Master of microevolution pg. 2
Transmitted across mucosal barriers through sexual contact and by direct blood-to-blood contact, HIV relies primarily on a “Trojan horse” approach to reach its target host cell, the helper T cell.
Somehow HIV escapes digestion by the scavenger cells and is presented intact—and thoroughly infectious—to the helper T cell. It hooks, and fuses with, the cell membrane and pulls itself inside. Then, like others in its family of “retroviruses,” it hijacks the cell’s reproductive machinery to make new copies of itself. (See “Secrets of a Deadly Virus”).
HIV replicates faster in helper T cells that are proliferating. “The virus is so in tune with how our immune system works that it’s evolved to thrive in the exact circumstances that the immune system uses to try to beat it back,” says D’Aquila.
Eventually, and it may take years, the population of helper T cells declines—some are killed by the virus; others by mechanisms that are not well understood. When the generals are taken out of the action, immune responses gradually become uncoordinated and ineffective even against weak invaders, called “opportunistic” infections, that otherwise would not gain a foothold in the body. The result: acquired immune deficiency syndrome (AIDS).