Lecture on Immunity

Overview

• Three Lines of Defense: Covers first, second, and third lines of defense in the immune system.
• Types of Immunity: Focus on acquired immunity, which is developed throughout life.

Types of Immunity

• Passive Immunity

  • Short-term immunity provided by another source.
  • Natural Passive Immunity: Antibodies transferred from mother to baby via breast milk.
  • Artificial Passive Immunity: Serum of antibodies given, e.g., for tetanus exposure.

• Active Immunity

  • Immunity developed after exposure to a pathogen or through vaccination.
  • Natural Active Immunity: Exposure to a pathogen like chickenpox leads to antibody development.
  • Artificial Active Immunity: Vaccination introduces a dead or partial pathogen to stimulate immunity without causing illness.

Lines of Defense

First Line of Defense

• Non-Specific: Physical and chemical barriers.
• Components:
  • Tears: Contain antimicrobial proteins.
  • Mucous Lining: Traps pathogens in the respiratory tract.
  • Skin: Physical barrier; sweat alters pH to deter bacterial growth.

Second Line of Defense

• Non-Specific: Occurs in tissues, not bloodstream.
• Inflammation Response: Swelling and fever as a response.
• Phagocytes: White blood cells that engulf and digest pathogens.
• Histamine Production: Induces swelling and enables white blood cell permeability.

Third Line of Defense

• Specific Response: Involves specific cells for targeted pathogens.
• Key Cells:
  • T Lymphocytes:
    • Helper T Cells (CD4): Initiate immune response, call B cells.
    • Killer T Cells: Destroy host cells infected by viruses or cancer.
    • Suppressor T Cells: Halt immune response once the threat is neutralized.
  • B Lymphocytes:
    • Develop into plasma cells to produce antibodies.
    • Memory cells for faster future responses.

Detailed Processes

Phagocytosis

• Phagocytes engulf pathogens, digest them with enzymes, and expel waste.

Antibody Production

• Antibodies: Y-shaped proteins that bind to antigens on pathogens.
• Functions:
  • Lyse bacterial cells, label pathogens for phagocytes, neutralize toxins.

Antigen Recognition

• Antigens: Proteins on cells that signal to the body whether a cell is foreign or not.
• Memory Cells: Retain information on pathogens for quicker response in future exposures.

Summary

• Pathogens: Cause diseases, e.g., viruses, bacteria.
• Defense Mechanisms: Employ non-specific and specific responses.
• Immune Cells: Work together to identify, destroy, and remember pathogens for future protection.