Same gene, two plagues?

The Black Death struck terror in Europe 650 years ago. Attacking the body's white blood cells, the disease wiped out one-fourth of Europe's population in four years. Yet some people miraculously avoided infection, a curious fact that has baffled scientists.

Today, another plague threatens the world--AIDS. About 30 million people worldwide carry the human immunodeficiency virus or HIV, which causes AIDS. Yet some people exposed to the virus seem to escape infection. This has led scientists at the National Cancer Institute in Maryland to re-examine the pair of plagues.

Both the Black Death bacteria and HIV attack macrophages, the white blood cells that ward off diseases. Could the plague's survivors have been protected by a specific gene, the part of a cell that carries hereditary traits? And could their descendants today have inherited that same gene that now helps them resist HIV?

Some scientists think so. They've discovered an HIV-resistance gene, which appears to be common among people whose ancestors lived in Europe during the Black Death, but not in those whose ancestors lived in plague-free areas. The gene suppresses a protein (a substance all living things need to grow), called CCR5, which HIV latches on to when attacking a macrophage.

"Many drug companies are already aiming drugs at CCR5," says Michael Smith, a scientist at the National Cancer Institute. "But it's important to understand this gene can't provide absolute protection against AIDS."