Herpes Simplex Virus Type 1 (HSV-1) infection of monocytic cells induces a strong release of chemokines in a Caspase-8-independent manner

Herpes simplex virus type 1 (HSV-1) is a widespread human pathogen that can establish lifelong persistence after primary infection. Although antiviral drugs are available, their efficacy is often limited by the emergence of resistant strains, particularly in immunocompromised patients or in those undergoing prolonged treatment. The absence of effective vaccines and the growing problem of resistance underscore the need to better understand the molecular interplay between HSV-1 and host immunity, as well as to explore alternative antiviral strategies. During HSV-1 infection, while epithelial cells can counteract pro-apoptotic signals through the expression of viral proteins, immune cells such as monocytes and dendritic cells (DCs) remain more susceptible to virus-induced apoptosis. In monocytic cells, HSV-1 establishes a low-permissive infection, yet increasing evidence indicates that death-related proteins may exert non-apoptotic functions during infection. Among these, caspase-8, classically known as an initiator of extrinsic apoptosis, has emerged as a versatile regulator implicated in necroptosis, autophagy, inflammatory signaling, and viral replication. This PhD project primarily investigated the role of caspase-8 in HSV-1 infection of monocytic cells, with a focus on viral immune evasion and modulation of host signaling pathways. Using CRISPR-Cas9-generated caspase-8-knockout THP-1 cells and wild-type or Us11/Us12-deleted HSV-1 strains, this work demonstrates that caspase-8 limits viral gene expression, restrains NF-κB activation, and tempers chemokine production, thereby contributing to the regulation of inflammatory responses. In addition, RIPK1 expression was found to be downregulated in caspase-8-deficient cells, further supporting its involvement in immune modulation. Here, “immunomodulation” refers to cell-intrinsic regulation of innate immune signaling in infected myeloid cells (captured by NF-κB activity, chemokine transcription, and RIPK1 expression) under the influence of viral immune-evasion factors (e.g., Us11) and caspase-8-dependent checkpoints. The construction of recombinant HSV-1 viruses carrying fluorescent tags enabled preliminary insights into virion trafficking and maturation, suggesting a potential role of caspase-8 in late stages of the viral life cycle. Altogether, these findings highlight caspase-8 as an important regulator of molecular pathways at the interface between HSV-1 and host immunity. In addition to this central mechanistic investigation, the thesis includes complementary studies exploring the antiviral activity of selected plant-derived products. Hydroethanolic extracts from cultivated wild olive leaves exhibited antiviral activity, with oleuropein identified as a major bioactive compound associated with reduced HSV-1 gene expression and protein synthesis while activating PKR and AP-1 signaling. Similarly, almond by-products, such as blanching skin and blanching water, have been shown to exhibit antiviral properties. These exploratory studies broaden the scope of the thesis by examining alternative antiviral approaches, without extensive mechanistic dissection. In conclusion, this work primarily advances the understanding of molecular signaling pathways during HSV-1 infection, particularly the role of caspase-8 in modulating viral replication and innate immune responses in monocytic cells, while secondarily highlighting plant-derived compounds as complementary sources of antiviral bioactivity. By combining mechanistic insights into caspase-8, NF-κB, and chemokine regulation with exploratory studies of natural bioactive molecules, this thesis contributes to a more comprehensive view of HSV-1-host interactions.