The light of evolution points toward reconstitution of the biome as the only reasonable therapy for a wide range of immune-associated disorders, including allergy, autoimmunity and perhaps autism.

It is now widely appreciated that humans did not evolve as a single species, but rather that humans and the microbiomes associated with us have co-evolved as a "super-organism", and that our evolution as a species and the evolution of our associated microbiomes have always been intertwined. This co-evolution has biological consequences that are readily apparent. For example, decades of work with gnotobiotic (microbe-free) animals consistently demonstrate that the painstaking separation of a mammal from its associated microbiome results in an underdeveloped immune system that is a mere shadow of its naturally occurring counterpart.

The vital role of the microbiome in shaping the development of the immune system is, thankfully, becoming widely appreciated and the subject of more intensive inquiry. On the other hand, it is less well appreciated that, like the microbiome, a wide range of our fellow eukaryotes have co-evolved with us and have become intertwined with the development of our immune system. All mammalian species with the exception of humans in post-industrial societies and their domesticated animals co-exist with a wide range of intestinal worms, called helminths. Unfortunately, we are only now beginning to appreciate the consequences of our deceptively painless separation from these animals.

The co-evolution of helminths and the organisms they colonize can be traced back far deeper than the evolution of mammals, to the beginnings of immune systems. From this view, the immune system can be seen as having evolved as an interface with symbiotic organisms more so than as a defense against invading organisms, although defense against invading organisms was almost certainly a part of that interface. The co-evolution of helminths and their host's immune systems has shaped the biology of both parties. Helminths have evolved to secrete dozens if not hundreds of molecules that exquisitely turn down the host immune system. Mechanisms by which several of these helminth-derived immunosuppressive "drugs" function have been elucidated, and generally appear to be adapted for specific host species. It is unreasonable to hope that host immune systems have not, in turn, adapted to the presence of helminths. The idea that natural selection has left us dependent on the immunosuppressive drugs produced by our evolutionary partners seems not only likely, but unavoidable.....

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First published in October 2010.

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