Scientists from The Scripps Research Institute and Sea Lane Biotechnologies have found an antibody that recognises the crucial structure that flu viruses use to attach to host cells, even though previously this structure had been thought too small for an antibody to grab effectively.
The immune protein manages to hit this precise spot by using just a small part of its target-grabbing apparatus. In so doing, it can neutralise a broad range of dangerous flu viruses.
"This highly focused binding to the receptor binding site using only a single loop on the antibody has never been seen before, and it's really fascinating; it gives us some good ideas about designs for vaccines and therapies," said Ian A Wilson, senior investigator of the study.
Researchers led by Ramesh R Bhatt of Sea Lane Biotechnologies began by collecting bone marrow from patients who had been exposed to certain key strains of flu.
The bone marrow is a "fossil record" of all the antibodies a person has ever made, researchers felt confident that the antibodies they were looking for would be there.
The researchers generated a "comprehensive flu library" of billions of antibodies. The unusual new antibody which they dubbed C05 was isolated.
C05 also protected cells in the lab dish from infection by these viruses. In mice, relatively low doses of C05 prevented infections despite influenza A exposures that would have been lethal.
The antibody worked as a therapy, too, rescuing 100 per cent of mice when administered up to three days after a flu infection had begun.
Further tests revealed a curious property of C05. Almost uniquely among broadly neutralising antibodies against influenza A, it specifically recognises and blocks the part of the flu virus that mediates viral attachment to host cells.
The researchers found that C05 effectively avoids grabbing the hypervariable regions around the flu "receptor binding site" (RBS).
This viral site is located on the heads of viral hemagglutinins, spiky structures of sugar and protein that coat the viral envelope.
CO5 uses a single elongated protein loop to reach in and make a "one-handed"
