SARS-CoV-2 virus-like particle variants alpha and delta mimic the native viruses in their differential inflammasome activating potential

The emerging SARS-CoV-2 variants are evolving to evade human immunity and differ in their pathogenicity. While evasion of the variants from adaptive immunity is widely investigated, there is a paucity of knowledge about their interactions with innate immunity. Inflammasome assembly is one of the most potent mechanisms of the early innate response to viruses, but when it is inappropriate, it can perpetuate tissue damage. In this study, we focused on the capacity of SARS-CoV-2 Alpha and Delta variants to activate the NLRP3 inflammasome. We compared the macrophage activation, particularly the inflammasome formation, using Alpha- and Delta-spike virus-like particles (VLPs). We found that VLPs of both variants activated the inflammasome even without a priming step. Delta-spike VLPs had a significantly stronger effect on triggering pyroptosis and inflammasome assembly in THP-1 macrophages than did Alfa-spike VLPs. Cells treated with Delta VLPs showed greater cleavage of caspase-1 and IL-1β release. Furthermore, Delta VLPs induced stronger cytokine secretion from macrophages and caused essential impairment of mitochondrial respiration in comparison to Alpha VLPs. Additionally, infection of primary human monocyte-derived macrophages with the SARS-CoV-2 variants confirmed the observations in VLPs. Collectively, we revealed that SARS-CoV-2 Delta had a greater impact on the inflammasome activation, cell death and mitochondrial respiration in macrophages than did the Alpha variant. Importantly, the differential response to the SARS-CoV-2 variants can influence the efficacy of therapies targeting the host's innate immunity.