Substance in Saliva Protects Babies from Mom's HIV

Babies with relatively high levels of a certain compound in their saliva are less likely to acquire HIV from their infected mothers at age one month, a new study shows.

The study, "Salivary Secretory Leukocyte Protease Inhibitor Is Associated with Reduced Transmission of Human Immunodeficiency Virus Type 1 Through Breast Milk," was published in the Journal of Infectious Diseases (2002;186: 1173-1176). The authors found that one-month-old babies with higher levels of secretory leukocyte protease inhibitor (SLPI) were half as likely to have acquired HIV from their mothers as babies with lower levels of the substance.

"SLPI is a protein that could be developed into a drug," said Dr. Carey Farquhar of the University of Washington-Seattle. He noted that it could eventually be possible to administer drugs that mimic the action of SLPI and help prevent babies from acquiring their mothers' HIV.

Previous studies have shown SLPI in saliva to have antiviral, antibacterial, and anti-inflammatory properties. One study suggested that this healing compound may explain why dogs and other animals lick their wounds. Prior research has also shown that SLPI, as well as other compounds in saliva, can combat HIV-1. However, only SLPI has been capable of combating the virus when tested in the lab at concentrations found in normal saliva.

For the current study, the authors tested 602 saliva samples from 188 infants born to HIV-1-infected mothers. Saliva samples were taken from the infants at birth and at ages 1, 3, and 6 months. Usually, the SLPI concentration in the infants' saliva dropped from birth to age 6 months.

Farquhar and his colleagues did not find an overall link between SLPI levels and the risk of mother-to-child infections. However, they noted that babies with high SLPI levels at age 1 month were half as likely as other babies to have become infected by HIV-1 from their mother's breast milk.

Although HIV does not often infect people after oral exposure -- which researchers have suggested could also be due to SLPI -- approximately 40 percent of all cases of mother-to-child transmission of HIV occur through breast milk, Farquhar said. He also pointed out that a baby becomes orally exposed to the mother's blood and genital secretions in the birth canal. In the womb, the baby drinks amniotic fluid, which also contains HIV.

Farquhar added that it might not be useful to test babies' SLPI levels at birth to gauge their susceptibility to infection. "We found that month 1 SLPI levels were associated with breast milk transmission, and in countries where HIV-infected women breast-feed their babies, it would probably be better to test maternal HIV viral load to determine how much virus the mother has in her body," he said.

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