Important note: Information in this article was accurate in March 1999. The state of the art may have changed since the publication date.AIDSWEEKLY Plus; Monday, March 15, 1999
Daniel J. DeNoon, Senior Editor
A central mystery to AIDS is why CD4(+) T cells drop precipitously after a long period in which they remain low but relatively stable. Virology studies show that a change in the virus occurs at this time with the appearance of syncytium-inducing strains capable of entering cells via the CXCR4 coreceptor.
Why is this so bad? Observers have noted that naive T cells bear the CXCR4 receptor and have suggested that when the virus learns to infect these cells it greatly increases the damage it is able to inflict. Now direct observations of T cell populations from infected individuals confirm this hypothesis.
"We posit that infection of naive cells reduces the already impaired T-cell renewal capacity," said Hetty Blaak of the Academic Medical Center, Amsterdam, Netherlands.
Blaak spoke in a presentation to the 6th Conference on Retroviruses and Opportunistic Infections, held January 31-February 4, 1999, in Chicago, Illinois.
Blaak and colleagues obtained T cells from 12 individuals infected with syncytium inducing (SI) and non-syncytium inducing (NSI) virus, and from eight individuals with NSI virus only. They then purified memory T cells (CD45RO phenotype) and naive T cells (CD45RA phenotype) and analyzed the presence of SI and NSI variants in each cell type.
"People infected with SI variants have far higher viral load in naive cells, and more naive than memory cells are infected," Blaak reported. "Naive cells are almost exclusively infected by SI variants."
Perhaps most conclusively, the researcher were able to correlate CD4 decline with the absolute SI load in naive cells. No such effect was seen for the presence of SI variants in memory cells.
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