Innate+Immunity

Innate Immunity Overview

Nonspecific Lines of Defense

  • First Line of Defense:

    • Intact Skin & Mucous Membranes: Acts as a physical barrier against pathogens.

  • Second Line of Defense:

    • Protective Cells, Blood-Borne Chemicals, & Processes: Includes various immune responses to combat pathogens when they breach the first line.

Learning Objectives

Key Concepts to Understand:

  1. Differentiate between Innate and Adaptive Immunity:

    • Innate immunity is nonspecific and present at birth, whereas adaptive immunity is specific and develops over time.

  2. Toll-Like Receptors (TLRs):

    • Membrane proteins that recognize pathogen-associated molecular patterns (PAMPs) to initiate immune responses.

  3. Role of Skin & Mucous Membranes:

    • Provide a physical barrier and secrete various substances to protect against pathogens.

  4. Physical vs Chemical Factors:

    • Physical Factors:

      • Skin, mucous membranes.

    • Chemical Factors:

      • Lysozyme, pH levels in various secretions.

    • Examples: (5 each)

      • Physical: Skin, tears, saliva, mucus, cilia.

      • Chemical: Lysozyme, defensins, gastric acid, sweat, sebum.

  5. Normal Microbiota:

    • Competes with pathogens and produces vitamins, contributing to the innate immune defense.

  6. Leukocytes Classification:

    • Types: Granulocytes (neutrophils, basophils, eosinophils) and agranulocytes (monocytes, lymphocytes).

    • Functions: Phagocytosis, inflammation, and specific immune responses.

  7. Phagocytosis:

    • Defined as the engulfing of pathogens by specialized cells (phagocytes).

    • Stages: Chemotaxis, adherence, ingestion, maturation, microbial killing, and elimination.

  8. Mechanisms to Avoid Destruction:

    • Pathogens have various strategies to evade phagocytosis.

  9. Stages of Inflammation:

    • Involves vasodilation, increased vessel permeability, and recruitment of leukocytes.

  10. Role of Cytokines:

    • Communicate between cells to regulate immune responses, including fever generation and inflammation.

  11. Complement System:

    • A set of proteins that assists in pathogen lysis & phagocyte recruitment; activated by three main pathways.

  12. Interferons:

    • Proteins that inhibit viral replication and activate immune cells.

  13. Iron-binding proteins:

    • Include proteins like transferrin and lactoferrin that sequester iron from pathogens.

  14. Antimicrobial Peptides:

    • Short proteins that disrupt microbial membranes and act as signaling molecules.

Detailed Components of Innate Immunity

First Line of Defense

Skin Structure:

  • Epidermis:

    • Outermost layer, composed of tightly packed cells, includes dendritic cells for immune surveillance.

  • Dermis:

    • Contains collagen and blood vessels.

Chemical Substances:

  • Antimicrobial peptides from dermal cells, sweat (lysozyme), and sebum (low pH).

Mucous Membranes

Function:

  • Protects body cavities that open to the environment

Actions:

  • Continual shedding, mucus secretion (goblet cells), and ciliary action.

Normal Microbiota

  • Competes with pathogens; produces vitamins and contributes to overall health.

Phagocytosis Process

  1. Chemotaxis: Movement of phagocytes towards infection.

  2. Adherence: Phagocyte binding to microorganisms.

  3. Ingestion: Membrane extensions (pseudopodia) engulf bacteria into phagosome.

  4. Fusion: Maturation to phagolysosome.

  5. Killing: Destruction via reactive nitrogen and oxygen species.

  6. Elimination: Expelling digested material.

Complement System

Activation:

  • Three pathways: classical (antibody-mediated), alternative (direct pathogen recognition), and lectin (microbial polysaccharide interaction).

Outcomes:

  • Inflammation, chemotaxis, opsonization, and lysis of pathogens.

Inflammation and Fever

Inflammation:

  • Characteristics: Redness, heat, swelling, pain.

  • Phases:

    1. Vasodilation & permeability increase.

    2. Phagocyte migration.

    3. Tissue repair.

Fever:

  • Triggered by pyrogens impacting the hypothalamus; enhances immune response.

Summary of Key Points

  • Innate immunity provides the first and second lines of defense against pathogens through physical barriers, chemical defenses, and immune cell actions.

  • Essential processes like phagocytosis, inflammation, and complement activation play a critical role in the body’s immediate response to infections.