Early and constant exposure to bacteria common in nature but not so much in cities builds our immune systems in many ways. Think about it. Who gets more exposure to allegens such as pollen and fungi?
I wrote about this a few years ago on my blog titled, “Eat Dirt.” That article was specifically aimed at a genus of bacteria called “Nitrosomas,” but could very well apply to other genera and fungi. Nitrisomas species live off of the form of nitrogen found in urine, urea. Believe it or not, they can live on your skin too, like under armpits. Nature's original deodarant.
Other ingested and inhaled allergens directly affect your internal immune system. For one, chronic low-level exposure stimutes the formation of Immunoglobulins G and M which “overpower” the release and activity of IgE. The IgE molecule (if unopposed) attaches to mast cells in your blood, causing the release of histamine, which is the chemical responsible for all those nasty and even deadly allergic reactions.
According to this 2013 study, rural bacteria also affect natural killer T-cells in the lungs of mice. I haven't read the science behind the article but assume it's valid:
https://www.livescience.com/36217-early-bacterial-exposure-immunity.html
Very good question, BTW.
