探討 T-bet 於人類臍帶血第一型自然殺手細胞中的調控機制

Abstract

CD4T (T helper cell, Th cell), CD8T (T cytotoxic cell, Tc cell), and NK (natural killer) cells play important roles in immune defense system. When CD4T cells encounter invading organisms, they will be activated and differentiate into two functionally distinct subsets, Th1 and Th2, with different cytokine profiles. Th1 cells secrete interleukin 2 (IL-2) and interferon r(IFN-r), and Th2 cells secrete the cytokines interleukin 4 (IL-4) and interleukin 13 (IL-13). The phenomenon of type I vs type II polarization was recently found in CD8T cells and NK cells. T-bet, a member of the T-box transcription factor family, may promote type I polarization by regulating transcription of the IFN-r gene. Regulation of T-bet was studied in YT and NK92 lymphoma cell lines of NK-cell origin. YT cells had a type-0 IL-4+/IFN-r+/T-betweak profile, whereas NK92 cells had a type-I IL-4-/IFN-r++/T-betstrong profile. Our data indicated that weak expression of T-bet in the YT cells was due to a translational block in T-bet mRNA, suggesting T-bet regulation at post-transcriptional level. To further investigate T-bet regulation in human primary T and NK cells, we isolated umbilical cord blood (UCB) CD4T, CD8T and NK cells to study the protein and mRNA expression patterns of T-bet in cytokine stimulated type I-polarized cells by flow cytometry and real time PCR. It was reported that there were three distinct populations of human UCB NK cells based on the density of surface expression of CD56, which are CD56-, CD56dim and CD56bright subset, respectively. In the earlier stage of type I polarization, between the period of stimulation day 0 (D0) to day 5-7 (D5-7), the percentage of CD56- subset was decreased and CD56bright subset was increased. There was about 2-fold higher T-bet mRNA and only 5-fold higher expression of T-bet protein in CD56bright subset than in CD56- subset, suggesting different expression of T-bet among the two subsets was due to its transcriptional level regulation. When cells were at totally type I-polarized day 14 (D14), we found T-bet was transcriptional regulated either as both T-bet transcript and protein expression were much higher than day 0 (D0) naive, undifferentiated NK cell. These data revealed transcriptional regulation of T-bet in UCB type I polarized NK cells from early stage of differentiation, day 0 (D0) to day 5-7 (D5-7) till day 14 (D14), when cell was totally type I polarized. Furthermore, we also showed transcriptional regulation of T-bet in type I polarized CD4T cells but post-transcriptional regulation in CD8T cells. Subsequently, in addition to analyze type I polarization based on IFN-r and T-bet expression traditionally, we also identified several type I surface markers, included CD56, specific for UCB type I polarized NK cells, and CD25 or CXCR3 for CD4T and CD8T cells. Taken together, these data showed T-bet regulation at transcriptional or post-transcriptional level is a critical event in the maturation of immune system and development of T and NK cells.