MOLECULAR DIAGNOSTICS LAB EXAM QUESTIONS AND ANSWERS
Describe the mechanism of ELISA. - (answer)Adsorbed antigen is bound by an IgG. The bound IgG is itself
bound by an IgG from another species. The second IgG is conjugated to a marker such as peroxidase
which can produce colored products from certain substrates.
Why is ELISA so sensitive? - (answer)The sensitivity of the ELISA is due to the high catalytic turnover
rates of the enzyme linked conjugate.
Why is it necessary to block unoccupied binding sites in the microtiter wells? - (answer)Because if not
blocked, the primary and secondary antibodies will be non-specifically adsorbed as well, producing false
positives.
Why is it important to have a positive control? - (answer)A positive control assures that the reagents and
plates are working properly.
Why can the onset of AIDS take several years? - (answer)Because HIV remains as a provirus until the T-
cell is activated by a specific antigen.
Why is anti-HIV-1 IgG screened instead of the virus itself? - (answer)Because during the early stages of
the disease very little circulating virus is present.
Why does the destruction of TH cells compromise the entire immune system? - (answer)TH cells
produce lymphokines which are required for T-cytotoxic, B-cell and macrophage growth and maturation.
How does HIV target TH cells? - (answer)The virus binds to TH cell CD4 receptors.
Why are there so many immunological variants of HIV? - (answer)High error rate of reverse
transcriptase.
The elimination of several steps in the ELISA could be accomplished if the primary antibody was made
into an enzyme conjugate. Why is this generally not done? - (answer)For every antigen the
corresponding IgG would have to be purified and conjugated. This would take too much time and would
not be cost effective.
Describe the mechanism of ELISA. - (answer)Adsorbed antigen is bound by an IgG. The bound IgG is itself
bound by an IgG from another species. The second IgG is conjugated to a marker such as peroxidase
which can produce colored products from certain substrates.
Why is ELISA so sensitive? - (answer)The sensitivity of the ELISA is due to the high catalytic turnover
rates of the enzyme linked conjugate.
Why is it necessary to block unoccupied binding sites in the microtiter wells? - (answer)Because if not
blocked, the primary and secondary antibodies will be non-specifically adsorbed as well, producing false
positives.
Why is it important to have a positive control? - (answer)A positive control assures that the reagents and
plates are working properly.
Why can the onset of AIDS take several years? - (answer)Because HIV remains as a provirus until the T-
cell is activated by a specific antigen.
Why is anti-HIV-1 IgG screened instead of the virus itself? - (answer)Because during the early stages of
the disease very little circulating virus is present.
Why does the destruction of TH cells compromise the entire immune system? - (answer)TH cells
produce lymphokines which are required for T-cytotoxic, B-cell and macrophage growth and maturation.
How does HIV target TH cells? - (answer)The virus binds to TH cell CD4 receptors.
Why are there so many immunological variants of HIV? - (answer)High error rate of reverse
transcriptase.
The elimination of several steps in the ELISA could be accomplished if the primary antibody was made
into an enzyme conjugate. Why is this generally not done? - (answer)For every antigen the
corresponding IgG would have to be purified and conjugated. This would take too much time and would
not be cost effective.
