Immune System Overview

Introduction

• Immune system is one of the most fascinating systems
• Functions to protect the body from pathogens
• Pathogens: viruses, bacteria, fungi, protists, parasitic worms

First Line of Defense

• External protection: skin and mucous membranes
• Non-specific defense, not selective

Second Line of Defense

• Inflammatory Response:
  • Triggered by injury such as stepping on a sharp stick
  • Mast cells release histamine
  • Histamine causes blood vessels to dilate and become leaky
  • White blood cells (e.g., macrophages) reach the site to consume pathogens
• Complement System:
  • Complements the immune system's actions
  • Attracts additional macrophages

Third Line of Defense: Adaptive Immunity

• Targeted response to a specific pathogen
• Divided into cell-mediated and humoral responses

Cell-Mediated Response

• Cytotoxic T Cells:
  • Destroy infected cells by causing apoptosis
  • Release perforin to create holes in the cell membrane
• Activation:
  • Infected cells present antigens to activate T cells
  • Macrophages process pathogens and present antigens
  • Helper T cells release signals to stimulate cytotoxic T cells

Humoral Response

• B Cells:
  • Produce antibodies
  • Antibodies bind specific antigens, deactivating pathogens
  • IgE antibodies protect against parasitic worms
• Activation:
  • Helper T cells stimulate B cells
  • B cells can also be activated by free antigens

Memory Cells and Vaccination

• Memory B and T cells remember antigens
• Vaccines introduce weakened/inactivated pathogens
• Enable efficient immune responses in future encounters

Conclusion

• The immune system is complex and crucial for protection
• Encouragement to explore and understand more