The selectin family of cell adhesion molecules mediates the tethering and rolling of leukocytes on blood vessel endothelium. It has been postulated that the molecular basis of this highly dynamic adhesion is the low affinity and rapid kinetics of selectin interactions. However, affinity and kinetic analyses of monomeric selectins binding their natural ligands have not previously been reported. Leukocyte selectin (L-selectin, CD62L) binds preferentially to O-linked carbohydrates present on a small number of mucin-like glycoproteins, such as glycosylation-dependent cell adhesion molecule-1 (Gly-CAM-1), expressed in high endothelial venules. Gly-CAM-1 is a soluble secreted protein which, following binding to CD62L, stimulates ␤ 2 -integrin-mediated adhesion of lymphocytes. Using surface plasmon resonance, we show that a soluble monomeric form of CD62L binds to purified immobilized GlyCAM-1 with a dissociation constant (K d ) of 108 M. CD62L dissociates from GlyCAM-1 with a very fast dissociation rate constant (>10 s ؊1 ) which agrees well with the reported dissociation rate constant of CD62L-mediated leukocyte tethers. The calculated association rate constant is >10 M ؊1 s ؊1. At concentrations just above its mean serum level (ϳ1.5 g/ml or ϳ30 nM), GlyCAM-1 binds multivalently to immobilized CD62L. It follows that soluble GlyCAM-1 may cross-link CD62L when it binds to cells, suggesting a mechanism for signal transduction.

The introduction of induced pluripotent stem cells (iPSCs) has opened up the potential for personalized cell therapies and ushered in new opportunities for regenerative medicine, disease modeling, iPSC-based drug discovery and toxicity assessment. Over the past 10 years, several initiatives have been established that aim to collect and generate a large amount of human iPSCs for scientific research purposes. In this review, we compare the construction and operation strategy of some iPSC banks as well as their ongoing development. We also introduce the technical challenges and offer future perspectives pertaining to the establishment and management of iPSC banks.

Benzodiazepines facilitate the inhibitory actions of GABA by binding to γ-aminobutyric acid type A receptors (GABAARs), GABA-gated chloride/bicarbonate channels, which are the key mediators of transmission at inhibitory synapses in the brain. This activity underpins potent anxiolytic, anticonvulsant and hypnotic effects of benzodiazepines in patients. However, extended benzodiazepine treatments lead to development of tolerance, a process which, despite its important therapeutic implications, remains poorly characterised. Here we report that prolonged exposure to diazepam, the most widely used benzodiazepine in clinic, leads to a gradual disruption of neuronal inhibitory GABAergic synapses. The loss of synapses and the preceding, time- and dose-dependent decrease in surface levels of GABAARs, mediated by dynamin-dependent internalisation, were blocked by Ro 15-1788, a competitive benzodiazepine antagonist, and bicuculline, a competitive GABA antagonist, indicating that prolonged enhancement of GABAAR activity by diazepam is integral to the underlying molecular mechanism. Characterisation of this mechanism has revealed a metabotropic-type signalling downstream of GABAARs, involving mobilisation of Ca2+ from the intracellular stores and activation of the Ca2+/calmodulin-dependent phosphatase calcineurin, which, in turn, dephosphorylates GABAARs and promotes their endocytosis, leading to disassembly of inhibitory synapses. Furthermore, functional coupling between GABAARs and Ca2+ stores was sensitive to phospholipase C (PLC) inhibition by U73122, and regulated by PLCδ, a PLC isoform found in direct association with GABAARs. Thus, a PLCδ/Ca2+/calcineurin signalling cascade converts the initial enhancement of GABAARs by benzodiazepines to a long-term downregulation of GABAergic synapses, this potentially underpinning the development of pharmacological and behavioural tolerance to these widely prescribed drugs.

Previous studies have shown that insulin-dependent diabetes can be induced in normal PVG.RT1u rats by a protocol of adult thymectomy and irradiation. The injection of CD4+ T cells from non-irradiated syngeneic donors prevents the onset of disease in approximately 50% of pre-diabetic recipients but all rats are protected if a particular subset of CD4+ cells is transferred. These protective cells express TCR alpha beta and have a memory phenotype, being CD45RClow RT6+. Further studies have demonstrated that the transfer of CD4+CD8- thymocytes, like that of unfractionated CD4+ peripheral T cells, also protects approximately half of recipients from diabetes suggesting that, as with the peripheral T cells, a functional heterogeneity may exist amongst CD4+CD8- thymocytes. In this study, we show that L-selectin is expressed by 50-60% of all CD4+CD8- thymocytes from 6-week-old rats. Adoptive transfer of these populations into thymectomized and irradiated rats revealed that the protection from diabetes observed by CD4+CD8- thymocytes was mediated almost entirely by the L-selectin+ subset. Cells with this phenotype were also able to mediate both humoral and cell mediated responses, providing primed B cells with help for secondary antibody responses and mediating local graft-versus-host reactions. L-selectin- CD4+CD8- thymocytes failed to mediate these responses. These data indicate that CD4+CD8- thymocytes must mature to the stage of L-selectin expression, before they can mediate normal T cell function. The implications of these results are discussed with respect to the possible role of murine NK1.1+ thymocytes in the control of autoimmunity.