Interaction and Mutual Activation of Different Innate Immune Cells Is Necessary to Kill and Clear Hepatitis C Virus-Infected Cells

Abstract

Innate immune cells can sense hepatitis C virus (HCV)-infected cells and respond with anti-viral actions including secretion of interferons (IFNs). In previous studies, the response of individual innate immune cells against HCV was analyzed in detail. We hypothesized that interaction of multiple innate immune cells increases the magnitude of the immune response and eventually leads to clearance of HCV-infected cells. To investigate this, we co-cultured Huh-7 HCV subgenomic replicon (SGR) cells with peripheral blood mononuclear cells (PBMCs). We confirm secretion of IFNα by plasmacytoid dendritic cells (pDCs) and IFNγ by natural killer (NK) cells in the co-culture setup. Moreover, we observed that also monocytes contribute to the anti-viral response. Flow cytometry and ImageStream analysis demonstrated that monocytes take up material from HCV SGR cells in co-culture with PBMCs. Preceding the uptake, PBMCs caused apoptosis of HCV SGR cells by tumor necrosis factor-related apoptosis inducing ligand (TRAIL) expression on NK cells. We observed that only the interplay of monocytes, pDCs, and NK cells resulted in efficient clearance of HCV SGR cells, while these cell populations alone did not kill HCV SGR cells. Despite similar TRAIL receptor expression on Huh-7 control cells and HCV SGR cells, HCV activated PBMCs specifically killed HCV SGR cells and did not target Huh-7 control cells. Finally, we showed that HCV replicating cells per se are sensitive toward TRAIL-induced apoptosis. Our results highlight the importance of the interplay of different innate immune cells to initiate an efficient, rapid, and specific response against HCV-infected cells.

Secretion of Hepatitis C Virus Replication Intermediates Reduces Activation of Toll-Like Receptor 3 in Hepatocytes

“…Secretion of HCV RNA in exosomes/EVs has been described in previous studies as an antiviral sensing process activating innate immune responses in DCs, NK cells, and monocytes, 10,36,37 inducing IFN responses and inhibiting viral replication. However, activation requires close cell-tocell contact.…”

Soluble Fc-Disabled Herpes Virus Entry Mediator Augments Activation and Cytotoxicity of NK Cells by Promoting Cross-Talk between NK Cells and Monocytes

“…Several recent studies suggest that NK cell function can be modulated via APCs such as monocytes, macrophages, and DC (36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47). These cells also express HVEM receptors.…”

“…Thus, dynamic regulation of these receptors especially on NK cells and cells interacting with NK cells via HVEM signaling provide a potential mechanism for control of activating and inhibitory signals depending on cellular context. NK cells interact with other immune cells for optimal cytokine production, cytotoxicity, and control of virally infected or tumor cells (36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47). There are several reports showing that monocytes, DC, and macrophages interact with NK cells and cooperate in the innate immune response for protection against pathogens (36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47).…”

Toll-Like Receptor 7 (TLR-7) and TLR-9 Agonists Improve Hepatitis C Virus Replication and Infectivity Inhibition by Plasmacytoid Dendritic Cells

“…proposed as the main mechanism of HCV infectivity inhibition mediated by pDCs (16,17). No differences in the pDC response in terms of IFN-␣ production were observed among Jc1, IR, and P100.…”

“…pDCs from chronically HCV-infected patients showed resting-state levels of maturation markers, but maintained the responsiveness to TLR stimulation, suggesting that pDCs could be a viable drug target (15). pDCs sense in vitro HCV-infected cells, produce IFN-␣, and inhibit HCV replication (16), and this ability is enhanced by interaction with other components of innate immunity (NK cells and monocytes) (17).…”