Bad though it has been, the AIDS epidemic would have been a great deal worse but for a strange and unexplained quirk.
Infected mothers, it was feared, would transmit HIV, the AIDS-causing virus, to their children when suckling them.
Mothers’ milk carries the virus, and suckling may last two years–which is plenty of time for transmission to happen. And indeed it does, but not nearly as often as was originally suspected.
Less than 10% of infants suckled by untreated infected mothers (those not on antiretroviral drugs, which suppress the virus’s reproduction) pick up HIV.
Why that should be has remained mysterious. But Genevieve Fouda of Duke University, in North Carolina, and her colleagues think they have the answer.
If they are right, many children have been spared AIDS by a fluke–but a fluke that could be used to develop a new weapon to attack it.
Clearly, something in milk disables HIV. Previous experiments had identified proteins that do this to a certain extent, but nowhere near enough to explain all the data. Those earlier searches must therefore have missed something crucial. Dr Fouda, as she describes in the Proceedings of the National Academy of Sciences, set out to find what it was.
Milk is a complex mixture of chemicals, so her problem was how to isolate one of them without knowing in advance which was responsible. That meant running raw milk through a series of processes, each of which divided it into smaller and smaller fractions, and testing each fraction for its HIV-neutralising quality on the way. That quality, it turns out, is concentrated in a single protein called tenascin-C. Further experiments showed that this protein disables HIV by locking onto a protein on the virus’s surface, and that it is as effective at doing so as antibodies generated by the immune system for that specific purpose.
This was a surprise, because tenascin-C is not an antibody, nor had it been suspected of having any antiviral function. Its known jobs are to help the development of the fetal brain and to assist in wound healing. That it is also the right shape to attach itself to HIV’s envelope protein seems a complete coincidence–which, indeed, it must be because AIDS is such a recent disease that evolution could not have had time to throw up a novel (and also ubiquitous) anti-HIV protein of this sort.
Whether tenascin-C, or something derived from it, can be deployed against HIV by doctors, rather than just by nature, remains to be seen. As far as possible, infected mothers are now given antiretroviral drugs–both for their own health and for the health of their suckling infants–so Dr Fouda’s discovery will probably not affect them directly.
For the wider campaign against AIDS, however, it could be of great importance. The generals running that campaign are now shifting their approach from defence to attack, and are talking of ways to bring about an AIDS-free world. For them, a natural human protein that neutralises the virus will be interesting indeed.
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