Following successful gene rearrangement at αβ T-cell receptor (TCR) loci, developing thymocytes express both CD4 and CD8 co-receptors and undergo a life-or-death selection event known as positive selection to identify cells expressing TCRs with potentially useful ligand specificities. Positively selected thymocytes must then decide whether to differentiate into CD4 + helper T cells or CD8 + cytotoxic T cells, a crucial decision known as CD4/CD8 lineage choice. This Review summarizes recent advances in our understanding of the cellular and molecular events involved in lineage fate decision and discusses them in the context of the major models of CD4/CD8 lineage choice.Throughout development, bipotential cells use environmental cues to determine cell fate, and elucidating the mechanisms by which they do so continues to be a fascinating area of investigation. An immunologically relevant example of bipotential cell-fate determination is the differentiation of CD4 + CD8 + (double positive, DP) thymocytes into either CD4 + helper T cells or CD8 + cytotoxic T cells. DP thymocytes are the first cells in the T-cell developmental pathway to express fully assembled αβ T-cell receptor (TCR) complexes on the cell surface ( Fig. 1), and it is the ligand specificity of their TCR that determines their subsequent developmental fate. αβTCRs are somatically generated transmembrane receptors with clonally unique structures that allow for a hugely diverse repertoire of recognition specificities. However, most thymocytes express αβTCRs that are incapable of engaging self MHC molecules and are therefore not useful to the host immune system. To eliminate cells expressing TCRs that cannot engage self MHC molecules, DP thymocytes are subjected to strict selection pressures in which cells bearing potentially useful TCR are the only ones signalled to survive and to continue their differentiation into functionally mature T cells. The vast majority of DP thymocytes do not receive TCR survival signals and undergo 'death by neglect' because their TCR cannot engage self MHC molecules. This life-or-death TCR mediated signalling event in DP thymocytes is referred to as 'positive selection' and results in the survival and maturation of cells bearing potentially useful TCRs.The success of positive selection in identifying potentially useful TCRs requires that DP thymocytes depend solely on signals downstream of TCR ligation for their survival, and that DP thymocytes be unresponsive to other survival signals. As a result, DP thymocytes are unique among T-lineage cells in that they are virtually refractory to the pro-survival cytokine interleukin-7 (IL-7), in part because DP thymocytes do not express receptors for IL-7 or most other pro-survival cytokines, and in part because DP thymocytes express high levels of SOCS1 (suppressor of cytokine signalling 1), a potent intracellular suppressor of cytokine signal transduction 1, 2 .Correspondence to A.S. e-mail: singera@mail.nih.gov. NIH Public Access Author ManuscriptNat Rev Immunol. Author manus...

Background Graphene and graphene-based nanocomposites are used in various research areas including sensing, energy storage, and catalysis. The mechanical, thermal, electrical, and biological properties render graphene-based nanocomposites of metallic nanoparticles useful for several biomedical applications. Epithelial ovarian carcinoma is the fifth most deadly cancer in women; most tumors initially respond to chemotherapy, but eventually acquire chemoresistance. Consequently, the development of novel molecules for cancer therapy is essential. This study was designed to develop a simple, non-toxic, environmentally friendly method for the synthesis of reduced graphene oxide–silver (rGO–Ag) nanoparticle nanocomposites using Tilia amurensis plant extracts as reducing and stabilizing agents. The anticancer properties of rGO–Ag were evaluated in ovarian cancer cells. Methods The synthesized rGO–Ag nanocomposite was characterized using various analytical techniques. The anticancer properties of the rGO–Ag nanocomposite were evaluated using a series of assays such as cell viability, lactate dehydrogenase leakage, reactive oxygen species generation, cellular levels of malonaldehyde and glutathione, caspase-3 activity, and DNA fragmentation in ovarian cancer cells (A2780). Results AgNPs with an average size of 20 nm were uniformly dispersed on graphene sheets. The data obtained from the biochemical assays indicate that the rGO–Ag nanocomposite significantly inhibited cell viability in A2780 ovarian cancer cells and increased lactate dehydrogenase leakage, reactive oxygen species generation, caspase-3 activity, and DNA fragmentation compared with other tested nanomaterials such as graphene oxide, rGO, and AgNPs. Conclusion T. amurensis plant extract-mediated rGO–Ag nanocomposites could facilitate the large-scale production of graphene-based nanocomposites; rGO–Ag showed a significant inhibiting effect on cell viability compared to graphene oxide, rGO, and silver nanoparticles. The nanocomposites could be effective non-toxic therapeutic agents for the treatment of both cancer and cancer stem cells.

The thymus generates major histocompatibility complex (MHC)-restricted alphabetaT cells that only recognize antigenic ligands in association with MHC or MHC-like molecules. We hypothesized that MHC specificity might be imposed on a broader alphabetaTCR repertoire during thymic selection by CD4 and CD8 coreceptors that bind and effectively sequester the tyrosine kinase Lck, thereby preventing T cell receptor (TCR) signaling by non-MHC ligands that do not engage either coreceptor. This hypothesis predicts that, in coreceptor-deficient mice, alphabeta thymocytes would be signaled by non-MHC ligands to differentiate into alphabetaT cells lacking MHC specificity. We now report that MHC-independent alphabetaT cells were indeed generated in mice deficient in both coreceptors as well as MHC ("quad-deficient" mice) and that such mice contained a diverse alphabetaT cell repertoire whose MHC independence was confirmed at the clonal level. We conclude that CD4 and CD8 coreceptors impose MHC specificity on a broader alphabetaTCR repertoire during thymic selection by preventing thymocytes from being signaled by non-MHC ligands.

T cell immunity requires the long-term survival of T cells that are capable of recognizing self antigens but are not overtly autoreactive. How this balance is achieved remains incompletely understood. Here we identify a homeostatic mechanism that transcriptionally tailors CD8 coreceptor expression in individual CD8+ T cells to the self-specificity of their clonotypic T cell receptor (TCR). 'Coreceptor tuning' results from interplay between cytokine and TCR signals, such that signals from interleukin 7 and other common gamma-chain cytokines transcriptionally increase CD8 expression and thereby promote TCR engagement of self ligands, whereas TCR signals impair common gamma-chain cytokine signaling and thereby decrease CD8 expression. This dynamic interplay induces individual CD8+ T cells to express CD8 in quantities appropriate for the self-specificity of their TCR, promoting the engagement of self ligands, yet avoiding autoreactivity.