Beating the HIV virus

In the late 1980s when the biology of HIV was just beginning to be unraveled, a lot of mathematical models predicted that AIDS would exterminate the African race. The picture was grim, and with no cure in sight, AIDS was to sink most of the African population, and hit rock bottom.

But nature knows no bottom. It always finds its own turning point ‘ its own equilibrium. Although HIV has perfected its weapons of attack, to infect every human being exposed to it, nature has spared a few members of the human family. Strange, but some people just can’t get HIV/AIDS. Hello?!

It’s called genetics. In the early 1990s, scientists noticed that some gay men, whose partners had developed full blown AIDS, were still HIV-negative, despite numerous episodes of unprotected sex. Termed Exposed Uninfected (EU) persons, these HIV-negative spouses have also been found in heterosexual partners, now called discordant couples, where one sexual partner is HIV-positive and the other is HIV-negative, despite having unprotected sex.

In another study, some Nairobi commercial sex workers, whose clients had died of AIDS, were still found to be HIV-negative even though they engaged in unprotected sex on many occasions. In Zambia, it has been reported that 21% of co-habiting couples having unprotected sex are discordant for HIV infection, meaning one partner is HIV-positive while the other is HIV-negative.

In HIV discordant men and women, there is an immune system device that helps the body escape HIV infection. Certain individuals inherit a trait to resist HIV infection. Nature has found a way to beat the virus! Infection to HIV is not a uniform trait in the population. No one is absolutely resistant but research has shown that some people are relatively resistant to infection. In some persons, exposure to HIV does not usually lead to infection. Although this could be due to insufficient viral loads, there is now abundant evidence that some individuals resist infection even when directly exposed to high amounts of HIV.

What biological mechanisms explain this phenomenon of HIV discordant individuals, where a couple engaging in unprotected sex for many years will have one partner HIV-positive and the other HIV-negative? The answer lies in cell mechanics and architecture.

A few lucky people are not infected by HIV because their cells are designed differently. Some people are resistant to HIV infection because of an unusual feature on their cells that prevents HIV attachment and passage into cells. How does HIV infect cells?

HIV attaches to a site on our cells called the CD4 receptor. The CD4 receptor is like a window through which HIV enters into body cells. But for efficient entry into cells, HIV attaches to another spot on our cells called the CCR5 co-receptor. The CCR5 molecule acts as the most efficient door through which HIV enters into body cells.

Now, in exposed unprotected persons-those that are HIV-negative despite repeated exposure to the virus through unprotected sex? their cells lack the CCR5 co-receptor. The CCR5 gene in EU persons contains a large mutation, a deletion of about 32 DNA base pairs that abolishes the production of the CCR5 molecule, hence HIV cannot enter into cells.

A genetic test has now been developed to detect the CCR5 mutation and pinpoint people that are resistant to HIV infection. Using genetic engineering techniques, stem cells (cells that produce all our body tissues) that lack the CCR5 co-receptor are now being developed to be used as vaccines against HIV.

Besides the EU persons, there are individuals that are HIV-positive but do not progress to AIDS. They can live for more than 16 years without developing AIDS. Such people are now called “non-progressors”. We have evidence that in non-progressors, the human leukocyte antigen (HLA) genes? code for proteins that play a major role in immunity against bacteria and viruses? are different.

Some changes in HLA genes produce higher levels of virus-specific cytotoxic T-cells that contribute to protection against HIV disease progression in infected individuals. In other words, HIV-positive individuals that stay for a long time without developing AIDS have strange immune systems that keep the virus latent and quiet.

Recently, it has also been found that in some non-progressors, the HIV virus is weaker than the normal strains. The weaker form of the virus has a slower replication capacity and therefore is not very infective. HIV fitness tests indicate that in non-progressors, the HIV has lost its strength? it is attenuated.

Genetic differences in the human host and the virus determine the course of HIV infection and progression to AIDS. Some people cannot be infected by HIV. Others can be infected but take very long to develop AIDS. Yet many others that get infected die within a few years.

The power to live lies in our genetics. But more importantly, the secret to a longer healthy life can be found in nurturing a positive mental attitude, having the hope to live with HIV, and the will power to beat the virus at its own game.

l KC is a lecturer at the University of Namibia. Email comments to: kchinsembu@unam.na

August 2006
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