Immune Cells and Key Biomarkers in COVID-19 Patients

Higher level of IP-10, MCP-1, IL-6, and functional exhaustion of cytotoxic lymphocytes, NK cells, and inflammatory monocytes causing excessive noneffective host immune responses which results in lung functional disability and quick mortality in COVID-19 patients. The aim of this study is to observe the associations of IP-10, MCP-1, IL-6, and lymphocytes and monocytes in peripheral blood with disease severity in COVID-19 patients. The study period was from March 2021 to January 2022. A total of 84 COVID-19 patients confirmed by positive RT-PCR and 28 healthy subjects were enrolled in this study. The peripheral venous blood sample was collected to detect the serum level of IP-10 and MCP-1 and IL-6 by ELISA method, immunophenotyping of lymphocytes, and monocyte was done by flow cytometry. The serum IP-10 level (pg/ml) was significantly higher among critical patients (1525 ± 1523.1) compared with severe (610.7 ± 879.2) and moderate patients (92.0 ± 100.4) and healthy controls (46.7 ± 77.3). Serum MCP-1 level was also higher among critical patients (1132.3 ± 1510.8) compared with severe (485 ± 968.3) and moderate patients (246.7 ± 367.8) and healthy controls (79.7 ± 64.0). Serum IL-6 level (pg/ml) was considerably higher among critical patients (102.02 ± 149.7) compared with severe (67.20 ± 129.5) and moderate patients (47.04 ± 106.5) and healthy controls (3.5 ± 1.8). Correlation among IP-10, MCP-1, IL-6, and monocyte showed statistically significant with disease severity (IL-6 = severe group, p < .001, and .867*** and critical group p < .001 and .887***; IP-10 = severe group, p < .001, and .809*** and critical group p < .001 and .827***; MCP-1 = severe group, p < .001, and .839*** and critical group p < .001 and .856***). T cells, B cells, NK cells, CD4+ T cells, CD8+ T cells and monocytes were significantly decreased in critical group compared with healthy, moderate, and severe group (p < .001), suggesting that count of lymphocytes and monocytes might be used as an indicator of disease severity. Increased expression of exhaustion marker CD94/NKG2A on NK cells and CD8+ T cells in severe and critical group might contribute to the disease pathogenesis. Serum level of MCP-1, IP-10, and IL-6 might be used as a diagnostic as well as prognostic marker for the assessment of COVID-19 outcome as it correlates with COVID-19 disease severity and mortality.