chapter_12_.pdf_1_

12.1 Defense Mechanisms of the Host: An Overview

• Host Defenses: A multilevel network of innate and adaptive protections, known as the first, second, and third lines of defense.

  • First Line of Defense: General, nonspecific barriers blocking invasion at entry points. Protects internal tissues from external pathogens.

  • Second Line of Defense (Innate Immunity): Internal protective mechanisms (e.g., inflammation, phagocytosis) initiated rapidly if the first line is breached.

  • Third Line of Defense (Adaptive Immunity): Specific responses involving lymphocytes that adapt to each invader, resulting in long-term immunity.

Page 2: Interaction Between Defense Mechanisms

• Immune defenses overlap, providing a comprehensive assault on invaders.

  • Immunology: The study of the immune system is relevant in various fields, including infections, cancer, and allergies.

• Key Functions of the Immune System:

  1. Surveillance for threats

  2. Recognition of foreign materials (antigens)

  3. Destruction of foreign entities (nonself)

• Antigens: Unique markers on cells and particles that immune cells use to determine its foreignness.

• Self vs. Nonself Recognition: The immune system identifies and attacks foreign substances while sparing self-cells.

  • Autoimmune Disorders: Mistakes in identification can lead to conditions such as rheumatoid arthritis.

• Markers and Pathogen-Associated Patterns (PAMPs): Shared characteristics that help the immune system to identify common threats.

Page 3: Tissues, Organs, and Cells Participating in Immunity

• The body contains various fluid compartments:

  • Intracellular, extracellular, lymphatic, cerebrospinal, and circulatory compartments.

• Lymphatic System:

  • Components: Network of vessels, cells, and organs (lymph nodes).

  • Functions:

    1. Return of extracellular fluid to circulation

    2. Drain off system for inflammation

    3. Surveillance and protection against foreign materials

Page 4: Lymphatic Fluid and Vessels

• Lymph: A fluid carrying white blood cells, fats, and debris through lymphatic circulation.

• Lymphatic Vessels: Function similarly to veins, with a one-way flow toward the heart. Depend on muscle movement for circulation.

Page 5: Bone Marrow and Thymus in Immune Cell Development

• Red Bone Marrow: Site of production for blood cells, including precursors to B and T lymphocytes.

• Thymus: Maturation site for T lymphocytes, crucial for adaptive immunity.

• Secondary Lymphoid Organs: Sites of activation for immune response (e.g., spleen and lymph nodes).

Page 6: The Spleen and Associated Lymphoid Tissues

• Spleen: Filters blood, removing damaged red blood cells and pathogens.

• Associated Lymphoid Tissues:

  • SALT (skin-associated lymphoid tissue)

  • MALT (mucosa-associated lymphoid tissue)

  • GALT (gut-associated lymphoid tissue)

Page 7: Hematopoiesis and Blood Cell Development

• Hematopoiesis: Process of blood cell production from pluripotent stem cells in the bone marrow.

• Differentiation: Stem cells evolve into specific blood cells under hormonal influence.

Page 8: Granulocytes and Lymphocytes

• Granulocytes: Contain dark-staining granules, essential for immune responses.

• Red Blood Cells: Make up a significant portion of blood cells.

• Monocytes: Differentiate into macrophages and dendritic cells after migrating from the bloodstream.

Page 9: Cytokines and Cell Communication

• Cytokines: Small proteins that regulate immune responses, cell development, and inflammation.

• Several cell types produce cytokines, influencing interactions within the immune system.

Page 10: First Line of Defense

• Inborn Defenses: Physical and chemical barriers preventing entry of pathogens.

Page 11: Physical Barriers at Body's Surface

• Skin and Mucous Membranes: Key components that provide a formidable barrier against pathogens.

  • Skin Layers: Stratum corneum and sebaceous secretions minimize pathogen access.

  • Mucous Membranes: Moist and capable of trapping and expelling microbes via various mechanisms.

Page 12: Chemical Barriers and Microbiome

• Chemical Defenses:

  • Enzymes and Acids: Such as lysozyme in tears and stomach acidity.

  • Microbiome: Zones of commensal bacteria that inhibit pathogen growth.

Page 13: The Second Line of Defense

• Innate Immune Mechanisms:

  1. Phagocytosis

  2. Inflammation

  3. Fever

  4. Antimicrobial products

Page 14: Phagocytosis

• Phagocytes: Essential in recognizing and eliminating pathogens through various mechanisms.

• Main Types: Neutrophils, macrophages, and dendritic cells.

Page 15: Phagocytosis Mechanisms

1. Chemotaxis: Movement towards inflammatory signals.

2. Adhesion: Interaction between phagocytes and pathogens.

3. Engulfment: Formation of a phagosome around the invader.

4. Destruction: Integration of lysosomal components for ingestion.

5. Elimination: Release of debris post-digestion.

Page 16: The Inflammatory Response

• Inflammation: Reaction to injury characterized by redness, warmth, swelling, pain, and sometimes loss of function.

• Functions:

  1. Attract immune components

  2. Repair tissue damage

  3. Block pathogen entry

Page 17: Stages of Inflammation

• Process includes:

  1. Injury reactions

  2. Vascular changes (dilation and constriction)

  3. Edema and pus formation

  4. Resolution and scar formation.

Page 18: Diapedesis and Chemotaxis

• Diapedesis: White blood cells migrating from vessels into tissues, aided by endothelial cells.

• Chemotaxis: Cells migrating towards chemotactic signals from sites of injury.

Page 19: Fever as Part of Immune Response

• Fever: Elevated body temperature signaling infection and triggering systemic immune responses.

  • Pyrogens: Substances triggering fever by resetting the hypothalamic set point.

Page 20: Benefits and Treatment of Fever

• Fever benefits include inhibiting pathogen growth and stimulating immune processes.

• Treatment considerations: high fevers carry risks and require mitigation in vulnerable individuals.

Page 21: Interferons in Immune Response

• Interferons: Proteins that aid in antiviral defense and immune regulation. They alter gene expression in host cells to inhibit pathogen proliferation.

Page 22: The Complement System

• Complement: A cascade of over 30 blood proteins enhancing immune reactions, with functions including pathogen destruction.

  • Complement Cascade Stages: Initiation, activation, polymerization, and membrane attack.

Page 23: Antimicrobial Peptides

• Antimicrobial Peptides: Short proteins capable of disrupting microbial membranes. They play roles in innate immunity and are of interest for therapeutic applications.