[Ultrastructural organization and reproduction of virions in Vero (E6) cells in influenza A/H1N1 pmd09 virus monoinfection and coinfection with SARS-CoV-2 (Delta and Omicron strains)].

Abstract

Introduction: RNA-containing viruses, especially influenza viruses, are of high epidemiological significance. The manifestation of COVID-19 has led to the registration of coinfection cases, the pathogenesis of which is poorly studied. The Vero (E6) cell line is widely used to study the morphogenesis of various viruses, including influenza and coronavirus. The aim of the work is to study the ultrastructure of Vero (E6) cells and the reproduction of viral particles during monoinfection with the influenza A virus and coinfection of this virus with two SARS-CoV-2 genovariants in dynamics 6, 18 and 24 hours after inoculation.

Materials and methods: The Vero (E6) cell line model was used for in vitro study of the viral infection effects and an analysis of the dynamics of changes in the number of intracellular viral particles. The study involved 4 experimental groups: Vero (E6) cells mono-infected with the influenza virus strain A/H1N1 pmd09 at a dose of 0.1 MOI; Vero (E6) cells co-infected with the influenza virus strain A/H1N1 pmd09 and Delta strain of SARS-CoV-2 at a total dose of 0.1 MOI; Vero (E6) cells co-infected with the influenza virus strain A/H1N1 pmd09 and Omicron strain of SARS-CoV-2 at a total dose of 0.1 MOI. In each study group, cells were monitored at time points of 6, 18, and 24 hours.

Results: After 6 h, no pathological structures were detected in all groups, except for virus-containing transport vesicles. After 18 h, vacuolization of the ER of varying degree was noted in all the studied groups. After 24 h, ultrastructural changes, namely vacuolization of organelles and/or compaction of the cytoplasm, were encountered in all groups comparatively more frequently than at 6 h and 18 h time points. . The dynamics of the number of viral particles increased significantly by 24 h time point in the monoinfection group. However, none of the coinfection groups demonstrated a tendency for the number of viral particles to change, since no statistically significant differences were found between the 6 h, 18 h, and 24 h stages.

Conclusion: The results obtained suggested that the interaction between A/H1N1 pmd09 and SARS-CoV-2 viruses contributed to an overall decrease in the formation of new virions in Vero (E6) cells in both cases of coinfection.