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Thursday, September 21st 2006

We Can Protect Mice From The Black Death

A new “type” of vaccine.

Sorry Doc, Won’t Be Needing You Anymore

When you recover from an infection, antibodies produced by your long-term immune cells often prevent you catching the same disease again. What enables you to survive that initial infection is “innate” immunity, a fiendishly complicated network of chemicals that recognise foreign invaders, unleash immediate defences against them and marshal long-term immunity.

Yersinia pestis, the bacterium that causes bubonic plague, possesses at least four mechanisms for evading our innate immune system. These include a switch that turns off the normal cell-surface molecules that strongly stimulate the innate immune system when plague gets into the body

Egil Lien and colleagues at the University of Massachusetts in Worcester created a strain of Yersinia that couldn’t make this one switch, leaving the other three mechanisms intact. To their amazement, they found that the bacterium was so disabled that the mice didn’t get sick, even when given very high doses of it.

If the mice were treated so they couldn’t make antibodies to the modified Yersinia, they still died – but nine days later. “The innate immunity keeps the mouse alive while it makes its long-term immunity. In the end, it needs both,” Lien says.

Crucially, the mice injected with the modified bacteria made effective antibodies that later completely protected them against normal plague.