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Battling AIDSYou've seen how the immune system successfully fights invaders such as the mumps virus. Why isn't it able to do the same with HIV? The reason is that the virus attacks the immune system's T cells, thus disrupting the body's immune response. Still, the immune system puts up a valiant fight, producing a billion new cells every day to combat the virus. A billion isn't enough, though, because a billion copies of the virus are also produced every day. The two forces continue to fight—day after day, month after month, sometimes year after year—until the immune system exhausts itself. Once this happens, the number of T cells drop dramatically. And with this vital component of the immune system missing, the body is left susceptible to other diseases. Fighting Other Invaders The attacker in Fighting Back was a virus. The immune system would respond similarly if the body were attacked by bacteria or other microorganisms. The Real World The sequence of events presented in this feature may seem somewhat involved—and yet, exactly how the immune system works is decidedly more complex and still not fully understood. Although much has been learned in the past decade, there is much left to be discovered. Search for a Vaccine | See HIV in Action | AIDS in Perspective The Virus Fighters | Fighting Back | Help/Resources Teacher's Guide | Transcript | Site Map | Surviving AIDS Home Editor's Picks | Previous Sites | Join Us/E-mail | TV/Web Schedule About NOVA | Teachers | Site Map | Shop | Jobs | Search | To print PBS Online | NOVA Online | WGBH © | Updated October 2000 |