Salivary Cytokines in Children with and Without Severe Disease Due to sars-cov-2 Infection

Background: Most children exposed to SARS-CoV-2 virus present with mild symptoms, but some may experience severe illnesses such as Multisystem inflammatory syndrome (MISC) or respiratory failure. Currently there are no established biomarkers to predict progression to severe disease. Although specific serum cytokines have been found to be higher in adults with severe COVID-19, their role as predictors of severe disease in children remains unclear. Further, the role of salivary cytokines in COVID-19 associated inflammation is unknown. Our objective was to compare cytokine levels in saliva of children with and without severe disease due to SARS-CoV-2 infection.

Methods: This prospective observational study, conducted at two tertiary children’s hospitals, was supported by a grant from the National Institute of Health RADx Program. Children ≤ 18 years of age with symptoms due to SARS-CoV-2 infection (positive PCR test, serology or immunological link) were enrolled after informed consent. Severe cases were defined as the occurrence of any of the following within 30 days of testing: diagnosis of MISC or Kawasaki disease, requirement for >2L oxygen, inotropes, mechanical ventilation or ECMO, or death. A saliva sample was obtained through passive drool using MicroSAL kits (Oasis Diagnostics) and a viral transport medium (VTM-C19, Biomed). Abundance levels of six cytokines (TNFR1, IL-13, IL-15, CCL7, CXCL10 and CXCL9) were measured in triplicate using microfluidic immunoassays (Ella, Protein Simple). Mean concentrations for each sample were determined against a standard curve and corrected for dilution. Levels of the six cytokines were compared between those with severe or non-severe SARS-CoV-2 symptoms using a non-parametric t-test. The relationship between salivary levels of individual cytokines was assessed among children with severe and non-severe SARS-CoV-2 using a Pearson correlation analysis

Results: A total of 150 children were enrolled from 03/29/2021 to 05/30/2021 (mean age of 7.1 years ± 5.7 years, 54.6% females). Of the total, 38 (25.3%) children met criteria for severe SARS-CoV-2 infection. CXCL10 displayed significantly (fold change>2, p<0.05) elevated levels in the saliva of children with severe SARS-CoV-2 (Figure 1). The relationship between levels of CXCL9 (MIG) and CXCL10 showed greater levels association (R2 = 0.93) in children with severe SARS-CoV-2 than in peers with non-severe SARS-CoV-2 (R2 = 0.65; Figure 2).

Conclusion: In this preliminary analysis of salivary cytokines among children with SARS-CoV-2 infection, we found CXCL10 displayed differential expression with severe symptoms. These findings may provide critical information about the pathophysiology of severe SARS-CoV-2. Confirmation in further studies is necessary.