Allergies on the rise, but your gut may help you fight them

On one hand, new research shows that pollen levels, a common cause of allergies, have been increasing for the past 10 years, and are likely to keep increasing across Europe in the upcoming years. On the other hand, another study is now suggesting that your gut bacteria may actually help you fight these allergies.

Almost 25% of all Germans suffer from allergies, and this number is likely to increase, according to a new a study led by Prof. Annette Menzel at the Technichal University Munich (TUM) that analyzed over 1200 long-term pollen series from 23 species of plants from multiple locations across Europe.

The study, published in the journal PLoS ONE on April 13 allowed researchers to calculate trends of annual pollen indices over the last 10 years, and to compare different allergenic pollen species in different climates. Their results show an increase of pollen concentrations over recent years. In Europe, pollen concentration has been on the rise by about 3% per year in urban areas, and by 1% in rural areas. The most likely reason for this pollen increase is climate change, but not necessarily due to increasing temperatures, but most likely due to increased concentrations of carbon dioxide (CO2) in the air, which promotes plant growth, and therefore, pollen production. On top of this, we now see an increased pollen season in Europe, fueled by the introduction of foreign plants and trees.

"In Germany, it is now only in November that we do not see allergenic pollen - so the season of suffering for people with hay fever is getting more serious," said Prof. Annette Menzel in a statement for the BBC. "On a local scale, planners should be more aware of what sort of problems may arise from the urban trees they're planting. Often they use birch trees, for example, because of their nice silver colour, not aware that they leave allergenic problems behind."

Now, this is just half of this story: there will likely be more pollen, and for longer time. But there is some good news. Gut bacteria, which have a win-win relationship with their human host, may be of some help.

An international team led by David Artis, and David Hill, from University of Pennsylvania, and which included researcher Ellen D Renner from Ludwig Maximilians University, Munich found that these gut bacteria might actually play an important role in influencing and controlling allergic responses.

Their study, published in the journal Nature Medicine on March 25, shows that selective manipulation of your gut bacteria may be beneficial in treating some allergic diseases.

"Studies in human patients suggest that changes in commensal populations or exposure to broad spectrum antibiotics can predispose patients to the development of systemic allergic diseases," Hill explains in a statement to the press. "In addition, previous studies in animal models have shown that commensal bacteria can influence local immune cells in the intestine. However, the cellular and molecular mechanisms by which commensal bacteria influence the host immune system, in particular the branches of the host immune system that regulate allergic inflammation, are not well understood."

In their study researchers focused on mice, studying a specific type of white blood cell called basophils, and the relationship between basophil responses and allergic disease. Mice where treated with antibiotics targeting specific gut bacteria with the goal of measuring how levels of circulating basophils in the blood were affected.

Their findings showed that mice treated with antibiotics, which reduced their natural gut bacterial flora, had a stronger allergic reaction. In their study they used a specific mouse model of allergic inflammation in the lung, which shares similarities with human asthma. Antibiotic treatment resulted in significantly elevated basophil responses as well as an increase in basophil-mediated allergic airway inflammation. Their results strongly suggest that gut bacteria are capable of influencing the response to allergens.

All in all, if you manage to cope with the upcoming rising tide of allergens, perhaps you should thank the little microbes living in your gut.