Who are our Old Friends?
Rook hypothesizes that the immune system has evolved to require input from at least three sources collectively called the Old Friends:
diverse range of species found on normal skin, gut, airways, urogenitary tract, etc
Transmitted by mothers and other family members
diverse range of species found on animals, soil, air, plants
Spp. which inhabit our indoor and outdoor environments
Helminths Salmonella, HAV, H. Pylori etc
Cause chronic infections – have to be tolerated, attempts to eliminate cause tissue-damage