This idea of course brings up lots of interesting hard-core biological questions, but since this is the blogosphere I'll throw out the random half-assed sci-fi scenario. Could infectious agents be helping us stay young? Perhaps periodic infections with nonlethal viruses selectively purge our decrepit ageing cells, while simulatenously stimulating their replacement with fresh ones derived from newly activated stem cells. Neutropic viruses might help to prune defunct neurons and thus stave off degeneratvie diseases like Alzheimer's or Parkinson's.
So, I propose a new cure for ageing. Virotherapy with benign, replication competent agents. Much more practical than 18th level magic-user Audbrey deGray's stem cell replacement. Move over StemEnhance, viral anti-ageing cream is on the way!
1. IFN-alpha activates dormant haematopoietic stem cells in vivo. Nature, 2009. Online Feb.
2. Drosophila Intestinal Response to Bacterial Infection: Activation of Host Defense and Stem Cell Proliferation. Cell Host and Microbe, 2009. Vol 5 pg 200.