COPD: Bacterial Infection Often Follows on Heels of Viral Infection

To assess potential mechanisms whereby rhinovirus might induce bacterial infections, the investigators measured sputum levels of two antimicrobial peptides found in the airways that are part of the lung’s innate defenses against infection: secretory leukocyte protease inhibitor (SLPI) and elafin.

Levels of both peptides fell in rhinovirus-infected COPD patients who developed bacterial infection before or at the time when bacterial load peaked. In contrast, levels remained the same or rose slightly in those who did not develop bacterial infection. Furthermore, lower levels of the peptides were correlated with higher bacterial loads.

"This would suggest that bacterial infection is a consequence of low SLPI and elafin levels in the airways," Dr. Mallia commented.

Finally, sputum levels of neutrophil elastase (an enzyme that could degrade the protective peptides) rose in rhinovirus-infected COPD patients who developed bacterial infection but remained essentially at baseline levels in their counterparts who did not.

"We hypothesize that possibly you have a sequence of events – viral infection, high neutrophil elastase levels, and degradation of SLPI and elafin – and that may progress to secondary bacterial infection," he said.

The study gives rise to several potential, related avenues of research, according to Dr. Mallia.

"Certainly, one of the things we are interested in is, Are there markers that can identify those people who are going to go on to develop bacterial infections?" he said. And some evidence suggests that in addition to having antibacterial activity, macrolide antibiotics also have antirhinovirus activity, which the investigators plan to test using their model.

Dr. Mallia reported previously having received research grants from Pfizer and GlaxoSmithKline, and currently receiving a travel grant from Boehringer Ingelheim. The study was funded in part by Pfizer and GlaxoSmithKline.