Expression of Toll-like receptors 3, 7, and 9 in peripheral blood mononuclear cells and prognosis of pneumonia in hospital-admitted coronavirus disease 2019 patients: is there an association?

Abstract Background Toll-like receptors (TLRs) identify the very early signs of cell damage or infection. They play essential roles in host immunity response against severe acute respiratory syndrome coronavirus 2 infection. The current study investigated the association between the TLR 3, 7, and 9 and the outcome and severity of coronavirus disease 2019 (COVID-19) pneumonia. Patients and methods Demographic characteristics, clinical presentations, radiological, and laboratory data were registered and analyzed. Real time polymerase chain reaction quantification (qRT-PCR) of TLRs on peripheral blood mononuclear cells in blood samples collected from COVID-19 patients. Results The study involved 74 hospital-admitted COVID-19 pneumonia patients. The majority of cases were critically ill (62.2%), while 2.7% were moderate and 35.1% were severe cases. Median TLR7 and TLR9 were significantly higher among critically ill cases in comparison to moderate and severe cases (3.3 and 4.5 vs. 2.2 and 2.7, P =0.001 and 0.002, respectively). Nonsurvivors (48.6%) showed significantly higher levels for TLR3, TLR7, and TLR9 ( P =0.000 for all). TLR7 and TLR9 had significant correlation with TLR3 (r=0.697, 0.705, and P =0.000 for both) while TLR7 showed a significant correlation with TLR9 (r=0.845 and P =0.000). TLR3, TLR7, and TLR9 had significant positive correlation with lymphocyte count, serum ferritin, C-reactive protein, D-Dimer ( P ≤0.001 for all). TLR7, TLR9, C-reactive protein, and D-Dimer were predictors for the severity of COVID-19 pneumonia. Conclusion Transcript levels of TLR3, TLR7, and TLR9 may be considered promising markers for estimating the clinical severity and outcome in COVID-19 patients.