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  3. Fat: what is it good for? Absolutely nothing, or so you might think. But obesity seems to protect mice against a fatal form of m

Fat: what is it good for? Absolutely nothing, or so you might think. But obesity seems to protect mice against a fatal form of m

admin2015-12-23  34
问题     Fat: what is it good for? Absolutely nothing, or so you might think. But obesity seems to protect mice against a fatal form of malaria—cerebral malaria. Working out how it has this effect might lead to new treatments for people.
    Although obesity is now on the rise in the developing world, it has traditionally been seen as a malaise of the rich. In contrast, malaria tends to be regarded as a disease of the poor, so few people have studied how the two conditions affect each other. In mice meanwhile, there are signs that diabetes, which often affects obese people, might offer some protectioa against malaria.
    To find out more about how obesity affects malaria in mice, Vincent Robert at the Institute for Development Research(IRD)in Paris, France, and colleagues injected 14 obese and 14 non-obese mice with the malaria parasite Plasmodium berghei. After six days, eight of the non-obese mice died from cerebral malaria, which causes coma and death in humans, and the rest died about two weeks later from severe anemia because the parasite had destroyed their red blood cells. In contrast, none of the obese mice showed signs of cerebral malaria. Although they all eventually succumbed to severe anemia and died 18 to 25 days after infection, anemia can be treated—so obesity did seem to offer mice some useful protection.
    Exactly how the obese mice resist malaria is not clear, says Delphine Depoix from the Museum of Natural History in Paris, but there are several possibilities. One clue lies in a mutation in the gene coding for the leptin, a hormone produced by fat cells, which makes the mice obese, but also controls the immune response. Previous research has shown that obese mice with the leptin mutation often react to infections with a "Th2" rather man "Thl" response. As Thl in mice is thought to trigger the inflammation mat helps cerebral malaria to kill its victims, Depoix speculates mat me Th2 response might be protecting me obese mice. Another possible explanation is that the abnormally high blood sugar associated with obesity in both mice and people "might compensate" for the low blood sugar caused by severe malaria, says Depoix, allowing me mice to better cope with parasite infection.
    Andrew Prentice of the London School of Hygiene and Tropical Medicine says that figuring out how me mice resist malaria will be crucial to developing new treatments for people with malaria. His colleague Christopher Whitty warns that any insights drawn from these results are preliminary: "Mouse models are always useful in raising hypotheses but cannot settle them as far as cerebral malaria is concerned."
After being injected with malaria parasite Plasmodium berghei, the obese mice
选项 A、died from cerebral malaria.
B、died from the destruction of their red blood cells caused by severe anemia.
C、died from infection without showing signs of cerebral malaria.
D、were still alive thanks to the useful protection of obesity.
答案C
解析 事实细节题。根据Plasmodium berghei定位到第三段。本段分析了老鼠在注射柏氏鼠疟原虫之后的反应，最后两句指出肥胖的老鼠虽严重贫血并最终死亡，但没有出现脑型疟的症状，故C项正确。A、B项是nonobese mice的反应；D项still alive与文意“感染疟疾18到25天后死亡”相悖。
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