The Human Immunodeficiency Virus that causes AIDS attacks the CD4+ T cells and reduces the individual's ability to fight off infections. HIV is spread through unprotected anal, vaginal, oral sex; sharing needles; and mother to child during pregnancy, childbirth, or through breastfeeding. AIDS is the Acquired Immune Deficiency Syndrome, and is the result of HIV infection. AIDS is an acute form of HIV infection. A diagnosis of AIDS means that an individual is living with HIV and also has a CD4+T-cell count of 200 or less and an opportunistic infection. (More on CD4+T cells shortly.) The virus can be passed spread from one person to another during anal, vaginal, and less commonly during oral sex. HIV can also be spread by sharing needles or equipment to inject drugs, tattoo or body pierce. It can also be passed from a mother with HIV to her baby. Currently there is no vaccine to prevent HIV infection nor is there a cure.
CD4+ T (a type of white blood cell that helps to protect the body from infection) tells the immune system how to perform when an infection occurs. But the HIV virus targets and destroys these cells, thus weakening the immune system. A healthy, uninfected person usually has 800 to 1,200 CD4+ T cells per cubic millimeter (mm3) of blood. During untreated HIV infection, the number of these cells in a person's blood progressively declines. When the CD4+ T cell count falls below 200, the HIV infected person becomes particularly vulnerable to the opportunistic infections and cancers that typify AIDS, the end stage of HIV disease. People with AIDS often suffer infections of the lungs, intestinal tract, brain, eyes, and other organs, as well as debilitating weight loss, diarrhea, neurologic conditions, and cancers such as Kaposi's sarcoma and certain types of lymphomas.
Structure of HIV and CD4+T Cell and the Infection Process
Courtesy of the Howard Hughes Medical Institute
Most scientists think that HIV causes AIDS by directly inducing the death of CD4+ T cells or interfering with their normal function, and by triggering other events that weaken a person's immune function. For example, the network of signaling molecules that normally regulates a person's immune response is disrupted during HIV disease, impairing a person's ability to fight other infections. The HIV-mediated destruction of the lymph nodes and related immunologic organs also plays a major role in causing the immunosuppression seen in people with AIDS. Immunosuppression by HIV is confirmed by the fact that medicines, which interfere with the HIV lifecycle, preserve CD4+ T cells and immune function as well as delay clinical illness.
[For more details on the structure and process of HIV, go to the National Institute of Allergy and Infectious Diseases' Fact Sheet]
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