Medicine & USMLE

Innate Immunity

  1. Innate Immunity
  2. Adaptive Immunity
  3. Macrophages
  4. Neutrophils
  5. Dendritic Cells
  6. Mast Cells
  7. Eosinophils
  8. Basophils
  9. Natural Killer Cells
  10. Antigens
  11. MHC I and II
  12. Antibodies
  13. B Lymphocytes Overview
  14. B Cell Stages
  15. B-Cell Activation
  16. Plasma B-Cells
  17. Memory B-Cells
  18. T-Lymphocytes Overview
  19. T-Cell Stages
  20. Types of Activated T-Cells


The innate immune system is one of two divisions of our immune system, protecting our body against infections by foreign pathogens. In general, the innate immune system acts quickly and non-specifically to any and all foreign pathogens. This is in sharp contrast to the adaptive immune system, which acts slowly and specifically to target a single kind of invader.

The innate immune system has many methods of achieving this fast and nonspecific protection. For one, it comprises various physical barriers and chemical secretions that generally block and protect us against all kinds of pathogens. Innate immunity also includes the inflammatory response, the complement system, and some cellular responses by white blood cells.

Key Points

  • Innate Immunity
    • Immune system is made up of two interconnected branches: innate and adaptive immunity
    • First line of defense against foreign pathogens
      • fast and non-specific response
    • Consists of:
      • Physical barriers
        • skin, mucosal surfaces (gastrointestinal tract, airways), cilia, eyelashes and other body hair
      • Secretions and chemicals
        • Digestive enzymes, blood chemicals, mucous, bile, gastric acid, saliva, tears, and sweat
      • Non-specific immune responses, including:
        • The inflammatory response
          • Consists of heat, pain, redness, and swelling, which generally makes body tissues less hospitable to invading pathogens and actively brings immune cells to the site of an infection by increasing blood flow to the area.
        • The complement system
          • Group of circulating proteins that marks pathogens for destruction and makes holes in the cell membrane of the pathogen.
        • Non-specific cellular responses
          • Innate immune cells that non-specifically engulf pathogens and release toxic chemicals to kill them