HIV and the immune system

AIDS is the most serious form of an illness caused by a virus called the Human Immunodeficiency Virus (HIV). Although it is well established that HIV is the primary cause of AIDS, it not fully understood how it does it. In general, the virus attacks or disables the body's immune system. Over time, if the immune system become seriously damaged, the body loses the ability to combat a variety of illnesses, called opportunistic infections (OI's ) or conditions. Each new infection further wears down the body's defenses. These infections and cancers, such as pneumocystis pneumonia (PCP) and Kaposi's sarcoma (KS), are the real killers of people with HIV.

This gradual destruction of the immune system, however, doesn't happen the same way in everyone, or at the same pace. In some people, it may not happen at all. In a small percentage of people, infection with HIV leads to destruction of the immune system very rapidly, in just a few years. But others remain well for 10 to 15 years or longer. On average, most people remain well for about 10 years before experiencing the first serious symptoms.

• Tests which measure the amount of virus in the bloodstream (called "viral load" tests) can generally predict how quickly HIV will damage the immune system. In effect, viral load tests tell you the expected rate of disease progression—the higher the number, the faster the progression. Effective treatments are now available which can greatly reduce the level of virus, thus slowing the rate of disease progression.
   
• Tests which measure the level of a certain type of white blood cells, called the CD4+ (CD 4 positive) can measure the decline of immune health. Many scientists feel that the CD4+ test tells you how far you have already progressed toward AIDS or AIDS-related infections. Treatment, however, can prevent or delay many of these infections, as well as slow the decline of the immune system.
   
• For long periods, often several years, the body seems to cope effectively with HIV in many people. The number and percentage of CD4+ cells fall, but slowly. During this period, most people suffer no obvious ill effects and feel normal. Despite this, most researchers believe that damage is being done to the immune system in this period. Many scientists believe that early intervention during this period may have the greatest impact.
   
• Without treatment, the body can slowly lose its ability to fight infections. Some infections, like pneumocystis pneumonia (PCP), become likely when the CD4+ count falls below 200 or 300. Minor infections can occur at counts higher than 300. Other life-threatening infections become more likely when the count falls below 50 or 100. Once the body loses its ability to fight these infections, it's unclear whether current treatment can restore it.

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