Increased IL-26 associates with markers of hyperinflammation and tissue damage in patients with acute COVID-19

Systemic increase in IL-26 is associated with severe COVID-19 and comorbid obstructive lung disease

Background

IL-26 is a key mediator of pulmonary host defense given its abundant expression in human airways and its established antibacterial properties. Moreover, recent studies indicate that IL-26 can also inhibit viral replication. Along these lines, we have previously reported an increase in the plasma concentration of IL-26 among patients with acute COVID-19 that is linked to harmful hyperinflammation. Nevertheless, it is still unclear whether this systemic increase in IL-26 relates to disease severity, sex, comorbidities, viral load, or the innate immune response in acute COVID-19.

Methods

IL-26 was quantified using ELISA in plasma samples from a large cohort of well-characterized patients with acute COVID-19 (n=178) and healthy controls (n=30). The plasma concentrations of SARS-CoV-2 nucleocapsid and spike protein, as well as those of IFN-α2a, IFN-β, and IFN-γ, were determined using electrochemiluminescence immunoassay. The concentration of double-stranded DNA was determined using fluorometry.

Results

The plasma concentration of IL-26 was increased in patients with severe/critical COVID-19, particularly among males and patients with comorbid obstructive lung disease. Moreover, the concentration of IL-26 displayed positive correlations with length of hospital stay, as well as with systemic markers of viral load, antiviral immunity, and extracellular DNA.

Conclusions

Systemic IL-26 is involved in severe COVID-19, especially in males and patients with comorbid obstructive lung disease. These findings argue that systemic IL-26 has pathogenic and antiviral relevance, as well as biomarker potential.

A Comprehensive Network Map of Interleukin-26 Signaling Pathway

Interleukin-26 (IL-26) is a cytokine that belongs to the IL-20 subfamily and is primarily expressed in T helper 1 cells and Th17 memory CD4+ cells. Its receptor complex, consisting of IL-20R1 and IL-10R2, activates a signaling pathway involving several proteins such as Janus kinase 1 and tyrosine-protein kinase, signal transducer and activator of transcription (STAT) 1, and STAT3. This leads to the initiation of downstream signaling cascades that play a crucial role in various biological processes, including inflammation, immune response regulation, atopic dermatitis, macrophage differentiation, osteoclastogenesis, antibacterial host defense, anti-apoptosis, and tumor growth. In this study, we curated literature data pertaining to IL-26 signaling. The curated map includes a total of seven activation/inhibition events, 16 catalysis events, 33 gene regulation events, 25 protein expression types, two transport events, and three molecular associations.

Interleukin 26 Induces Macrophage IL-9 Expression in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease with chronic inflammation, bone erosion, and joint deformation. Synovial tissue in RA patients is full of proinflammatory cytokines and infiltrated immune cells, such as T help (Th) 9, Th17, macrophages, and osteoclasts. Recent reports emphasized a new member of the interleukin (IL)-10 family, IL-26, an inducer of IL-17A that is overexpressed in RA patients. Our previous works found that IL-26 inhibits osteoclastogenesis and conducts monocyte differentiation toward M1 macrophages. In this study, we aimed to clarify the effect of IL-26 on macrophages linking to Th9 and Th17 in IL-9 and IL-17 expression and downstream signal transduction. Murine and human macrophage cell lines and primary culture cells were used and stimulated by IL26. Cytokines expressions were evaluated by flow cytometry. Signal transduction and transcription factors expression were detected by Western blot and real time-PCR. Our results show that IL-26 and IL-9 colocalized in macrophage in RA synovium. IL-26 directly induces macrophage inflammatory cytokines IL-9 and IL-17A expression. IL-26 increases the IL-9 and IL-17A upstream mechanisms IRF4 and RelB expression. Moreover, the AKT-FoxO1 pathway is also activated by IL-26 in IL-9 and IL-17A expressing macrophage. Blockage of AKT phosphorylation enhances IL-26 stimulating IL-9-producing macrophage cells. In conclusion, our results support that IL-26 promotes IL-9- and IL-17-expressing macrophage and might initiate IL-9- and IL-17-related adaptive immunity in rheumatoid arthritis. Targeting IL-26 may a potential therapeutic strategy for rheumatoid arthritis or other IL-9 plus IL-17 dominant diseases.

Biomarkers in long COVID-19: A systematic review

Purpose

Long COVID, also known as post-acute sequelae of COVID-19, refers to the constellation of long-term symptoms experienced by people suffering persistent symptoms for one or more months after SARS-CoV-2 infection. Blood biomarkers can be altered in long COVID patients; however, biomarkers associated with long COVID symptoms and their roles in disease progression remain undetermined. This study aims to systematically evaluate blood biomarkers that may act as indicators or therapeutic targets for long COVID.

Methods

A systematic literature review in PubMed, Embase, and CINAHL was performed on 18 August 2022. The search keywords long COVID-19 symptoms and biomarkers were used to filter out the eligible studies, which were then carefully evaluated.

Results

Identified from 28 studies and representing six biological classifications, 113 biomarkers were significantly associated with long COVID: (1) Cytokine/Chemokine (38, 33.6%); (2) Biochemical markers (24, 21.2%); (3) Vascular markers (20, 17.7%); (4) Neurological markers (6, 5.3%); (5) Acute phase protein (5, 4.4%); and (6) Others (20, 17.7%). Compared with healthy control or recovered patients without long COVID symptoms, 79 biomarkers were increased, 29 were decreased, and 5 required further determination in the long COVID patients. Of these, up-regulated Interleukin 6, C-reactive protein, and tumor necrosis factor alpha might serve as the potential diagnostic biomarkers for long COVID. Moreover, long COVID patients with neurological symptoms exhibited higher levels of neurofilament light chain and glial fibrillary acidic protein whereas those with pulmonary symptoms exhibited a higher level of transforming growth factor beta.

Conclusion

Long COVID patients present elevated inflammatory biomarkers after initial infection. Our study found significant associations between specific biomarkers and long COVID symptoms. Further investigations are warranted to identify a core set of blood biomarkers that can be used to diagnose and manage long COVID patients in clinical practice.