Membrane attack complex

Definition

The membrane attack complex (MAC) is a structure formed on the surface of pathogens, primarily by the complement system, which leads to the lysis or destruction of the target cell. This complex is composed of complement proteins that assemble into a pore-like structure, allowing the influx of water and ions into the pathogen, ultimately causing it to swell and burst. The MAC is crucial in the immune response against various infectious agents, including parasites.

5 Must Know Facts For Your Next Test

1. The MAC is primarily formed by complement proteins C5b, C6, C7, C8, and multiple molecules of C9, which create a channel through the target cell's membrane.
2. This complex is particularly effective against gram-negative bacteria and certain parasites, helping the immune system eliminate these pathogens efficiently.
3. The formation of the MAC can be triggered by pathways activated by antibodies or directly through pathogen recognition by complement proteins.
4. Parasitic infections can lead to various immunopathological responses; the presence of MAC indicates an active immune response trying to control the infection.
5. However, some parasites have developed mechanisms to evade the effects of the MAC, thereby contributing to their survival in host organisms.

Review Questions

• How does the membrane attack complex contribute to the immune response against parasitic infections?
  • The membrane attack complex plays a key role in the immune response against parasites by forming pores in their membranes, leading to cell lysis. This direct action helps eliminate extracellular parasites effectively. By creating these pores, the MAC facilitates the influx of ions and water into the parasite, causing it to swell and ultimately burst, which is vital for controlling infections caused by various parasitic organisms.
• Evaluate the significance of complement activation pathways in the formation of the membrane attack complex during parasitic infections.
  • The complement activation pathways are crucial for forming the membrane attack complex as they initiate a cascade that leads to its assembly on pathogen surfaces. Both the classical and alternative pathways can trigger MAC formation in response to parasitic infections. Understanding these pathways helps illustrate how immune responses are tailored to target different pathogens effectively while highlighting potential vulnerabilities that some parasites exploit to avoid destruction.
• Discuss how evasion strategies employed by parasites can impact the efficacy of the membrane attack complex in host defense.
  • Parasites have evolved various evasion strategies that can significantly reduce the effectiveness of the membrane attack complex in host defense. Some parasites modify their surface structures or produce regulatory proteins that inhibit complement activation or prevent MAC assembly. These adaptations allow them to survive despite an active immune response. Understanding these mechanisms is crucial for developing targeted therapies that can enhance host defense against such parasitic infections.

Related terms

Complement system: A group of proteins that work together to enhance the ability of antibodies and phagocytic cells to clear pathogens from an organism.

Lysis: The breakdown or destruction of a cell, often by the action of an external agent like the membrane attack complex.

Cytokines: Signaling proteins that mediate and regulate immunity, inflammation, and hematopoiesis.