Researchers at the University of Michigan (UM) have found that people with asthma who take nutritional supplements, cold remedies, and fortified foods to boost their immunity to prevent and fight colds might be putting themselves at risk for a severe asthma flare-up. Their findings appear in the journal PLoS Pathogens.
The study, using a novel mouse model, showed that, in the airways, the immune response to the common cold is actually maladaptive. Mice that were engineered to have a reduced innate immune response to the common cold actually showed less—not more—airway inflammation and bronchoconstriction following infection.
“You often hear that people want to boost their immunity to prevent and fight colds,” said Marc B. Hershenson, MD, professor of pediatrics and communicable diseases and director of the division of pediatric pulmonology at UM. “However, boosting the immune response could increase inflammation. Up to now there have been no convincing data supporting the theory that the immune response might be deleterious. In our study, we offer the first direct evidence that limiting the immune response reduces the manifestations of rhinovirus infection.”
Hershenson, the study’s senior author, added, “In our model, cold-induced asthma flare-ups were caused by the body’s immune response to the virus, not the virus itself. Chemicals produced by the immune system inflame cells and tissues, causing asthma symptoms such as cough and wheeze.”
The research team hypothesized that limiting the immune response to viral infection would actually reduce their symptoms. Using a rhinovirus 1B, a cold virus strain that replicates in mouse lungs, they infected mice deficient in MDA5 and TLR3—two receptors that trigger the protective defenses of the immune system against viruses and other pathogens.
MDA5-deficient mice showed a delayed defensive response to the infection, leading to a small increase in the level of virus in the lungs. Nevertheless, these mice showed less airway inflammation and bronchoconstriction following infection compared to wild-type mice. TLR3-deficient mice also showed diminished airways responses.
In addition, MDA5- and TLR3-null mice that were made asthmatic by exposure to allergen showed decreased airway inflammatory and contractile responses in response to rhinovirus infection compared to normal mice. These results suggest that, in the context of rhinovirus infection, reducing the mouse’s innate immune system led to reduced inflammatory signaling pathways and reduced airways inflammation and hyper-responsiveness.
“This study shows that, once you have a cold, elements of the immune response actually make the symptoms worse,” said Hershenson. “A better strategy might be to modulate the immune response in asthma patients with colds.”
Source: Univeristy of Michigan Health System
