当代研究生英语读写教程完形下册(3)

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By measuring the amount of HIVs genetic material in various representative tissue samples from infected people, and extrapolating form these 1.samples to the entire body, Haase estimates that at most 1 in 2,500 cells, maybe fewer, is infected with HIV. This is nowhere near enough for direct cell killing to account for the depletion in their numbers that 2.leads to AIDS.

Haase says that his own work now shows that large numbers of CD4 cell ate becoming 3.trapped in lymph tissue, and he believes that HIV also 4.disrupts the production of new cells. In common with a number of other researchers, he also believes that HIV may cause the 5.loss of uninfected CD4 cells by triggering abnormally high levels of cell suicide ,or apoptosis-a separate process that has been a subject of research throughout the 1990s .

Taken together, these 6.findings clearly suggest that HIV keeps the 7.immune system in a state of constant activation, and unbalances it in four 8.ways :by trapping mature cells ,by stopping the production of new cells, by triggering abnormally high rates of apoptosis and by killing a small but significant 9.number of cells ，