Chapter 16: Introduction to the Native Immune System

Overview of the Immune System

• Immune system consists of both inborn and adaptive components.
• Innate Immunity:
  • Inborn, requires no prior exposure to pathogens.
  • Provides a constant level of defense.
  • Does not improve upon repeated exposure.
• Adaptive Immunity:
  • Develops immunity through exposure and memory formation.
  • Adaptive over time and improves with repeated exposure.

Definition of Immunity

• Ability to fight off disease, not necessarily prevent it entirely.
• Lack of immunity leads to susceptibility to disease.

First Line of Defense: Barriers in Innate Immunity

Physical Barriers

• Skin:
  • Stratified, keratinized outer layer.
  • Acts as a protective barrier to pathogens.
• Tears and Lacrimal Apparatus:
  • Keep microorganisms out of eyes.
• Saliva:
  • Washes microorganisms off teeth.
• Mucous Membranes:
  • Trap particles in upper respiratory tract.
  • Ciliary escalator moves mucus out of respiratory tract.
• Urine:
  • Rinses and pushes bacteria away from urogenital tract.

Chemical Barriers

• Stomach Acid:
  • Sterilizes food, preventing pathogens from entering the body.
• Sweat and Skin Oil:
  • Sweat is salty, can inhibit bacterial growth.
  • Skin oil is antifungal; earwax is mildly acidic and antimicrobial.
• Enzymes in Saliva:
  • Such as lysozyme, which degrades peptidoglycan in gram-positive bacteria.

Normal Flora as Barriers

• Role of Normal Bacteria:
  • Occupy space, preventing pathogenic bacterial colonization.
  • Example: Intestinal bacteria prevent opportunistic pathogens like C. diff.
• Impact of Antibiotics:
  • Antibiotic treatment can disrupt normal flora, allowing pathogens like C. diff to colonize.

Conclusion

• Innate immune system's barriers are crucial to preventing disease via physical, chemical, and biological means.
• Understanding these defenses is essential to comprehending how the body initially wards off infections.