Expanding insect cell models for arboviruses: comparing the chikungunya virus replication and cellular host response in Spodoptera frugiperda Sf9 and Aedes albopictus C6/36 cells

The chikungunya arbovirus (CHIKV) is a persistent health problem with an expanding geographical range of mosquito vectors, but with poorly understood mechanisms regarding insect host specificity. Here, we sought to investigate an alternative model for CHIKV studies, aiming to improve our understanding of its biology in insects. We therefore set out to assess the ability of viruses to multiply in the lepidopteran Sf9 cells, comparing viral infection with C6/36 mosquito cells, commonly used for CHIKV maintenance. Viral exposure of Sf9 cells led to impaired viability and cytopathic effects, with RT-qPCR and immunofluorescence confirming CHIKV infection and production of viral particles, although with yields lower than those observed in C6/36 cells. Transmission electron microscopy revealed infection-induced morphological alterations in Sf9 and C6/36 cells, particularly associated with the endoplasmic reticulum and mitochondria. Viral particles were observed in vesicles and also extracellularly, anchored to the cell membrane. Budding of vesicles containing multiple viral particles were noticeable in Sf9, but not in C6/36, while infectivity was confirmed for CHIKV derived from both cells. Autophagy-like structures were noticed in infected C6/36 cells, supported by expression of the LC3B marker in these cells only. The results validate Sf9 cells as a novel permissive model for the investigation of CHIKV interactions in insects.