More on How HIV Causes AIDS

More on How HIV Causes AIDS

A significant part of NIAID research is devoted to the pathogenesis of HIV disease. Studies on pathogenesis address the complex mechanisms that result in the destruction of the immune system of an HIV-infected person. A detailed understanding of HIV and how it establishes infection and causes AIDS is crucial to identifying and developing effective drugs and vaccines to fight HIV and AIDS.

Overview

Untreated HIV disease is characterized by a gradual deterioration of immune function. Most notably, crucial immune cells called CD4 positive (CD4+) T cells are disabled and killed during the typical course of infection. These cells, sometimes called "T-helper cells," play a central role in the immune response, signaling other cells in the immune system to perform their special functions.

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/mm³, a 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.

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.