[A] What route does HIV take after it enters the body to destroy the immune
system [B] How and when did the long-standing belief concerning AIDS and HIV
crop up [C] What is the most effective anti-HIV therapy [D] How does HIV
subvert the immune system [E] In the absence of a vaccine, how can HIV be
stopped [F] Why does AIDS predispose infected persons to certain types of
cancer and infections In the 20 years since the first cases of
AIDS were detected, scientists say they have learned more about this viral
disease than any other. Yet Peter Piot, who directs the United
Nations AIDS program, and Stefano Vella of Rome, president of the International
AIDS Society, and other experts say reviewing unanswered questions could prove
useful as a measure of progress for AIDS and other diseases.
Among the important broader scientific questions that
remain: 41．_____________. A long-standing belief is that
cancer cells constantly develop and are held in check by a healthy immune
system. But AIDS has challenged that belief. People with AIDS are much more
prone to certain cancers like non-Hodgkins lymphomas and Kaposi’s sarcoms, but
not to breast, colon and lung, the most common cancers in the United States.
This pattern suggests that an impaired immune system, at least the
type that occurs in AIDS, does not allow common cancers to
develop. 42．_______________. When HIV is transmitted
sexually, the virus must cross a tissue barrier to enter the body. How that
happens is still unclear. The virus might invade directly or be carried by a
series of different kinds of cells. Eventually HIV travels
through lymph vessels to lymph nodes and the rest of the lymph system. But what
is not known is how the virus proceeds to destroy the body’s CD-4 cells that are
needed to combat invading infectious agents. 43．_______________.
Although HIV kills the immune ceils sent to kill the virus, there is
widespread variation in the rate at which HIV infected people become ill with
AIDS. So scientists ask: Can the elements of the immune system responsible for
that variability be identified If so, can they be used to stop progression to
AIDS in infected individuals and possibly prevent infection in the first
place 44．_______________. In theory, early treatment should
offer the best chance of preserving immune function. But the new drugs do not
completely eliminate HIV from the body so the medicines, which can have
dangerous side effects, will have to be taken for a lifetime and perhaps changed
to combat resistance. The new policy is expected to recommend that treatment be
deferred until there are signs the immune system is weakening.
Is a vaccine possible There is little question that
an effective vaccine is crucial to controlling the epidemic. Yet only one has
reached the stage of full testing, and there is wide controversy over the degree
of protection it will provide. HIV strains that are transmitted in various areas
of the world differ genetically. It is not known whether a vaccine derived from
one type of HIV will confer protection against other
types. 45．_______________. Without more incisive, focused
behavioral research, prevention messages alone will not put an end to the global
epidemic.