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.
Despite the imperfect picture of how HIV destroys the immune system, a
number of things are well established:
- 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
- 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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