During the COVID-19 pandemic, multiple SARS-CoV-2 variants emerged, each with distinct pathogenicity and transmissibility. This study investigated the role of the viral spike (S) protein in disease progression, focusing on the highly virulent S variant. The Delta S protein exhibited enhanced cleavage efficiency at the S1/S2 junction, resulting in partial dissociation of the S1 subunit, with detectable levels of extracellular S1. Unexpectedly, transient expression of Ancestral and Delta S protein induced by a recombinant vesicular stomatitis viral vector caused mild pulmonary inflammation, neutrophil activation, microthrombosis, and ~40% mortality in transgenic K18-hACE2 mice between 8 and 16 days, similar to post-COVID sequelae. The diseased mice displayed splenic atrophy and systemic inflammation, with elevated serum IGFBP-1 and CXCL13 levels. Consistent with the animal findings, serum samples from long COVID patients showed significantly elevated IGFBP-1 levels. CXCL13 levels were particularly elevated in patients with more severe long COVID symptoms. Notably, treatment with the antiplatelet agent aspirin significantly reduced both mortality and weight loss in mice exposed to Delta S protein expression. These findings suggest that SARS-CoV-2 S protein-associated coagulation and systemic inflammation during infection may contribute to the development of post-acute sequelae of COVID-19.IMPORTANCEOur study investigates the distinctive pathogenic properties of the SARS-CoV-2 spike (S) protein from highly virulent variants, with a particular focus on its delayed pathological effects in mice. Using a vesicular stomatitis virus (VSV) vector to transiently express the Ancestral and Delta variant S proteins in K18-hACE2 mice, we observed minimal acute symptoms initially; however, approximately 40% of the mice developed mild pulmonary inflammation, neutrophil activation, and microthrombosis, leading to death between 8 and 16 days post-infection. This delayed pathology was accompanied by elevated circulating levels of CXCL13 and IGFBP-1. Consistent with these findings, serum samples from long COVID patients also showed significantly increased IGFBP-1 levels, while CXCL13 levels were particularly elevated in individuals with more severe long COVID symptoms. These findings provide important observational evidence that may guide future mechanistic studies on long COVID and inform the development of potential therapeutic approaches.
Long Covid