CCR7 Signals Are Essential for Cortex–Medulla Migration of Developing Thymocytes

Upon TCR-mediated positive selection, developing thymocytes relocate within the thymus from the cortex to the medulla for further differentiation and selection. However, it is unknown how this cortex–medulla migration of thymocytes is controlled and how it controls T cell development. Here we show that in mice deficient for CCR7 or its ligands mature single-positive thymocytes are arrested in the cortex and do not accumulate in the medulla. These mutant mice are defective in forming the medullary region of the thymus. Thymic export of T cells in these mice is compromised during the neonatal period but not in adulthood. Thymocytes in these mice show no defects in maturation, survival, and negative selection to ubiquitous antigens. TCR engagement of immature cortical thymocytes elevates the cell surface expression of CCR7. These results indicate that CCR7 signals are essential for the migration of positively selected thymocytes from the cortex to the medulla. CCR7-dependent cortex–medulla migration of thymocytes plays a crucial role in medulla formation and neonatal T cell export but is not essential for maturation, survival, negative selection, and adult export of thymocytes

Gene Dosage–limiting Role of Aire in Thymic Expression, Clonal Deletion, and Organ-specific Autoimmunity

Inactivation of the autoimmune regulator (Aire) gene causes a rare recessive disorder, autoimmune polyendocrine syndrome 1 (APS1), but it is not known if Aire-dependent tolerance mechanisms are susceptible to the quantitative genetic changes thought to underlie more common autoimmune diseases. In mice with a targeted mutation, complete loss of Aire abolished expression of an insulin promoter transgene in thymic epithelium, but had no effect in pancreatic islets or the testes. Loss of one copy of Aire diminished thymic expression of the endogenous insulin gene and the transgene, resulting in a 300% increase in islet-reactive CD4 T cells escaping thymic deletion in T cell receptor transgenic mice, and dramatically increased progression to diabetes. Thymic deletion induced by antigen under control of the thyroglobulin promoter was abolished in Aire homozygotes and less efficient in heterozygotes, providing an explanation for thyroid autoimmunity in APS1. In contrast, Aire deficiency had no effect on thymic deletion to antigen controlled by a systemic H-2K promoter. The sensitivity of Aire-dependent thymic deletion to small reductions in function makes this pathway a prime candidate for more subtle autoimmune quantitative trait loci, and suggests that methods to increase Aire activity would be a potent strategy to lower the incidence of organ-specific autoimmunity

Mediators of lifestyle behaviour changes in obese pregnant women. Secondary analyses from the DALI lifestyle randomised controlled trial

A better understanding of what drives behaviour change in obese pregnant overweight women is needed to improve the effectiveness of lifestyle interventions in this group at risk for gestational diabetes (GDM). Therefore, we assessed which factors mediated behaviour change in the Vitamin D and Lifestyle Intervention for GDM Prevention (DALI) Lifestyle Study. A total of 436 women, with pre-pregnancy body mass index ≥29 kg/m 2 , ≤19 + 6 weeks of gestation and without GDM, were randomised for counselling based on motivational interviewing (MI) on healthy eating and physical activity, healthy eating alone, physical activity alone, or to a usual care group. Lifestyle was measured at baseline, and at 24–28 and 35–37 weeks of gestation. Outcome expectancy, risk perception, task self-efficacy and social support were measured at those same time points and considered as possible mediators of intervention effects on lifestyle. All three interventions resulted in increased positive outcome expectancy for GDM reduction, perceived risk to the baby and increased task self-efficacy. The latter mediated intervention effects on physical activity and reduced sugared drink consumption. In conclusion, our MI intervention was successful in increasing task self-efficacy, which was related to improved health behaviours

Nfkb2 variants reveal a p100-degradation threshold that defines autoimmune susceptibility

NF-κB2/p100 (p100) is an inhibitor of κB (IκB) protein that is partially degraded to produce the NF-κB2/p52 (p52) transcription factor. Heterozygous NFKB2 mutations cause a human syndrome of immunodeficiency and autoimmunity, but whether autoimmunity arises from insufficiency of p52 or IκB function of mutated p100 is unclear. Here, we studied mice bearing mutations in the p100 degron, a domain that harbors most of the clinically recognized mutations and is required for signal-dependent p100 degradation. Distinct mutations caused graded increases in p100-degradation resistance. Severe p100-degradation resistance, due to inheritance of one highly degradation-resistant allele or two subclinical alleles, caused thymic medullary hypoplasia and autoimmune disease, whereas the absence of p100 and p52 did not. We inferred a similar mechanism occurs in humans, as the T cell receptor repertoires of affected humans and mice contained a hydrophobic signature of increased self-reactivity. Autoimmunity in autosomal dominant NFKB2 syndrome arises largely from defects in nonhematopoietic cells caused by the IκB function of degradation-resistant p100

Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at √s=0.9 and 2.36 TeV

Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at root s = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between -2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN(ch)/d eta vertical bar(vertical bar eta vertical bar and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date

Deletion of self-reactive CCR7– thymocytes in the absence of MHC expression on thymic epithelial cells

