questions 10

Hypersensitivity

Topic updated on 05/20/17 2:32pm

Snapshot
  • A 12-year-old boy presents to the emergency department with dyspnea and urticaria. His symptoms began approximately 30 minutes after being stung by bee. Medical history is significant for asthma and an allergy to shellfish. On physical exam, breathing is labored, and wheezes are appreciated on pulmonary auscultation. Airway, breathing, and circulation is intact. The boy is immediately started on intramuscular epinephrine. (Anaphylaxis)
Introduction
  • Hypersensitivity reactions (HSR) can be considered as an overreactive immune response
  • HSR can be classified into four categories
    • type I, II, III, and IV
      • type I, II, and III are antibody mediated
      • type IV is cell mediated
  • Speed of reaction
    • type I HSR is immediate (fastest)
    • type IV HSR is delayed (slowest)
Type I HSR (Anaphylactic and Atopic)
  • Mechanism of action
    • initial exposure to an allergen causes
      • Th2 cells to stimulate (via IL-4 and -13) B-cells to produce
        • IgE antibodies which attaches to
          • mast cells and basophils (these are said to be sensitized)
    • second exposure to the allergen causes
      • IgE cross-linking on mast cells and basophil which results in
        • the immediate release of vasoactive amines (e.g., histamine and heparin) that can cause
          • vascular leakage
          • bronchoconstriction
          • intestinal hypermotility
          • inflammation
    • since the antibodies are pre-formed, the reaction is immediate
      • a few hours after the immediate response ensues, a late-phase reaction occurs
        • which is mediated by downstream products of the arachidonic acid cascade such as
          • prostaglandins
          • leukotrienes
  • Clinical disorders
    • refer to chart
  • Diagnostic testing
    • allergen-specific IgE can be assessed with
      • skin testing for allergic disease
Type II HSR (Cytotoxic)
  • Mechanism of action
    • antibodies are directed against tissue specific antigens which can result in
      • opsonization
      • complement activation
      • neutrophil and macrophage recruitment
      • NK cell killing
      • impair cell function if targetting a cellular receptor
  • Clinical disorders
    • refer to chart
  • Diagnostic testing
    • direct Coombs test
      • assesses antibodies that are attached directly to the erythrocyte surface
    • indirect Coombs test
      • assesses antibodies that are unbound in the serum
Type III HSR (Immune-Complex)
  • Mechanism of action
    • antibodies bind to self or foreign antigen forming immune complexes
      • immune complexes activate the complement cascade and results in
        • systemic manifestations
  • Clinical disorders
    • refer to chart
Type IV HSR (Cell-Mediated)
  • Mechanism of action
    • T-cell-mediated tissue injury resulting from
      • CD8+ T-cells directly killing a target cell
      • pre-sensitized CD4+ helper T-cells are exposed to the insult, which results in
        • cytokine release (delayed-type HSR), which leads to
          • macrophage activation and
            • inflammation
  • Clinical disorders
    • refer to chart
Summary
 
Hypersensitivity Reactions
Hypersensitivity Reaction Type
Pathophysiology
Clinical Examples
Type I (anaphylactic and atopic)
  • Immediate
  • Antigens cross-link IgE antibodies triggering
    • vasoactive amine release (e.g., histamine) 
  • Anaphylaxis
    • allergens
      • bee sting
      • food (e.g., peanuts)
      • drugs
  • Asthma
    • allergens
      • inhaled materials
  • Allergic rhinitis
    • allergens
      • animals
      • trees
Type II (cytotoxic)
  • Antibodies are directed against cell-surface antigens resulting in
    • opsonization
    • complement activation
    • neutrophil and macrophage recruiting
    • NK cell killing
    • impairment of cellular function
  • Autoimmune hemolytic anemia
    • antigen
      • erythrocyte membrane proteins
  • Acute rheumatic fever
    • antigen
      • myocardial antigens via cross-reacting with S. pyogenes M protein
  • Goodpasture syndrome
    • antigen
      • type IV collagen
  • Immune thrombocytopenic purpura
    • antigen
      • platelet membrane proteins
  • Myasthenia gravis
    • antigen
      • acetylcholine receptors
  • Graves' disease
    • antigen
      • TSH receptors
  • Erythroblastosis fetalis 
    • antigen
      • Rh antigen
  • Pemphigus vulgaris
    • antigen
      • desmosomes
Type III (immune-complex)
  • IgG antibodies complexes with self or foreign antigens resulting in
    • complement activation
  • Serum sickness
  • Arthus reaction
  • Systemic lupus erythematosis
  • Polyarteritis nodosa
  • Poststreptococcal glomerulonephritis
Type IV (cell mediated)
  • CD8+ T-cells directly destroy the target cell
  • Pre-sensitized CD4+ helper T-cell releases cytokines when re-exposed to the offending material
  • Notice this does NOT involve antibodies
  • Type I diabetes meilltus
  • Contact dermatitis
  • Tuberculin test
 

