In-Depth Notes on The Vertebrate Immune System

Lecture Context

  • The lecture discusses the vertebrate immune system, focusing on innate and adaptive immunity in response to flu virus infection.

Homeostasis and Thermoregulation

  • Homeostatic mechanisms regulate internal environments to counteract large external fluctuations.
  • Endotherms (e.g., mammals, birds) and ectotherms (e.g., reptiles) exhibit varied adaptations for temperature regulation.
  • Osmoregulation is vital for animal cells, confirming to osmotic environments:
    • Hyperosmotic: Higher solute concentration outside leads to cell shriveling.
    • Hypoosmotic: Lower solute concentration outside can cause cells to burst.
    • Isoosmotic: Balanced conditions with no net water movement.

Innate Immunity

  • Barrier Defenses: Protect against pathogens

    • Skin: Thickened outer surface deters entry.
    • Mucous Membranes: Secrete mucus to trap pathogens.
    • Secretions: Such as saliva and tears, wash away pathogens.

  • Internal Defenses:

    • Phagocytic Cells: Fetch and destroy pathogens by recognizing unique molecules.
    • Natural Killer Cells: Identify and induce apoptosis in infected/cancerous cells.
    • Antimicrobial Proteins:
    • Interferons: Secreted by infected cells, inhibit viral reproduction.
    • Complement Proteins: Assist in pathogen destruction and inflammation.

  • Inflammatory Response: Triggered by injured or infected tissues, producing histamines (increase blood flow) and cytokines (recruit immune cells).

    • Results in localized inflammation, aiding pathogen response.

Adaptive Immunity

  • Specific to vertebrates, involving tailored responses to unique pathogens.

  • Humoral Response:

    • B cells and antibodies respond to pathogens in body fluids.

  • Cell-Mediated Response:

    • T-cells and cytotoxic cells focus on intracellular pathogens.

  • B Cells and T Cells:

    • Lymphocytes produced in bone marrow:
    • B cells mature in bone marrow, relevant for humoral immune response.
    • T cells mature in thymus, critical for cell-mediated immunity.
    • Each produces receptors specific to binding particular antigens.

  • Memory Cells:

    • Long-lived cells formed post-infection or vaccination, enabling rapid response upon subsequent antigen exposure.

Antigen Recognition

  • Antigens possess epitopes: distinct sites recognized by immune receptors.
  • The immune system's ability to target numerous epitopes improves effectiveness against pathogen mutations.

Response Mechanism Details

  • Plasma Cells: Effector B cells secreting antibodies that neutralize pathogens and mark them for destruction.
  • Antibodies promote opsonization, aiding phagocytic activity, and activate complement pathways leading to pathogen lysis.
  • Cytotoxic T Cells: Bind and destroy infected cells via perforin and granzymes causing apoptosis.

Summary of Key Points

  • Innate Immunity:
    • Rapid, generalized response using skin, mucous membranes, phagocytic cells, NK cells, and antimicrobial proteins.
  • Adaptive Immunity:
    • Slower, specific response characterized by memory formation, antibody production, and T-cell responses.
Homework & Review Questions
  1. Why is it critical that phagocytic cells recognize essential components of pathogens?
  2. Describe the incorrect statement about complement proteins in immunity.
  3. Identify the T cell type that lyses infected cells.
  4. What is the primary function of antibodies in the immune system?
  5. Explain the role of memory cells in secondary immune responses.