In a finding that could help develop a potential HIV vaccine, American scientists have identified a set of antibodies that can block one of the key ways the AIDS virus gains entry into blood cells.

The study by researchers at the Duke University Medical Center expands traditional notions about how the immune system fights HIV and offers a potential new strategy for HIV vaccine design.

In most infections, antibodies that fight off invading pathogens show up quickly and get right to work but with HIV, the most powerful antibodies typically don’t materialise until weeks or even months after initial infection - way too late to be effective, Journal of Experimental Medicine reported.

“The beauty of this newly identified set of antibodies, called polyreactive anti—phospholipid antibodies, is that they are so potent against the type of virus that establishes infection during mucosal transmission,” said lead author Anthony Moody.

“Our research suggests we may be able to harness them and enhance their anti—viral activity with a vaccine to fight HIV directly,” Moody said adding “the antibodies, PGN632, P1, IS4 and CL1, do not appear to have any pathogenic features, even though other members of the class do,” Mr. Mooody said.

“Earlier studies by others have demonstrated that anti—phospholipid antibodies have anti—viral effects, but what we have done in this paper is to show how they do that,” Mr. Moody said.

In a series of laboratory tests on blood taken from HIV—infected patients as well as healthy volunteers, the team found that when these antibodies bind to monocytes or white blood cells, they cause them to secrete substances called chemokines that block HIV from docking with its favourite entry point into a blood cell, the CCR5 receptor.

“In other words, they don’t go after individual viral particles directly, but instead, indirectly, by creating a chemical roadblock at one of the virus’ most commonly used portals.”

That doesn’t happen all the time, however. The study showed antiviral activity in only 85 per cent of the blood they tested and only in the presence of monocytes.

The researchers believe the finding has particular strategic importance because most of the HIV strains use the CCR5 receptor to gain entry into a cell. Since it is one of the earliest events in the process of infection, being able to potentially intervene at that juncture could be meaningful.

While the findings still have to be tested clinically, they do suggest a new way the immune system might be manipulated to thwart HIV, said senior author Barton Haynes.

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