Differential Cytokine Signatures of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and Influenza Infection Highlight Key Differences in Pathobiology

Abstract

Background: Several inflammatory cytokines are upregulated in severe coronavirus disease 2019 (COVID-19). We compared cytokines in COVID-19 versus influenza to define differentiating features of the inflammatory response to these pathogens and their association with severe disease. Because elevated body mass index (BMI) is a known risk factor for severe COVID-19, we examined the relationship of BMI to cytokines associated with severe disease.

Methods: Thirty-seven cytokines and chemokines were measured in plasma from 135 patients with COVID-19, 57 patients with influenza, and 30 healthy controls. Controlling for BMI, age, and sex, differences in cytokines between groups were determined by linear regression and random forest prediction was used to determine the cytokines most important in distinguishing severe COVID-19 and influenza. Mediation analysis was used to identify cytokines that mediate the effect of BMI and age on disease severity.

Results: Interleukin-18 (IL-18), IL-1β, IL-6, and tumor necrosis factor-α (TNF-α) were significantly increased in COVID-19 versus influenza patients, whereas granulocyte macrophage colony-stimulating factor, interferon-γ (IFN-γ), IFN-λ1, IL-10, IL-15, and monocyte chemoattractant protein 2 were significantly elevated in the influenza group. In subgroup analysis based on disease severity, IL-18, IL-6, and TNF-α were elevated in severe COVID-19, but not in severe influenza. Random forest analysis identified high IL-6 and low IFN-λ1 levels as the most distinct between severe COVID-19 and severe influenza. Finally, IL-1RA was identified as a potential mediator of the effects of BMI on COVID-19 severity.

Conclusions: These findings point to activation of fundamentally different innate immune pathways in severe acute respiratory syndrome coronavirus 2 and influenza infection, and emphasize drivers of severe COVID-19 to focus both mechanistic and therapeutic investigations.

Keywords: COVID-19; Cytokines; Influenza; Obesity; SARS-CoV-2.

Figure 1.

Cytokines and chemokines in influenza and COVID-19 compared with healthy controls. Differences between the COVID-19 cohort (blue) or influenza cohort (orange) and healthy controls (gray) were determined by 2-tailed t test after adjusting for sex and age. Differences between the COVID-19 cohort and influenza cohort for each analyte were determined by 2-tailed t test after adjusting for sex, age, and BMI. FDR was obtained using the Benjamini-Hochberg procedure. Statistical significance is indicated by NS, *, **, or *** above the brackets indicating FDR >0.25, <0.25, <0.1, or <0.05, respectively. Abbreviations: BMI, body mass index; COVID-19, coronavirus disease 2019; FDR, false discovery rate; NS, not significant.

Figure 2.

Cytokines and chemokines elevated in severe disease compared with mild/moderate disease and according to infection. A, Differences between disease severity subgroups were determined by 2-tailed t test after adjusting for sex, age, and BMI. Participants who received steroids before cytokine measurement were excluded. Differences between the severe COVID-19 cohort (green) and severe influenza cohort (orange) for each analyte were determined by 2-tailed t test after adjusting for sex, age, and BMI. False discovery rate (FDR) was obtained using the Benjamini-Hochberg procedure. Statistical significance is indicated by NS, *, **, or *** above the brackets indicating FDR >0.25, <0.25, <0.1, or <0.05 respectively. B, Top: Cytokines/chemokines higher in the COVID-19 cohort compared with influenza (left), influenza compared with COVID-19 (right) both COVID-19 and influenza compared with healthy controls, but not significantly different between COVID-19 and influenza (overlap center). Bottom: Cytokines/chemokines elevated in severe COVID-19 relative to mild/mod COVID-19 (left side), those elevated in severe influenza relative to mild/mod influenza (right side), and those that are elevated in severe forms of both diseases (overlap center). Abbreviations: BMI, body mass index; COVID-19, coronavirus disease 2019; NS, not significant.

Figure 3.

Multivariable analysis based on random forest revealed the most important variables in distinguishing severe COVID-19 and severe influenza. Feature importance was obtained from the random forest model for predicting severe COVID-19 versus severe influenza. The color indicates the log₂ fold change of the analyte signal between severe COVID-19 and severe influenza. Red color indicates a higher value in COVID-19 and blue color indicates a higher value in influenza. Abbreviation: COVID-19, coronavirus disease 2019.

Figure 4.

Mediation analysis of BMI and IL-1RA on COVID-19 severity. A, BMI (X axis) was plotted versus IL-1RA level (Y axis). The yellow line is a linear regression line for the COVID-19 cohort and the blue line is a linear regression line for the influenza cohort. The Pearson’s correlation coefficient between IL-1RA and BMI is 0.34 for the COVID-19 cohort and 0.15 for the influenza cohort. B, Diagram of the mediation analysis of BMI and IL-1RA on COVID-19 severity while controlling for diabetes and heart disease. The indirect, direct, and total effects were showed in the diagram. Statistical significance is indicated by *, **, or *** representing FDR <0.25, <0.1, or <0.05, respectively. Abbreviations: BMI, body mass index; COVID-19, coronavirus disease 2019; FDR, false discovery rate; IL, interleukin.