University of Texas Medical Branch at Galveston
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DATE: Feb. 9. 1999
CONTACT: Tom Curtis, (409) 772-2455; [email protected]
SOURCE: Samuel Baron, M.D., professor of microbiology and immunology,
(409) 772-2325; [email protected]

Holy Spit! Saliva Kills HIV-Infected Cells, Disables AIDS Virus

GALVESTON, TX -- Though millions of people around world are infected with the AIDS virus, there have been remarkably few reports of its spread by kissing, dental treatment, biting or coughing. Even among those people whose bodies are actively shedding the human immunodeficiency virus (HIV), their saliva usually contains only non-infectious components of the virus. Three researchers at the University of Texas Medical Branch at Galveston (UTMB) wondered why this should be so and completed a series of experiments that suggested a surprising explanation.

As reported in the just-published issue of the journal Archives of Internal Medicine, their answer is that human spit appears to be powerfully protective because it contains so little salt. The researchers' test-tube studies indicate that saliva inactivates more than 90 percent of the HIV-infected blood cells, breaking the virus apart into non-infectious components and thus blocking by about 10,000-fold the production of HIV and other viruses in those cells.

Researchers Samuel Baron, Joyce Poast and Miles W. Cloyd were led to their new conclusions by puzzling findings in previous studies which showed that proteins in saliva seem to neutralize or disable the AIDS virus by only two- to fivefold. If that was all the protection available then why, they wondered, was HIV almost completely absent in infected people's saliva? Virus-fighting salivary antibodies also seemed to be present in concentrations too low to explain this lack of virus. Looking for some other factor that might explain the nearly complete dearth of HIV in saliva, the researchers hypothesized that the chief reason for the absence of the virus was the fact that saliva is only one-seventh as salty as most other body fluids.

Salt is necessary to keep cells alive, explains Dr. Baron, professor of medicine and immunology at UTMB. If you place red blood cells, which contain salt, in a glass of drinking water, he notes, they will promptly absorb the liquid, swell up, and explode. Virtually the same thing happens to blood cells, known as leukocytes, that can harbor HIV or other viruses, Baron's and his colleagues' results showed.

But while kissing those with AIDS may be safe thanks to saliva's low-salt content, there is strong evidence that some other activities, such as oral sex or breast feeding with an infected individual, are good ways to spread the disease. Why doesn't saliva protect people in those cases?

According to the new research, breast milk, colostrum (pre-milk fluid in nursing women), seminal fluid, and balanced salt solution (a solution approximating the salts present in the body) may act to replace the salts missing in saliva, thus providing the infected cells an environment salty enough in which to survive and transmit virus. Both semen and breast milk seem to overwhelm saliva's ability to kill HIV-infected cells, Baron says.

"If you add the infected cells to a large amount of blood, semen or breast milk, and then you add saliva, any of those three fluids will protect the infected cells from being killed by saliva," Baron says. "This is consistent with other evidence that those three fluids can transmit HIV. But in the presence of saliva and the absence of those three fluids, HIV appears to be transmitted only rarely."

Currently, a number of researchers are testing various compounds that might work like saliva to destroy infected cells and thus protect against HIV. Baron himself is exploring the use of bile detergents, a cheap and naturally occuring substance in the body that he says is a hundred times more effective than saliva at demolishing the cell membrane and killing HIV-infected cells. It uses its detergent activity to break up the infected cell.

Baron stresses that the study involved only a small number of subjects: six HIV-negative people who provided either saliva, blood that was later infected with the AIDS virus in the laboratory, or both blood and saliva. The experiments also employed human blood cells and mouse cells that were infected with a "surrogate virus" that was easier to detect, vesicular stomatitis virus (VSV). These experiments must be repeated and verified by other researchers, Baron says, before definitive conclusions can be drawn.

But Baron is hopeful. "If this natural defense can be adapted from the mouth to the vagina and rectum, then it's possible that a substantial percentage of the 5.8 million cases of HIV transmission that occur each year might be prevented," he says.


or an abstract of this paper, visit the Archives of Internal Medicine Web site at

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