Innate Immune Sensing of Modified Vaccinia Virus Ankara (MVA) Is Mediated by TLR2-TLR6, MDA-5 and the NALP3 Inflammasome

Abstract

Modified vaccinia virus Ankara (MVA) is an attenuated double-stranded DNA poxvirus currently developed as a vaccine vector against HIV/AIDS. Profiling of the innate immune responses induced by MVA is essential for the design of vaccine vectors and for anticipating potential adverse interactions between naturally acquired and vaccine-induced immune responses. Here we report on innate immune sensing of MVA and cytokine responses in human THP-1 cells, primary human macrophages and mouse bone marrow-derived macrophages (BMDMs). The innate immune responses elicited by MVA in human macrophages were characterized by a robust chemokine production and a fairly weak pro-inflammatory cytokine response. Analyses of the cytokine production profile of macrophages isolated from knockout mice deficient in Toll-like receptors (TLRs) or in the adapter molecules MyD88 and TRIF revealed a critical role for TLR2, TLR6 and MyD88 in the production of IFNβ-independent chemokines. MVA induced a marked up-regulation of the expression of RIG-I like receptors (RLR) and the IPS-1 adapter (also known as Cardif, MAVS or VISA). Reduced expression of RIG-I, MDA-5 and IPS-1 by shRNAs indicated that sensing of MVA by RLR and production of IFNβ and IFNβ-dependent chemokines was controlled by the MDA-5 and IPS-1 pathway in the macrophage. Crosstalk between TLR2-MyD88 and the NALP3 inflammasome was essential for expression and processing of IL-1β. Transcription of the Il1b gene was markedly impaired in TLR2−/− and MyD88−/− BMDM, whereas mature and secreted IL-1β was massively reduced in NALP3−/− BMDMs or in human THP-1 macrophages with reduced expression of NALP3, ASC or caspase-1 by shRNAs. Innate immune sensing of MVA and production of chemokines, IFNβ and IL-1β by macrophages is mediated by the TLR2-TLR6-MyD88, MDA-5-IPS-1 and NALP3 inflammasome pathways. Delineation of the host response induced by MVA is critical for improving our understanding of poxvirus antiviral escape mechanisms and for designing new MVA vaccine vectors with improved immunogenicity.

Inflammasomes and its importance in viral infections

“…NLRP3 senses both non-enveloped and enveloped DNA viruses [69,70]. Studies on non-enveloped viruses such as adenovirus have shown conflicting results regarding the role of the inflammasome.…”

Active Infection of Human Blood Monocytes by Chikungunya Virus Triggers an Innate Immune Response

“…Whole blood contains the different blood cell subsets in normal distribution and allows analysis of early viral innate response of the different immune cells in a more physiological context (32). Whole blood samples from three healthy donors were inoculated with the IMT strain CHIKV at different MOI conditions (MOI 1 and 10), and cells were collected at 24 hpi.…”

Cytotoxins of the human pathogen Aeromonas hydrophila trigger, via the NLRP3 inflammasome, caspase‐1 activation in macrophages

“…However, accumulating evidence indicates that infection with many pathogens including bacteria, viruses and fungi induces the proinflammatory cell death of infected macrophages through the activation of caspase-1 [5][6][7][8][9][10][11][12][13][14][15][16][17]. The Nod-like receptor (NLR) family, pyrin domain containing 3 (NLRP3) is critical for caspase-1 activation and the secretion of IL-1b and IL-18 in response to multiple microbial molecules and endogenous danger molecules, whereas the NLR family, CARD domain containing 4 (NLRC4) protein is believed to sense bacterial flagellin and induce caspase-1 activation [18,19].…”