Which innate defense acts as chemical messengers against viral infections?

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Interferons are signaling proteins (cytokines) produced in response to viral infections that act as chemical messengers to coordinate antiviral defenses. When a cell detects a viral threat, it releases interferons which bind to receptors on neighboring cells, triggering pathways that turn on antiviral genes. This creates an antiviral state by inhibiting viral replication (for example, through PKR and RNase L pathways) and by boosting immune activities, such as enhancing natural killer cell function and increasing MHC class I expression to improve viral antigen presentation. While fever and inflammation are part of the overall response to infection and the complement system aids in pathogen elimination, interferons specifically serve as the rapid, cell-to-cell communication signals that warn and prepare other cells to resist viral spread.