A Novel Role for Viral-Defective Interfering Particles in Enhancing Dendritic Cell Maturation

Abstract

Dendritic cell (DC) maturation is a crucial event in the development of adaptive immune responses that confer long-lasting protection against reinfection with the same virus. Sendai virus strain Cantell has a particularly strong ability to mature DCs independently of type I IFNs and TLR signaling, currently the best-described pathways for the induction of DC maturation. In this study, we demonstrate that defective-interfering (DI) particles present in Sendai virus-Cantell stocks are required for its robust DC maturation ability. DI particles contain incomplete genomes that are unable to replicate unless the viral polymerase is supplied by coinfection with complete virus. Accordingly, the improvement in the virus-induced maturation of DCs provided by DI particles requires standard virus coinfection and likely results from increased production of dsRNA replication intermediaries. This unique ability of DI particles to stimulate DC maturation cannot be mimicked by simply increasing the dose of standard virus. Furthermore, viruses with weak DC maturation abilities can be converted into potent DC stimulators with the addition of DI particles, supporting a potential application for DI particles as a novel natural adjuvant for viral immunizations.

MDA5 Participates in the Detection of Paramyxovirus Infection and Is Essential for the Early Activation of Dendritic Cells in Response to Sendai Virus Defective Interfering Particles

“…We have previously demonstrated that, differently from most wild-type SeV strains, DCs are capable of detecting SeV strain Cantell (SeV-C) and robustly produce cytokines even in the presence of functioning immune antagonists (20). The DC response to SeV-C requires the presence of defective interfering (DI) particles, known to enhance the induction of type I IFN in infections with many different viruses (21)(22)(23)(24).…”

“…Sequences for mouse and human primers used in this study are shown in Table I. Primers used for detection of SeV NP mRNA were previously published (20). For analysis, fold inductions were calculated over mock-infected values and representations of copy number are based on an empirical estimate of 2500 for the number of ␤-actin transcripts per cell (32).…”

“…SeV-(HD) and NDV were grown in 10-day embryonated eggs. SeV-HD was depleted of DI particles as previously described (20). In short, eggs were infected at an empirically determined dilution high enough to ensure less than one infectious dose per egg (10 7 dilution).…”

“…LLCMK2 cells were used to titrate SeVs and NDV. pDI particles were prepared as previously described (20). Encephalomyocarditis virus (EMCV) was grown and titered in baby hamster kidney cells in the absence of serum.…”

“…Nonadherent DCs were collected and infected after 6 days in culture. Mouse DCs were prepared according to a previously published protocol ensuring the production of immature DCs (20,31). Bone marrow cells isolated from mouse tibias and femurs were depleted of CD4, CD8, B220, and MHC class II positive cells by magnetic bead separation.…”