Microbiology, 2021

20 • Review Questions 849
20.4 EIAs and ELISAs
• Enzyme immunoassays (EIA) are used to
visualize and quantify antigens. They use an
antibody conjugated to an enzyme to bind the
antigen, and the enzyme converts a substrate
into an observable end product. The substrate
may be either a chromogen or a fluorogen.
• Immunostaining is an EIA technique for
visualizing cells in a tissue
(immunohistochemistry) or examining
intracellular structures
(immunocytochemistry).
• Direct ELISA is used to quantify an antigen in
solution. The primary antibody captures the
antigen, and the secondary antibody delivers an
enzyme. Production of end product from the
chromogenic substrate is directly proportional
to the amount of captured antigen.
• Indirect ELISA is used to detect antibodies in
patient serum by attaching antigen to the well of
a microtiter plate, allowing the patient (primary)
antibody to bind the antigen and an enzymeconjugated
secondary antibody to detect the
primary antibody.
• Immunofiltration and
immunochromatographic assays are used in
lateral flow tests, which can be used to
diagnose pregnancy and various diseases by
REVIEW QUESTIONS
Multiple Choice
1. For many uses in the laboratory, polyclonal
antibodies work well, but for some types of
assays, they lack sufficient ________ because
they cross-react with inappropriate antigens.
a. specificity
b. sensitivity
c. accuracy
d. reactivity
2. How are monoclonal antibodies produced?
a. Antibody-producing B cells from a mouse
are fused with myeloma cells and then the
cells are grown in tissue culture.
b. A mouse is injected with an antigen and then
antibodies are harvested from its serum.
c. They are produced by the human immune
system as a natural response to an infection.
d. They are produced by a mouse’s immune
system as a natural response to an infection.
detecting color-labeled antigen-antibody
complexes in urine or other fluid samples
20.5 Fluorescent Antibody
Techniques
• Immunofluorescence assays use antibodyfluorogen
conjugates to illuminate antigens for
easy, rapid detection.
• Direct immunofluorescence can be used to
detect the presence of bacteria in clinical
samples such as sputum.
• Indirect immunofluorescence detects the
presence of antigen-specific antibodies in
patient sera. The fluorescent antibody binds to
the antigen-specific antibody rather than the
antigen.
• The use of indirect immunofluorescence assays
to detect antinuclear antibodies is an
important tool in the diagnosis of several
autoimmune diseases.
• Flow cytometry uses fluorescent mAbs against
cell-membrane proteins to quantify specific
subsets of cells in complex mixtures.
• Fluorescence-activated cell sorters are an
extension of flow cytometry in which
fluorescence intensity is used to physically
separate cells into high and low fluorescence
populations.
3. The formation of ________ is a positive result in
the VDRL test.
a. flocculant
b. precipitin
c. coagulation
d. a bright pink color
4. The titer of a virus neutralization test is the
highest dilution of patient serum
a. in which there is no detectable viral DNA.
b. in which there is no detectable viral protein.
c. that completely blocks plaque formation.
d. that reduces plaque formation by at least
50%.