How does the immune system protect the body from disease?

The immune system protects the body from disease by identifying, neutralizing, and eliminating harmful invaders like bacteria, viruses, fungi, and parasites. It also detects and removes damaged or abnormal cells, including cancerous cells. Here’s how it works:

1. First Line of Defense: Physical and Chemical Barriers

• Skin: Acts as a physical barrier preventing pathogens from entering the body.
• Mucous Membranes: Found in the respiratory, digestive, and urogenital tracts, they trap microbes.
• Chemical Defenses:
  • Stomach Acid: Kills ingested pathogens.
  • Enzymes in Saliva and Tears: Destroy microbial cell walls.
  • Sweat and Oil: Create an acidic environment on the skin that deters microbial growth.

2. Second Line of Defense: Innate Immune Response

• Rapid and Non-Specific: This defense responds quickly to all pathogens without targeting specific ones.
• Key Components:
  • Phagocytes: White blood cells like macrophages and neutrophils engulf and destroy pathogens.
  • Natural Killer (NK) Cells: Destroy infected or abnormal cells by inducing apoptosis (programmed cell death).
  • Inflammatory Response:
    • Increased blood flow to the site of infection brings more immune cells.
    • Redness, heat, swelling, and pain help localize and combat infection.
  • Complement Proteins: Help destroy pathogens by marking them for destruction or directly lysing their membranes.
  • Fever: Elevated body temperature inhibits microbial growth and enhances immune activity.

3. Third Line of Defense: Adaptive Immune Response

• Specific and Memory-Based: Targets specific pathogens and remembers them for faster response in the future.
• Key Components:
  • Lymphocytes:
    • B Cells: Produce antibodies that bind to specific antigens (markers on pathogens), neutralizing them or marking them for destruction.
    • T Cells:
      • Helper T Cells: Activate other immune cells like B cells and cytotoxic T cells.
      • Cytotoxic T Cells: Kill infected cells directly.
  • Antibodies: Specialized proteins that neutralize pathogens or facilitate their destruction.
• Memory Cells:
  • Long-lived B and T cells remain after an infection and respond quickly if the same pathogen re-enters the body.

4. Regulation and Coordination

• Cytokines: Signaling proteins that coordinate the activity of immune cells.
• Immune Surveillance: Constant monitoring of the body for abnormal cells or pathogens.

5. Vaccination and Immune Training

• Vaccines introduce harmless parts of a pathogen to train the immune system to recognize and respond more effectively to real infections.

6. Balance and Tolerance

• Self vs. Non-Self Recognition: The immune system distinguishes between the body’s cells (self) and foreign invaders (non-self).
• Regulatory Mechanisms: Prevent the immune system from attacking healthy cells, reducing the risk of autoimmune diseases.

By working through these layers of defense, the immune system protects the body from infections and promotes overall health.