東邦大学英語2012年第5問
An antibody that recognizes all strains of influenza A could be a universal vaccine blueprint. Scientists have found an antibody that inactivates all influenza A subtypes. The antibody-binding site, tucked away in a stable region of the virus, might form the first lasting vaccine against flu.
The influenza virus constantly mutates, forcing scientists to play catch-up and produce a new seasonal vaccine each year. But Antonio Lanzavecchia, an author on the new study, says that observing the human immune response to influenza convinced him that it would be possible to design a vaccine that prevails over mutation.
"During the 2009 H1N1 pandemic, we found some people with antibodies to multiple viral subtypes." says Lanzavecchia. Antibodies, which are produced by white blood cells called B cells, bind to specific target sites, inactivating viruses or flagging them for destruction by other immune cells.
To test the cross-reactivity of influenza antibodies, the team screened B cells from eight human donors who had been infected with or immunized against different influenza strains. They took the B cells early in the immune response, when the repertoire of antibodies they secrete is at its most diverse.
After looking at 104,000 B cells, they hit the jackpot. "Our F16 antibody is the first one ever found that reacts to all 16 of the influenza A subtypes." says Lanzavecchia.
The finding follows other reports of broadly reactive influenza antibodies, but these could only bind to either group 1 viruses, such as the H1N1 'swine flu' and the avian influenza H5N1, or group 2 viruses, which include the seasonal H3N2 strains.
"Finding antibodies to all strains of one group was exciting," says immunologist Patrick Wilson from the University of Chicago, ''but getting one to both groups is stunning."
The antibody itself is not a vaccine, but it could be an instruction manual for making one. The scientists say that a small protein mimicking the part of the virus bound by the F16 antibody might cajole the immune system into making similarly cross-reactive antibodies.
To zero in on the binding site, Lanzavecchia's team used X-ray crystallography. Their structure shows that the F16 antibody binds to the stem region of influenza's haemagglutinin protein. Most influenza antibodies bind to the more accessible head region of haemagglutinin.
Because much of the head region is not essential for viral function, it can mutate-allowing the virus to evade immune attack. By contrast, the stem region has a structure that is easily disrupted by mutations, so needs to stay stable.
"The stem is so well conserved between influenza subtypes that I would expect there to be high selective pressure against mutation in this area," says Wilson. He says there is a real chance a vaccine based on the haemagglutinin stem could work in humans. Previous work has shown that mice immunized with a small stem protein were protected against multiple influenza strains.
- 61. The word "stable" is closest in meaning to
- a. unchanging
- b. vulnerable
- c. established
- d. accessible
- 62. The term "prevails over" is closest in meaning to
- a. covers
- b. is absorbed by
- c. responds to
- d. overcomes
- 63. The word "flagging" probably means
- a. planting
- b. marking
- c. damaging
- d. binding
- 64. The word "secrete" is closest in meaning to
- a. eliminate
- b. multiply
- c. discharge
- d. consume
- 65. The word "mimicking" is closest in meaning to
- a. imitating
- b. bothering
- c. attacking
- d. countering
- 66. The term "zero in on" is closest in meaning to
- a. focus on
- b. reduce from
- c. attach to
- d. subtract from
- 67. The word "accessible" is closest in meaning to
- a. influenced
- b. vulnerable
- c. influential
- d. reachable
- 68. The word "evade" is closest in meaning to
- a. disrupt
- b. avoid
- c. notice
- d. protect
- 69. The term "this area" probably refers to
- a. the stem region
- b. the head region
- c. the antibodies
- d. the binding sites
- 70. Why did Antonio Lanzavecchia first believe that it would be possible to make a lasting vaccine against the flu virus?
- a. He discovered that viruses constantly mutate.
- b. He saw that some people lacked an immune response.
- c. He noticed that some people had antibodies that protected against several strains of the virus.
- d. He screened eight subjects who had produced cross-reactive antibodies.
- 71. Why did the scientists test B cells early in the immune response phase?
- a. B cells produce the strongest antibodies early in the immune response.
- b. B cells produced later in the immune response will not react to enough virus subgroups to be useful.
- c. Most human donors produce B cells only at the beginning of the immune response phase.
- d. B cells early in the immune response produce the greatest variety of antibodies.
- 72. How is the new F16 antibody different from previous antibodies?
- a. It attaches to both group 1 and group 2 flu viruses.
- b. It can combine virus groups 1 and 2 together.
- c. It is the first antibody that affects H3N2 flu strains.
- d. It is the first time that scientists were able to find all strains of viruses together.
- 73. How might the F16 antibody be useful for combating the flu virus?
- a. Scientists can use the F16 antibody to create more haemagglutinin proteins.
- b. It can help scientists make a vaccine based on the binding site of the flu virus.
- c. The F16 antibody can be used as a vaccine.
- d. The F16 antibody zeroes in on the binding site and activates the virus.
- 74. How does the F16 antibody attach to the flu virus?
- a. It attaches to the stem of the haemagglutinin protein.
- b. It attaches to the head of the haemagglutinin protein.
- c. It connects to both the head and the stem regions of the haemagglutinin protein.
- d. It binds to the flu virus while it is mutating.
- 75. Why doesn't the stem region of the flu virus mutate?
- a. It conserves itself against influenza antibodies.
- b. It is not accessible enough for mutations to occur.
- c. It will be damaged if it mutates.
- d. It is not essential for viral function.