I am forever trying to work out why I (and many other PWC's) feel incredibly better in certain locations around the world. The standard theory for this is mold, but sometimes I find this too simplistic. I have started to wonder about the effects of pollutants, since I tend to feel better in locations that are quite remote and have clean air. I came across this paper, which shows that small particles (micrometric) stimulate the innate immune system differently to nanoparticles. Nanoparticles, found in air pollution, cause plasmacytoid dendritic cells to produce interferon-alpha. That links back to DeMeirlier's research. These nanoparticles, which have been on the rise due to the increasing number of diesel vehicles, have recently be found in human brains, produce multi-organ toxicity in fish, and enter in the bloodstream for 3 months after exposure. This seems to be cutting edge research.