Exposure to Salmonella infection in mice showed a significant decrease in inflammation within the animals’ airways, a new study has found, upholding the popular “hygiene hypothesis,” which states that sterile environments produce offspring with weak immune systems.

The rise of immune system disorders in the Western world is often linked to the hygiene hypothesis. Babies are born into a climate that is sterilized and disinfected at every turn, and the slightest sniffle merits antibiotics. Proponents of the hypothesis suggest this is making people vulnerable to infection as adults. The present study, to be published in the March issue of Infection and Immunity, adds to the evidence advocating for greater exposure to such bacteria through safe methods.

Prior research into Salmonella’s impact on allergies has shown that children who were infected had lower rates of asthma later in life than other adults who were never infected as kids. The mechanism of the present study is the same in mice models, explains lead author Venkateswaran Ganesh. Ganesh and his colleagues found the bacteria reduced the production of an inflammatory compound called interleukin-4, which is produced by T helper-2 cells, a key part of the body’s immune system.

Behind the T helper-2 cells, in fact, was an increase in production of a certain type of "myeloid" immune cell. Here myeloid refers to the immune cells of the bone marrow. Essentially, because asthma is characterized by an inflammation of the airways, a Salmonella infection has the collateral effect of targeting the mechanisms behind that inflammation. "By performing cell culture assays and studies in rodents, we could determine the influence of myeloid cells on Th2 cells,” Ganesh remarked in a statement.

More than 26 million American adults — or 8.2 percent — suffer from asthma, with 9.5 percent of children also carrying the condition, according to the Centers for Disease Control and Prevention. Such prevalence has researchers pushing for treatment options that harness the Salmonella bacteria in safe, clinical settings. This could come in the form of commensal bacteria — helpful inhabitants of the body — and samples of the bacteria that act similarly to probiotics, which introduce the body to cultures of the infection in small, fightable doses.

While the term suggests uncertainty, certain researchers argue the hygiene hypothesis is anything but conjecture. Dr. Molly Fox, lead author of a study last year that sought to include Alzheimer’s as a disease of the same ilk, believes weak immunity may explain the neurological disorder’s increased presence in Western countries.

“The increase in adult life expectancy and Alzheimer’s prevalence in developing countries is perhaps one of the greatest challenges of our time,” Fox said in a University of Cambridge news release. “Today, more than 50 percent of people with Alzheimer’s live in the developing world, and by 2025 it is expected that this figure will rise to more than 70 percent.”

Source: Ganesh V, Baru A, Hesse C. Salmonella Typhimurium Infection Induced CD11b+Gr1+ Cells Ameliorate Allergic Airway Inflammation. Infection and Immunity. 2013.