Chpt 19 Disorders Associated with the Immune System

Disorders Associated with the Immune System
Chapter 19

Hypersenstivity: sensitivity beyond what is considred normal. It occurs in people who have been previously sensitized by exposure to an antigen (allergen). Once sensitized, another exposure to the antigen triggers an immune response that damages host tissue. Based on mechanism and time, there are 4 types of hypersensitivity reactions:

I Type I (Anaphylaxis) Reactions
A. Mechanisms:
1. Involve IgE and the release of mediators such as histamine by mast cells and basophils (granulated cells)
2. involve allergens, sensitization and triggering
B. Time course: rapid, usually within 30 minutes
C. Clinical manifestations
1. Systemic anaphylaxis: System wide dramatic response to an allergen. Treated with epinephrine.
a. causes:
i. hormones: insulin, vasopressin
ii. antibiotics: penicillin, amphotericin B
iii. other: diazepam (valium), barbiturates
2. Localized anaphylaxis (atopic diseases): usually associated with antigens that are ingested or inhaled. Antihistamines to treat.
a. causes
i. peanuts
ii. tree nuts
iii. shellfish
iv. dairy
v. egg whites
vi. wasp or bee stings
vii. inhalants such as: pollen, fungal spores, animal dander, house dust mites
b. Allergic rhinitis symptoms
i. itchy, teary eyes
ii. congested nasal passages
iii. sneezing
3. Asthma
a. causes
i. allergens, irritants, exertion, stress
ii. triggers airway narrowing and mucus production
b. incidence
i. number of cases and deaths has increased significantly
c. symptoms
i. cough, wheezing, difficulty breathing
ii. reversible airway obstruction
d. treatment
i. smooth muscle relaxants
ii. corticosteroids
4. Hives (Urticaria)
a. cause: usually food or drugs
b. symptoms: swollen plaques on the skin
5. Food allergies
a. most common causes: wheat, eggs, milk, fish, peanuts, strawberries, tomatoes, crustaceans, nuts
b. symptoms: hives, itching, swollen lips, nausea, vomiting
c. treatment: antihistamines, avoiding contact of sensitizing agents
D. Prevention
1. desensitization: consists of a series of injections with a small dose of the antigen.
II Type 2 (Cytotoxic) Reactions
A. Mechanisms
1. involve antibodies (IgG, IgM) and causing cell damage
B. Time course: variable, usually 5 – 12 hours
1. ex: transfusion reactions
a. ABO
b. Rh
c. Target is donor RBCs
d. Hemolytic disease of the newborn (Rh disease)
i. Rh – mother
ii. Rh+ fetus, or ABO incompatible
III Type 3 (Immune Complex) Reactions
A. Mechanisms
1. involve antibodies (IgG or IgM) forming immune complexes and triggering local tissue damage
2. antigen: exogenous or endogenous
B. Time Course: variable, usually 3 – 8 hours
IV Type 4 (Delayed) Reactions (Delayed Cell-Mediated Reactions/Hypersensitivity)
A. Mechanisms
1. involve T cells and macrophages triggering inflammation
B. Time Course: slow, usually 24 – 48 hours
C. Clinical manifestations
1. Contact dermatitis
a. localized to the skin
b. maximum response 24 – 48 hours after exposure
c. symptoms: erythema, induration, sometimes blistering
d. triggered by certain materials: metals, clothing, rubber, leather, cosmetics, plants (poison ivy)
e. TB test: intentionally trigger a type 4 reaction for diagnosis

**** Only hypersensitivity is being covered in this chapter, not autoimmunity. That is why I did not outline the rest of the chapter.