Lecture Notes: Innate Immunity - Part 1

Overview of the Immune System

• Two basic parts:
  • Innate immunity (nonspecific/innate immune response)
  • Adaptive immunity (specific/adaptive immune response)
• Three lines of defense:
  • First Line: Part of innate immunity, keeps microbes out
  • Second Line: Part of innate immunity, initial defense inside the body
  • Third Line: Part of adaptive immunity, specialized cells respond to specific microbes

Innate Immunity

• Innate Immunity: Nonspecific, general defense against all microbes (viruses, bacteria)
• First Line of Defense:
  • Purpose: Prevent infection by keeping microbes out
  • Components:
    • Physical Barriers:
      • Skin: Thick, mechanically strong, waterproof barrier due to keratin
      • Mucous Membranes: Thin, fragile, not waterproof, found in respiratory, digestive, urogenital systems, and conjunctiva; contain goblet cells producing mucus to trap microbes
  • Washing Processes:
    • Lacrimal Apparatus: Tears wash over eyes, drain into stomach where acid kills microbes
    • Ciliary Escalator: In trachea, moves mucus (trapping microbes) away from lungs to stomach
    • Saliva Production: Saliva washes microbes from teeth to stomach
    • Urination: High pressure flushes microbes from urethra, preventing UTIs

Chemical Factors

• Sebum: Oil on skin that is acidic, inhibits microbial growth, maintains skin integrity
• Lysozyme: Found in various secretions, breaks down peptidoglycan in bacterial cell walls
• Saliva: Contains lysozyme, acts as a washing mechanism
• Gastric Juice: Very low pH, kills bacteria
• Urine/Vaginal Secretions: Contains lysozyme, slightly acidic to discourage microbial growth

Normal Flora

• Microbial Antagonism: Permanent flora competes with transient flora, preventing infection

Introduction to the Immune System Components

• Lymphatic System:
  • Lymphatic Vessels & Nodes: Drain fluid from tissues, bring microbes to lymph nodes containing white blood cells
  • Lymphatic Organs: Include red bone marrow (white blood cells), spleen, thymus (over heart), and lymph nodes
• Blood Components:
  • Plasma: Contains nutrients, gases, and proteins (antibodies and complement)
  • Formed Elements: White blood cells (leukocytes) originate from hematopoietic stem cells

White Blood Cells (Leukocytes)

• Granulocytes:
  • Neutrophils: Phagocytose microbes, die after one phagocytosis, numerous
  • Basophils: Release histamine, trigger inflammation
  • Eosinophils: Anti-parasitic, target protozoa/helminths
• Agranulocytes:
  • Monocytes: Immature macrophages, become macrophages in tissues
  • Macrophages: Phagocytose many microbes, types include:
    • Wandering Macrophages: Move through tissues
    • Fixed Macrophages: Reside permanently in tissues (Kupffer cells in liver, microglial cells in CNS, Langerhans cells in skin)

Summary

• First Line of Defense: Physical/chemical barriers and normal flora, aim to prevent infections
• Second Line of Defense (Covered in Part 2): Involves white blood cells and responses like inflammation
• Third Line of Defense: Specific immune response, detailed in Chapter 17