Chimpanzee Genome
571
has mere anecdotal character – the medi-
cal relevance of involved diseases such as
AIDS, hepatitis, or certain types of cancer
is sufFcient to draw attention to this is-
sue. Differences in the disease spectrum
between two species can be attributed to
two different causes: differences in en-
vironmental influences such as diet and
differing genetic predispositions. In re-
cent years, the environmental conditions
for captive chimpanzees have become in-
creasingly similar to those of humans.
This, however, had no substantial effect
on the differences of their respective dis-
ease spectra. Therefore, the existence of
crucial genetic differences between the
two species must be assumed whose iden-
tiFcation comprises the main relevance
of biomedical studies on chimpanzees.
Conveniently, the identiFcation of candi-
dates for these genetic differences can be
achieved by a comparison of the genome
sequences of chimpanzees and humans
and does not require experimental studies
on chimpanzees.
As an outlook, the medical consequences
of biomedical studies on chimpanzees
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genetic basis is understood as to why this
speciesislesssusceptibletocertainhuman
diseases, cure or even prevention of these
diseases can be imagined by mimicking
the chimpanzee phenotype in well-deFned
disease-relevant parts of human biology.
4.3
Chimpanzees and Infectious Diseases
Maybe the most widely recognized bio-
medical difference between chimpanzees
and humans is their different susceptibil-
ity to AIDS upon infection with HIV-1
(Human ImmunodeFciency Virus 1), the
most common cause of AIDS in humans.
While chimpanzees rarely display AIDS-
like syndromes, the progression to AIDS
in humans is common. This difference
is generally explained by the evolutionary
history of HIV-1. It is suggested that HIV-
1 originated from the chimpanzee virus
SIV (Simian ImmunodeFciency Virus)
that crossed the species border only about
50 years ago. Thus, the low susceptibil-
ity to AIDS in chimpanzees could be due
to a long coevolution of virus and host
in a way that contemporary chimpanzees
get infected by the virus but due to an
efFcient control of the virus load do not
develop the disease. Humans, in contrast,
who have become exposed to the virus only
recently, lack the immunological ability for
virus control and thus, suffer from AIDS.
Obviously, the missing development of
the disease renders chimpanzees inade-
quate as a model to study the progress of
AIDS. Other primate species, such as the
rhesus macaque appear to be more suit-
able since AIDS-like symptoms have been
observed in these species subsequent to
infection with SIV. However, the genetic
reasons for the adapted immune response
that cause the relative resistance against
AIDS in chimpanzees are of consider-
able interest. They might point toward
novel therapeutic approaches to prevent
the progression to AIDS in HIV-infected
humans. Initial insights suggest that dif-
ferences in the allele combination in the
major histocompatibility complex – a col-
lection of genes correlated with immune
response – between humans and chim-
panzees is responsible for their varying
susceptibility to AIDS.
Similar to the case of infection with HIV-
1 and progression to AIDS, chimpanzees
reduce the risk of long-term complications
of hepatitis infections by an effective con-
trol of the virus load in the organism. Thus,
there appears to be a general capability in
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