Flow cytometric analysis of lymphocyte subsets, monocytes, and HLA-DR expressions on these cells in patients with COVID-19

We aimed to investigate the lymphocyte subsets and monocytes by flow cytometry and the correlations between their HLA-DR expressions and inflammatory markers in patients with COVID-19. The study included 49 patients with COVID-19 and 42 healthy controls. Blood samples were taken into EDTA tubes. WBC counts were analyzed by the Sysmex/XN-1000i device, and lymphocyte subsets and monocytes were analyzed by flow cytometry. The percentage of HLA-DR expression on cells and median fluorescence intensity (MFI) values were recorded to detect activation. Lymphocyte counts were calculated using the dual-platform method. Correlations between antigen expression and ferritin, CRP, and D-dimer levels were analyzed. The patient group had lower WBC and lymphocyte counts but significantly higher monocyte counts and neutrophil/lymphocyte ratios compared to controls (p=0.009, p=0.045, respectively). The patient group had significantly lower T lymphocyte counts (p=0.008). B lymphocyte counts and percentages were lower (p<0.001, p=0.004) in the patient group. There was no significant difference between the two groups in terms of NK cells. T helper and T cytotoxic lymphocyte counts were significantly lower, but there was no change in CD4/CD8 ratios. The percentage of HLA-DR expression on T lymphocytes, HLA-DR MFI values of T cytotoxic cells, and HLA-DR MFI values of CD16+ monocytes were significantly increased in the patient group (p=0.001, p=0.004, p<0.001, respectively). CRP was positively correlated with HLA-DR expression on T lymphocytes (r=0.501, p<0.001). HLA-DR MFI values may be an important marker for demonstrating the function of both T cytotoxic cells and CD16+ monocytes in COVID-19.