The Immune System Overview

Introduction

• The immune system is one of the most fascinating systems in the body.
• It protects the body from pathogens like viruses, bacteria, fungi, protists, and parasitic worms.
• The immune system works tirelessly to protect the body, often unnoticed.

Pathogens and First Line of Defense

• Pathogens: Harmful organisms like viruses, bacteria, fungi, protists, and parasitic worms.
• First Line of Defense:
  • Skin: Acts as a barrier to prevent pathogen entry.
  • Mucous Membranes: Found in areas like the nose, also block pathogens.
  • This defense is non-specific, meaning it's not selective.

Second Line of Defense: Inflammatory Response

• Inflammatory Response: Kicks in if pathogens bypass the first line.
• Mast Cells:
  • Release substances like histamine.
  • Histamine dilates blood vessels, making them leakier.
  • Helps white blood cells (e.g., macrophages) reach infection sites.
• Macrophages: White blood cells that consume pathogens.
• Complement System: Supports immune functions by attracting macrophages.

Third Line of Defense: Specific (Adaptive) Immunity

• Adaptive Immunity: Offers a targeted response to specific antigens.
• Antigens: Substances recognized as non-self, usually parts of pathogens.

Types of Adaptive Responses

Cell-Mediated Response

• Cytotoxic T Cells:
  • Destroy infected cells by inducing apoptosis.
  • Use proteins like perforin to kill infected cells.
• Activation of Cytotoxic T Cells:
  • Triggered by antigens presented by infected cells or consumed by macrophages.
  • Helper T cells bind to macrophages and release signals stimulating cytotoxic T cells.

Humoral Response

• B Cells: White blood cells responsible for producing antibodies.
• Antibodies:
  • Y-shaped proteins binding antigens to neutralize pathogens.
  • Found in blood, mucus, saliva, and more.
  • Classes include IgE (e.g., against worms, allergic reactions).
• Activation of B Cells:
  • Stimulated by helper T cells or directly by free antigens.

Memory Cells and Vaccination

• Memory Cells:
  • Memory B cells and T cells remember antigens for faster future response.
• Vaccines:
  • Introduce inactive or weakened pathogens to build memory cells without causing disease.

Conclusion

• The immune system is complex yet vital for protection against diseases.
• There are entire fields and textbooks dedicated to the study of the immune system.
• Encouragement to continue exploring the immune system's intricacies.