Semen gives us a Christmas gift

In what for me is one of the most novel papers I have read this year, researchers in the US, Spain and Germany have found that human semen has a protein that aids HIV in increasing its transmission and attachment to host cells in the female genital tract. This paper in Cell is fascinating and reveals a novel mode through which HIV acts to its advantage by latching on to a rare protein in semen. This protein can possibly increase the spread of infectious HIV through sex more than 100,000 times.

In a nutshell, the authors found a protein in human semen- prostatic acidic phosphatase (PAP)- which can kind of pick up infectious HIV particles and transmit them. This protein can increase the transmission of HIV several thousand fold. As an interesting and significant side-point, the rate of transmission of HIV through sex is actually pretty crummy and that is one of the reasons the AIDS epidemic is not as bad as it could have been (No, I am not advocating unsafe sex...unless your favourite game is Russian roulette)

But in an even more novel development, the authors find that PAP forms amyloid fibrils that constitutes the form in which HIV gets transmitted. HIV latches on to this amyloid form and then infects host cells much more efficiently. Interestingly, now about 30 disorders have been found in which amyloid has been involved. Nor is amyloid restricted to Alzheimer's Aß peptide. Many proteins can form the characteristic conformational signature of amyloid under the right conditions. Amyloid increasingly seems to be a timeless passenger whose fate has been possibly intertwined with ours for millennia.

I will leave it to you to read the paper and will probably have more detailed thoughts later. But the paper illustrates several points; firstly, how evolution again may have adapted HIV to take advantage of its natural environment. Semen is the lifeblood of HIV when it's sexually transmitted and any modification that allows the virus to thrive in semen and take advantage of the biomolecular machinery in semen will prove hugely important to it. Several other substances in semen also buttress HIV, a virus that is so fragile that exposure to the natural environment incapacitates it in seconds. Basic amines in semen like spermine for example can neutralise the dangerous acidic environment of the vagina. It is one of the grim ironies of nature that a life-form that is extraordinarily susceptible to the elements wreaks havoc in the human world on an unparalleled scale. The paper also illustrates a possible point of intervention in stopping the transmission of HIV, although much detail needs to be fleshed out before rational therapy can be contemplated.

But most importantly, the paper again indicates how fascinating science is, where novel insights keep on transforming both basic and applied science. Stem cells, a novel and hiterto unnoticed paradigm about how antibiotics work, and now this. Good year for the biomedical community and good year for Cell. And this paper is definitely one of the better Christmas gifts the medical world could have received.

Opinion