Lecture Notes: The Complement System

Introduction

• Presenter: Leslie Samuel from Interactive Biology TV
• Topic: Understanding the complement system in the immune response
• Objective: Gain a better understanding of how the complement system functions

Overview of the Complement System

• A series of proteins found in the blood, involved in immune responses
• Origin: Proteins made in the liver and sent to the blood
• Naming: Proteins are named C1 to C9 for simplicity

Pathways in the Complement System

1. Classical Pathway

• Triggered by: Antigen-antibody complex
• Process:
  • C1 Activation: Binds to antigen-antibody complex
  • Cascade Effect: C1 activates C2 and C4, splitting them into fragments
  • C3 Convertase Formation: Combination of fragments from C2 and C4
  • C3 Activation: C3 split into C3a (diffuses and attracts phagocytes) and C3b (tags pathogens)
  • C3b Role: Tags pathogen, activates C5 to split
  • Membrane Attack Complex (MAC): Formed by C5b, C6, C7, C8, C9 creating a hole in the pathogen membrane, leading to its destruction

2. Alternative Pathway

• Difference from Classical: Does not involve antigens or C1, C2, C4
• Start Point: C3 binds directly to pathogen
• Process:
  • Interacts with proteins Factor P, B, and D
  • Similar cascade continues as in the classical pathway

Functions of the Complement System

• Recruits phagocytes to the infection site
• Tags pathogens for destruction
• Forms the MAC to destroy pathogens by creating membrane holes

Key Differences

• Classical Pathway: Part of specific immune response involving antibodies
• Alternative Pathway: Non-specific, directly binds to pathogens without antibodies

Conclusion

• Efficiency: Demonstrates body's optimized mechanism to protect against pathogens
• Next Topic Preview: T-cells and their role in adaptive immunity

Closing Remarks

• Complement system's role is critical in immune defense and pathogen destruction
• Further exploration of immune responses in upcoming sessions