ch4 bio310

Chapter 4: Immune System

Lesson Outcomes

  • Students should be able to describe and explain homeostatic imbalances of immunity:

    • a) Immunodeficiency

    • b) Autoimmune diseases

    • c) Hypersensitivities

Homeostatic Imbalances of Immunity

  1. Immunodeficiency

  2. Autoimmune Disease

  3. Hypersensitivities

1. Immunodeficiencies

  • Definition: A medical condition in which the body lacks normal ability to resist infection.

  • May arise from:

    • Congenital conditions

    • Acquired conditions impacting immune cell functionality or production of specific molecules (e.g., phagocytes or complement system).

  • Abnormal immune cell behavior.

  • Examples include:

    • Severe Combined Immunodeficiency (SCID)

    • Acquired Immunodeficiency Syndrome (AIDS)

Severe Combined Immunodeficiency Syndromes (SCID)

  • Genetic defects lead to a significant reduction of B and T cells.

  • Abnormalities in interleukin receptors.

  • Infants have little to no protection from diseases.

  • Treatment typically requires bone marrow transplant.

'Bubble Baby Disease'

  • SCID is also known as 'bubble baby disease.'

  • Results in a highly compromised immune system, nearly absent immune response.

  • Victims are highly susceptible to infections, famously represented by David Vetter who lived in a sterile environment.

2. AIDS (Acquired Immunodeficiency Syndrome)

  • Caused by the Human Immunodeficiency Virus (HIV).

  • Virus transmission methods:

    • Body secretions: blood, semen, vaginal secretions

    • From infected mothers to fetuses

    • Routes include blood transfusions, contaminated needles, and sexual intercourse.

  • First recognized in the U.S. in 1981.

Impact of HIV

  • HIV targets and destroys helper T cells.

  • Helper T cells are crucial for activating B cells (antibody secretion) and cytotoxic T cells (infected cell destruction).

  • Virus replicates in lymph nodes during asymptomatic phase (about 10 years without treatment).

  • Symptoms appear when lymph nodes can no longer contain the virus, leading to immune system failure.

Role of Helper T Cells

  • Activates B cells to produce antibodies.

  • Assists macrophages in destroying pathogens and activates cytotoxic T cells.

AIDS Symptoms

  • Characterized by:

    • Severe weight loss

    • Night sweats

    • Swollen lymph nodes

    • Increased frequency of opportunistic infections:

      • Pneumonia (Pneumocystis pneumonia)

      • Kaposi’s sarcoma (a cancer of blood vessels)

  • Symptoms may take 5-10 years to manifest after HIV infection.

Stages of AIDS

Phase I

  • Duration: Weeks to a few years post-infection.

  • Symptoms: Flu-like symptoms (chills, fever, fatigue, body aches).

  • Initial decline in T cell population followed by rebound as antibodies are produced.

  • Individuals become 'HIV-positive' but do not yet exhibit AIDS.

Phase II

  • Duration: 6 months to over 10 years.

  • The virus progressively destroys helper T cells.

  • Increased vulnerability to opportunistic infections and persistent flu-like symptoms may occur.

Phase III

  • Defined by helper T cell count <200/mm3 of blood along with opportunistic infections or HIV-associated cancer such as:

    • Pneumonia

    • Meningitis

    • Tuberculosis

    • Kaposi’s sarcoma

    • Non-Hodgkin’s lymphoma

3. Autoimmune Diseases

  • Arise from immune system's failure to recognize self-antigens, leading to autoimmune attacks on body tissues.

  • Distinction between self (friend) and foreign antigens is lost.

  • Can affect specific organs or multiple tissues.

Examples of Autoimmune Diseases

  • Rheumatoid Arthritis: Destroys joints.

  • Systemic Lupus Erythematosus (SLE): Affects multiple body systems including skin, joints, and blood vessels.

  • Multiple Sclerosis (MS): Destroys myelin in the brain and spinal cord.

  • Myasthenia Gravis: Impairs nerve-skeletal muscle communication.

  • Graves’ Disease: Overproduction of thyroid hormone leading to hyperthyroidism.

  • Juvenile (Type I) Diabetes Mellitus: Destroys pancreatic beta cells, leading to insulin deficiency.

Characteristics of Autoimmune Diseases

  • Multiple Sclerosis (MS):

    • Affects ages 20-50, more common in women.

    • Destroys myelin sheaths, resulting in central nervous system plaques and inflammation.

  • Myasthenia Gravis:

    • Fatigability affecting muscle coordination, particularly in eyelid movement and facial expressions.

  • Graves' Disease:

    • Overproduction of thyroid hormone with characteristic eye protrusion.

  • Juvenile Diabetes:

    • Insulin deficiency results in increased blood glucose and symptoms like frequent urination and hunger.

  • Systemic Lupus Erythematosus (SLE):

  1. Occurs 9 times more in women.

  2. Characterized by the classic butterfly rash and systemic symptoms.

Glomerulonephritis

  • Severe kidney function impairment with inflammation of glomeruli.

  • Symptoms: Hematuria, proteinuria, edema, and hypertension.

Rheumatoid Arthritis

  • Autoimmune attack on synovial membranes, causing pain and stiffness in joints.

Triggers of Autoimmune Diseases

  • May include:

    • Foreign antigens resembling self-antigens

    • Previous infections (e.g., rheumatic fever damages heart)

    • Gene mutations and trauma-related changes in self-antigens.

4. Hypersensitivities

  • Definition: Abnormal immune responses to harmless antigens, causing discomfort rather than death.

  • Different types based on:

    • Time course

    • Involvement of antibodies or T cells.

Immediate Hypersensitivity

  • Caused by B lymphocyte (antibody) response to allergens within seconds/minutes.

  • Symptoms appear quickly upon contact and may last about half an hour.

  • Treatments include antihistamines, epinephrine, or allergy shots.

Delayed Hypersensitivity

  • Results from T cell responses appearing 24-72 hours post-exposure.

  • Involves inflammation from macrophages or cytotoxic T cells.

Conclusion

  • Understanding the immune system's complexities, including immunodeficiency, autoimmunity, and hypersensitivity reactions, is crucial for diagnosing and treating various immune disorders.

Hypersensitivity reactions are abnormal immune responses to harmless antigens, leading to discomfort. Immediate hypersensitivity involves B lymphocytes (antibody response) and occurs within seconds/minutes, while delayed hypersensitivity results from T cell responses, appearing 24-72 hours post-exposure.