What Is AIDS?

AIDS stands for Acquired imunodeficiency (or immune deficiency) Syndrome. It results from infection with a virus called HIV, which stands for human immunodeficiency virus. This virus infects key cells in the human body called CD4-positive (CD4+) T cells. These cells are part of the body's immune system, which fights infections and various cancers.

When HIV invades the body's CD4+ T cells, the damaged immune system loses its ability to defend against diseases caused by bacteria, viruses, and other microscopic organisms. A substantial decline in CD4+ T cells also leaves the body vulnerable to certain cancers.

There is no cure for AIDS, but medical treatments can slow down the rate at which HIV weakens the immune system. As with other diseases, early detection offers more options for treatment and preventing complications.

AIDS affects women differently than it does men, and it presents unique issues related to sexuality, childbearing, and side effects of treatments.

What Is The Difference Between HIV And AIDS?

The term AIDS refers to an advanced stage of HIV infection, when the immune system has sustained substantial damage. Not everyone who has HIV infection develops AIDS.

When HIV progresses to AIDS, however, it has proved to be a universally fatal illness. Few people survive five years from the time they are diagnosed with AIDS, although this is increasing with improvements in treatment techniques.

Experts estimate that about half the people with HIV will develop AIDS within 10 years after becoming infected. This time varies greatly from person to person, however, and can depend on many factors, including a person's health status and health-related behaviors.

People are said to have AIDS when they have certain signs or symptoms specified in guidelines formulated by the U.S. Centers for Disease Control and Prevention (CDC).

The CDC's definition of AIDS includes:

• All HIV-infected people with fewer than 200 CD4+ T cells per cubic millimeter of blood (compared with CD4+ T cell counts of about 1,000 for healthy people)
• People with HIV infection who have at least one of more than two dozen AIDS-associated conditions that are the result of HIV's attack on the immune system

AIDS-associated conditions include:

• Opportunistic infections by bacteria, fungi, and viruses. Opportunistic infections are infections that are rarely seen in healthy people but occur when a person's immune system is weakened.
• The development of certain cancers (including cervical cancer and lymphomas)
• Certain autoimmune disorders Autoimmune disorders are illnesses that result when the immune system attacks an individual's own tissues or cells.

Most AIDS-associated conditions are rarely serious in healthy individuals. In people with AIDS, however, these infections are often severe and sometimes fatal because the immune system is so damaged by HIV that the body cannot fight them off.

The History Of AIDS

The symptoms of AIDS were first recognized in the early 1980s:

• In 1981, a rare lung infection called Pneumosystis carinii pneumonia began to appear in homosexual men living in Los Angeles and New York.
• At the same time, cases of a rare tumor called Kaposi's sarcoma were also reported in young homosexual men. These tumors had been previously known to affect elderly men, particularly in parts of Africa. New appearances of the tumors were more aggressive in the young men and appeared on parts of the body other than the skin.
• Other infections associated with weakened immune defenses were also reported in the early 1980s. Groups most frequently reporting these infections in the early 1980s were homosexuals, intravenous drug users, and people with hemophilia, a blood disorder that requires frequent transfusions. Blood and sexual transmission were therefore suspected as the sources for the spread of the infections.

In 1984, the responsible virus was identified and given a name. In 1986, it was renamed the human immunodeficiency virus (HIV).

What Causes AIDS?

HIV is a type of virus called a retrovirus. Like all viruses, it must invade the cells of other organisms to survive and reproduce. HIV multiplies in the human immune system's CD4+ T cells and kills vast numbers of the cells it infects. The result is disease symptoms.

Nice To Know: There are two forms of HIV: HIV-1 is the more common and more potent form. This form of HIV has spread throughout the world. HIV-2, which is less potent that HIV-1, is found predominantly in West Africa. It is also more closely related to two HIV-like viruses found in monkeys. There also are different strains of the virus, which makes it difficult to find one single treatment.

About The Immune System

Our bodies use a natural defense system to protect us from bacteria, fungi, viruses, and other microscopic invaders. This system includes general, nonspecific defenses as well as weapons custom-designed against specific health threats:

• Innate, or nonspecific, immunity is the first line of defense. Our skin, tears, mucus, and saliva, as well as the swelling that occurs after an infection or injury, contain types of immune cells and chemicals that attack disease-causing agents attempting to invade the body.
• Adaptive, or specific, immunity uses specialized cells and proteins called antibodies to attack invaders that get past the first line of defense. These weapons target specific proteins called antigens, found on the surface of the invading organism. The immune system can quickly rally these custom-tailored defenses if this particular invader attacks again.

There are two types of adaptive immune responses:

• The humoral immune response involves the action of specialized antibody-producing white blood cells. The antibodies (proteins produced by the immune system to fight infectious agents such as viruses), which circulate in the blood and other body fluids, can recognize specific antigens (substances that stimulate the production of antibodies). They latch onto the viruses, bacteria, toxins, and other substances that bear these antigens, targeting them for destruction.
• The cell-mediated immune response involves the action of another group of specialized white blood cells that direct and regulate the body's immune responses or directly attack cells that are infected or cancerous.

How Do White Blood Cells Help Fight Disease?

White blood cells, particularly macrophages and B and T lymphocytes, play central roles in the immune system's defenses against viruses and other foreign invaders.

• Macrophages contribute to both nonspecific and specific immune responses. These versatile cells act as scavengers, engulfing and digesting microbes and other foreign material in a cell-eating process called phagocytosis. They also, upon encountering an invading organism, release chemical messengers that alert other cells of the immune system and summon T lymphocytes to the scene.
• B lymphocytes, or B cells, serve as the body's antibody factories. Each antibody is targeted to recognize and bind to an antigen from a specific invader. When antibodies circulating through blood and body fluids encounter this invader, they mark it for destruction.
• T lymphocytes, or T cells, are part of the cellular immune response. Some T cells, like CD4+ T cells (also called "helper" T cells), direct and regulate the body's immune responses. Others are killer cells that attack cells that are infected or cancerous.

How Does HIV Infection Become Established In The Body?

Researchers have found evidence that immune-system cells called dendritic cells may begin the process of infection. After exposure, these special cells may bind to and carry the virus from the site of infection to the lymph nodes, where other immune system cells become infected.

HIV targets cells in the immune system that display a protein called CD4 on their surface. Such cells are called CD4-positive (CD4+) cells.