Healthy vaginal tract lining no barrier against HIVJanuary 17th, 2009 - 5:38 pm ICT by IANS
Washington, Jan 17 (IANS) The human immunodeficiency virus (HIV) can penetrate healthy vaginal tract lining during sexual intercourse. This lining had earlier been thought to be an effective barrier against the deadly virus.”This is an unexpected and important result,” said Thomas Hope, principal investigator and professor of cell and molecular biology at the Northwestern University Feinberg School of Medicine. “We have a new understanding of how HIV can invade the female vaginal tract.”
“Until now, science has really had no idea about the details of how sexual transmission of HIV actually works,” Hope added. “The mechanism was all very murky.”
Hope, his Northwestern colleagues, and collaborators at Tulane University discovered that interior vaginal skin is vulnerable to HIV invasion at the level where it naturally sheds and replaces skin cells, a point where the cells are not as tightly bound together.
Women and female adolescents now account for 26 percent of all new HIV cases in the US, according to the Centres for Disease Control (CDC).
Based on its most recent analysis of 2005 data, the CDC estimated that there were 56,300 new HIV infections that year and traced 31 percent of the total to high-risk heterosexual contact. More than half of the new cases of HIV infection worldwide are in women.
Hope expects his findings, if confirmed by future studies, will provide information to help develop microbicides and vaccines to protect against HIV.
“We urgently need new prevention strategies or therapeutics to block the entry of HIV through a woman’s genital skin,” Hope said. While condoms are 100 percent effective in blocking the virus, “people don’t always use them for cultural and other reasons”, he noted.
By labelling the HIV viruses with photo-activated fluorescent tags, Northwestern researchers were able to view the virus as it penetrated the outermost lining of the female genital tract, called the squamous epithelium, in female human tissue obtained from a hysterectomy and in animal models.
Researchers found that HIV penetrated the genital skin barrier primarily by moving quickly - in just four hours - between skin cells to reach 50 microns beneath the skin, a depth similar to the width of a human hair.
This is the depth at which some of the immune cells targeted by HIV are located. HIV penetration was more common in the outermost superficial layers of skin and likely occurred during the normal turnover and shedding of skin cells. In the shedding process, the skin cells are no longer as tightly bound together so water - and HIV - can easily enter.
“As pieces of the skin flake off, that’s the loose point in the system where the virus can get in,” Hope said, according to a Northwestern release.
Previously, scientists thought that the HIV invaded a woman’s immune system through the single layer of skin cells that line her cervical canal. “That was always thought to be the weak point in the system,” Hope said.
However, a previous trial in Africa in which women used a diaphragm to block the cervix did not reduce transmission. Nor are women who have had hysterectomies less vulnerable to contracting HIV through sex.
Hope presented his findings at the American Society for Cell Biology’s 48th annual meeting in San Francisco Friday.
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