Isolation and Characterization of Clinical RSV Isolates in Belgium during the Winters of 2016–2018

Van der Gucht, Winke; Stobbelaar, Kim; Govaerts, Matthias; Mangodt, Thomas; Barbezange, Cyril; Leemans, Annelies; De Winter, Benedicte; Van Gucht, Steven; Caljon, Guy; Maes, Louis; De Dooy, Jozef; Jorens, Philippe; Smet, Annemieke; Cos, Paul; Verhulst, Stijn; Delputte, Peter L.

The F protein is indispensable for virus infection [39] and its activity can be linked to the formation of syncytia [36, 40] . Mean syncytium size and mean syncytium frequency were determined after 48h of infection with a 0.6% Avicel ®® overlay to minimize free particle movement. The presence of Avicel ®® would promote the formation of syncytia rather than spread and the formation of new syncytia during the incubation period. Even with minimal free particle movement, different sizes of syncytia containing 2-180 nuclei per cell are formed by the clinical isolates. For example, BE/ANT-B20/17 clearly forms large syncytia without infected satellite cells, which suggests that the produced particles remain more cell associated, and virus spread in HEp-2 cells may be facilitated through syncytia formation rather than particle release. This could also be observed from the replication kinetics and infectious virus production: the number of infected cells rapidly increases, and about 80% of the culture is infected after 48h, whereas the amount of infectious virus in the supernatant is lower compared to most other clinical isolates. This suggests that the production of infectious virus particles is either limited or faulty in HEp-2 cells for this isolate. A full characterization of the production of defective interfering particles could provide an explanation.