The Myeloid LSECtin Is a DAP12-Coupled Receptor That Is Crucial for Inflammatory Response Induced by Ebola Virus Glycoprotein

Abstract

Fatal Ebola virus infection is characterized by a systemic inflammatory response similar to septic shock. Ebola glycoprotein (GP) is involved in this process through activating dendritic cells (DCs) and macrophages. However, the mechanism is unclear. Here, we showed that LSECtin (also known as CLEC4G) plays an important role in GP-mediated inflammatory responses in human DCs. Anti-LSECtin mAb engagement induced TNF-α and IL-6 production in DCs, whereas silencing of LSECtin abrogated this effect. Intriguingly, as a pathogen-derived ligand, Ebola GP could trigger TNF-α and IL-6 release by DCs through LSECtin. Mechanistic investigations revealed that LSECtin initiated signaling via association with a 12-kDa DNAX-activating protein (DAP12) and induced Syk activation. Mutation of key tyrosines in the DAP12 immunoreceptor tyrosine-based activation motif abrogated LSECtin-mediated signaling. Furthermore, Syk inhibitors significantly reduced the GP-triggered cytokine production in DCs. Therefore, our results demonstrate that LSECtin is required for the GP-induced inflammatory response, providing new insights into the EBOV-mediated inflammatory response.

Ebolaviruses Associated with Differential Pathogenicity Induce Distinct Host Responses in Human Macrophages

“…EBOV GP-mediated cytokine induction in monocyte-derived dendritic cells is triggered not only by TLR4 but also by C-type lectin domain family 4 member G (CLEC4G/ LSECtin) (34). Expression of LSECtin on MDMs depends on IL-4 stimulation (54), and unstimulated MDMs, as used in the presented study, do not express LSECtin (54).…”

“…It has been reported that this activation is triggered by the interaction of the EBOV glycoprotein (GP) with Toll-like receptor 4 (TLR4) (6,(27)(28)(29)(30)(31)(32)(33). In addition, GP has been shown to interact with C-type lectin domain family 4 member G (CLEC4G/LSECtin) on monocyte-derived dendritic cells, leading to the induction of an inflammatory response (34). A hallmark of severe EBOV disease and a predictor of fatal outcome is the induction of a strong inflammatory response as shown by elevated levels of inflammatory cytokines and chemokines (2-6, 8, 35).…”

The role of mononuclear phagocytes in Ebola virus infection

“…-28,63,69 A recent longitudinal study in a patient with severe EVD demonstrated that virus load in PBMCs correlates well with serum RNA levels,69 suggesting that virus replication in PBMCs contributes significantly to overall virus load. Consistent with the possibility that circulating monocytes support EBOV infection, Versteeg et al showed that at later times during experimental infection bone marrow derived monocytes 22,25,72,75,80,87,[95][96][97][98]. However, a recently appreciated caveat to these studies is the observation that bone marrow monocytes matured in vitro produce a heterogeneous population of cells, with cultures containing both DCs and M s 99.…”

“…As a number of different cell types in addition to macrophages and DCs express TLR4, many additional host cells may contribute to the TLR4‐elicited cytokine storm that EBOV causes. Finally, in addition to TLR4, other currently unexplored EBOV/macrophage receptor interactions and subsequent signaling events may contribute to the production of the proinflammatory cytokines …”

“…Finally, in addition to TLR4, other currently unexplored EBOV/macrophage receptor interactions and subsequent signaling events may contribute to the production of the proinflammatory cytokines. 86,87 A natural question that follows from these studies is how critical is myeloid cell activation to EBOV pathogenesis? Does the production of proinflammatory cytokines from these cells in response to EBOV contribute to virus-associated pathology?…”