The immune system is made up of a variety of different types of cells (e.g., leuckocytes, lymphocytes, phagocytes, B cells, CD8+ cells). HIV targets CD4+ cells, also called helper T-cells. Health care professionals often use the terms "CD4+ cell" and "T-cell" interchangeably. Helper T-cells are immune system managers. They "instruct" other cells when to start and stop carrying out their various duties.

HIV and the Immune System
HIV interferes with the immune response in the following ways:

• HIV replicates more quickly than the immune system cells and challenges the immune system's speed and efficacy.

• HIV targets CD4+ cells, the cellular managers of the immune system, destroying their ability to activate other immune system cells.

• HIV destroys the CD4+ cells and puts demands on the body to replace them.

Healthy, uninfected people have between 800 and 1200 CD4+ cells per mm of blood. HIV causes the number of CD4+ cells to decline to dangerously low levels, making a person infected with the virus very vulnerable to the opportunistic infections (e.g., cancers, neurological conditions, diarrhea, weight loss) that characterize AIDS. This also puts the person at high risk for unusual infections. According to the Centers for Disease Control, a CD4+ cell count below 200/mm is a criterion for AIDS.

Overview
HIV Virus
AIDS
Transmission
Treatment

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