How true is it that some genes that protected people from the Black Death are the same genes that are now protecting people from HIV today?

We put this question to Mark Marsh from University College London...

There was a hypothesis a little while ago that a mutation in one of the receptor proteins; a so-called Delta 32 for CCR5, might have had some protective effects against the plague. I'm not sure that that's ever really been verified, but it's certainly true that the Delta 32 allele, if one has two copies of that gene, there's no functional receptor for the virus, so individuals with that genetic composition are in general resistant to infection.