BIODEFENCE
genome have been catalogued. By contrast only a very small number of benefi cial mutations have been detected. Could these somehow be used to create new treatments that can combat new and more virulent forms of disease?
Delta 32 – miracle gene? One example stands out that merits detailed study. By careful sampling of individuals whose families can be traced back to those who survived the Great Plague, a benefi cial mutation called CCR5 Delta-32 was identifi ed. CCR5 (Cysteine-cysteine chemokine receptor 5) Delta 32 arises because 32 of the chemical base pairs have been deleted from the gene. It turns out that this mutation provides humans that inherit it from both their parents with some
Above: WHO map highlighting the extent of the SARS virus in 2003. Leſt : An image of a new form of the SARS Virus detected in February 2013. Below: Schematic drawing of SARS coronavirus.
Image: Elizabeth R Fischer/Rocky Mountain Laboratory
Source: Drazen JM14
natural in-built defences against certain forms of disease. Could mutations like CCR5 Delta-32 provide a key to help mitigate the impact of future pandemics? The results of the analysis pinpointed a window in which a mutation occurred that was subsequently passed down through the generations. Using models to predict the inheritance of the gene, it is possible to suggest that those that survived the Black Death passed on CCCR5 Delta-32 to subsequent generations and that helped improve the survival rate during the Great Plague in London.
Other scientists question that conclusion – pointing to evidence that suggests the CCCR5 Delta 32 mutation arose much earlier in human history. Recent experiments have shown that the plague virus Yersinia pestis can infect mammalian cells by other means undermining the arguments about its role in the Black Death and the Great
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Plague. The mere presence of the CCCR5 Delta-32 mutation does not completely explain why some people survived. Today one copy of the CCCR5 Delta-32 mutation has been found in around 10-14% of the Caucasian population. These subjects can still become infected with the AIDS virus. Studies have shown that 1% have two copies which increases the subject’s ability to resist certain forms of plague virus. There is also a clear geographical strata north to south in Europe, with instances of the mutation being much higher in northern countries.
Possession of the CCCR5 Delta-32 mutation does not
necessarily mean a subject will not get AIDS. Some variants of AIDS do bind to cells using other proteins, such as CXCR4. What the CCCR5 Delta 32 mutation lacks is a receptor onto which the AIDS virus can bind and enter immune cells. Of course having the CCCR5 Delta-32 mutation can also have its drawbacks: it is also strongly associated with chronic and life-threatening liver disease. Nevertheless at a time when terrorist groups maintain an active interest in the potential of biological weapons and new viruses occur in nature, the research into the ways in which the spread of infections can be disrupted is essential, and may in the future help us avoid the repeated ravages of pandemic plagues. ❚❙
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