Understanding the Complement System

Introduction

• Presenter: Leslie Samuel from Interactive Biology TV
• Topic: The complement system in the immune response
• Objective: Understand what complement proteins are and their function

What is the Complement System?

• A series of proteins found in the blood
• Part of the immune responses
• Proteins are made in the liver
• Proteins are named with a 'C' followed by a number (C1 through C9)

Pathways of the Complement System

Classical Pathway

• Triggered by an antigen-antibody complex
• Process:
  1. C1 Activation: Binds to antigen-antibody complex
  2. C2 and C4 Separation: Splits into two fragments each
  3. Formation of C3 Convertase: A fragment of C2 and C4 combine
  4. C3 Activation: Splits into C3a and C3b
  5. C3a: Attracts phagocytes to the infection site
  6. C3b: Tags pathogen for destruction and splits C5 into C5a and C5b
  7. Formation of Membrane Attack Complex: C5b joins C6, C7, C8, and C9
  8. Destruction: Complex creates a hole in the pathogen’s membrane causing it to rupture

Alternative Pathway

• Starts with the direct binding of C3 to the pathogen
• Skips antigen-antibody complex and C1, C2, C4
• Process:
  1. C3 Activation: Direct binding to pathogen
  2. Interaction with Factor P, B, and D
  3. Continues similar to Classical Pathway

Key Points

• Classical Pathway: Part of specific immune response (antibody recognizes antigen)
• Alternative Pathway: Part of non-specific immune response (C3 binds directly)
• Both pathways recruit phagocytes, tag pathogens, and form membrane attack complexes

Conclusion

• The complement system is a highly efficient method for targeting and destroying pathogens
• Significance in protecting the body from infections

Next Topic

• Exploration of T-cells and their role in adaptive immunity