Learning Objectives: By the end of this lesson, students should be able to describe the components and functions of innate immunity, differentiate innate from adaptive immunity, and explain how the innate immune system recognizes and responds to pathogens.

Introduction

Innate immunity is the body’s first line of defense against infectious agents. It acts rapidly and non-specifically, eliminating pathogens and damaged cells and initiating adaptive immunity.

Components of Innate Immunity

1. Anatomic and Physical Barriers
   • Skin: physical barrier, acidic pH, antimicrobial peptides
   • Mucous membranes: trap pathogens in the respiratory, GI, and GU tracts
   • Normal flora: compete with pathogens for nutrients and attachment
2. Physiologic Barriers
   • Temperature: Fever inhibits microbial growth
   • pH: acidic environments limit pathogen survival
   • Antimicrobials & cytokines: defensins, lysozyme, interferons
3. Complement System
   • A series of blood and tissue proteins that opsonize pathogens, promote inflammation, and form membrane attack complexes
4. Cellular Defenses
   • Phagocytes: macrophages, neutrophils, engulf and destroy microbes
     • Granulocytes: eosinophils, basophils, mast cells, fight parasites and mediate inflammation
5. Inflammation
   • Local response to infection or injury: redness, heat, swelling, pain
   • Recruits immune cells to the site of infection and facilitates pathogen clearance

Characteristics of Innate Immunity

• Intrinsic: present at birth, no prior exposure needed
• Limited specificity: recognizes PAMPs (pathogen-associated molecular patterns) and DAMPs (damage-associated molecular patterns)
• Limited diversity: only a small number of pattern recognition receptors (PRRs)
• No memory: response is not enhanced upon subsequent exposure

Question: Match the innate immunity components to their main function: