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Influenza susceptibility higher among patients with asthma
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Patients with asthma are at increased risk for more severe influenza disease, according to research published in the Journal of Allergy and Clinical Immunology.
“The mechanisms underlying the increased susceptibility to viral infections in those with asthma are poorly understood, but it has been suggested that the skewing toward Th2 immunity results in deficient Th1 antiviral immunity,” Ben Nicholas, PhD, from the University of Southampton, and colleagues wrote. “Understanding of antiviral immunity in asthma is also complicated by the immunosuppressive effects of [inhaled corticosteroids (ICSs)]or oral corticosteroids, standard treatments in asthma.”
The researchers noted that although corticosteroids may protect against severe outcomes in patients with asthma carrying influenza infection, systemic corticosteroids in individuals without asthma cause delayed viral clearance. To determine the differences in influenza susceptibility between asthma patients receiving ICS compared with healthy individuals, Nicholas and colleagues examined bronchial biopsies of both demographics ex vivo.
“We wanted to look into whether immune system differences explain why asthmatics are more likely to end up in the hospital if they get the flu than the general population,” Nicholas said in a press release. “This is important, as flu can cause a person’s asthma symptoms to get worse.”
The researchers mimicked in vivo conditions by infecting the biopsies with influenza and exposing them to external ICS, fluticasone propionate, whereas biopsies intended to mimic healthy patients were infected with influenza without the presence of a corticosteroid. The researchers then enzymatically dispersed the biopsies with collagenase, which allowed for infected cells and activation markers to be counted by multicolor flow cytometry.
According to study results, epithelial cell infection between healthy patients and those with asthma was not different, although viral shedding was significantly less in those with asthma. The researchers observed that biopsies that had simulated asthma also showed suppression of T-cell activation caused by infection, and the HLA-DR expression on epithelial cells did not change.
Additionally, secreted mediator responses (innate defense, chemokines and proinflammatory cytokines) were weakened in asthmatic samples when compared with healthy samples.
“The samples from healthy people showed a strong immune system–triggering reaction to the flu virus,” Nicholas said in the release. “But in lung samples from asthma patients, this reaction was much weaker.”
The researchers also noted that the lack of effect from corticosteroids in healthy samples may suggest that the reduced viral shedding and defective T-cell activation seen in patients with asthma may, in fact, be independent of corticosteroid treatment.
“We hope these results help researchers better understand why asthmatics are more affected by influenza and help find new treatments for common lung infections, which often make asthma symptoms worse,” Nicholas said. – by Katherine Bortz
Disclosure: The researchers report no relevant financial disclosures.
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