How HIV Affects the Immune System

HIV infection is characterized by a gradual loss of immune function. Specifically, crucial immune cells, called CD4+T cells, are disabled and killed during the typical course of HIV infection. These cells, also known as T helper cells, play a central role in the body’s immune response; they signal other cells in the immune system to perform special functions. A healthy, uninfected individual has approximately 1000 CD4+T cells per cubic millimetre (µL) of blood.

When HIV enters a person’s CD4+T cells, it uses the cells to replicate or make copies of itself. This process destroys the CD4+T cells and the CD4+T "count" goes down. As CD4+T cells are destroyed, the person’s immune system becomes weaker.

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During the course of HIV infection, CD4+T cells are disabled and killed.

When the CD4+ T cell count falls below 200/µL, the person becomes vulnerable to infections known as "opportunistic infections" and cancers that typify AIDS.