first half detailed

Host Defenses Overview

  • Combination of Innate and Adaptive Immunity

    • Innate immunity: Non-specific protection

    • Adaptive immunity: Specific protection designed for particular pathogens

  • Three Lines of Host Defense:

    1. First Line: Physical and chemical barriers (skin, mucous, etc.)

    2. Second Line: Innate immune responses (phagocytosis, inflammation)

    3. Third Line: Adaptive immune responses (B and T cells)

First Line of Defense

  • Physical Barriers: Skin (sloughing off), mucous membranes

  • Chemical Barriers:

    • Tears and Saliva: Contain lysozyme which breaks down cell walls of bacteria

    • pH Levels: Acidic environments inhibit microbial growth

  • Normal Microbiota: Compete with pathogens, preventing growth through crowding and resource depletion

Immunological Functions of the Immune System

  • Surveillance: Continuously monitors the body for pathogens

  • Recognition: Differentiates between self and non-self (foreign material)

  • Destruction: Targets and eliminates harmful invaders

Second Line of Defense

  • Innate Immunity: Immediate response upon pathogen invasion

  • Key Components:

    • Phagocytosis:

    • Phagocytes engulf and destroy pathogens

    • Steps:

      • Chemotaxis: Movement towards infection site

      • Ingestion

      • Formation of phagolysosome

      • Destruction of pathogen

      • Excretion of waste

    • Inflammation:

    • Goals: Mobilize immune components, repair tissue, destroy pathogens

    • Stages:

      • Injury response: Vasodilation increases blood flow

      • Edema: Fluid accumulation leads to swelling

      • Pus formation: Accumulation of white blood cells and dead cells

    • Fever: Elevated body temperature inhibits microbial growth and stimulates immune cell activities

  • Antimicrobial Products: Mechanisms like interferons and the complement system assist in attacking pathogens

Lymphatic System

  • Structure:

    • Network of vessels and organs (lymph nodes, spleen, thymus)

  • Function:

    • Returns extracellular fluid to blood

    • Filters pathogens from lymphatic fluid

    • Provides sites for immune cell action

Hematopoiesis (Blood Cell Formation)

  • Origin: All blood cells arise from hematopoietic stem cells in bone marrow

  • Types of Cells:

    • Leukocytes: White blood cells, including Lymphocytes (B and T Cells), Neutrophils, and Macrophages

    • Non-leukocytes: Red blood cells and platelets

Adaptive Immunity (Third Line of Defense)

  • Key Players:

    • B Cells: Produce antibodies upon activation

    • T Cells:

      • Helper T Cells: Regulate immune response and assist B cells

      • Cytotoxic T Cells: Destroy infected or cancerous cells

    • Memory Cells: Provide long-lasting immunity

  • Stages of Activation:

    • Exposure to the antigen

    • Presentation by antigen-presenting cells (APCs)

    • Clonal selection and expansion of specific lymphocytes

Cytokines

  • Definition: Small molecules that regulate various aspects of immunity and inflammation

  • Types:

    • Pro-inflammatory: E.g., Interleukin-1 (IL-1), Tumor Necrosis Factor (TNF)

    • Anti-inflammatory: E.g., Interleukin-10 (IL-10)

  • Functions: Stimulate, suppress, and control immune responses

Immunization and Vaccination

  • Types:

    • Active Immunity: Develops through exposure to antigens

    • Passive Immunity: Direct transfer of antibodies (e.g., breast milk)

    • Vaccinations: Expose immune system to antigens without causing disease

Vaccine Types

  • Whole Organism Vaccines: Killed (e.g., Hepatitis A) or Live Attenuated (e.g., MMR)

  • Subunit Vaccines: Use specific epitopes (e.g., Novavax)

  • DNA Vaccines: Insert DNA encoding antigen proteins into host cells