The Roman Celsus in the 1st century A.D. identified four classical signs of inflammation: Calor, dolor, rubor, and tumor; these are heat, pain, redness, and swelling. Some of the most annoying symptoms of a cold involve vascular congestion of mucous membranes, from increased blood flow leading to tissue swelling (tumor), increased warmth (calor), and mucus production. A new study suggests that of the inflammation hallmarks, calor may be critically important in defending us against viral infections, such as the common cold.
Carl Zimmer’s article in the New York Times today describes Akiko Iwasaki’s work on temperature and rhinovirus infection. The temperature of air in the nose may be a key risk factor for infection by rhinoviruses, the organism causing the common cold. The bottom line: cold temperature impairs cellular immunity and facilitates infection by the virus. Having gotten over one of these infections recently, I was very intrigued but not surprised by this work. The study’s author also hinted that fever is beneficial in preventing further infection by the virus. We have covered this hypothesis several times on this blog, e.g here and here. Ed LeGrand and I have written about the host defense function of elevated temperatures as a stressor that harms invaders more than ourselves.
My thought for today is: if cold air and tissues in the nose are an Achilles heel for us, allowing easy infection by rhinoviruses, does inflammation in the nose generate a localized fever that protects us?
A combination of a local defenses and body-wide defenses might be important in fighting infection. This view was proposed by Day and LeGrand in the Journal of Theoretical Biology. The study they published, Synergy of local, regional, and systemic non-specific stressors for host defense against pathogens suggests that combining local and systemic stresses like fever might be particularly valuable in preventing pathogen invasion. I will cover their new paper in more detail in the next post of this blog.
As a final thought, cold air induces rhinorrhea (runny nose) in many people even in the absence of infection. This vasomotor rhinorrhea involves tissue edema and increased blood flow. Maybe cold rhinorrhea prevents viral infections from getting established by expelling mucus and raising the temperature. If this is true, taking cold and allergy medications that prevent Celsus’s dolor, tumor, and calor might do more harm than good.