Tumour Cell-Associated Heterogeneity in Antiviral Immunity Shapes Influenza Responses and Immune-Modulatory Signalling in Lung Cancer

Background/Objectives: Respiratory viral infections occur within the same anatomical niche as lung cancer, yet how lung cancer cells respond to infection and how these responses influence antiviral and inflammatory signalling remain poorly understood. This study investigated innate immune responses to influenza A virus (IAV) infection across a panel of lung epithelial cell lines. Methods: Non-malignant bronchial epithelial and non-small cell lung cancer (NSCLC) cell lines representing adenocarcinoma and squamous cell carcinoma were infected with IAV. Antiviral and inflammatory gene expression, viral RNA and protein detection, infection-induced cell death, pattern recognition receptor expression, and immune checkpoint ligand expression were assessed using molecular, biochemical and flow cytometric approaches. Interferon (IFN) receptor blockade and mitochondrial reactive oxygen species scavenging were used to investigate selected signalling mechanisms. Results: NSCLC cell lines exhibited heterogeneous innate immune responses to IAV infection, with differential regulation of RNA-sensing pathways and canonical antiviral signalling components. Although IFN responses were retained, NSCLC cells exhibited reduced infection-induced apoptosis and prolonged viral RNA and protein detection compared with non-malignant epithelial cells. IAV infection was also associated with changes in DNA-sensing receptor expression, including TLR9, and increased expression of the immune checkpoint ligand PD-L1. Conclusions: These findings identify substantial cell line-associated heterogeneity in antiviral responses to IAV across lung epithelial cell lines, including NSCLC cells. The observed differences in viral RNA and protein detection, cell death responses and immune-modulatory signalling provide a framework for understanding how respiratory viral infections may interact with lung cancer cells to shape antiviral and inflammatory responses within the tumour environment.