References



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Qbank (8 Questions)

TAG
(M1.IM.1) While playing in the woods with friends, a 14-year-old African-American male is bitten by an insect. Minutes later he notices swelling and redness at the site of the insect bite. Which substance has directly led to the wheal formation? Topic Review Topic

1. IFN-gamma
2. Histamine
3. IL-22
4. Arachidonic acid
5. IL-4

PREFERRED RESPONSE ▶
TAG
(M1.IM.1) A 32-year-old female presents with a three month history of oral ulcerations and blisters throughout her body. When the physician examined the skin, she noted that when the skin was rubbed it sloughed off and formed blisters within a few minutes. A skin biopsy was performed and analyzed via immunofluorescence using anti-IgG antibodies (Figure A). Which of the following antibodies is also involved or found in a similar type of hypersensitivity reaction as in the case mentioned? Topic Review Topic
FIGURES: A          

1. IgE against the proteins in apitoxin
2. Anti-glomerular basement membrane
3. Anti-dsDNA
4. IgE against pollen
5. Anti-Smith

PREFERRED RESPONSE ▶
TAG
(M1.IM.4) A 32-year-old pregnant woman (para 2) presents to the clinic for a routine ultrasound; Image A displays the ultrasound findings. The fetus has become anemic and levels of unconjugated bilirubin have increased dramatically. Which type of hypersensitivity reaction has occurred and what is mediating the disease state? Topic Review Topic
FIGURES: A          

1. Type I hypersensitivity; antibody-mediated opsonization
2. Type II hypersensitivity; antibody-mediated opsonization
3. Type II hypersensivity; cell killing via cytotoxic T cells
4. Type III hypersensitivity; cell killing via cytotoxic T cells
5. Type IV hypersensitivity; cell killing via NK cells

PREFERRED RESPONSE ▶
TAG
(M1.IM.29) A 28-year-old female suffering from a urinary tract infection is given trimethoprim-sulfamethoxazole (TMP-SMX) by her physician. Several days later, she begins to experience itchiness and joint pain. Laboratory and histologic analysis reveals vasculitis and antibody complexes deposited near the basement membrane of the glomerulus. What other serological finding is expected with this presentation? Topic Review Topic

1. Decreased levels of IgE
2. Increased levels of IgE
3. Decreased neutrophil count
4. Increased serum levels of complement protein C3
5. Lowered serum levels of complement protein C3

PREFERRED RESPONSE ▶
TAG
(M1.IM.37) A 30-year-old Caucasian male presents with hemoptysis and uremia. Blood tests show the presence of anti-basement membrane antibodies specific for collagen located in glomerular and pulmonary basement membranes. The patient undergoes plasmaphoresis to help reduce the amount of anti-basement membrane antibodies. Which of the following diseases is of the same hypersensitivity category as this disease? Topic Review Topic

1. Myasthenia gravis
2. Systemic lupus erythematosus
3. A PPD test
4. Seasonal allergies
5. Poison ivy rash

PREFERRED RESPONSE ▶
TAG
(M1.IM.50) While hunting, a 45-year-old Caucasian male is stung by a bee. He begins to feel unwell and is taken to the hospital. Upon arrival, it is noted that the patient is hypotensive with a blood pressure of 60/40 mmHg. Furthermore, the patient is tachycardic and edematous. What is responsible for this patient's presentation? Topic Review Topic

1. Free IgE binding to the antigen
2. IgE on mast cell surfaces binding to the antigen
3. IgE activation of complement
4. Complexes of IgE binding to the antigen
5. IgE on eosinophils binding to the antigen

PREFERRED RESPONSE ▶
TAG
(M1.IM.60) A 5-year-old African American female has experienced recurrent respiratory infections. To determine how well her cell-mediated immunity is performing, a Candida skin injection is administered. After 48 hours, there is no evidence of induration at the injection site. Of the following cell types, which one would have mediated the reaction? Topic Review Topic

1. Plasma cells
2. Basophils
3. T-cells
4. Mast cells
5. Fibroblasts

PREFERRED RESPONSE ▶
TAG
(M1.IM.61) You are working in the emergency room of a children's hospital when a 4-year-old girl is brought in by ambulance due to "difficulty breathing." The patient had been eating lunch on a school field trip when she suddenly complained of abdominal pain. Shortly thereafter, she was noted to have swelling of the lips, a rapidly developing red rash and difficulty breathing. In the ambulance her blood pressure was persistently 80/50 mmHg despite intramuscular epinephrine. In the course of stabilization and work up of the patient, you note an elevated tryptase level. What is the mechanism behind this elevated tryptase level? Topic Review Topic

1. IgG production by plasma cells
2. IgM mediated complement activation
3. Cross-linking of IgE on mast cells
4. Antibody-antigen immune complexes
5. Cross-linking of IgG on mast cells

PREFERRED RESPONSE ▶
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