(1) Chapter 19: Disorders of Immune System

What disorders are associated with the immune system?

Infection (failure to eliminate pathogens), cancer (failure of immunological surveillance by NK cells), aging (immune system becomes less effective), immunosuppressive drugs, autoimmune diseases, blood transfusion/transplant rejection, and hypersensitivity (allergy).

Why are the elderly and very young more susceptible to infections and cancer?

The elderly have declining immune function with age, while the very young have immature immune systems.

What is an autoimmune disease?

A loss of self-tolerance where the immune system can no longer distinguish self from non-self, causing immune attacks against the body's own tissues. Women are more commonly affected due to genetic/gender predisposition.

What is the hygiene hypothesis?

Reduced childhood exposure to microbes and parasites decreases immune tolerance to harmless antigens, increasing allergies and asthma. This is more common in urban and developed areas.

What is dysbiosis and why is it important?

Dysbiosis is an imbalance of normal microbiota, often caused by prolonged antibiotics. It reduces anti-inflammatory butyrates, allows Clostridium difficile overgrowth, and contributes to inflammatory bowel disease.

How is Clostridium difficile treated according to the lecture?

Fecal microbiota transplant ("poop pills") restores healthy gut microbiota by replacing bacteria lost after prolonged antibiotic use.

Compare ulcerative colitis and Crohn's disease.

Ulcerative colitis causes chronic inflammation and ulcers in the colon and rectum. Crohn's disease causes chronic inflammation throughout the GI tract, involves excessive TNF-α and IL-12, and may improve with whipworm eggs that suppress helper T-cell pathways.

What is hypersensitivity?

An exaggerated immune response against an antigen that is normally harmless.

What are the four types of hypersensitivity?

Type I: Anaphylactic (IgE); Type II: Cytotoxic (IgG/IgM); Type III: Immune Complex; Type IV: Delayed Cell-Mediated (T cells).

Summarize Type I hypersensitivity.

Type I is an IgE-mediated reaction occurring within minutes (<30 min). IgE binds mast cells and basophils, causing degranulation and release of histamine, leukotrienes, and prostaglandins that attract neutrophils and eosinophils.

Localized vs. systemic anaphylaxis.

Localized affects one area (hay fever, asthma, hives). Systemic affects the entire body, causing widespread vasodilation, edema, hypotension, circulatory collapse, and possible death (anaphylactic shock).

Know the medications for Type I hypersensitivity.

Albuterol = bronchodilator; Xolair (omalizumab) = IgE blocker; Singulair (montelukast) = leukotriene blocker; Epinephrine = emergency treatment for anaphylactic shock by causing vasoconstriction.

What is desensitization therapy?

Gradually increasing doses of an allergen stimulate IgG production instead of IgE. Most effective for inhaled allergens and insect venom.

Summarize Type II hypersensitivity.

IgG or IgM bind cell antigens, activate complement and macrophages to lyse cells, and cause damage in about 5–12 hours. Examples: transfusion reactions and Rh incompatibility.

Know the ABO blood groups.

Type A: A antigen/anti-B antibodies; Type B: B antigen/anti-A antibodies; Type AB: A and B antigens/no antibodies (universal recipient); Type O: no A or B antigens/anti-A and anti-B antibodies (universal donor).

What causes hemolytic disease of the newborn?

An Rh− mother carrying an Rh+ fetus becomes sensitized after the first pregnancy. During a later Rh+ pregnancy, maternal anti-Rh antibodies cross the placenta and destroy fetal red blood cells.

How does RhoGAM prevent hemolytic disease of the newborn?

Given at about 28 weeks of pregnancy or shortly after delivery, RhoGAM contains anti-Rh antibodies that destroy fetal Rh+ cells before the mother develops her own antibodies.

Summarize Type III hypersensitivity.

Antigen-antibody immune complexes deposit in tissues, activate complement, attract neutrophils, and cause inflammation within 2–8 hours. Examples include serum sickness, Arthus reaction, and glomerulonephritis.

Summarize Type IV hypersensitivity.

A delayed (24–48 hour) T-cell-mediated reaction. First exposure causes sensitization and memory T cells; re-exposure causes tissue damage. Examples: poison ivy, contact dermatitis, latex allergy, tuberculosis skin test, and transplant rejection.

What is Graves disease?

Autoantibodies stimulate TSH receptors on the thyroid, causing hyperthyroidism, goiter, bulging eyes, increased heart rate, sweating, and heat intolerance.

What is myasthenia gravis?

Autoantibodies block acetylcholine receptors at the neuromuscular junction, preventing muscle stimulation and causing progressive muscle weakness that may lead to respiratory failure.

What is systemic lupus erythematosus (SLE)?

Autoantibodies attack cellular components (including DNA), causing immune complex deposition, kidney damage, and the characteristic butterfly rash.

What is rheumatoid arthritis?

Immune complexes deposit in joints, activate complement, and cause chronic inflammation that destroys cartilage and bone, beginning with the small joints of the hands and feet.