Higher secretion of Th1- and Th17-typical cytokines or expression of Th17 molecular markers in cells of CD26high group
To investigate the association of CD26 expression with CD4 cell differentiation, the percentages of T helper subpopulations were determined by flow cytometry after cells were labeled with fluorescence-conjugated antibodies against corresponding cytokines or cell surface markers. The results showed that the percentages of cells secreting Th1-typical cytokine IL-2 and IFN-γ in the CD26high group were significantly higher than those in the CD26low group (Figure 5A) . The percentage of cells secreting IL-2 in the CD26high group was approximately three times that of the CD26low group (25.93±5.39% vs. 8.89±5.85%), and the percentage of cells secreting IFN-γ in the CD26high group was about seven times that of the CD26low group (30.17±11.14%vs. 4.45±2.63%). Similarly, in Figure 5B , the percentages of cells secreting Th17-typical cytokines (IL-6, IL-17, IL-22) or expressing biomarkers (IL-23R, CD196 and CD161) were evidently higher in the CD26high group than in the CD26low group. The percentages of cells secreting IL-6 or lL-17 in the CD26high group were about 7-fold of that in the CD26low group (28.11% vs. 4.12%, 31.28% vs. 4.32%). The percentage of cells secreting IL-22 in the CD26high group was 5.4-fold compared to the CD26low group (31.05% vs. 5.74%). The percentage of cells expressing IL-23R was even higher in the CD26high group, 7-fold of that in the CD26low group (35.93% vs. 4.98%). In addition, the percentages of cells expressing Th17 surface biomarkers CD196 and CD161 in the CD26high group were 2.8-fold and 3-fold of that in the CD26low group (34.73%vs. 12.35%, 42.52% vs. 13.59%), respectively. Histogram analysis showed that the expression levels of Th1 and Th17 typical cytokines (IL-2, IFN-γ, IL-6, IL-17, IL-22) or a Th17 typical surface marker (IL-23R) in the cells of the CD26high group were much higher in relation to the cells of CD26lowgroup (Figure 5C) . These results suggest that the expression of CD26 is involved in the regulation of the differentiation and functions of Th1 and Th17 subpopulations of T lymphocytes.
On the other hand, the percentages of cells secreting Th2-typical cytokines either IL-4 or IL-13 showed exceptionally low and no significant differences between the CD26high group and the CD26low group (Figure 5A) . Similarly, the histogram analysis showed that there were no significant differences in the expression levels of Th2 cytokines (IL-4 and IL-13) in cells between the CD26high group and the CD26lowgroup (Figure 5C) . In addition, the percentages of cells expressing molecular markers of regulatory T cells (CD25+Foxp3+ or CD4+Foxp3+) in the CD26high group did not have significant differences to that in the CD26low group (Figure 5D) . These results suggest that the CD26 expression is not correlated to the differentiation and functions of Th2 and Tregs subpopulations of T lymphocytes after antigen stimulation.