AIDS - Causes

AIDS develops when HIV attacks and destroys certain types of cells that are part of the immune system. The immune system consists of all those cells, tissues, and substances that protect the body from infection by foreign bodies, such as bacteria. An important element of the immune system is a group of white blood cells that include helper T cells, macrophages (pronounced MAK-ruh-fages), and monocytes (pronounced MON-uh-sites). These cells attack foreign bodies and prevent them from causing disease and infection.

After it enters the body, HIV attaches itself to a certain part of these cells called the CD4 protein. The virus then takes command of the chemical changes that take place within the cell. It orders the cell to start making copies of the HIV virus. It eventually causes the cell's death. As the cell dies, it breaks apart and releases many new copies of the HIV. The new HIV cells then travel through the bloodstream and attack other white blood cells.

As white blood cells die, the immune system becomes weaker. The body is no longer able to fight back against infection. Infections that would normally be relatively harmless, such as the common cold (see common cold entry), can become life-threatening to someone who is HIV positive.