AIDS is not a kissing disease, and now researchers think they have found at least one reason why.
Their discovery: a protein in human saliva that keeps the AIDS virus from infecting white blood cells.AIDS does not appear to be transmitted readily through kissing or oral sex. In fact, it's difficult to even find HIV, the AIDS virus, in the saliva of people who are infected.
"It has been known for many years that the spread of HIV through saliva is not extensive," Dr. Tessie McNeely said Monday. "That's why we were prompted to look for the physiological reason for that."
McNeely, a researcher at the National Institute of Dental Research, believes she has found it.
A protein in saliva called secretory leukocyte protease inhibitor, or SLPI (pronounced slippy), attaches itself to white blood cells and protects them from infection.
Just how SLPI does this is unclear. But it may open up new strategies for AIDS medicines. Researchers from a biotechnology company, Synergen Inc. of Boulder, Colo., which owns rights to develop SLPI, contributed to McNeely's study.
McNeely said it may be possible to inject SLPI directly into the bloodstream to keep the virus from attacking blood cells. SLPI already circulates in the blood, but in extremely low levels.
Saliva contains other molecules that help disarm microbes in the mouth. But even when many of these are removed from saliva, it continues to protect cells from HIV.
"This is a very nice piece of work," commented Dr. Earl J. Bergey of the State University of New York at Buffalo.
However, Bergey said there may be many things in saliva, not just SLPI, that fight HIV.