[Differential analysis and clinical significance of the counts and function of cytotoxic cells in patients with COVID-19].

Objective To analyze changes in the counts and functional markers expression levels (of Granzyme B and Perforin) in cytotoxic cells [including natural killer (NK) cells and cytotoxic T lymphocytes (CTLs)] in COVID-19 patients and investigate their clinical significance. Methods A total of 72 patients with primary COVID-19 infection and 28 patients with reinfection were recruited from December 10, 2022, to June 1, 2023, at the First Affiliated Hospital of Nanchang University. The primary infection group comprised 57 non-severe cases (39 febrile outpatients and 18 hospitalized patients) and 15 severe cases. Seventeen healthy controls were enrolled during the same period. Flow cytometry was used to detect cytotoxic cell counts and functions. Receiver operating characteristic (ROC) curves were analyzed to identify optimal diagnostic and prognostic indicators, and the diagnostic and prognostic efficacy of combined multiple indicators was also evaluated. Results Compared with the control group, patients with COVID-19 had significantly lower counts and percentages of CD3+ T and CD8+ T lymphocytes, along with a lower NK cell count. However, the percentage of NK cells and the expression levels of perforin and granzyme B in CD3+ T and CD8+ T lymphocytes were significantly higher in patient group. The expression level of Granzyme B in NK cells was also significantly elevated. The combined use of four indicators (CD3+ T lymphocyte count, CD8+T lymphocyte count, the expression levels of Perforin and Granzyme B in CD8+ T lymphocytes) exhibited the optimal diagnostic value for COVID-19. Severe patients had lower NK cell counts and percentages than non-severe patients, and these two indices effectively distinguished severe from non-severe cases, with area under the curve (AUC) values of 0.903 and 0.899, respectively. The counts of CD3+ T lymphocytes, CD3+CD8+ T lymphocytes, and CD3-CD19+ B lymphocytes in COVID-19 reinfected patients from fever clinics were significantly higher than those in primary infection cases, but remained lower than the control group. Conclusion COVID-19 patients exhibit a significant reduction in cytotoxic cell counts accompanied by enhanced functional compensation. NK cell counts and percentages correlate with disease severity. These findings provide important insights into the immune status of COVID-19 patients and may guide clinical diagnosis, severity assessment, and immunotherapeutic strategies.