Saliva as a Potential Specimen to Monitor IL-6, TNF-α and IL-10 in COVID-19 Patients

The SARS-CoV-2 instigated "cytokine storm" elicited upon infection is known to majorly cause lung injury and even mortality in severe cases. Early clinical prognosis to alleviate the exaggerated release of inflammatory cytokines is thus looked upon. Considering the recent attention and advantages of saliva as a clinical specimen, i.e. ease and painlessness of collection, which does not require trained staff and could allow self-sampling, the present study attempts to explore saliva for detection of IL-6, TNF-α and IL-10 which constitute major inflammatory genes that are elevated in COVID-19 using RT-PCR. Blood specimens of the same patients were also parallelly assessed to compare and validate the inflammatory marker expression. A total of 64 COVID-19 subjects who met the inclusion criteria were enrolled in this pilot study. Paired samples of blood and saliva from each patient were collected as per standard sampling protocols. RNA from all specimens were extracted using Qiagen RNA Blood Mini Kit and subjected to RT-PCR. IL-6, TNF-α and IL-10 expression were assessed in Ct (cycle threshold) values. It was observed that all 64 (100%) patients expressed IL-6 gene and TNF-α gene, whereas only 7 (5.19%) patients expressed IL-10 in both blood and saliva samples. The mean Ct values of IL-6 gene expressed in blood and saliva were 26.68 ± 2.26 and 28.53 ± 3.11 respectively. Similarly, the mean Ct values of TNF-α gene expressed in blood and saliva were 27.98 ± 2.45 and 28.92 ± 3.70 respectively. The observed mean Ct values of IL-10 gene expressed in blood and saliva were 31.26 ± 3.96 and 30.11 ± 4.12 respectively. Accordingly, the results indicate that inflammatory genes IL-6, TNF-α and IL-10 were detectable in both patient saliva as well as in blood. Moreover, mean Ct values of IL-6, TNF-α and IL-10 in both samples were found to be comparable. This finding thus suggests the possible use of saliva as an alternative specimen to blood for monitoring inflammation in COVID-19 patients.