To understand how CD8 expression is regulated during the transition process from CD4+8+ (CD4 and CD8 double positive, DP) to CD4-8+ (CD8 single positive, CD8SP) cells in the thymus, the involvement of Runx proteins in the alteration of chromatin configuration was investigated. Using the chromatin immunoprecipitation assay, we first demonstrated that Runx proteins bind to the stage-specific CD8 enhancer, as well as the CD4 silencer, in CD8SP thymocytes. Among Runx family members, Runx3 expression was initiated in DP thymocytes receiving a positive selection signal and increased in concert with differentiation to the CD8SP stage. Furthermore, reactivation of the CD8 gene, as well as CD4 silencing, was suppressed in positively selected thymocytes of Runx dominant-negative transgenic mice. These results suggest that Runx proteins, especially Runx3, are involved in lineage specification of CD8 T cells and provide important information for understanding the mechanism for the mutually exclusive expression of coreceptors in mature thymocytes.

We have recently fabricated dye-sensitized solar cells (DSSCs) comprising nanofibrous TiO(2) membranes as electrode materials. A thin TiO(2) film was pre-deposited on fluorine doped tin oxide (FTO) coated conducting glass substrate by immersion in TiF(4) aqueous solution to reduce the electron back-transfer from FTO to the electrolyte. The composite polyvinyl acetate (PVac)/titania nanofibrous membranes can be deposited on the pre-deposited thin TiO(2) film coated FTO by electrospinning of a mixture of PVac and titanium isopropoxide in N,N-dimethylformamide (DMF). The nanofibrous TiO(2) membranes were obtained by calcining the electrospun composite nanofibres of PVac/titania as the precursor. Spectral sensitization of the nanofibrous TiO(2) membranes was carried out with a ruthenium (II) complex, cis-dithiocyanate-N,N(')-bis(2,2(')-bipyridyl-4,4(')-dicarboxylic acid) ruthenium (II) dihydrate. The results indicated that the photocurrent and conversion efficiency of electrodes can be increased with the addition of the pre-deposited TiO(2) film and the adhesion treatment using DMF. Additionally, the dye loading, photocurrent, and efficiency of the electrodes were gradually increased by increasing the average thickness of the nanofibrous TiO(2) membranes. The efficiency of the fibrous TiO(2) photoelectrode with the average membrane thickness of 3.9 µm has a maximum value of 4.14%.

A main role for interleukin-4 (IL-4) is in humoral immunity, and follicular helper CD4(+) T (Tfh) cells may be an intrinsic IL-4 source. Here we demonstrate that conserved noncoding sequence 2 (CNS2) is an essential enhancer element for IL-4 expression in Tfh cells but not in Th2 cells. Mice with a CNS2 deletion had a reduction in IgG1 and IgE production and in IL-4 expression in Tfh cells. Tracking of CNS2 activity via a GFP reporter mouse demonstrated that CNS2-active cells expressed several markers of Tfh cells: CXCR5, PD-1, and ICOS; the transcriptional master regulator Bcl6; and the cytokines IL-21 and IL-4. These CNS2-active cells were mainly localized in B cell follicles and germinal centers. The GFP(+) Tfh cells were derived from GFP(-) naive T cells after in vivo systemic immunization. These results indicate that CNS2 is an essential enhancer element required for IL-4 expression in Tfh cells controlling humoral immunity.

The Runx family of transcription factors is thought to regulate the differentiation of thymocytes. Runx3 protein is detected mainly in the CD4−8+ subset of T lymphocytes. In the thymus of Runx3-deficient mice, CD4 expression is de-repressed and CD4−8+ thymocytes do not develop. This clearly implicates Runx3 in CD4 silencing, but does not necessarily prove its role in the differentiation of CD4−8+ thymocytes per se. In the present study, we created transgenic mice that overexpress Runx3 and analyzed the development of thymocytes in these animals. In the Runx3-transgenic thymus, the number of CD4−8+ cells was greatly increased, whereas the numbers of CD4+8+ and CD4+8− cells were reduced. The CD4−8+ transgenic thymocytes contained mature cells with a TCRhighHSAlow phenotype. These cells were released from the thymus and contributed to the elevated level of CD4−8+ cells relative to CD4+8− cells in the spleen. Runx3 overexpression also increased the number of mature CD4−8+ thymocytes in mice with class II-restricted, transgenic TCR and in mice with a class I-deficient background, both of which are favorable for CD4+8− lineage selection. Thus, Runx3 can drive thymocytes to select the CD4−8+ lineage. This activity is likely to be due to more than a simple silencing of CD4 gene expression.

No abstract