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Biology of a Sneeze: Rebooting the Airway’s Defense

Scanning electron micrograph of cilia in action in the respiratory tract.Climatologists recently predicted that the 2012 allergy season might be one of the worst on record and based on my own experiences so far this spring, I’m inclined to agree. I’ve been hit hard by congestion, itchy eyes, and worst of all, chronic bouts of uncontrollable sneezing. So when I learned that researchers in the Perelman School of Medicine Department of Otorhinolaryngology: Head and Neck Surgery are in the midst of some interesting research looking at the biology of sneezing, I was quite curious to get the inside scoop.

It might seem obvious -- allergens attack (in the form of pollen, dust mites, and pet dander) and our immune system feels compelled to expel these foreign invaders through a powerful sneeze. But it’s much more complicated than that, especially for patients who already have chronic sinus issues, says Noam Cohen, MD, PhD, assistant professor of Otorhinolaryngology: Head and Neck Surgery. Dr. Cohen is the senior author of a new study, out in the May issue of the Journal of the Federation of American Societies for Experimental Biology , that examined the biology of the effects of a sneeze on the inner structures of the nose.

“Very little is known about the effects of sneezing on the cells within the nose and sinuses,” he says. “As a matter of fact, almost nothing is known about sneezing.  As an ear, nose, and throat physician who deals with problems of the nose, frequent sneezing is a very common complaint I encounter from my patients.  So we wanted to know: why do people with problems with their noses, such as the common cold, chronic sinusitis, or allergies, sneeze more than people with no problems in the nose or sinuses.”

The cells lining ours noses and the sinuses (cilia) constantly produce mucus to trap the debris that we breathe in.  This mucus is then cleared to the throat where it is typically swallowed or coughed up.  When the normal mechanics of clearing the mucus are overwhelmed by thick or infected mucus, we sneeze to drive this mucus out of our nose.  

Cohen and his colleagues wanted to know whether the mechanics of this force had any effect on the cilia and if it varied between patients with chronic sinus issues and people with otherwise healthy sinuses.  “Our interest in this concept arose from prior work by our research team that demonstrated that the ability to clear mucus from the nose is greatly compromised in sinusitis patients,” he says.  

To explore this question, the researchers used cells from a mouse nose that were grown in incubators.  With this approach, they were able to measure how these cells clear mucus and study if they responded to a "puff" of air that simulates the sneeze.  Once they worked out the chemical pathways involved in the cells’ response to the simulated sneeze, they replicated some of the experiments in human sinus and nasal tissue. Using the human sinus and nasal samples, they showed that tissue from sinusitis patients does not respond to the "sneeze" in the same manner as tissue obtained from patients who do not have sinusitis.

“What we found was that the pressure force of the sneeze activates the process by which our cells clear mucus (mucociliary clearance) --  like rebooting or hitting ‘control/alt/delete’ on a computer,” he says.  “Since nothing was known about the cells’ response to a sneeze, this was a novel finding.”

Cohen says that it is still unclear what the biologic process is that responds to the pressure wave - i.e., the sensor that activates the cellular response during a sneeze, but researchers at Penn are continuing to study this area. But to put it simply, he says “If sneezing reboots the system for clearing mucus from the nose and patients with disorders of the nose cannot 'reboot,’ this potentially explains why they sneeze more often.”

He predicts that if researchers can understand why patients with chronic sinus issues do not reboot, it’s possible to develop novel therapies (nasal sprays, irrigations or oral medications) that can help these people reboot their system and help them clear the infected and thick mucus.

So I wanted to know, does that mean we might be able to one day drastically reduce, or even eliminate, sneezing for us sorry sinus sufferers?

“Probably not, the sneeze is a very important defense mechanism that we do not want to suppress,” Cohen says.  “However, if we can understand why in certain people the cells in the nose do not respond to the sneeze and we can correct that defect, instead of constantly sneezing, one or two sneezes should get the job done.”





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