Immune System Notes

The Immune System: Our Body's Defense Force

The immune system is the body's defense against threats like mechanical injuries, germs, and foreign particles. It's divided into innate and adaptive immunity.

Innate Immunity (Nonspecific)

  • First line of defense; doesn't differentiate between pathogens.
  • Goal: Prevent intruders from entering or neutralize them if they do.
  • Components:
    • Physical Barriers:
      • Skin: The largest organ, providing a protective covering.
      • Mucus lining: Traps pathogens in organs.
    • Chemical Barriers:
      • Lysozyme: Found in tears.
      • Acid in the Stomach: Kills ingested pathogens.
    • Normal Flora/Microbial Community:
      • Found in the genitourinary tract.
      • Competes with pathogens for resources.
Inflammation
  • Triggered by mast cells that release histamine when they detect suspicious objects.
  • Histamine alerts the body, increasing blood flow to the affected area.
  • Results in inflammation and the recruitment of leukocytes (white blood cells).
  • Allergic reactions occur when the body mounts an immune response to harmless substances like dust.
Leukocytes (White Blood Cells) in Innate Immunity
  • VIPs with access to the body, excluding the brain and spinal cord.
    • Phagocytes:
      • Neutrophils:
        • Most abundant leukocytes.
        • Patrol the body and quickly reach breach sites.
        • Kill infectious cells and form pus after death.
      • Macrophages:
        • Engulf pathogens; can consume around 100 pathogens.
        • Located in specific areas rather than freely roaming.
        • Detect and kill rogue cells, like cancer cells.
      • Natural Killer Cells (NKCs):
        • Detect and destroy infected or abnormal cells.
        • Monitor cells for the Major Histocompatibility Complex (MHC) protein.
        • Normal cells produce MHC; abnormal cells don't.
        • NKCs bind to cells lacking MHC, release chemicals, and destroy them.
      • Dendritic Cells:
        • Located in areas exposed to the external environment (e.g., nose, lungs).
        • Act as a link between innate and adaptive immunity.
        • Eat pathogens and present antigens to adaptive immune cells.
Antigens
  • Molecules on the surface of pathogens.
  • Detected by the adaptive immune system for recognition.
  • Dendritic cells present antigens to T cells; macrophages can also do this.

Adaptive (Acquired) Immunity

  • More efficient; differentiates between pathogens.
  • Components: T lymphocytes (T cells) and B lymphocytes (B cells).
T Cells
  • Mediate cell-mediated immune response after an infection occurs.
    • Helper T Cells:
      • Receive signals from dendritic cells or macrophages.
      • Form effector T cells to recruit other white blood cells.
      • Create memory T cells to remember antigens for future infections.
    • Cytotoxic T Cells:
      • Induce "mercy killing" of heavily infected cells.
B Cells
  • Mediate humoral immune response when pathogens have entered but haven't caused disease.
  • Produce antibodies that bind to pathogen antigens (lock and key).
  • Antibodies tag pathogens for macrophages to engulf and kill.
  • Also produce memory B cells.
Memory Cells
  • Both B and T memory cells maintain records of past infections.
  • Strengthen and solidify future immune responses.

Comparison of Innate and Adaptive Immunity

  • Innate:
    • Quicker (hours).
    • Nonspecific.
    • Strong initial response.
  • Adaptive:
    • Slower (days to mount a response).
    • Specific.
    • Provides long-term immunity after initial exposure.

Conclusion

Our immune system protects us daily, deserving respect for maintaining our health.