Innate Immune Response Lecture Notes

Chapter 14: Innate Immune Response

History

  • Metchnikoff

    • Discovered phagocytes.

    • Awarded the Nobel Prize for contributions to the understanding of immunity.

Overview of Immune System

  • Innate Immunity:

    • Provides routine protection against pathogens.

  • Adaptive Immunity:

    • Develops throughout life in response to antigens.

14.2. First-Line Defenses: Physical Barriers

  • Physical Barriers:

    • The body's borders that protect against pathogen entry.

Skin

  • Dermis:

    • Comprised of tightly woven fibrous connective tissue.

  • Epidermis:

    • Many layers of epithelial cells consisting of:

    • Stratified Epithelium

    • Columnar Epithelium

Mucous Membranes

  • Present in the following tracts:

    • Digestive Tract

    • Respiratory Tract

    • Genitourinary Tract

  • Constantly bathed in secretions (e.g., mucous).

    • Specific examples:

    • Eye

    • Respiratory tract

    • Digestive tract

    • Urogenital tract

    • Anus

    • Skin

    • Mouth

Antimicrobial Substances

  • Role: Protect skin and mucous membranes from pathogens.

  • Examples include:

    • Salt: Creates an inhospitable environment for pathogens.

    • Lysozyme:

    • Enzyme that degrades peptidoglycan in bacterial cell walls.

    • Peroxidase:

    • Breaks down hydrogen peroxide, producing reactive oxygen species that can kill pathogens.

    • Lactoferrin:

    • Binds iron, limiting availability to bacteria.

    • Defensins:

    • Form pores in the membranes of microbes, leading to cell death.

Normal Microbiota (Flora)

  • Definition: Beneficial microorganisms that reside on the body.

  • Examples include:

    • Escherichia coli

    • Lactobacillus

    • Candida albicans

    • Clostridium

14.3. Cells of Immune System

  • Hematopoiesis:

    • The process of formation for immune cells in the body.

Types of Stem Cells

  • Hematopoietic Stem Cell (Originates in Bone Marrow)

    • Common Lymphoid Progenitor leads to:

    • T lymphocytes (T cells)

    • B lymphocytes (B cells)

    • Common Myeloid Progenitor leads to:

    • Myeloblasts: Develop into granulocytes (e.g., Neutrophils, Eosinophils, Basophils).

    • Monoblast: Precursor of monocytes and macrophages.

    • Other cell types:

      • Mast Cells

      • Erythrocytes (Red Blood Cells)

      • Thrombocytes (Platelets): Involved in clotting.

Functions of Blood Cells

  • Red Blood Cells (RBCs):

    • Function in carrying oxygen throughout the body.

  • Platelets:

    • Play a crucial role in blood clotting mechanisms.

  • White Blood Cells (WBCs):

    • Responsible for immune defense against pathogens.

14.4. Cell Communication

  • Definition: Coordination of cell responses through various signaling mechanisms.

  • Methods of Communication:

    • Surface Receptors:

    • Act as the “eyes” and “ears” of the cell, detecting extracellular signals and facilitating responses.

    • Adhesion Molecules:

    • Allow cells to adhere to each other, facilitating necessary interactions in immune responses.

    • Cytokines:

    • Act as the “voices” of cells, mediating and regulating immunity and inflammation.

Types of Cytokines

  • Chemokines:

    • Induce chemotaxis, guiding cells to sites of infection or inflammation.

  • Colony-stimulating Factors (CSFs):

    • Stimulate the multiplication and differentiation of various immune cells.

  • Interferons (IFNs):

    • Exhibit antiviral properties.

  • Interleukins (ILs):

    • Play critical roles in regulating immune responses.

  • Tumor Necrosis Factor (TNF):

    • Involved in mediating inflammation and triggering apoptosis (programmed cell death).

14.6. Complement System

  • Definition: A group of proteins that assists the activities of the adaptive immune system.

  • Components:

    • Proteins are present in the blood and bathing tissues.

    • Components are classified and named as C1 through C9, representing different parts of the complement cascade, which enhances the ability to clear pathogens from an organism.

14.9. Fever

  • Definition: A physiological response that serves as an important host defense mechanism.

  • Significance:

    • Fever is a strong indicator of infectious disease, particularly bacterial infections.

  • Temperature Regulation Center (located in the brain):

    • Normal Temperature: Approximately 37°C (98.6°F).

    • During Infection: The body raises temperature in response to pyrogens, which are substances that induce fever and can be produced by pathogens or immune cells.