For HIV to be able to damage your immune system, the virus first needs to be able to enter specific white blood cells in your immune system called CD4 cells. Once inside a CD4 cell the virus begins to replicate, producing new copies of itself which then go on to infect other CD4 cells.

HIV treatment either interferes with HIV’s ability to replicate or with its ability to enter CD4 cells in the first place. These treatments have proven to be so effective that most people with HIV can now expect to live a long and healthy life [1].

When treatment stops HIV from replicating effectively, your viral load (the number of HIV copies in your blood) will start to fall. As the number of HIV copies in your blood falls, there are fewer numbers of HIV copies available to damage your immune system.

The aim of HIV treatment is to get your viral load to below 50 – that is 50 HIV copies per microlitre of your blood. The standard test for viral load cannot detect less than 50 copies per microlitre, so once your viral load has fallen this far it is referred to as undetectable. Even though it is undetectable, there is still HIV in your body.

After starting HIV treatment, it can take anywhere from a few weeks to several months for your viral load to become undetectable. Sometimes however the drugs don’t work as well as they should, possibly because your HIV is resistant to one or more of the drugs you are taking. If this happens then you and your doctor should think about changing the drugs you are taking for ones that work more effectively.

When your viral load is undetectable, there aren’t enough HIV copies in your blood to infect and destroy your CD4 cells as fast as your body makes new ones. Your body will be able to replace CD4 cells destroyed by HIV and as such your CD4 count will start to rise and your immune system’s ability to fight infection will improve.

As long as you continue to take your anti-HIV drugs on time without missing doses, your body should be able to keep HIV suppressed. This should then allow your immune system to remain strong enough to fight infections and keep you healthy.

"About a year ago my viral load started to rise, and my CD4 count started falling. Then eight months ago my viral load had reached 250,000 and my CD4 count had fallen below 300 so I decided there was no point delaying things any more and in December I began treatment. Within a month my viral load had fallen to under 300 and my CD4 count had risen to over 500. Within the next month my viral load had become undetectable and my CD4 count risen even more. I couldn’t believe how well the drugs were working. Since then my CD4 count has continued to rise and I feel healthier and fitter than I have for quite a long time." (Craig, 34)

References
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1 HIV Life Expectancy Approaching Normal. Michael Smith, North American Correspondent, MedPage Today, June 27, 2008.