Immune System Notes

Overview of the Immune System

  • The immune system guards against diseases through various types of responses.

Viral Infections

  • Common Cold:
    • Caused by rhinoviruses (over 100 identified).
    • Symptoms result from infection of mucus membranes in the respiratory tract.

Viruses vs. Bacteria

  • Viruses:

    • Non-living particles containing genetic material.
    • Hijack host cells for reproduction.
    • Cannot be treated with antibiotics.
    • Examples: Rhinovirus, Influenza virus.

  • Bacteria:

    • Living organisms with metabolism and DNA.
    • Can reproduce independently.
    • Sensitive to antibiotics which target bacterial processes (e.g., cell wall production).
    • Examples: E. coli, Streptococcus.

Body Defenses

  • External Barriers:
    • Intact skin, mucus membranes.
  • Innate Immune Response:
    • Phagocytic cells, natural killer cells, inflammation, fever.
  • Adaptive Immune Response:
    • Cell-mediated (T cells), humoral (B cells).

First Line of Defense

  • Non-specific defenses include:

    • Intact Skin:

    • Sloughing of dead skin cells inhibits colonization by bacteria.

    • Sweat and oils contain antimicrobial substances.

    • Mucus and Cilia:

    • Mucus traps pathogens and contains lysozymes that break down bacterial walls.

    • Cilia help move mucus and trapped invaders out of the lungs.

    • Phagocytes:

    • Include macrophages and neutrophils.

    • Seek and destroy pathogens; respond to inflammation.

Inflammatory Response

  • Role of Inflammation:

    • Initiated by mast cells releasing histamine.
    • Causes swelling and increased blood flow to the site of injury.
    • May lead to a rise in local temperature to inhibit pathogen growth.

  • Role of Fever:

    • Elevates body temperature to combat infection.
    • Enhances the activity of interferons and immune cells.
    • Some doctors recommend allowing low-grade fevers to persist.

Specific Immune Defenses

  • Memory Formation:

    • Immune system retains a memory of specific pathogens for faster responses upon re-exposure.

  • Key Players in Immune Response:

    • Macrophages, T cells (helper, cytotoxic, memory), B cells (plasma, memory) and antibodies.

Understanding Antibodies

  • Proteins that target and tag invasive microbes for destruction.
  • Generated via B cells; facilitate recognition of antigens (foreign substances).
  • Free antibodies tag pathogens, signaling them for destruction.

T Cells and B Cells in Immune Response

  • Helper T Cells:

    • Recognize antigens, stimulate other immune cells (B cells).
    • Critical in signaling the immune response; inhibited by HIV in AIDS.

  • B Cells:

    • Produce antibodies; differentiate into plasma and memory cells upon activation.
    • Plasma cells secrete antibodies; memory cells remember pathogens for future encounters.

Immune Response Expansion

  • Clonal Selection:
    • An antigen binds to a specific B cell, triggering its rapid division.
  • This results in a clonal expansion with identical cells that can effectively combat the specific pathogen.

Antibody Functions

  • Antibodies bind to antigens, neutralizing invaders and tagging them for elimination by white blood cells.

Roles of 'Killer' T Cells

  • Cytotoxic T cells directly attack and destroy infected or cancerous cells.

Immune System Regulation

  • Helper T cells can halt the immune response once the invader is cleared.
  • Formation of memory T cells prepares the immune system for potential future infections.

Assistance from Medical Science

  • Antibiotics:

    • Target and eliminate bacteria but not viruses.
    • Mechanisms include slowing replication or interfering with cell wall formation.

  • Vaccines:

    • Contain killed or weakened pathogens that stimulate an immune response without causing illness.
    • Create long-lasting memory within the immune system against certain diseases.

Addressing Common Myths

  • Vaccine Misconceptions:
    • Vaccines do not cause the flu or lead to serious illnesses like autism.
  • The flu vaccine is effective; it does not weaken the immune system.

Understanding Immune Challenges

  • Cold Myths:

    • Colds and influenza are distinct; not caused by being cold.

  • Cold vs. Flu Symptoms:

    • Colds typically present mild symptoms, while flu symptoms are more severe (fever, body aches, fatigue).

Recognition of Other Viruses and Conditions

  • The term “stomach flu” is misleading; it refers to viruses affecting the digestive system.

  • Allergies:

    • Reactions to harmless allergens like pollen; involve histamine release causing symptoms.

  • Autoimmune Disorders:

    • Occur when the immune system mistakenly attacks 'self' proteins, leading to conditions like multiple sclerosis.

  • Cancer and AIDS:

    • Cytotoxic T cells play a role in destroying cancer cells, but rapid cell division can surpass T cell responsiveness.
    • AIDS is caused by HIV which targets T-helper cells, making it a severe immune deficiency.

  • Preventive Measures for HIV:

    • Avoid exposure to infected bodily fluids as the virus is fragile in the environment.

  • Severe Immune Deficiency (SCID):

    • A genetic disorder affecting the immune system; experimental gene therapy shows promise in treatment.