Mumbai: 

Infected: HIV has already attached itself to the sperm cell and is indicated in green

Clean: The introduction of mannan blocks the HIV and the cells (red) remain normal

After a series of experiments and extensive research, scientists at the National Institute for Research in Reproductive Health, Parel, have made an astounding discovery that could help combat the dreaded AIDS virus.

Experiments to find a solution that would prevent HIV from entering the body through sexual intercourse began five years ago, when doctors identified an HIV receptor in the sperm that was distinct from the conventional CD4 receptor (see box). By blocking this receptor, an HIV- infected person can have sexual intercourse without transmitting the virus.

"Sperm and vaginal cells didn't have the CD4 receptor, but they were still carrying and receiving the HIV virus passed on through sexual intercourse," said Dr Atmaram Bandivdekar, assistant director at the centre. "If the experiments with subsequent pre-clinical trials are successful, this could help in developing a strategy to stop the transmission of HIV through sexual intercourse," he added.

The team is the first in the world to identify this special mannose receptor protein in the sperm. Furthermore, it was seen that when a sugar compound called mannan (see picture) was added to the receptor, it completely blocked the binding of HIV to the sperm.

"We suspect that the mannan would have to be applied locally at every sexual instance, but it is too early to commit, as the experiments are still at the laboratory stage," he added.

According to Bandivdekar, the tests have been particularly successful in sperm cells and are still underway with vaginal cells. However, any person who has sexually transmitted infections other than HIV or abrasions on their sexual organs will still be susceptible to the virus.

Sexual intercourse is the primary cause of HIV transmission, apart from blood transfusion, sharing of infected needles and mother-child transmission.

What's a CD4 receptor?

CD4 protein is considered to be the sole source responsible for HIV binding and entry into cells in the body. However, sperm as well as vaginal cells which are responsible for HIV transmission do not have CD4 protein. These cells instead have the mannose receptor.