Impact of serum IL-10 level on the clinical outcome of COVID-19 patients and the development of post-COVID pulmonary fibrosis.

A characteristic feature of the cytokine storm in coronavirus disease 2019 (COVID-19) is the dramatic elevation of serum interleukin 10 (IL-10). This may be a negative feedback mechanism to suppress inflammation. However, this IL-10 elevation may contribute to COVID-19 severity. In our study, we aimed to evaluate the effect of serum IL-10 level on patients' clinical outcome and the incidence of post-COVID19 pulmonary fibrosis. This was a prospective observational study, included 100 patients, confirmed to have COVID-19, Of these, 50 patients had COVID-19 without evidence of pneumonia in computed tomography (CT) scans (group I) and the other 50 patients had COVID-19 pneumonia (group II). Our results showed a significant increase in serum ferritin level in patients with COVID pneumonia. However, no difference was found in serum C-reactive protein (CRP) nor D-Dimer between both groups. There was a statistically significant increase in serum IL-10 in patients with COVID pneumonia compared with COVID patients without pneumonia (p < 0.001). Fibrosis was developed in 35 patients (70%) with COVID pneumonia after 3 months and 4 of them died, however, all patients without pneumonia survived. Among age, serum IL-10, aspartate aminotransferase (AST), alanine transaminase (ALT), elevated serum IL-10 was found to be an independent predictor of pneumonia (p=0.32). However, there was no significant effect for IL-10 on patients' clinical outcome. There was a statistically significant correlation between serum IL-10 levels and oxygen (O2) demand, CRP and D-Dimer (p= 0.015, p=0.034 and p=0.042, respectively). The higher the level of IL-10 the less fibrosis detected in follow up CT scans (p=0.038). In conclusion, even though IL-10 was significantly associated with disease severity (higher in pneumonia), elevated serum Il-10 has an independent role in decreasing the incidence of post-COVID-19 pulmonary fibrosis.