Scientists believe that they have made a 1) __________ breakthrough in fighting HIV- they have shown what happens when an infection-fighting antibody attacks a 2) __________ in HIV's 3) __________ defences. Finding a vaccine against HIV has been very difficult because the proteins on the surface of the virus are continually mutating, but they have shown an antibody, called b12, attacking a weak spot of the virus where the protein is 4) __________. The virus is able to 5) __________ rapidly to avoid 6) __________ by the immune system, and is also covered in sugary molecules which block access by antibodies. 7) __________, certain parts of the virus must remain 8) __________ unchanged so that it can catch hold of and enter human cells. One protein that sticks out from the surface of the virus and binds to receptors on host cells is one such region, which makes it a target for vaccine development.
Previous analyses of the 9) __________ of people that have been able to keep HIV from developing into AIDS for long periods of time 10) __________ revealed a 11) __________ group of antibodies - including b12 - that seem to fight HIV with some degree of 12) __________. The latest study showed how the antibody and 13) __________ protein interact. Scientists hope that revealing the 14) __________ of this bond in such 15) __________ detail will provide clues about how best to attack HIV.