Collectively, our data led us to nominate GZMB as a viral target via transcriptomics; indicated that BV01 is efficiently and specifically cleaved by GZMB in vitro; suggested, based on immunostaining, that the cells producing GZMB are enriched in lungs infected with PR8 (viral pneumonia) compared to SP (bacterial pneumonia); and validated that GZMB itself is upregulated in a model of influenza based on immunohistochemistry and mRNA expression. Here, GZMB is linked to bacterial pneumonia.