Semen protein may explain why HIV is so hard to combat

HIV infects human immune cells by turning the infection-fighting proteins of these cells into a "backdoor key" that lets the virus in.

Researchers have now found that another protein is involved as well.

A peptide in semen that sticks together and forms structures known as "amyloid fibrils" enhances the virus's infection rate by up to an astonishing 10,000 times, the findings showed.

The HIV fibrils are known as semen-derived enhancers of viral infection (SEVI).

How and why these fibrils enhance infection and cause toxicity in the body's cells remains unknown.

"Amyloid fibrils play an important role in a number of prominent diseases, such as Parkinson's, Alzheimer's and others, and it is absolutely essential that we understand how they work if we have any hope of developing new drugs to stop them," said lead author Ian Musgrave from the University of Adelaide in Australia.

In laboratory studies, the team found that the HIV fibrils are toxic towards cells from the nervous system. They also found that even when the fibril is broken apart, its constituent elements continue to be toxic.

"This suggests that you cannot just prevent one part of SEVI from aggregating and being toxic to cells. You need to shut the whole thing down or stop it from forming in the first place," Musgrave added.

The findings were published online in the journal Biochimica et Biophysica Acta.