Exposure to Common Environmental Bacteria May be Source of Some Allergic Inflammation

New research published in the Journal of Leukocyte Biology suggests that certain strains of Pseudomonas aeruginosa cause white blood cells to produce high levels of histamine, which worsens the severity of inflammation and infection.

Could some cases of asthma actually be caused by an allergic reaction to a common environmental bacteria? New research findings suggest that this idea may not be as far-fetched as it seems. In a research report appearing in the February 2012 print issue, researchers show a link between common environmental bacteria and airway inflammation. Specifically, their research suggests that some strains of Pseudomonas aeruginosa cause white blood cells to produce very high levels of histamine, which in turn leads to inflammation, a hallmark symptom of asthma.

"We hope that these findings in mice will encourage human-focused research regarding bacterial stimulation of histamine production by white blood cells, like neutrophils, that are not traditionally associated with allergic inflammation," says George Caughey, MD, a researcher involved in the work from the Veterans Affairs Medical Center and University of California in San Francisco. "Such research could improve our understanding of inflammation in bacterial infections, and help us to craft therapies for relief of inflammation and its consequences for short and long-term health."

To make this discovery, scientists studied the effect of two strains of pseudomonas bacteria on isolated mouse white blood cells tasked with killing bacteria, called neutrophils. Results showed that one strain killed the neutrophils, but the second strain produced substances that caused the neutrophils to increase their production of histamine significantly. To see if their discovery was applicable outside of the test tube, the histamine-stimulating strain was then used to infect mice to produce bronchitis and pneumonia. These mice experienced a significant increase of histamine in their airways and lungs. Additional work showed that the bacteria persuade neutrophils to produce histamine by causing them to make much more of the key enzyme in histamine synthesis (histidine decarboxylase) than neutrophils would otherwise do in the unstimulated state.

"Despite advances in diagnosing and treating the symptoms of asthma and allergy, our understanding of the underlying initiating events remains elusive," says John Wherry, PhD, deputy editor of the Journal of Leukocyte Biology. "This report helps shed light on how an 'everyday organism' might trigger asthma and allergy from an immune cell type not normally thought to be involved in allergic disease."