PHENOTYPIC CHARACTERISTICS OF DOUBLE-POSITIVE T CELLS IN THE PERIPHERAL BLOOD OF HEALTHY ADULTS

Abstract

Introduction. Recent studies have shown that healthy adults have circulating double-positive (DP) T cells in small concentrations. These T cells develop from CD4+ and CD8+ T cells and have simultaneous expression of CD4 and CD8 on their surface. According to the expression of CD4 and CD8, DP T cells can be divided into two subpopulations: CD4brightCD8dim and CD4dimCD8bright. The phenotypic and functional features of these subpopulations are currently not fully understood. The aim of the study was to identify the phenotypic characteristics of CD4brightCD8dim and CD4dimCD8bright T cells in the peripheral blood from healthy adults depending on the expression of maturation antigens. Methods. Phenotyping was performed by flow cytometry using antibodies against the following human cell-surface antigens: CD57 (FITC-conjugated), CD62L (ECD-conjugated), CD28 (PerCP/Cy5.5-conjugated), CD27 (Pe/Cy7-conjugated), CD4 (APC-conjugated), CD8 (APC-AF700-conjugated), CD3 (APC-AF750-conjugated), CD45RA (Pacific Blue-conjugated), and CD45 (Krome Orange-conjugated). The differences between the groups were estimated using Mann–Whitney U-test. Results were presented as median and interquartile range (25%; 75%). Results. A total pool of DP T cells was detected, constituting 0.73% (0.42; 1.61) of the total CD3+ T cell population at a total concentration of 11 cells/1μL (6; 20). The percentage of CD4brightCD8dim and CD4dimCD8bright T cells was within 0.25% (0.18; 0.44) and 0.29% (0.20; 0.98) at concentrations of 4 cells/1μL (2; 7) and 5 cells/1μL (2; 12), respectively. Effector memory cells (CD45RA–CD62L–) and effector memory cells re-expressing CD45RA (CD45RA+CD62L–) were predominant in CD4brightCD8dim T cells, whereas central memory phenotype (CD45RA+CD62L+) was predominant in CD4dimCD8bright T cells. In addition, a reduced level of the “naïve” phenotype (CD45RA+CD62L+) was noted in CD4brightCD8dim and CD4dimCD8bright T cell populations. An increase in CD57 expression on the surface of CD4brightCD8dim T cells with a simultaneous decrease in CD27 and CD28 was also detected if compared to CD4+ T cells. In turn, CD4dimCD8bright T cells increase the expression of CD28 and decrease the expression of CD57 on their surface if compared to CD8+ T cells. Conclusion. DP T cells have a more mature phenotype and often represented by memory cells.