Microbiology, 2021

20 • Review Questions 851
15. Suppose you need to quantify the level of CD8 T
cells in the blood of a patient recovering from
influenza. You treat a sample of the patient’s
white blood cells using a fluorescent mAb
against CD8, pass the cells through a flow
cytometer, and produce the histogram shown
below. The area under the peak to the left (blue)
is three times greater than the area of the peak
on the right (red). What can you determine from
these data?
16. In the data described in the previous question,
the average fluorescence intensity of cells in the
second (red) peak is about ________ that in the
first (blue) peak.
a. three times
b. 100 times
c. one-third
d. 1000 times
17. In a direct fluorescent antibody test, which of
the following would we most likely be looking
for using a fluorescently-labeled mAb?
a. bacteria in a patient sample
b. bacteria isolated from a patient and grown
on agar plates
c. antiserum from a patient smeared onto a
glass slide
d. antiserum from a patient that had bound to
antigen-coated beads
a. There are no detectable CD8 cells.
b. There are three times as many CD4 cells
than CD8 cells.
c. There are three times as many CD8 cells
than CD4 cells.
d. CD8 cells make up about one-fourth of the
total number of cells.
Fill in the Blank
18. When we inject an animal with the same
antigen a second time a few weeks after the
first, ________ takes place, which means the
antibodies produced after the second injection
will on average bind the antigen more tightly.
19. When using mAbs to treat disease in humans,
the mAbs must first be ________ by replacing
the mouse constant region DNA with human
constant region DNA.
20. If we used normal mouse mAbs to treat human
disease, multiple doses would cause the patient
to respond with ________ against the mouse
antibodies.
21. A polyclonal response to an infection occurs
because most antigens have multiple ________,
22. When slowly adding antigen to an antiserum,
the amount of precipitin would gradually
increase until reaching the ________; addition
of more antigen after this point would actually
decrease the amount of precipitin.
23. The radial immunodiffusion test quantifies
antigen by mixing ________ into a gel and then
allowing antigen to diffuse out from a well cut in
the gel.
24. In the major cross-match, we mix ________
with the donor red blood cells and look for
agglutination.
25. Coombs’ reagent is an antiserum with
antibodies that bind to human ________.
26. To detect antibodies against bacteria in the
bloodstream using an EIA, we would run a(n)
________, which we would start by attaching
antigen from the bacteria to the wells of a
microtiter plate.
27. In flow cytometry, cell subsets are labeled using
a fluorescent antibody to a membrane protein.
The fluorogen is activated by a(n) ________ as
the cells pass by the detectors.
28. Fluorescence in a flow cytometer is measured
by a detector set at an angle to the light source.
There is also an in-line detector that can detect
cell clumps or ________.