5 HYPERSENSITIVITY Flashcards
(1) Which of the following is a description of a type I hypersensitivity reaction?
A. Ragweed antigen cross-links with IgE on the surface of mast cells, causing release of preformed mediators and resulting in symptoms of an allergic reaction
B. Anti-Fya from a pregnant woman crosses the placenta and attaches to the Fya antigen-positive RBCs of the fetus, destroying the RBCs
C. Immune complex deposition occurs on the glomerular basement membrane of the kidney, leading to renal failure
D. Exposure to poison ivy causes sensitized T cells to release lymphokines that cause a localized inflammatory reaction
A. Ragweed antigen cross-links with IgE on the surface of mast cells, causing release of preformed mediators and resulting in symptoms of an allergic reaction
Type I immediate hypersensitivity (anaphylactic) responses are characterized by IgE molecules binding to mast cells via the Fc receptor. Cross linking of surface IgE caused by binding of allergens causes the mast cell to degranulate, releasing histamine and other chemical mediators of allergy. Answer B describes a type II reaction; C describes a type III reaction; and D describes a type IV reaction.
(2) Why is skin testing the most widely used method to test for a type I hypersensitivity reaction?
A. It causes less trauma and is more cost effective than other methods
B. It has greater sensitivity than in vitro measurements
C. It is more likely to be positive for IgE-specific allergens compared with other methods
D. It may be used to predict the development of further allergen sensitivity
B. It has greater sensitivity than in vitro measurements
Skin testing is considered much more sensitive than in vitro tests that measure either total or antigen specific IgE.
(3) Which in vitro test measures IgE levels against a specific allergen?
A. Histamine release assay
B. Radioimmunosorbent test (RIST)
C. Fluorescent allergosorbent test (FAST)
D. Precipitin radioimmunosorbent test (PRIST)
C. Fluorescent allergosorbent test (FAST)
FAST is a fluorescent assay that measures specific IgE; RIST and PRIST tests are radioimmunoassays that measure total IgE. The FAST procedure and a chemiluminescent assay have replaced the radioallergosorbent test (RAST), for measuring allergen specific IgE. The histamine release assay is a more general assay.
(4) A patient who is blood group O is accidentally transfused with group A blood and develops a reaction during the transfusion. What antibody is involved in this type II reaction?
A. IgM
B. IgE
C. IgG and IgE
D. IgG
A. IgM
IgG and IgM are the antibodies involved in a type II cytotoxic reaction. Naturally occurring anti-A in the form of IgM is present in the blood of a group O individual and would cause an immediate transfusion reaction. Cell destruction occurs when antibodies bind to cells causing destruction via complement activation, thereby triggering intravascular hemolysis.
(5) Which test would measure the coating of RBCs by antibody as occurs in hemolytic transfusion reactions?
A. Indirect antiglobulin test (IAT)
B. Direct antiglobulin test (DAT)
C. ELISA
D. Hemagglutination
B. Direct antiglobulin test (DAT)
The DAT measures antibody that has already coated RBCs in vivo. DAT and direct IFAs use anti-Ig to detect antibody-sensitized cells.
(6) Which test detects antibodies that have attached to tissues, resulting in a type-II cytotoxic reaction?
A. Indirect immunofluorescence
B. Direct immunofluorescence (DIF)
C. Immunofixation electrophoresis (IFE)
D. Hemagglutination
B. Direct immunofluorescence (DIF)
The direct IFA detects the presence of antibody that may cause a type II cytotoxic reaction. For example, renal biopsies from patients with Goodpasture syndrome exhibit a smooth pattern of fluorescence along the basement membrane after reaction with fluorescein isothiocyanate (FITC)–conjugated anti-Ig. The reaction detects antibodies against the basement membrane of the glomeruli.
(7) Which of the following conditions will most likely result in a false-negative DAT test?
A. Insufficient washing of RBCs
B. Use of heavy chain–specific polyclonal anti human Ig
C. Use of excessive centrifugal force
D. Use of a sample obtained by finger puncture
A. Insufficient washing of RBCs
Insufficient washing can cause incomplete removal of excess or unbound Igs and other proteins, which may neutralize the antiglobulin reagent.
(8) Which of the following tests will detect circulating immune complexes in the serum of some patients with systemic autoimmune diseases, such as RA?
A. Direct IFA
B. Enzyme immunoassay (EIA)
C. Assay of cryoglobulins
D. IAT
C. Assay of cryoglobulins
Most autoimmune diseases involve the formation of antigen–antibody complexes that deposit in tissues, causing local inflammation and necrosis induced by complement activation, phagocytosis, white blood cell (WBC) infiltration, and lysosomal damage. Some patients make monoclonal or polyclonal antibodies with RF activity that bind to serum Igs, forming aggregates that are insoluble at 4°C. These circulating immune complexes are detected by allowing a blood sample to clot at 37°C, transferring the serum to a sedimentation rate tube, and then incubating the serum at 4°C for 3 days.
(9) What immune elements are involved in a positive skin test for tuberculosis?
A. IgE antibodies
B. T cells and macrophages
C. NK cells and IgG antibody
D. B cells and IgM antibody
B. T cells and macrophages
T cells and macrophages are the immune elements primarily responsible for the clinical manifestations of a positive tuberculosis test. Reactions usually take 48 to 72 hours to reach peak development and are characteristic of localized type IV cell-mediated hypersensitivity. The skin reaction is characterized by a lesion containing a mononuclear cell infiltrate.
(10) A patient receives a transfusion of packed RBCs and fresh frozen plasma (FFP) and develops an anaphylactic, nonhemolytic reaction. She reports receiving a transfusion 20 years earlier. She had no reaction to the previous transfusion, but she did feel “poorly” a few weeks later. Which of the following transfused substances most likely elicited the reaction?
A. IgA
B. Group A antigen
C. Rho (D) antigen
D. An antigen belonging to the Duffy system
A. IgA
The fact that this is a nonhemolytic reaction suggests that a non-RBC antigen may be involved. Selective IgA deficiency occurs in approximately one in 700 individuals and is often asymptomatic. Individuals deficient in IgA may make an antibody against the α-heavy chain if they are exposed to IgA via a transfusion. This antibody may lead to a serum sickness reaction if the IgA is still present after antibody formation. This could explain the “poor feeling” the patient had after the initial transfusion. A subsequent transfusion may lead to an Arthus reaction if IgG anti-IgA is present or an anaphylactic reaction if IgE anti-IgA is present.
(11) A patient deficient in the C3 complement component would be expected to mount a normal:
A. Type I and IV hypersensitivity response
B. Type II and IV hypersensitivity response
C. Type I and III hypersensitivity response
D. Type II and III hypersensitivity response
A. Type I and IV hypersensitivity response
Complement is involved in types II and III hypersensitivity; thus an individual deficient in C3 will be deficient in those responses. The complement deficiency should have no effect on IgE (type I) or cell-mediated (type IV) hypersensitivities.
