Hypersensitivity HARR Flashcards
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 red cells of the fetus, destroying the red cells
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
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
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 than other methods
D. It may be used to predict the development of further allergen sensitivity
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
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)
Fluorescent allergosorbent test (FAST)
The FAST is a fluorescent assay that measures specific IgE; the RIST and PRIST tests are radioimmunoassays that measure total IgE. The FAST procedure has replaced the RAST, or radioallergosorbent assay. The histamine release assay measures the amount of histamine. Allergen-specific IgE assays are available based upon solid-phase enzyme immunoassay. The allergen is covalently bound to a cellulose solid phase and reacts with specific IgE in the serum. After washing, enzyme (β-galactosidase)-labeled monoclonal anti-IgE is added. The unbound antibody
conjugate is washed away and fluorogenic substrate (4-methylumbelliferyl-β-D-galactose) is added. Fluorescence is directly proportional to specific IgE.
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
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.
Which test would measure the coating of red cells by antibody as occurs in hemolytic transfusion reactions?
A. Indirect antiglobulin test (IAT)
B. Direct antiglobulin test (DAT)
C. ELISA
D. Hemagglutination
Direct antiglobulin test (DAT)
The DAT test measures antibody that has already coated RBCs in vivo. Direct antiglobulin and direct immunofluorescence tests use anti-immunoglobulin to detect antibody-sensitized cells.
Which test detects antibodies that have attached to tissues, resulting in a type-II cytotoxic reaction?
A. Migration inhibition factor assay (MIF)
B. Direct immunofluorescence (IF)
C. Immunofixation electrophoresis (IFE)
D. Hemagglutination
Direct immunofluorescence (IF)
The direct IF test detects the presence of antibody that may cause a type II cytotoxic reaction. For example, renal biopsies from patients with Goodpasture’s syndrome exhibit a smooth pattern of fluorescence along the basement membrane after reaction with fluorescein isothiocyanate (FITC) conjugated anti-immunoglobulin. The reaction detects antibodies against the basement membrane
of the glomeruli
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
Insufficient washing of RBCs
Insufficient washing can cause incomplete removal of excess or unbound immunoglobulins and other proteins, which may neutralize the antiglobulin reagent.
Which of the following tests is used to detect
circulating immune complexes in the serum of
some patients with systemic autoimmune diseases such as rheumatoid arthritis?
A. Direct immunofluorescence
B. Enzyme immunoassay
C. Assay of cryoglobulins
D. Indirect antiglobulin test
Assay of cryoglobulins
Most autoimmune diseases involve the formation of antigen–antibody complexes that deposit in the tissues, causing local inflammation and necrosis induced by complement activation, phagocytosis, WBC infiltration, and lysosomal damage. Some
patients make monoclonal or polyclonal antibodies with rheumatoid factor activity that bind to serum immunoglobulins, 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
All of the following tests may be abnormal in a
type III immune complex reaction except:
A. C1q-binding assay by ELISA
B. Raji cell assay
C. CH50 level
D. Mitogen response
Mitogen response
Mitogen stimulation is used to measure T-cell, B-cell, and null-cell responsiveness, which is important in patients displaying anergy and other signs of immunodeficiency. The C1q assay and the Raji cell assays detect circulating immune complexes that are present during a type III reaction. The CH50 level is usually decreased owing to complement activation by the immune complexes. Raji cells are derived from a malignant B-cell line that demonstrates
C3 receptors but no surface membrane
immunoglobulin. Immune complexes that have fixed complement will bind to Raji cells and can be identified using radiolabeled or enzyme labeled anti-immunoglobulin. More recently, a C3 binding ELISA assay has replaced the Raji cell procedure.
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
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 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.
What is measured in the CH50 assay?
A. RBC quantity needed to agglutinate 50% of
antibody
B. Complement needed to lyse 50% of RBCs
C. Complement needed to lyse 50% of antibody-sensitized RBCs
D. Antibody and complement needed to sensitize 50% of RBCs
Complement needed to lyse 50% of antibody-sensitized RBCs
The CH50 is the amount of complement needed to lyse 50% of standardized hemolysin-sensitized sheep RBCs. It is expressed as the reciprocal of the serum dilution resulting in 50% hemolysis. Low levels are associated with deficiency of some complement components and active systemic autoimmune diseases in which complement is being consumed.
What type of disorders would show a decrease in C3, C4, and CH50?
A. Autoimmune disorders such as SLE and RA
B. Immunodeficiency disorders such as common variable immunodeficiency
C. Tumors
D. Bacterial, viral, fungal, or parasitic infections
Autoimmune disorders such as SLE and RA
The pattern of decreased C3, C4, and CH50 indicates classic pathway activation. This results in consumption of complement and is associated with SLE, serum sickness, subacute bacterial endocarditis, and other immune complex diseases. The inflammatory response seen in malignancy and acute infections gives rise to an increase in complement components. Immunodeficiency caused by an inherited deficiency in complement constitutes only about 1% of immunodeficiency diseases. Such disorders reduce the CH50 but involve a deficient serum level of only one complement
factor
All of the following tests measure phagocyte
function except:
A. Leukocyte adhesion molecule analysis
B. Di Hydro rhodamine reduction assay
C. NBT test
D. IL-2 (interleukin-2) assay
IL-2 (interleukin-2) assay
The Di-hydro rhodamine reduction assay and NBT tests are used to diagnose chronic granulomatous disease, an inherited disorder in which phagocytic cells fail to kill microorganisms owing to a defect in peroxide production (respiratory burst). Leukocyte adhesion deficiency is associated with a defect in the production of integrin molecules on the surface of WBCs and their granules. IL-2 is a cytokine produced by activated Th and B cells. It causes B-cell proliferation and increased production of antibody, interferon, and
other cytokines. IL-2 can be measured by EIA and is used to detect transplant rejection, which is associated with an increase in the serum and urine levels
