Membrane Attack Complex - Terminal Steps of Complement Pathways (Part V) (FL-Immuno/17)

Summary

This video explains the complement system, a key component of the immune response. It covers the three pathways of complement activation—alternative, lectin, and classical—each leading to the generation of C3 convertase. The C3 convertase cleaves C3 into C3b and C3a, with C3b binding to microbial surfaces to promote opsonization and phagocytosis. The process also triggers inflammation through smaller fragments. The most crucial consequence is the formation of the membrane attack complex (MAC), which creates pores in the microbial membrane, causing cell lysis and pathogen destruction.

Takeaways

• 😀 The complement system consists of serum proteins that assist immune cells in destroying pathogens.
• 😀 There are three pathways of complement activation: the alternative pathway, lectin pathway, and classical pathway.
• 😀 All three complement pathways generate C3 converts, which are crucial for complement activation.
• 😀 C3 converts in the alternative pathway are represented by the C3bBb complex, while in the lectin and classical pathways, it is represented by the C4b2a complex.
• 😀 The cleavage of C3 into C3b and C3a is a critical step in complement activation.
• 😀 C3b binds to the microbial surface, promoting opsonization and enhanced phagocytosis.
• 😀 C3a and C5a act as chemoattractants, recruiting phagocytes and contributing to inflammation.
• 😀 Smaller fragments like C3a and C5a induce degranulation of M cells and basophils, promoting vascular dilation and permeability.
• 😀 The most important consequence of complement activation is the formation of the membrane attack complex (MAC), which destroys pathogens.
• 😀 C5 converts are formed when C3b binds to the C3 converts, cleaving C5 into C5a and C5b, with C5b contributing to the MAC formation.
• 😀 The membrane attack complex creates pores in the microbial cell membrane, leading to cell lysis and destruction of the pathogen.

Q & A

What are the three pathways of complement activation mentioned in the video?

The three pathways of complement activation discussed are the alternative pathway, the lectin pathway, and the classical pathway.

What is the role of C3 convertases in the complement system?

C3 convertases are enzymes that cleave C3 into two smaller fragments, C3b and C3a. C3b binds to microbial surfaces, while C3a is released to trigger inflammation.

What is the function of the smaller fragment C3a released during complement activation?

C3a acts as a chemoattractant, recruiting phagocytes to the site of infection, and it also induces the degranulation of mast cells and basophils, promoting inflammation.

How does complement activation contribute to opsonization?

C3b molecules bind covalently to microbial surfaces and act as opsonins, which enhances the uptake and killing of microbes by phagocytosis due to the binding of C3b receptors on phagocytes.

What is the most important consequence of complement activation?

The most important consequence of complement activation is the formation of the membrane attack complex (MAC), which causes destruction of the pathogen by forming pores in the microbial cell membrane.

How is the C5 convertase formed in the complement system?

C5 convertase is formed when one or more C3b proteins bind to the C3 convertase enzyme, which then cleaves C5 into C5a and C5b fragments.

What is the role of C5b in the complement system?

C5b contributes to the formation of the membrane attack complex (MAC) by initiating the assembly of complement proteins that form a pore in the microbial cell membrane, leading to pathogen destruction.

What is the structure and function of the membrane attack complex (MAC)?

The membrane attack complex (MAC) is a structure formed by complement proteins that creates holes or pores in the microbial cell membrane, leading to the destruction of the microbe through osmotic lysis.

What proteins are involved in the formation of the membrane attack complex (MAC)?

The proteins involved in the formation of MAC include C5b, C6, C7, C8, and multiple C9 molecules. These proteins work together to form the transmembrane pore that destroys the microbial cell.

What happens when the membrane attack complex (MAC) forms pores in the microbial membrane?

When MAC forms pores in the microbial membrane, extracellular fluid flows into the cell through the transmembrane channels, resulting in osmotic lysis and the destruction of the pathogen.