key term - Membrane attack complex

Definition

The membrane attack complex (MAC) is a structure formed by the terminal components of the complement system that creates pores in the membranes of target cells, leading to cell lysis and death. This complex plays a vital role in the innate immune response by directly attacking pathogens, contributing to the overall defense mechanisms of the body.

5 Must Know Facts For Your Next Test

1. The membrane attack complex is primarily composed of complement proteins C5b, C6, C7, C8, and multiple C9 molecules that assemble on the surface of pathogens.
2. MAC formation leads to the insertion of a pore into the target cell membrane, allowing ions and water to enter, causing the cell to swell and burst.
3. This mechanism is particularly effective against Gram-negative bacteria, which have thinner cell walls compared to Gram-positive bacteria.
4. In addition to direct lysis, the membrane attack complex also helps attract immune cells to the site of infection by promoting inflammation.
5. Dysfunction in MAC formation can lead to increased susceptibility to infections or contribute to autoimmune diseases due to improper targeting of self-cells.

Review Questions

• How does the membrane attack complex contribute to the innate immune response and what is its mechanism of action?
  • The membrane attack complex contributes to the innate immune response by forming pores in the membranes of pathogens, leading to their destruction. It assembles on target cell surfaces after complement proteins are activated, ultimately inserting multiple C9 molecules that create a hole in the membrane. This process causes cytolysis, resulting in cell lysis and death, thus eliminating threats and aiding in immune defense.
• Discuss the role of the membrane attack complex in combating different types of pathogens, especially regarding Gram-negative bacteria.
  • The membrane attack complex plays a crucial role in targeting various pathogens, with a significant impact on Gram-negative bacteria. These bacteria are particularly susceptible because their thinner outer membrane allows for easier insertion of MAC. When MAC forms on these bacteria, it disrupts their integrity and leads to cell lysis, making MAC an essential mechanism in controlling infections caused by Gram-negative organisms.
• Evaluate how dysfunctions related to the membrane attack complex can influence both susceptibility to infections and potential autoimmune conditions.
  • Dysfunctions in the formation or regulation of the membrane attack complex can lead to increased vulnerability to infections because pathogens may evade destruction. Conversely, an overactive MAC may mistakenly target and destroy healthy host cells, contributing to autoimmune conditions. This duality highlights the importance of proper MAC function in maintaining a balanced immune response that effectively protects against pathogens while preventing damage to self-tissues.

Related terms

Complement System:

A group of proteins that work together to enhance the immune response, including opsonization, inflammation, and direct lysis of pathogens.

Cytolysis: The process in which a cell is destroyed due to the rupture of its membrane, often facilitated by the action of the membrane attack complex.

Innate Immunity: The first line of defense in the immune system that provides immediate but non-specific protection against pathogens.