The HIV virus that causes AIDS is present in the milk of HIV-infected mothers, yet only about 10% of infants who nurse from HIV-infected mothers get infected. In the past it was thought that ingestion is simply a poor route to HIV infection. Now it turns out there’s another reason – human milk contains a protein that latches onto the surface coating of the virus, preventing it from infecting the infant. The protein, called Tenascin-C, normally plays a role in wound healing and fetal development. Its antiviral properties are apparently just a lucky coincidence; it couldn’t have evolved during the course of human evolution to combat HIV, because HIV didn’t exist until recently.
Will Tenascin-C become an important weapon in the fight against HIV infection? Probably not. HIV-infected mothers are already given antiretroviral drugs and they already have Tenascin-C in their milk, so purified Tenascin-C might not add much of a benefit to them or their infants. And it’s unlikely that Tenascin C would work if it were to be given intravenously to patients with established HIV infections. Nevertheless, the finding that a natural human protein can inactivate the HIV virus before it infects the host is leading to renewed hope that a drug with similar properties could be developed. An AIDS-free world may just be within our reach.