A gene mutation that protects some people from infection with the virus that causes AIDS may have protected people hundreds of years ago from plague, researchers said Friday.

Scientists at the National Cancer Institute think it's a reasonable explanation of why up to 15 percent of white people - but not blacks or Asians - have the mutation, and they are gathering evidence to back up their theory."It just hit me in the face. It wasn't an idea, it was an accumulation of data," said Steve O'Brien, an NCI molecular biologist who headed the team.