Western blot analysis showed that infection with Delta variant, but not the WT strain, significantly increased levels of both cleaved caspase-3 and cleaved PARP when unexposed to PM compared to non-infected, non-PM-exposed controls (Figures 4A, D), consistent with SARS-CoV-2-induced human lung epithelial cell apoptosis (Zhu et al., 2020; Liang et al., 2024). Here, CASP3 is linked to infection.