sick. In fact, the eukaryotic component of the microbiota has been a fact of human life for millions of years. In areas of the world where such eukaryotic microbes are endemic, a majority of the population maintains them without any adverse effects. Only during the past century, and only in more developed parts of the world, has the eukaryotic component of the microbiota been virtually eliminated due to clean water, better hygiene, and a high-quality food supply.
There is some evidence that the abrupt (in evolutionary terms) loss of the eukaryotic component of the microbiota by people who live in developed countries may have contributed to a number of adverse effects, such as allergies and IBD. One current hypothesis is that helminths, and possibly protozoa as well, stimulate the arm of the immune system that consists of IgE, eosinophils, mast cells, and other cell types that are negatively associated with allergies and IBD. Support for this hypothesis arises from the fact that early stimulation of the gastrointestinal immune system by eukaryotic microbes allows this part of the immune response to develop normally. Conversely, failure to experience this type of stimulation may, in some people, predispose them to disease caused by overstimulation of the inflammatory response. The impact of the loss of these eukaryotic microbes on the bacterial microbiota has not yet been explored thoroughly, but efforts are now moving in this direction.
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