Analysis of differential gene expression of pro-inflammatory cytokines in the nasopharyngeal milieu of mild & severe COVID-19 cases

Abstract

Introduction: A subset of individuals with COVID-19 can suffer from a severe form of the disease requiring breathing support for respiratory failure and even death due to disease complications. COVID-19 disease severity can be attributed to numerous factors, where several studies have associated changes in the expression of serum pro-inflammatory cytokines with disease severity. However, very few studies have associated the changes in expression of pro-inflammatory changes in the nasopharyngeal milieu with disease severity. Therefore, in the current study, we performed differential gene expression analysis of various pro-inflammatory cytokines in the nasopharyngeal milieu of mild & severe COVID-19 cases.

Material and method: For this retrospective, cross-sectional study, a total of 118 nasopharyngeal swab samples, previously collected from mild and severe (based on the WHO criteria) COVID-19 patients were used. A real-time qPCR was performed to determine the viral loads and also evaluate the mRNA expression of eight cytokines (IL-1, IL-2, IL-4, IL-6, IL-10, IFN-γ, TGF-β1, and TNF-α). Subsequently, an unpaired T-test was applied to compare the statistical difference in mean expression of viral loads and each cytokine between the mild and severe groups, while the Pearson correlation test was applied to establish a correlation between disease severity, viral load, and cytokines expression. Similarly, a multivariable logistic regression analysis was performed to assess the relationship between different variables from the data and disease severity.

Results: Out of 118 samples, 71 were mild, while 47 were severe. The mean viral load between the mild and severe groups was comparable (mild group: 27.07± 5.22; severe group: 26.37 ±7.89). The mRNA expression of cytokines IL-2, IL-6, IFN- γ, and TNF-α was significantly different in the two groups (p<0.05), where the Log2 normalized expression of IL-2, IL-6, IFN- γ, and TNF-α was found to be 2.2-, 16-, 2.3-, and 1.73-fold less in the severe group as compared to the mild group. Furthermore, we also observed a significant positive correlation between all the cytokines in the severe group. The multivariate analysis showed a significant relationship between age, IL-6, and disease severity.

Conclusion: This decreased expression of certain cytokines (IL-2, IL-6, TNF-α, and IFN-γ) in the nasopharyngeal milieu may be considered early biomarkers for disease severity in COVID-19 patients.

Fig 1. Viral loads and cytokine expression in mild vs severe group.

The figure shows A) viral loads (Ct values) distribution, B) expression of cytokines (mean ΔCt values) in mild and severe groups, while C) shows Log2 normalized fold change (2^(-ΔΔCt)) in cytokine expression in severe groups relative to the mild group. B) The line above bars with an asterisk sign indicates a significant difference (p<0.05) in the expression of the tested genes between the mild and severe groups.