The selection of αβ T cells in the thymus is punctuated by checkpoints at which thymocytes differentiate or undergo apoptosis. Wave 1 deletion is defined as apoptosis within nascent αβ T-cell antigen receptor (TCR)-signalled thymocytes that lack CCR7 expression. The antigen-presenting cell (APC) types that mediate wave 1 deletion are unclear. To measure wave 1 deletion, we compared the frequencies of TCRβ + CD5 + Helios + CCR7– cells in nascent thymocyte cohorts in mice with normal or defective apoptosis. This thymocyte population is small in mice lacking major histocompatibility complex (MHC) expression. The scale of wave 1 deletion was increased by transgenic expression of the self-reactive Yae62 TCRβ chain, was almost halved when haemopoietic APCs lacked MHC expression and, surprisingly, was unchanged when epithelial cells lacked MHC expression. These findings demonstrate efficiency, and some redundancy, in the APC types that mediate wave 1 deletion in the normal mouse thymus.</p

p53 Efficiently Suppresses Tumor Development in the Complete Absence of Its Cell-Cycle Inhibitory and Proapoptotic Effectors p21, Puma, and Noxa

Activation of apoptosis through transcriptional induction of Puma and Noxa has long been considered to constitute the critical (if not sole) process by which p53 suppresses tumor development, although G1/S boundary cell-cycle arrest via induction of the CDK inhibitor p21 has also been thought to contribute. Recent analyses of mice bearing mutations that impair p53-mediated induction of select target genes have indicated that activation of apoptosis and G1/S cell-cycle arrest may, in fact, be dispensable for p53-mediated tumor suppression. However, the expression of Puma, Noxa, and p21 was not abrogated in these mutants, only reduced; therefore, the possibility that the reduced levels of these critical effectors of p53-mediated apoptosis and G1/S-cell-cycle arrest sufficed to prevent tumorigenesis could not be excluded. To resolve this important issue, we have generated mice deficient for p21, Puma, and Noxa (p21−/−puma−/−noxa−/− mice). Cells from these mice were deficient in their ability to undergo p53-mediated apoptosis, G1/S cell-cycle arrest, and senescence. Nonetheless, these animals remained tumor free until at least 500 days, in contrast to p53-deficient mice, which had all succumbed to lymphoma or sarcoma by 250 days. Interestingly, DNA lesions induced by γ-irradiation persisted longer in p53-deficient cells compared to wild-type or p21−/−puma−/−noxa−/− cells, and the former failed to transcriptionally activate several p53 target genes implicated in DNA repair. These results demonstrate beyond a doubt that the induction of apoptosis, cell-cycle arrest, and possibly senescence is dispensable for p53-mediated suppression of spontaneous tumor development and indicate that coordination of genomic stability and possibly other processes, such as metabolic adaptation, may instead be critical

Multilineage Potential and Self-Renewal Define an Epithelial Progenitor Cell Population in the Adult Thymus

Thymic epithelial cells (TECs) are critical for T cell development and self-tolerance but are gradually lost with age. The existence of thymic epithelial progenitors (TEPCs) in the postnatal thymus has been inferred, but their identity has remained enigmatic. Here, we assessed the entire adult TEC compartment in order to reveal progenitor capacity is retained exclusively within a subset of immature thymic epithelium displaying several hallmark features of stem/progenitor function. These adult TEPCs generate mature cortical and medullary lineages in a stepwise fashion, including Aire+ TEC, within fetal thymus reaggregate grafts. Although relatively quiescent in vivo, adult TEPCs demonstrate significant in vitro colony formation and self-renewal. Importantly, 3D-cultured TEPCs retain their capacity to differentiate into cortical and medullary TEC lineages when returned to an in vivo thymic microenvironment. No other postnatal TEC subset exhibits this combination of properties. The characterization of adult TEPC will enable progress in understanding TEC biology in aging and regeneration

Thymospheres are formed by mesenchymal cells with the potential to generate adipocytes, but not epithelial cells

Summary: Evidence suggests that a stem-cell-driven differentiation hierarchy maintains the dynamic thymic epithelial cell (TEC) network that governs T lymphocyte development. The identification of TEC stem/progenitor cells has been a major focus in the field, and several candidates with contrasting phenotypes have been described. We sought to determine the provenance and function of the only population reported to exhibit TEC stem cell properties in the adult, a Foxn1− EpCAM− cell that generates so-called thymospheres. We provide evidence that the thymosphere-forming cell (TSFC) is not a TEC stem cell but can incorporate bystander TECs into thymospheres, providing an explanation for the epithelial activity ascribed to these structures. TSFCs were found to share a phenotype, transcriptional profile, and developmental origin with thymic fibroblasts and can generate adipocytes. In summary, this study redefines the nature of bipotent TEC stem/progenitor cells in the adult thymus and highlights a potentially important mesenchymal progenitor population. : The phenotype of putative bipotent epithelial stem/progenitor cells in the adult thymus has been controversial. Sheridan et al. find that a prominent candidate, the FoxN1−EpCAM− sphere-forming cell, harbors no epithelial stem/progenitor capacity and present evidence that they are a unique intrathymic mesenchymal stromal/stem cell population with adipocyte differentiation capacity. Keywords: thymus, thymic epithelial cell, stem cell, progenitor, thymosphere, MSC, mesenchyme, adipocyt