Membrane Attack Complex

Definition

The membrane attack complex (MAC) is a protein structure formed by the complement system, a part of the immune response, that can puncture and destroy target cells by creating pores in their cell membranes. It is a key component of the body's chemical defenses against pathogens and other threats.

5 Must Know Facts For Your Next Test

1. The membrane attack complex is composed of multiple complement proteins that assemble into a ring-shaped structure on the target cell membrane.
2. Formation of the MAC is the final step in the complement system's classical and alternative activation pathways, which are triggered by the presence of pathogens or damaged cells.
3. Once assembled, the MAC creates a pore in the target cell membrane, allowing water and ions to flow in and out, leading to osmotic imbalance and cell lysis.
4. The MAC is an important defense mechanism against Gram-negative bacteria, which have a weaker outer membrane that the complex can more easily penetrate.
5. Regulation of the MAC is crucial to prevent damage to the body's own cells, and is controlled by various complement inhibitor proteins.

Review Questions

• Explain the role of the membrane attack complex in the immune system's chemical defenses.
  • The membrane attack complex is a key component of the complement system, which is part of the body's innate immune response. When the complement system is activated, the MAC assembles on the surface of target cells, such as pathogens or damaged cells, and creates pores in their membranes. This disrupts the cell's integrity, leading to its lysis and destruction. The MAC is an important chemical defense mechanism that helps eliminate threats to the body without the need for specialized immune cells.
• Describe the process of pore formation by the membrane attack complex and how it leads to cell lysis.
  • The membrane attack complex is composed of multiple complement proteins that assemble into a ring-shaped structure on the target cell membrane. Once fully formed, the MAC inserts itself into the cell membrane, creating a pore or hole. This pore allows water and ions to flow freely in and out of the cell, disrupting the cell's osmotic balance and leading to its rupture or lysis. The release of the cell's contents ultimately results in its destruction, making the MAC an effective means of eliminating pathogens and other threats through a direct physical mechanism.
• Analyze the importance of regulating the membrane attack complex to prevent damage to the body's own cells.
  • While the membrane attack complex is a powerful tool in the immune system's chemical defenses, its activity must be carefully regulated to prevent harm to the body's own cells. The complement system, including the MAC, is controlled by various inhibitor proteins that prevent the complex from assembling on healthy cells. Dysregulation of the MAC can lead to autoimmune disorders, where the body's own tissues are mistakenly targeted and destroyed. Therefore, the precise regulation of the membrane attack complex is crucial to maintain the balance between effective pathogen elimination and the protection of the body's own cells and tissues.

Related terms

Complement System: A group of blood proteins that work together to destroy pathogens, facilitate phagocytosis, and promote inflammation as part of the innate immune response.

Pore Formation: The process by which the membrane attack complex inserts itself into a cell membrane, creating a hole or pore that disrupts the cell's integrity and leads to its lysis (bursting).

Lysis: The rupturing or disintegration of a cell, often caused by the membrane attack complex, leading to the release of the cell's contents and ultimately its destruction.