"Discovered: A Natural Protein in Breast Milk That Fights HIV"

"For decades, public health officials have puzzled over a surprising fact about HIV: Only about 10-20 percent of infants who are breastfed by infected mothers catch the virus. Tests show, though, that HIV is indeed present in breast milk, so these children are exposed to the virus multiple times daily for the first several months (or even years) of their lives."

Now, a group of scientists and doctors from Duke University has figured out why these babies don’t get infected. Human breast milk naturally contains a protein called Tenascin C that neutralizes HIV and, in most cases, prevents it from being passed from mother to child. Eventually, they say, the protein could potentially be valuable as an HIV-fighting tool for both infants and adults that are either HIV-positive or at risk of contracting the infection."

The research, published today in Proceedings of the National Academy of Sciences, was inspired by previous work by other researchers showing that, both in tissue cultures and live mice, breast milk from HIV-negative mothers was naturally endowed with HIV-fighting properties. Scientists suggested that a few different proteins in the milk could potentially be responsible, but no one knew which one."

Tenascin C’s presence in breast milk, though, prompts a deeper question: Why would milk naturally include a protein that battles HIV, a virus that evolved extremely recently in our evolutionary history, sometime in the early 20th century?

“I don’t think it’s in breast milk to combat HIV specifically, but there have been other, related infections that have passed through breastfeeding,” Permar says. “Our work has shown that Tenascin C’s activity isn’t specific to HIV, so we think it’s more of a broad-spectrum anti-microbial protein.”

In other words, Tenascin C is effective at combating a large variety of infections (perhaps related to its role in adults, where it holds various types of tissue together, necessitating receptors that can bind to a wide array of different cells). The fact that it happens to bind at just the right spot on HIV’s outer envelope so that it combats the virus’ transmission, as Permar puts it, is “a gift from evolution.”

Smithsonian.com