as part of the first line of defense against infections.

5 Must Know Facts For Your Next Test

1. The formation of the membrane attack complex is a result of the terminal pathway of complement activation and is crucial for targeting pathogens like bacteria and some viruses.
2. Once formed, the MAC inserts itself into the lipid bilayer of the target cell's membrane, creating pores that disrupt membrane integrity.
3. The effectiveness of the MAC can vary depending on the type of pathogen; some organisms have evolved mechanisms to resist MAC-mediated lysis.
4. The membrane attack complex is not only involved in direct pathogen elimination but also enhances inflammation and attracts immune cells to sites of infection.
5. Deficiencies or dysfunctions in components that form the MAC can lead to increased susceptibility to infections and highlight its importance in maintaining immune defense.

Review Questions

• How does the membrane attack complex contribute to innate immunity and what is its mechanism of action?
  • The membrane attack complex contributes to innate immunity by forming pores in the membranes of pathogens, leading to their destruction. This occurs after complement proteins are activated and assemble to form the MAC on the pathogen's surface. The created pores disrupt the osmotic balance within the pathogen, causing cell lysis and ultimately leading to death. This mechanism allows for rapid elimination of invading microorganisms as part of the body’s first line of defense.
• Discuss how complement activation pathways lead to the formation of the membrane attack complex and its implications for pathogen elimination.
  • Complement activation pathways, which include classical, alternative, and lectin pathways, converge at a point where key components like C3 convertase are generated. This leads to further cleavage of complement proteins and ultimately forms C5 convertase. The resulting C5b binds to C6 and C7, initiating assembly into the membrane attack complex. The implications for pathogen elimination are significant; by disrupting bacterial membranes through lysis, the MAC plays a vital role in controlling infections and enhancing overall immune responses.
• Evaluate how variations in pathogen resistance mechanisms impact the efficacy of the membrane attack complex and innate immune responses.
  • Variations in pathogen resistance mechanisms significantly impact the efficacy of the membrane attack complex by allowing certain pathogens to evade lysis. For instance, some bacteria produce protective capsules or enzymatic inhibitors that prevent complement proteins from assembling effectively on their surfaces. This resistance not only reduces direct damage from MAC formation but also alters innate immune responses, leading to prolonged infections and potentially increased severity of disease. Understanding these interactions highlights both challenges in infectious disease management and opportunities for developing targeted therapies.

Related terms

Complement System: A group of proteins in the blood that enhance the ability of antibodies and phagocytic cells to clear pathogens from an organism.

Lysis: The process of breaking down or destroying a cell's membrane, resulting in the release of its contents.

C5b-9: The components that combine to form the membrane attack complex; C5b initiates the assembly of the MAC, followed by the recruitment of C6, C7, C8, and multiple C9 molecules.