Monocyte-mediated thrombosis linked to circulating tissue factor and immune-paralysis in COVID-19
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections cause coronavirus disease 2019 (COVID-19) and are associated with inflammation and coagulopathy and high incidence of thrombosis. Myeloid cells (M?) help coordinate the initial immune response in COVID-19. Although we appreciate that M? lie at the nexus of inflammation and thrombosis, the mechanisms that unite the two in COVID-19 remain largely unknown. In this study, we employed systems biology approaches including proteomics, transcriptomics, and mass cytometry to define the circulating proteome and circulating immune cell phenotypes in subjects with COVID-19. In a cohort of COVID-19 subjects (n=35), circulating markers of inflammation (CCL23, IL-6) and vascular dysfunction (ACE2, tissue factor [TF]) were elevated in subjects with severe compared with mild COVID-19. Additionally, although the total white blood cell (WBC) counts were similar between COVID-19 groups, CD14+ monocytes from severe COVID-19 subjects expressed more TF. At baseline, transcriptomics demonstrated increased IL-6, CCL3, ACOD1, C5AR1, C5AR2, and TF in severe COVID-19 subjects compared with controls. Using “stress” transcriptomics, we found that circulating immune cells from severe COVID-19 subjects had evidence of profound immune paralysis with greatly reduced transcriptional activation and release of inflammatory markers in response to Toll-like receptor (TLR) activation. Finally, sera from severe (but not mild) COVID-19 subjects activated human monocytes and induced TF expression. Taken together, these observations further elucidate the pathological mechanisms that underlie immune dysfunction and coagulation abnormalities in COVID-19, contributing to our growing understanding of SARS-CoV-2 infections that could also be leveraged to develop novel diagnostic and therapeutic strategies. Overall design: To investigate if the circulating immune cells from Severe COVID-19 subjects are primed and hyperresponsive to inflammatory stimuli.  To define the baseline activation state and circulating immune cell responses to stress, we obtained PBMC from severe COVID-19 subjects and age-matched controls  and stimulated them with the TLR4 ligand LPS (1 ug /ml for 2 hours). After TLR-4 ligand stimulation RNA was isolated and and processed for RNA-seq