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tion is likely to be useful for assessing phenotypic changes that occur in cells
from infected persons.
CONCLUSION
The investigation of HIV-1 infection and disease pathogenesis has been sig-
ni®cantly a¨ected by the capacity to analyze single cells by ¯ow cytometry. The
technology provides for fast and e½cient analysis of large numbers of cells,
measuring for multiple parameters simultaneously. Moreover, the capability of
sorting selected populations based on the analysis on a ¯ow cytometer adds
a signi®cant dimension to the potential for investigating the consequences of
HIV-1 infection in vivo and in vitro.
Nevertheless, ¯ow cytometric analysis has been hampered by a major limi-
tation: the poor sensitivity of the analysis compared with other techniques.
Most importantly, many molecules are expressed in functionally signi®cant
amounts that cannot be detected by the most sensitive current ¯ow cytometric
methods.
Enzymatic ampli®cation technology allows for a 100-fold enhancement of
the ¯uorescent signal and, consequently, the expression of molecules that could
not be detected by standard procedures can now be observed. To be able to
track the expression levels of functionally signi®cant molecules on a cell-by-cell
basis in an e½cient and timely manner represents a major improvement in the
technical capabilities for investigators working to understand the pathogenesis
of HIV-1 disease.
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