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Published on: December 10, 2013
Recent Clinical Isolates of Enterovirus D68 Have Increased Replication and Induce Enhanced Epithelial Immune Response
Mark K Devries1, Yury A Bochkov1, Michael D Evans2
1Department of Pediatrics, School of Medicine and Public Health, University of Wisconsin, Madison, WI 53792, USA.
Abstract:
In 2014, enterovirus D68 (EV-D68), previously associated primarily with mild respiratory illness, caused a large outbreak of severe respiratory illness and, in rare instances, paralysis. We compared the viral binding and replication of eight recent EV-D68 clinical isolates collected both before and during the 2014 outbreak and the prototype Fermon strain from 1962 in cultured HeLa cells and differentiated human primary bronchial epithelial cells (BEC) to understand the possible reasons for the change in virus pathogenicity. We selected pairs of closely related isolates from the same phylogenetic clade that were associated with severe vs. asymptomatic infections. We found no significant differences in binding or replication in HeLa cell cultures between the recent clinical isolates. However, in HeLa cells, Fermon had significantly greater binding (2-3 logs) and virus progeny yields (2-4 logs) but a similar level of replication (1.5-2 log increase in viral RNA from 2 h to 24 h post infection) compared to recent isolates. In differentiated BECs, Fermon and the recent EV-D68 isolates had similar levels of binding; however, the recent isolates produced 1.5-2-log higher virus progeny yields than Fermon due to increased replication. Interestingly, no significant differences in replication were identified between the pairs of genetically close recent EV-D68 clinical isolates despite the observed differences in associated disease severity. We then utilized RNA-seq to define the transcriptional responses in BECs infected with four recent EV-D68 isolates, representing major phylogenetic clades, and the Fermon strain. All the tested clinical isolates induced similar responses in BECs; however, numerous upregulated genes in antiviral and pro-inflammatory response pathways were identified when comparing the response to clinical isolates versus Fermon. These results indicate that the recent emergence in severe EV-D68 cases could be explained by an increased replication efficiency and enhanced inflammatory response induced by newly emerged clinical isolates; however, host factors are likely the main determinants of illness severity.
Insights
Recent enterovirus D68 (EV-D68) strains show increased replication and inflammation compared to older strains, potentially explaining severe illness outbreaks. Host factors, however, remain key determinants of disease severity.
Area of Science:
- Virology
- Immunology
- Epidemiology
Background:
- Enterovirus D68 (EV-D68) caused a severe outbreak in 2014, differing from its typical mild respiratory illness.
- Understanding changes in EV-D68 pathogenicity is crucial for public health.
- Previous studies focused on mild EV-D68 strains, leaving the 2014 outbreak's drivers unclear.
Purpose of the Study:
- To investigate the viral binding, replication, and host transcriptional response of recent EV-D68 clinical isolates compared to the 1962 Fermon strain.
- To identify potential virological factors contributing to the increased severity observed during the 2014 EV-D68 outbreak.
Main Methods:
- Compared binding and replication of eight recent EV-D68 isolates and the Fermon strain in HeLa and human bronchial epithelial cells (BECs).
- Utilized RNA-sequencing (RNA-seq) to analyze transcriptional responses in BECs infected with selected EV-D68 strains.
- Selected closely related clinical isolates associated with severe versus asymptomatic infections for comparative analysis.
Main Results:
- Recent EV-D68 isolates showed higher replication and progeny yields in BECs compared to the Fermon strain.
- Fermon strain exhibited greater binding and progeny yields in HeLa cells, but similar replication to recent isolates.
- Transcriptional analysis revealed enhanced antiviral and pro-inflammatory responses induced by recent clinical isolates in BECs compared to Fermon.
- No significant replication differences were found between recent EV-D68 isolates with varying disease severity.
Conclusions:
- Increased replication efficiency and enhanced inflammatory responses in recent EV-D68 clinical isolates may contribute to severe illness.
- Differences in viral pathogenicity are not solely explained by genetic proximity or cell culture models.
- Host factors likely play a significant role in determining the severity of EV-D68 infection.
