Complement System Made Easy- Immunology- Classical Alternate & Lectin pathway

Summary

This video explores the complement system, a crucial part of innate immunity, highlighting its activation pathways (classical, alternative, and lectin) and immune effects, such as opsonization, cell lysis, chemotaxis, and mast cell activation, which bolster the body's defense against pathogens.

Takeaways

• 😀 The complement system is a group of about 20 plasma proteins that play a crucial role in innate immunity.
• 🧬 The term 'complement' is used because this system enhances or complements our immune response.
• 📚 Complement proteins are primarily synthesized in the liver and are widely distributed throughout body tissues and fluids.
• 🔍 The complement system is activated through three main pathways: the classical pathway, the alternative pathway, and the lectin pathway.
• 🌐 The classical pathway is triggered by the interaction between antibodies and antigens, activating the C1 component of the complement system.
• 🔬 In the classical pathway, C1 cleaves C4 into C4a and C4b, leading to the formation of C14b2 (C3 convertase), which further splits C3 into C3a and C3b.
• 🌀 The alternative pathway is primarily triggered by bacterial endotoxin, a lipopolysaccharide compound found in the outer membrane of gram-negative bacteria.
• 🍀 The lectin pathway is activated by the binding of mannose-binding lectin (MBL) to specific sugars on the surface of pathogens like Neisseria and Salmonella.
• 🛡️ Complement proteins contribute to immune effects such as opsonization, where C3b activates neutrophils and macrophages to engulf foreign microorganisms.
• 💥 The membrane attack complex (C5b-9) formed by the complement system can rupture bacterial cell walls, leading to bacterial destruction.
• 🚑 Complement factors like C3a, C4a, and C5a are involved in chemotaxis, attracting neutrophils and macrophages to the site of infection, and activating mast cells and basophils to release inflammatory mediators.

Q & A

What is the complement system?

The complement system is a group of about 20 plasma proteins that play an essential role in innate immunity. It enhances or complements our immune response.

Where are the complement system proteins primarily synthesized?

The complement system proteins are mainly synthesized in the liver.

How does the complement system become activated?

The complement system becomes activated through various pathways including the classical pathway (triggered by antibody-antigen reactions), the alternative pathway (triggered by bacterial endotoxins), and the lectin pathway (triggered by mannose-binding lectin).

What is the classical pathway and how is it triggered?

The classical pathway is one of the activation pathways of the complement system. It is triggered by the interaction between antibodies and antigens, which activates the C1 component of the complement system.

What happens when the C1 component is activated in the classical pathway?

When the C1 component is activated, it cleaves the C4 component into C4a and C4b. C1 combines with C4b to form C1q4b, which is an enzyme that converts C2 into C2a and C2b, forming the C3 convertase.

What is the alternative pathway and what triggers it?

The alternative pathway is another activation pathway of the complement system, mainly triggered by bacterial endotoxins, which are lipopolysaccharide compounds found in the outer membrane of gram-negative bacteria.

How does the spontaneous hydrolysis of Factor C3 initiate the alternative pathway?

The spontaneous hydrolysis of Factor C3 converts it to C3b, allowing the attachment of Factor B. Factor D then splits Factor B into Ba and Bb, with Bb combining with C3b to form the C3 convertase of the alternative pathway.

What is the lectin pathway and how does it depend on mannose-binding lectin?

The lectin pathway is an activation pathway of the complement system that depends on the protein known as mannose-binding lectin (MBL). MBL recognizes glucose and mannose residues in the cell walls of certain organisms, activating a protease called MASP (mannose-binding lectin-associated serine protease).

What are the immune effects of the complement system?

The immune effects of the complement system include opsonization (enhancing phagocytosis), cell lysis (rupture of bacterial cell walls), chemotaxis (attracting neutrophils and macrophages), and activation of mast cells and basophils (releasing inflammatory mediators).

What is the role of C5b-6789 in the complement system?

C5b-6789 is the membrane attack complex in the complement system. It has the effect of rupturing bacterial cell walls, destroying a large amount of bacterial load.