Researchers from the National Institutes of Health (NIH) have found that a protein in seminal fluid speeds up the spread of HIV in uterine tissue. The protein, called interleukin 7 (IL-7), is from a family of proteins that regulate the immune response. IL-7 is found in normal semen, but is found at high levels in the semen of men with HIV infection.
The researchers created a culture system of small pieces of cervical tissue and used it to simulate male-to female HIV transmission. They then observed the spread of the virus to tissue under controlled conditions at the laboratory. In tissue containing IL-7 at levels found in the semen of HIV-infected men, the virus spread more quickly than to tissue that was not treated with IL-7. The researchers suggest that IL-7 alone or along with other molecules foster male-to-female HIV transmission. Also, it is possible that the level of IL-7 in semen determines how infectious a specific HIV-infected male is for a female partner.
HIV targets T cells, a type of immune cell that helps organize the body's defenses against disease-causing organisms. The T cells die quickly when they are infected with HIV, before the virus can produce a large number of copies of itself. The researchers found that in isolated pieces of cervical tissue, HIV-infected T cells live longer in the presence of IL-7 and continue to produce the virus. IL-7 also stimulated uninfected T cells to divide, thus increasing their number. The new T cells are additional targets for the virus to enable it to increase its spread. Researchers believe that one day it may be possible to prevent or delay HIV transmission by blocking seminal IL-7. The researchers said that they need additional studies to confirm the observations.
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