Innate Immunity.pptx

Module Four: Innate Immunity

Objectives

  • Understanding innate immunity concepts:

    • Skin as a chemical and physical barrier against microbes.

    • Role of mucous membranes in innate immunity.

    • Importance of the lacrimation process in the first line of defense.

    • Function of normal flora in innate immunity.

    • Hematopoiesis and formation of blood components; distinction between granulocytes and agranulocytes.

    • Steps in phagocytosis and its role in eliminating invaders.

    • Blood elements involved in non-phagocytotic killing of microbes.

    • Mechanism of interferons as non-specific defenses against pathogens.

    • Steps and functions of inflammation in the second line of defense.

    • Stages of fever onset and its significance in the second line of defense.

Host Defenses: Overview

  • Composed of two categories:

    • Innate defenses: Nonspecific, first line of defense.

    • Adaptive defenses: Specific, targeting particular pathogens.

The Body’s First Line of Defense

Role of Skin in Innate Immunity

  • Composition:

    • Epidermis: Multiple layers of tightly packed cells, difficult for pathogens to penetrate; facilitates shedding of dead cells.

    • Dermis: Contains collagen fibers for abrasion resistance.

    • Epidermal dendritic cells: Phagocytize pathogens.

Chemical Defenses of Skin

  • Secrets that defend:

    • Perspiration: Contains salt which inhibits pathogen growth; antimicrobial peptides; lysozyme to destroy bacterial cell walls.

    • Sebum: Keeps skin pliable; lowers pH, inhibiting many bacteria.

Role of Mucous Membranes in Innate Immunity

  • Composition:

    • Epithelium: Thin outer layer; tightly packed cells that prevent pathogen entry; continual shedding removes microorganisms.

    • Connective layer: Supports the epithelium.

Comparative Overview of Skin and Mucous Membranes (Table 15.1)

  • Skin vs. Mucous Membranes:

    • Layers, cell living status, mucus presence, and other chemical defenses.

Role of Lacrimal Apparatus in Innate Immunity

  • Functions of lacrimal apparatus:

    • Produces and drains tears; blinking distributes tears, washing the eye surface.

    • Contains lysozyme which destroys bacteria.

Role of Normal Microbiota in Innate Immunity

  • Microbial antagonism:

    • Compete with pathogens; consume nutrients, create an unfavorable environment for pathogens, stimulate the second line of defense, and promote health by providing vitamins.

Other First-Line Defenses

  • Antimicrobial peptides: Present in skin and membranes; act against various microbes.

  • Chemical Secretions (Table 15.2): Include saliva, stomach acid, bile, and urine that eliminate or inhibit pathogens.

The Body’s Second Line of Defense

Components of Blood

  • Formed elements in plasma:

    • Types: Erythrocytes (oxygen transport), platelets (clotting), leukocytes (defense).

    • Divided into granulocytes and agranulocytes.

Phagocytosis Process

  • Phagocytes stages in elimination:

    1. Chemotaxis

    2. Adherence

    3. Ingestion

    4. Fusion

    5. Killing

    6. Elimination.

Nonphagocytic Killing

  • Mechanisms:

    • Eosinophils: Attack parasitic worms.

    • Natural Killer (NK) cells: Secrete toxins on infected or tumor cells.

    • Neutrophils: Produce reactive chemicals and NETs to kill invaders.

Nonspecific Chemical Defenses

  • Toll-like receptors (TLRs): Bind to PAMPs triggering immune responses including apoptosis and inflammation.

  • Interferons: Released by infected cells to inhibit viral spread, causing symptoms related to viral infections.

  • Complement system: Serum proteins activated to lyse foreign cells triggered by several pathways.

Inflammation

  • Definition: Nonspecific tissue response to damage.

  • Characteristics: Redness, heat, swelling, pain.

  • Types: Acute (short-term, beneficial) vs. Chronic (longer-term).

Steps in Inflammation Process

  • Acute inflammation:

    • Quick development; enhances blood vessel dilation and permeability, leading to phagocyte migration and tissue repair.

Fever Response

  • Fever definition: Body temperature >37°C triggered by pyrogens affecting the hypothalamus.

  • Types of pyrogens: Include bacterial toxins and lysis products.