Patients Hospitalized with COVID-19 Demonstrate Distinct Plasma Cytokine and Chemokine Concentrations in vivo and TLR-Mediated Cytokine and Chemokine Production in Whole Blood in vitro.

Introduction: SARS-CoV-2's continued global health impact underscores the importance of ongoing pathogenesis research. Insights into the host's first line of defense against severe COVID-19 identify actionable biomarkers, informing disease management or therapeutics. Yet, the innate immune response, including cytokines, chemokines, adenosine deaminases (ADAs) and Toll-like receptors (TLRs), relevant to COVID-19 remain incompletely characterized.

Methods: Peripheral blood was longitudinally collected between May 2020 and March 2021 from COVID-19 hospitalized adults (N = 79) and healthy controls (HCs) (N = 14; not tested, assumed COVID-negative, no viral exposure or symptoms). Heparinized blood was fractionated for plasma cryopreservation and in vitro whole blood TLR-stimulation employing TLR-3, -4, and -7/8 agonists. Post-stimulation culture supernatants were analyzed using multiplex and enzymatic assays.

Results: Upon hospitalization, plasma concentrations of IFNγ, IL-6, CXCL10, and ADAs were significantly upregulated compared to convalescent time points and HCs. Participants with fatal COVID-19 exhibited higher IL-27, CXCL10, and ADAs concentrations upon admission. Plasma cytokines, chemokines, and ADAs were positively correlated and associated with distinct temporal patterns. TLR-stimulated cell cultures from patients produced reduced IFNα2, IFNγ, IL-12p40, and IL-12p70 compared to HCs or later time points.

Conclusion: Higher plasma concentrations of IL-27, CXCL10, and ADAs at admission were associated with severe COVID-19 and mortality. Reduced TLR-mediated IFNα2, IFNγ, and IL-12p70 production suggests COVID dampens Th1-polarizing innate immune responses, providing insight into immunological sequelae of SARS-CoV-2 infection.