Evaluation of Lymphocyte Subtypes in COVID-19 Patients.

Background: Although many aspects of the COVID-19 disease have not yet been clarified, dysregulation of the immune system may play a crucial role in the progression of the disease. In this study, the lymphocyte subsets were evaluated in patients with different severities of COVID-19.

Materials and methods: In this prospective study, the frequencies of peripheral lymphocyte subsets (CD3⁺, CD4⁺, and CD8⁺ T cells; CD19⁺ and CD20⁺ B cells; CD16⁺/CD56⁺ NK cells, and CD4⁺/CD25⁺/FOXP3⁺ regulatory T cells) were evaluated in 67 patients with confirmed COVID-19 on the first day of their admission.

Results: The mean age of patients was 51.3 ± 14.8 years. Thirty-two patients (47.8%) were classified as severe cases, and 11 (16.4%) were categorized as critical. The frequencies of blood lymphocytes, CD3⁺ cells, CD25⁺FOXP3⁺ T cells, and absolute count of CD3⁺ T cells, CD25⁺FOXP3⁺ T cells, CD4⁺ T cells, CD8⁺ T cells, and CD16⁺56⁺ lymphocytes were lower in more severe cases compared to the milder patients. The percentages of lymphocytes, T cells, and NK cells were significantly lower in the deceased patients. (p= 0.002 and p= 0.042, p=0.006, respectively).

Conclusion: Findings of this cohort study demonstrated that the frequencies of CD4⁺, CD8⁺, CD25⁺FOXP3⁺ T cells, and NK cells differed in the severe cases of COVID-19. Moreover, lower frequency of T cells and NK cells could be predictors of mortality in these patients.