Researchers said they have figured out how a rare antibody sees past the disguises of HIV -- a finding that may lead to a vaccine. The antibody, taken from an unusual patient whose body can resist the virus, recognizes and attacks HIV, unlike most of the body's defenses.

"Nothing like this has ever been seen before," research leader Ian Wilson of the Scripps Research Institute in La Jolla, Calif., said in a statement.

Antibodies are usually able to recognize an invader by structures on its surface, called antigens, and can either call in help or neutralize the invader themselves by pasting themselves against it. Most vaccines in use today stimulate the production of neutralizing antibodies.

The human body makes plenty of antibodies against HIV, but the virus disguises itself with human sugars. One antibody, 2G12, seems to be able to see past this disguise. Austrian researchers discovered it a decade ago in a patient who seemed to resist AIDS. Wilson and colleagues said they have figured out how 2G12 works: It recognizes that while HIV is covered up with human sugars, they are not arranged in a human-like way. The antibody does this with a special structure of its own, which Wilson and colleagues have crystallized and imaged.

"The Fab (antigen-recognition) arms are interlocked," said Scripps researcher Dennis Burton, who worked on the study. "That is a unique arrangement, and it is good for recognizing a cluster of shapes like sugars on a virus."

The next step is to use the antibody's structure as a template to design an antigen to stimulate the production of 2G12 or another antibody that will neutralize HIV, the researchers said. The full report, "Antibody Domain Exchange Is an Immunological Solution to Carbohydrate Cluster Recognition," is published in the June 27 issue of Science (2003;300:2065-2071).

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