Day one:
After you've tested positive

May 2008     View PDF     En español

HIV and your immune system

HIV (human immunodeficiency virus) is the virus that causes AIDS (Acquired Immune Deficiency Syndrome). Being HIV-positive does not mean that you have AIDS, but it does mean that you may develop AIDS. HIV attacks your immune system, gradually impairing how it functions.

Your immune system helps keep your body healthy by recognizing and attacking foreign substances, like viruses or bacteria. Over time, if it becomes seriously damaged or weakened by HIV, your body loses its ability to fight certain infections and cancers. These are called oppor­tunistic infections (OIs).

AIDS is the most serious outcome of HIV infection. It occurs once your immune system has been significantly damaged. If you have certain OIs, it will lead to an AIDS diagnosis. This is because the presence of these OIs in your body points to a significantly damaged immune system.

An AIDS diagnosis will also be given if the counts of your immune system cells (called CD4+ T cells or simply CD4s) fall below 200. These cells are the key players in your immune system. Their “normal” range in a healthy HIV-negative person is 500–1,500 cells/mm3.

This gradual destruction of the immune system doesn’t happen the same way in everyone, or even at the same pace. In some, it may not happen at all. In a small percentage of people, HIV destroys their immune systems very rapidly, in just a few years. But others remain well for 10–15 years or longer. On average, without using HIV therapy, most people remain well for about ten years before facing their first serious symptoms.

A number of things are well known about HIV infection:

• Viral load tests measure the amount of HIV in the bloodstream. They can generally predict how quickly HIV will damage the immune system. In effect, these tests predict the loss of CD4 cells: the higher the number, the greater the risk of damage to your immune system. Using effective treat­ments can greatly reduce the level of HIV and slow its rate of disease progression.
• CD4 cell count tests measure the level of CD4 cells, a certain type of white blood cell. These tests can measure the decline of your immune health. However, taking HIV therapy can slow the decline of your immune health. In fact, many people who start HIV therapy experience a significant increase in their CD4 counts.
• For long periods, often several years, the body copes effectively with HIV in many people. The number and per­centage of CD4 cells fall, but slowly. During this period, most people feel normal and suffer no obvious ill effects. Despite this, most researchers believe that damage is still being done to the immune system. Many scientists believe that early inter­vention during this time may have the greatest impact, though others remain skeptical. They believe the possible side effects from early treatment might outweigh its benefits.
• Without treatment, the body slowly loses its ability to fight infections. Some infections, like Pneumocystis jiroveci pneumonia (sometimes called PCP), become likely when CD4 counts fall below 300 or 200. Minor infections can occur at counts above 300. Other life-threatening infections become more likely when the count falls below 100 or 50.