HIV researchers have suspected for some time that an unknown molecule or complex is able to stop HIV and other retroviruses from being released from the cell surface.

In HIV, this antiviral activity is antagonised by an accessory protein called Vpu, which is required for efficient HIV-1 particle release.

Paul Bieniasz, Stuart Neil and Trinity Zang from Rockefeller University in the US have tracked down a protein that they believe causes the retention of virions on infected cell surfaces.

They have identified the membrane protein CD317 (also known as BST2 or HM1.24) as the candidate, giving the protein the new name of 'tetherin' to reflect its ability to tether the virions to the infected cell surface.

Using a variety of methods, the researchers have shown that Vpu is used by HIV for particle release in order to neutralise tetherin's activity. In engineered cells with depleted levels of CD317, HIV no longer needed Vpu for release.

The authors say their findings strongly suggest that a major function of Vpu is to facilitate virus spread by antagonising tetherin-induced particle retention.

They suggest inhibition of Vpu function and mobilisation of tetherin's antiviral activity is a potential therapeutic strategy for HIV/AIDS.

The study, Tetherin inhibits retrovirus release and is antagonized by HIV-1 Vpu, is published in the January 17 issue of Nature.