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Viruses that cause respiratory diseases by infecting cells in the airways can deal their victim a second blow by making it easier for bacteria to cause follow-up infections, according to findings by St. Jude investigators.
This “one-two” blow delivered by viruses and bacteria has been long suspected. But now, the St. Jude team has shown how viruses that infect cells lining the respiratory tract put out the welcome mat for subsequent bacterial visitors.
Results of the study, led by Elisabeth Adderson, MD, Infectious Diseases, appear in the February 2006 issue of Journal of Virology.
Adderson’s team infected epithelial cells from different parts of the human respiratory system with respiratory syncytial virus (RSV) human parainfluenza virus 3 (HPIV-3) and influenza virus. The researchers then observed what happened after adding two types of bacteria that cause respiratory infections: Streptococcus pneumoniae and a particular type of Haemophilus influenzae. Epithelial cells line the surface of the respiratory tract, exposed to air and the germs it carries.
The investigators discovered that respiratory viruses trigger changes in the surfaces of epithelial cells that help the bacteria stick to them. The changes varied, depending on the particular cell and virus, but in general they involved the appearance of special proteins on the surface to which the bacteria could bind.
For example, HPIV-3 increased bacterial attachments to epithelial cells from the area of the respiratory tract called the bronchus; but these same viruses had much less effect on epithelial cells from deeper in the respiratory tract.
“Investigators studying the interactions between respiratory cells and disease-causing viruses must keep in mind these different responses among cells and viruses and in order to interpret their findings correctly,” Adderson said.
The other St. Jude authors are Vasanthi Avadhanula, Carina Rodriguez, MD, Yan Wang, Richard Webby, PhD, and Glen Ulett, PhD, all from Infectious Diseases. Rodriguez is currently at the University of South Florida, Tampa; and Ulett is currently at the University of Queensland, Australia.
Last update: April 2006