Lymphocyte Subsets in Mild COVID-19 Pediatric Patients

Objective: The reasons for a high prevalence of asymptomatic or mild coronavirus disease (COVID-19) and rare severe disease in children have been explained by non-immune and immune mechanisms. This study aimed to evaluate the immune system’s response to severe acute respiratory syndrome coronavirus 2 by investigating lymphocyte subsets. Materials and Methods: This study included 33 coronavirus disease positive children, of whom 12 had mild disease and 21 had an asymptomatic infection as the patient group and 26 age- and gender-matched healthy children as the control group. The demographic information, symptoms, physical examination findings, complete blood count, C-reactive protein (CRP), procalcitonin, and lymphocyte subsets were recorded in all subjects. Results: Leukocyte, lymphocyte, monocyte count, and hemoglobin levels of our pediatric coronavirus disease patients were similar to the control group. Neutrophil was lower in the coronavirus disease cases compared to the control group. CRP and procalcitonin levels of asymptomatic cases were similar to the control group. B cell count, CD8+ T cell count, and CD4/CD8 ratio (dividing the CD4 cell count by the CD8 cell count) ratio were similar in the patient and control groups. Natural killer, T cell, and CD4+ T cell counts were significantly higher in the whole patient group compared to the control group. Conclusion: One reason for mild severe acute respiratory syndrome coronavirus 2 infection in children may be an increase in some lymphocyte subsets such as natural killer cells, T cell, and CD4+ T cell. Understanding the answer to the question of why children develop more protective immunity to the virus could be an essential step for developing new treatments.