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PGI Study
Greater exposure to HIV virus builds stronger defence
Aditi Tandon
Tribune News service

Chandigarh, October 20
In the first report of its kind from India, investigators from the PGI have studied the mechanisms that protect certain individuals from HIV infection despite repeated exposure to the HIV virus. Such study was earlier reported from Kenya.

Published in four international journals over the past year, the PGI study makes an important contribution to the ongoing global research on the development of HIV vaccine, which depends heavily on the understanding of factors that prevent HIV in some people. The study also has the potential of guiding pharmaceutical firms to produce better drugs.

The idea behind the present work, funded by the Indian Council for Medical Research, was to detail inherent immune responses that offer some people natural protection against HIV. For this purpose, the investigators analyzed the genetic composition of exposed uninfected (EU) individuals, who did not become HIV positive despite regular, unprotected contact with their HIV infected partners.

The sample was taken out of 30 heterosexual couples who attended PGI’s Immunodeficiency Clinic. All these individuals had had regular unprotected sexual contact with infected partners within six months prior to sampling.

The findings were revealing. They showed that there was a smaller group of people who actually required sustained exposure to the HIV virus to keep them protected from HIV infection. This significant finding stands against the conventional wisdom that the more a person is exposed to HIV virus, the more likely he/she is to acquire HIV infection.

In the study group in question, the investigators, through sophisticated tests, found that the more recent a person’s exposure to HIV virus by way of sexual contact with the infected partner, the stronger his/her protective mechanisms against HIV.

“In the EUs we sampled, we discovered that sustained unprotected exposure actually enhanced the activities that prevent HIV. In medical terms, we say that exposure to virus increased T-helper and granule dependent cytotoxic T lymphocytes (CTLs) activity among these people and they never got infected,” said Dr Ajay Wanchu of the Department of Internal Medicine, PGI, who conceived the study. The study has been jointly conducted by the Department of Internal Medicine, PGI, Department of Biochemistry, Panjan University and the Department of Medical Microbiology, PGI.

Besides the above-mentioned finding, the study concluded that EUs had excess quantity of molecules called chemokines in their blood. “These molecules sit on the surface of CD4 T cells, which the HIV virus attacks. By sitting so, they prevent the entry of the virus, offering to the person concerned natural resistance from HIV. We found that persons in our study group were inherently able to produce more chemokines to block CD-4 cell - the receptor of HIV virus - and thus prevent infection,” explained Dr Wanchu, adding that all the persons studied were into monogamous (single partner) relations, which means that even monogamous relationships are enough to elicit protective responses that keep the HIV virus at bay.

Such individuals who do not get infected despite repeated exposure to HIV virus have earlier been described among the sex workers of Kenya. From India, they have been described for the first time by the PGI. Also, whereas the study group in Kenya was involved with many partners, the one in India had single partners, indicating that monogamous relationships can also produce mechanisms for protection from HIV.

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