Little known, according to Huffnagle, is that the gut is also involved in immune defense against respiratory diseases. Pathogens arriving in the airways are transported by the cilia of the bronchial mucosa toward the pharynx and swallowed from there. This way they reach the gut, where the immune system recognizes them. Defense cells are formed that also reach the lungs via the blood, where they help fight the infection. Very interesting article. For someone with chronic allergies, finally a glimmer of hope - because previous allergy medications are either chemical sledgehammers or symptom suppressants. But one would have to get at the real causes of allergies; then one could finally get rid of these annoying problems.
At passe.par.tout I found the original article.