The Human Immune System: First Line of Defense

Overview

  • The human immune system is incredibly complex, second only to the brain.

  • It comprises numerous organs, a transport network, and billions of cells organized like an army.

  • It protects the body from microorganisms and cancerous cells.

First Line of Defense: Initial Response to Invasion

  • When the body is invaded damaged or dying cells release chemical alarm signals.

Macrophages: The First Responders

  • Macrophages = large cells that attack and kill bacteria.

  • They engulf bacteria and digest them alive.

  • Each macrophage can consume up to 100 bacteria.

  • They release chemical signals calling for reinforcements.

Neutrophils: Suicide Warriors

  • Neutrophils are short-lived cells whose sole purpose is to kill.

  • They attack bacteria by vomiting deadly chemicals or devouring them.

  • Neutrophils cause collateral damage to the body's own cells.

  • Some neutrophils explode, releasing a toxic net of DNA and chemicals that trap and kill bacteria.

Inflammation: Fluid and Complement Proteins

  • Blood vessels release fluid into the infected area, causing inflammation (swelling, redness, warmth).

  • The fluid contains complement proteins, which are automated liquid weapons.

  • Complement proteins stun and kill bacteria by creating holes in their membranes.

Dendritic Cells: Intelligence Officers and Activation of the Second Line of Defense

  • If the first line of defense is overwhelmed, dendritic cells come in

  • Dendritic cells collect samples of the bacteria by breaking them down into tiny parts and displaying them on their surface.

  • They then travel to the lymph nodes to find a helper T cell with the appropriate weapon to fight the specific bacteria.

Helper T Cells: Commanders of the Immune Response

  • The immune system has cells with weapons against every possible disease.

  • Dendritic cells activate the appropriate helper T cell by presenting the bacterial antigens.

  • Activated helper T cells clone themselves, creating a large army of specialized cells.

Second Line of Defense: Amplifying the Immune Response

  • The second line of defense is slower to activate but more effective.

  • Helper T cells split into two groups:

    • One group travels to the battlefield to stimulate macrophages, invigorating them to kill more effectively.

    • The other group activates B cells, which are antibody factories.

B Cells: Antibody Production

  • Helper T cells activate specific B cells that can produce the right antibodies for the invading bacteria.

  • Activated B cells clone themselves and produce up to 2,000 antibodies per second.

  • Antibodies bind to bacteria, immobilizing them and making them easier targets for immune cells.

Resolution and Immunity

  • As the infection is cleared, immune cells begin to die off.

  • Some helper T cells become memory cells, guarding the tissue against future infections.

  • Some B cells remain and continue to produce antibodies, providing long-term immunity.