Biology Reference
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the antibodies tested gave excellent levels of ¯uorescence intensity, and three
other antibodies gave marginal shifts. However, the signi®cance of these ®nd-
ings is not clear because no isotype/subtype controls were shown. Moreover,
PubMed lists no additional investigations with these antibodies, although a
similar antibody has since been described that binds to clade E isolates and
cross-reacts with viruses from other clades (Gorny et al., 1998).
Other investigators have obtained murine monoclonal antibodies speci®c for
HIV-1 gp120 that have been used for ¯ow cytometric analysis ( Laman et al.,
1992; Moore et al., 1993; Pincus et al., 1989). A murine monoclonal antibody
speci®c for HIV-1 gp120 of strain IIIB was obtained and shown to produce
histograms that were clearly shifted in comparison to both isotype control-
stained infected cells and speci®c antibody-stained uninfected cells ( Pincus et
al., 1989). Another murine monoclonal antibody was obtained and tested by
¯ow cytometry ( Laman et al., 1992). This antibody, IIIB-V3-13 produced a
shift in ¯uorescence comparing infected with uninfected cells, but no isotype/
subtype control was included. Moreover, the shift obtained, seen with ¯uores-
cence read on a linear scale, was marginal at best. Eight di¨erent murine
monoclonal antibodies were used to probe the available structure of oligomeric
gp120 on the cell surface of H9 cells transfected with a HIV-1 molecular clone
(Moore et al., 1993). Isotype control immunoglobulins were not used in this
study. Unfortunately, no histograms were shown.
Analysis of intracellular viral antigens has not been any more successful.
Most investigators have assessed the structural protein, HIV-1 p24, in PBMC
from infected patients (Costigliola et al., 1992; Holzer et al., 1993; McSharry
et al., 1990; Ohlsson-Wilhelm et al., 1990). These studies were conducted to
obtain a relevant marker of disease progression in the patients, and high pro-
portions of p24-expressing CD4
cells (up to 25%) were found in infected
patients compared with the levels of infected cells detected by sensitive poly-
merase chain reaction (PCR) techniques. The failure to obtain independent
con®rmation of expression was worrisome. In fact, cells found to be expressing
p24 by a ¯ow cytometric technique were found to be no more likely to contain
HIV-1 provirus than cells determined to be negative for p24 expression by ¯ow
cytometry ( Kux et al., 1996). The high levels of p24 expression in CD4
cells
may have been the result of the failure of the investigators to include isotype/
subtype controls in their studies along with the relatively high levels of non-
antigen-speci®c binding found in cells from HIV-1-infected persons compared
with healthy volunteers. Moreover, in this same study it was clear that patient
cells did not include de®nitive subsets expressing p24, which would produce a
bimodal distribution of ¯uorescence intensities. Rather there were shifts in the
entire population of cells (Cameron et al., 1998). It is easy for proportions of
positive cells to be fallacious in the situation where entire populations shift and
a somewhat arbitrary cut-o¨ value is used to assign positivity.
Flow cytometry, for either cell surface viral glycoproteins or intracellular
viral proteins, has not been found to be useful in studies of the expression of
HIV-1 viral proteins. Nevertheless, the availability of this technology would
