Chinese researchers said on Thursday they had found a gene in rats that seemed to produce a compound that defends against sexually transmitted diseases.
It has the potential for powerful effects against various microbes, including the AIDS virus and those causing other sexually transmitted diseases, the researchers report in this week's issue of the journal Science.
And it may have contraceptive effects as well, which, when understood, could help lead to development of a microbicide - an agent that can work like a condom in gel or cream form, the researchers said.
The team, at the Chinese Academy of Sciences in Shanghai and the Chinese University of Hong Kong, looked at the sex organs of rats, which reproduce promiscuously and seem to have at least some natural protection against sexually acquired infectious diseases.
They focused on the epididymis, an organ in the testicles involved in sperm production. "It may also act as a reservoir of sexually transmitted bacteria," the researchers, led by Peng Li, wrote.
In the epididymis they found a gene controlling a peptide - a particle of a protein - called Bin1b. There are possible equivalents in humans and chimpanzees.
The peptide is related to a group of known anti-microbial molecules called beta-defensins. None has ever before been found to work in the testicles, but they are found in human saliva, lungs and areas of the urogenital tract.
Bin1b seems to be unique to the rat male reproductive organs.
Tests showed it suppressed the growth of the common E. coli bacteria, which the researchers said suggested the peptide acts as a line of defense in the male organ.
They think it may be involved in nurturing sperm along as well as in defending against invaders such as bacteria. Thus it could be a used as a basis for a drug that would work as a contraceptive and as a microbicide.
Such a drug is a high priority for many AIDS researchers, who realize that people will not always use condoms to protect themselves against HIV.
Studies have shown that men often refuse to use them, and activists have clamored for development of a product that mostly women, but men too, can use to quietly protect themselves from infection.
But it is hard to find an agent that will kill germs without damaging delicate genital tissues.
Researchers were extremely disappointed last year when they found nonoxynol-9, a common spermicide, in fact irritated the tissues of prostitutes participating in a study and increased rather than decreased their chances of becoming infected with HIV.