Researchers from the University of Michigan Medical School found that, in mice, antibiotics may be responsible for changing the makeup of the bowel flora. A change in bowel flora could affect the way the immune system responds to common allergens in the lungs. According to one of the researchers, antibiotics eliminate bacteria in the GI tract. The destruction of the normal bacteria enabled fungi to take control.

In earlier experiments, researchers have found that fungi produce oxylipins. Oxylipins are molecules that are associated with the level of immune responses. Oxylipins in the GI tract help prevent the production of regulatory T cells (a type of white blood cell) for ingested allergens. The result is that T cells in the respiratory system can become sensitive to allergens, leading to allergy symptoms and, in some cases, asthma.

The University of Michigan researchers tested this idea on mice. The mice were given Candida albicans (a yeast) orally after being given antibiotics for five days. The Candida served to inoculate the GI tract with yeast—in other words, change the makeup of the intestinal flora. Another group of mice received no antibiotics or oral Candida albicans. The mice were then injected with common mold spores. The mice that were given antibiotics and exposed to C. albicans displayed higher rates of hypersensitivity to mold, as opposed to the mice that weren’t given any antibiotics.