Immune Diseases: Allergies, Autoimmune Diseases, and HIV

Although immunity is a powerful defense system, excessive reactions, malfunctions, and reduced function can cause disease. We will learn about representative immune diseases.

Basic Knowledge

Allergy: A phenomenon in which the immune system overreacts to normally harmless substances(pollen・food・mites・medicines).
・Type I(immediate type): The main roles are IgE antibodies and histamine release from mast cells. Hay fever・food allergies・anaphylactic shock.
・Type IV(delayed type): T cells are involved. Tuberculin reaction・contact dermatitis.
Autoimmune diseases: Diseases in which the immune system mistakenly recognizes components of its own body as foreign and attacks them.
・Rheumatoid arthritis(attacks joints)
・Type I diabetes(attacks pancreatic β cells→unable to produce insulin)
・Systemic lupus erythematosus(SLE)(attacks connective tissue throughout the body)
・Hashimoto's disease(chronic thyroiditis)(attacks the thyroid gland)
Immunodeficiency: A disease in which immunity is reduced. A representative example is AIDS(acquired immunodeficiency syndrome), which occurs when the HIV virus infects and destroys helper T cells. Because the command center is lost, adaptive immunity as a whole stops functioning, and pathogens that normally do not trouble healthy people cause severe disease(opportunistic infections).

Further Study

The mechanism of Type I allergy is precise. During the first invasion, IgE antibodies are produced, and IgE binds to the surface of mast cells, creating a state of sensitization. When the same allergen enters a second time and is captured by IgE on the mast-cell surface, chemical mediators such as histamine are released all at once, causing vasodilation, mucus secretion, and bronchoconstriction. In severe anaphylactic shock, blood pressure can drop suddenly and airway obstruction can occur, so first aid with an EpiPen(epinephrine auto-injector) is necessary.
Autoimmune diseases occur when immune tolerance(the mechanism that prevents reactions to the body's own components) breaks down. Genetic, infectious, and environmental factors interact in complex ways. In Type I diabetes, the pancreatic β cells that produce insulin are destroyed, so lifelong insulin injections are necessary(it differs from Type II diabetes, a lifestyle-related disease).
HIV infects by binding to the CD4 molecule on helper T cells. When the command center is lost, both humoral and cell-mediated immunity collapse, and people may die from diseases such as Pneumocystis pneumonia and Kaposi's sarcoma that healthy people do not normally develop. Today, anti-HIV drugs can suppress viral growth and prevent AIDS from developing even after infection, but a cure has not yet been found.

Points to Note

① Distinguish the three categories: allergy(excessive response), autoimmune disease(mistaken attack), and immunodeficiency(reduced function). ② HIV is the name of the virus, while AIDS is the syndrome that develops from HIV infection. Infection≠disease onset. ③ Do not confuse Type I diabetes(autoimmune・often begins at a young age) with Type II diabetes(lifestyle-related・often begins in adulthood). ④ Antihistamines are effective for Type I allergy symptoms(such as hay fever), while steroid drugs are generally effective against inflammation.

Practice

1. Name the antibody and cell that play the main roles in hay fever.
2. What cells does HIV infect and destroy?
3. What is the general name for diseases such as rheumatoid arthritis and Type I diabetes, which occur when the immune system attacks the body itself?