Altered increase in STAT1 expression and phosphorylation in severe COVID-19

Rincon-Arevalo, H.; Aue, A.; Ritter, J.; Szelinski, F.; Khadzhynov, D.; Zickler, D.; Stefanski, A.-L.; Lino, A. C.; Koerper, S.; Eckardt, K.-U.; Schrezenmeier, H.; Doerner, T.; Schrezenmeier, E.

The interferon pathway represents a key antiviral defense mechanism and is being considered as a therapeutic target in COVID-19. Both, substitution of interferon and blocking interferon signaling through JAK STAT inhibition to limit cytokine storms have been proposed. However, little is known so far about possible abnormalities in STAT signaling in immune cells during SARS-CoV-2 infection. In the current study, we investigated downstream targets of interferon signaling, including STAT1, 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 an 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. Most interestingly, Siglec-1 and STAT1 in CD14+ monocytes and plasmablasts showed lower expression among severe COVID-19 cases compared to mild cases. Contrary to the baseline whole protein 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- and IFN-{gamma} stimulation of PBMCs from patients with severe COVID-19. The data suggest impaired STAT1 transcriptional upregulation among severely infected patients which may represent a potential predictive biomarker and may allow stratification of patients for certain interferon-pathway targeted treatments.