Immune System Quiz

Introduction

• Thucydides recognised people who got sick from a disease once weren't reinfected.
• The immune system protects against microscopic pathogens (bacteria, fungi, viruses).
• Distinct evolutionary impacts of cancer and pathogens.
• Cancer, often after the reproductive period, has little evolutionary impact.
• Pathogens influence natural selection by favouring resistant individuals.
• The immune system assists in tissue repair and regeneration.

Defence Lines Immune System

• First line: Skin, tears, eyelashes, acid secretions prevent pathogen entry.
• Most pathogens don't enter but some use bodily openings as entry points.
• Second line: White blood cells target pathogens entering the body.
• Inflammation focuses on the infection site. Diverse white blood cells (leukocytes) have specific roles: Natural Killer (NK) cells kill infected cells; phagocytic cells engulf and destroy pathogens; granulocytes release toxins to kill large pathogens.

Immune Defence Processes

• First line intact: Skin/mucous membranes prevent pathogen entry. Macrophages and dendritic cells monitor tissues.
• Barrier breakdown: Injury or infection lets pathogens in. Macrophages activate inflammation.
• Arrival of white blood cells: Blood vessels widen to allow cell passage. Macrophages and dendritic cells engulf pathogens.
• Third line activation: Dendritic cells alert lymphocytes, stimulating antibody production and killer cell activation. B cells produce antibodies. T cells destroy infected cells.
• Immune Memory: Trained lymphocytes rapidly respond to repeated pathogen attack.

Great Figures in Immunology

• Edward Jenner (1749-1823): Discovered that cowpox infection provided protection against smallpox. Developed the first vaccine.
• Louis Pasteur (1822-1895): Microorganisms cause diseases. Developed rabies, anthrax, and cholera vaccines.
• Emil von Behring: Demonstrated effective use of antibodies for disease treatments via passive vaccination.

Active vs Passive Vaccination

• Active: Introduces a weakened pathogen to stimulate an immune response, creating long-term immunity
• Passive: Administer pre-made antibodies for immediate, short-term protection; does not stimulate long-term immunity

Targets of the Immune System

• Intracellular infections hide within cells, requiring strong cell-mediated responses (e.g., T cells). Extracellular pathogens are easier to target.

Cells of the Immune System

• Phagocytes (e.g., macrophages, neutrophils) engulf and destroy pathogens.
• Neutrophils: Granulocyte, rapid response (4-6 hours), flexible, penetrate infected tissues.
• Dendritic cells: Capture pathogens and present antigens to activate adaptive immunity
• Granulocytes: Perform exocytosis (release toxins) to fight pathogens, dangerous to the cell due to released toxins.

Types of Immune System Cells

• Eosinophils: Fight multicellular parasites, involved in allergic responses.
• Basophils: Inflammation mediators; participate in allergic reactions.
• Mast cells: Release chemical mediators (e.g., histamine) during immune reactions.
• Lymphocytes: crucial for adaptive immunity.
  • T cells (kill infected cells, helper cells)
  • B cells (produce antibodies)
  • Natural killer (NK) cells kill infected cells without needing further instructions.

Summary of Cells

• Leukocytes (white blood cells) originate from hematopoietic stem cells.
• Phagocytes (macrophages, dendritic cells, neutrophils), monocytes, granulocytes (eosinophils, basophils, mast cells), and lymphocytes (T cells, B cells, and NK cells)

Immune System Divisions

• Innate: Includes natural killer cells and phagocytes; provides immediate, non-specific defense.
• Adaptive (Acquired): Includes B and T cells; provides targeted, specific, and long-lasting immunity against diseases.
• Barrier: Skin, soluble proteins (e.g., complement).
• Mediators: Substances like IL-1 and TNF-alpha.

Primary vs Secondary Immune Responses

• Primary: First exposure to an antigen; slower response, lower antibody concentration.
• Secondary: Subsequent exposure to the same antigen; faster, stronger response, higher antibody concentration due to immune memory.

Cytokine Concentration

• Cytokine levels increase with exposure, signalling immune activity.
• Innate response generates non-specific defense via cytokines.
• Adaptive response produces faster, stronger immunity upon re-exposure

Adaptive Immunity

• Initial immune response (7-14 days): Antibodies and T cells target infection, leading to short-term protection
• Protective immunity (14-35 days): Antibodies and effector cells prevent reinfection; immune system doesn't return to a steady state.
• Immunological memory (months/years): Rapid, intense response for repeated infection, minimal symptoms, and often asymptomatic infections.