By By Holly Goodwin May 24, 2011 in Health According to biologists at the University of Liverpool the plagues of the Middle Ages have made 10 percent of Europeans HIV-resistant. Professor Christopher Duncan and Dr Susan Scott from the University of Liverpool’s School of Biological Sciences used a These resistant individuals carry a mutation known as CCR5-delta 32 that O'Brien goes on to say that is highly unusual to have no ill effects after having a gene knocked out such as the case in CCR5. "Most genes, if you knock them out, cause serious diseases like cystic fibrosis or sickle cell anemia or diabetes. But CCR5-delta32 is rather innocuous to its carriers. The reason seems to be that the normal function of CCR5 is redundant in our genes; that several other genes can perform the same function." Scientists managed to trace the mutation to 700 years ago , a time when plagues, including the bubonic plague, were sweeping across Europe. The places hardest hit by the plagues are the ones that now have the highest levels of resistance to HIV.Professor Christopher Duncan and Dr Susan Scott from the University of Liverpool’s School of Biological Sciences used a computer model to show how selected diseases provided the evolutionary pressure necessary to force the frequency of the mutation up from 1in 20,000 to the values today of 1 in 10.These resistant individuals carry a mutation known as CCR5-delta 32 that inhibits the CCR5 cellular receptor used to gain access to the immune system by HIV and other diseases. The mutation effectively presents immunity to HIV and other diseases that use the CCR5 cellular receptor as a gateway into the immune system. Dr. Stephen J. O'Brien of the National Institutes of Health in Washington D.C. says, "In order to have total resistance to HIV, you have to carry two doses of the mutated gene -- one from each parent. If you get only one dose, you will not be resistant to infection. However, you may be able to delay the onset of HIV once you become infected. That's because, in patients with one copy of the mutation, the amount of 'portals' or 'doorways' that HIV can use is reduced by about 50 percent. That slows down virus replication, which is the most important factor in AIDS progression."O'Brien goes on to say that is highly unusual to have no ill effects after having a gene knocked out such as the case in CCR5. "Most genes, if you knock them out, cause serious diseases like cystic fibrosis or sickle cell anemia or diabetes. But CCR5-delta32 is rather innocuous to its carriers. The reason seems to be that the normal function of CCR5 is redundant in our genes; that several other genes can perform the same function." More about HIV, Virus, Retrovirus, Immunity, Mutation More news from HIV Virus Retrovirus Immunity Mutation