## 4 Discussion  
Deregulation of the host miRNAs has been observed in a number of infections including studies involving HSV-1 [21; 23; 26; 29; 39; 40; 41; 42; 43; 44; 45; 46; 47]. However, the discrepancy between the different studies (i.e., miRNAs that were deregulated) was quite significant, indicating a strong dependence on the miRNAome of the cells used in the experiments. In this study, we aimed to investigate the deregulation of miRNAs in the primary cells, and in two completely unrelated experiments to identify a genuine miRNA response of the infected cells. We showed that miR-183, -96, -182, and -375 are the only reproducibly deregulated miRNAs in a number of primary cells, but not in all cancer-derived cells. The observed discrepancy with cancer cell lines and different studies can be explained by the fact that cancer cell lines can have dramatically altered miRNAomes [73], which probably masks the potential upregulation. Another possibility is that the pathways leading to the transcriptional activation of the cluster are lost in cancer cells (i.e., not responsive to the ICP0-mediated upregulation). A recent study by [PERSON] et al. in which the authors analyzed the miRNA expression in tears of patients with herpes epithelial keratatitis and found that among many, miR-182 and miR-183 were upregulated, supporting the idea that the activation of miR-183/96/182 represents the innate antiviral response to HSV-1 infection [47]. Similarly, the same cluster has been found upregulated in other herpesvirus infections [27] and also in completely distant RNA viruses [74; 75; 76]), which indicates a conserved innate antiviral response mechanism. Indeed, although the exact role of this cluster in antiviral defense is yet to be elucidated, there are multiple lines of evidence indicating an important role in the control of innate and adaptive immunity (reviewed in [77]). miRNAs of the cluster target protein phosphatase 2 catalytic subunit alpha (PPP2 CA) and tripartite motif-containing 27 (TRIM27), a negative regulator of IRF3, STAT1, and TBK1 [76], promote IFN production and signaling. The enhanced IFN signaling can lead to the reduction in virus replication, as has been shown for vesicular stomatitis virus [76]. Moreover, [PERSON] et al. showed that the signal transducer and activator of transcription 5 (STAT5)-mediated activation of miR-182 by interleukin 2 receptor (IL-2R) initiates a positive feedback response by targeting FoxO1 and promotes the clonal expansion of activated helper T lymphocytes [66]. Taken together, one might expect that the upregulation of the miR-183/96/182 cluster will affect HSV-1 infection; however, our results show that this is not the case, which is not surprising. In fact, HSV-1 has developed numerous mechanisms to circumvent the host antiviral defense of the cell including various functions of incoming virion/tegument proteins and proteins expressed after infection (reviewed in [78; 79]). For example, only the TBK-1/IRF3/IFN axis is targeted by at least five different viral proteins, ICP0, ICP27, ICP34.5, US3, and vhs (reviewed in [78; 79]). This indicates that activation of the miR-183/96/182 cluster might be part of an early cellular response to virus infection, preceding the adaptation of large DNA viruses to it. However, [PERSON] et al. found that the expression of the miR-183/96/182 cluster is repressed in cells latently infected with Epstein-Barr virus (EBV mediated by EBV-encoded latent membrane protein 1 (LMP-1)) [28]. These results show that, for the virus, the roles of the miR-183/96/182 cluster in the latency program might be in contrast to productive infection and that their control might be required to enable efficient latent infection. It is difficult to predict a role for these miRNAs in the establishment and/or maintenance of latent HSV-1, particularly in the absence or limited ICP0 expression, however, this is yet to be revealed. On the other hand, one can argue that miRNAs cannot have a meaningful role during productive HSV-1 infection.