Association of SARS-COV-2 viral RNAemia, IL- 6 gene polymorphism, serum IL-6 and peripheral blood lymphocytes and monocytes with disease severity in COVID-19 patients

Coronavirus disease 2019 (COVID-19) is a fatal pandemic viral disease caused by the severe acute respiratory syndrome corona virus type-2 (SARS-CoV-2). The aim of this study is to observe the associations of IL-6, SARS-COV-2 viral load (RNAemia), IL- 6 gene polymorphism and lymphocytes and monocytes in peripheral blood with disease severity in COVID-19 patients. This study was carried out from March 2021 to January 2022. RT-PCR positive 84 COVID-19 patients and 28 healthy subjects were enrolled. Blood was collected to detect SARS-COV-2 viral RNA (RNAemia) by rRT-PCR, serum IL-6 level by chemiluminescence method, SNPs of IL-6 by SSP-PCR, immunophenotyping of lymphocytes and monocyte by flow cytometry. Serum IL-6 level (pg/ml) was considerably high among critical patients (102.02 ± 149.7) compared to severe (67.20 ± 129.5) and moderate patients (47.04 ± 106.5) and healthy controls (3.5 ± 1.8). Serum SARS-CoV-2 nucleic acid positive cases detected mostly in critical patients (39.28%) and was correlated with extremely high IL-6 level and high mortality (R = .912, P < 0.001). Correlation between IL-6 and monocyte was statistically significant with disease severity (severe group, p < 0.001, and 0.867*** and critical group p < 0.001 and 0.887***). In healthy controls, moderate, severe and critically ill COVID-19 patients, IL-6 174G/C (rs 1800795) GG genotype was 82.14%, 89.20%, 67.85% and 53.57% respectively. CC and GC genotype had strong association with severity of COVID-19 when compared with GG genotype. Significant statistical difference found in genotypes between critical and moderate groups (p < 0.001, OR-10.316, CI-3.22–23.86), where CC genotype was associated with COVID-19 severity and mortality. The absolute count of T cell, B cell, NK cell, CD4+ T cells and CD8+ T cells were significantly decreased in critical group compared to healthy, moderate and severe group (P < 0.001). Exhaustion marker CD94/NKG2A was increased on NK cells and CD8+ cytotoxic T cell among critical and severe group. Absolute count of monocyte was significantly increased in critical group (P < 0.001). Serum IL-6, IL-6 174 G/C gene and SARS-CoV-2 RNAaemia can be used in clinical practice for risk assessment; T cell subsets and monocyte as biomarkers for monitoring COVID-19 severity. Monoclonal antibody targeting IL-6 receptor and NKG2A for therapeutics may prevent disease progression and decrease morbidity and mortality.