The
interferon pathway, a key
antiviral defense mechanism, is being considered as a therapeutic target in
COVID-19. Both, substitution of
interferon and JAK/STAT inhibition to limit
cytokine storms have been proposed. However, little is known about possible abnormalities in STAT signaling in immune cells during
SARS-CoV-2 infection. We investigated downstream targets of
interferon signaling, including STAT1, STAT2, pSTAT1 and 2, and IRF1, 7 and 9 by flow cytometry in 30 patients with
COVID-19, 17 with mild, and 13 with severe
infection. We report upregulation of STAT1 and IRF9 in mild and severe
COVID-19 cases, which correlated with the IFN-signature assessed by
Siglec-1 (CD169) expression on peripheral monocytes. Interestingly,
Siglec-1 and STAT1 in CD14+ monocytes and plasmablasts showed lower expression among severe cases compared to mild cases. Contrary to the baseline STAT1 expression, the phosphorylation of STAT1 was enhanced in severe
COVID-19 cases, indicating a dysbalanced JAK/STAT signaling that fails to induce transcription of
interferon stimulated response elements (ISRE). This abnormality persisted after IFN-α and IFN-γ stimulation of PBMCs from patients with severe
COVID-19. Data suggest impaired STAT1 transcriptional upregulation among severely infected patients may represent a potential predictive
biomarker and would allow stratification of patients for certain
interferon-pathway targeted treatments.