Relationship Between Blood Immune Cell Composition and COVID-19 Susceptibility and Post-Infection Sequelae Using Full-Spectrum Flow Cytometry

OBJECTIVE: To investigate the immune mechanisms underlying susceptibility to COVID-19 and the development of sequelae. STUDY DESIGN: A cross-sectional observational study. Place and Duration of the Study: Clinical Laboratory, Jilin Province People's Hospital, Jilin, China, from 14th to 30th December 2022. METHODOLOGY: Seventy-one individuals were investigated, including 56 individuals who had recovered from COVID-19 infection and 15 uninfected individuals. Immunophenotypic analysis of B, T, and NK lymphocytes in peripheral blood samples was performed using full-spectrum flow cytometry. The differences in immune cell populations defined by the traditional gating strategy and the unsupervised algorithm between groups were analysed. Categorical data were compared between groups using the chi-square test. Quantitative data were compared using the t-test or Mann-Whitney U test. RESULTS: Compared to uninfected individuals, recovered individuals, especially those with sequelae, had significantly higher counts of lymphocytes, T cells, NKT cells, CD8+T cells, CD4+CD28+T cells, CD4+CD38+T cells, CD8+CD28+T cells, CD8+CD38+T cells, CD69+T cells, and Tregs. An increase in these lymphocytes may contribute to immune homeostasis. Meanwhile, the CD38+NKT cell count was significantly decreased in the recovered individuals. Moreover, an upregulation of T-cells, NKT cells, CD4+T cells, CD8+T cells, CD4+CD28+T cells, CD4+CD38+T cells, CD8+CD28+T cells, CD8+CD38+T cells, CD69+T cells, Treg cells, and CD38+NKT cells was observed in patients with sequelae. CONCLUSION: This study showed that the lymphocyte subgroups' counts were associated with COVID-19 infection and post-infection sequelae. These findings may contribute to understanding the mechanism of COVID-19 infection and recovery. KEY WORDS: COVID-19, Full-spectrum flow cytometry, Traditional gating strategy, Unsupervised algorithm, Blood immune cells, Suscep- tibility, Sequelae.