Antigen recognition determinants of gammadelta T cell receptors

The molecular basis of gammadelta T cell receptor (TCR) recognition is poorly understood. Here, we analyze the TCR sequences of a natural gammadelta T cell population specific for the major histocompatibility complex class Ib molecule T22. We find that T22 recognition correlates strongly with a somatically recombined TCRdelta complementarity-determining region 3 (CDR3) motif derived from germ line-encoded residues. Sequence diversity around these residues modulates TCR ligand-binding affinities, whereas V gene usage correlates mainly with tissue origin. These results show how an antigen-specific gammadelta TCR repertoire can be generated at a high frequency and suggest that gammadelta T cells recognize a limited number of antigens.     

HLA and NK cell inhibitory receptor genes in resolving hepatitis C virus infection

Natural killer (NK) cells provide a central defense against viral infection by using inhibitory and activation receptors for major histocompatibility complex class I molecules as a means of controlling their activity. We show that genes encoding the inhibitory NK cell receptor KIR2DL3 and its human leukocyte antigen C group 1 (HLA-C1) ligand directly influence resolution of hepatitis C virus (HCV) infection. This effect was observed in Caucasians and African Americans with expected low infectious doses of HCV but not in those with high-dose exposure, in whom the innate immune response is likely overwhelmed. The data strongly suggest that inhibitory NK cell interactions are important in determining antiviral immunity and that diminished inhibitory responses confer protection against HCV.     

Antigen recognition by variable lymphocyte receptors

Variable lymphocyte receptors (VLRs) rather than antibodies play the primary role in recognition of antigens in the adaptive immune system of jawless vertebrates. Combinatorial assembly of leucine-rich repeat (LRR) gene segments achieves the required repertoire for antigen recognition. We have determined a crystal structure for a VLR-antigen complex, VLR RBC36 in complex with the H-antigen trisaccharide from human blood type O erythrocytes, at 1.67 angstrom resolution. RBC36 binds the H-trisaccharide on the concave surface of the LRR modules of the solenoid structure where three key hydrophilic residues, multiple van der Waals interactions, and the highly variable insert of the carboxyl-terminal LRR module determine antigen recognition and specificity. The concave surface assembled from the most highly variable regions of the LRRs, along with diversity in the sequence and length of the highly variable insert, can account for the recognition of diverse antigens by VLRs.     

Molecular recognition by self-assembled monolayers of cavitand receptors

It is shown by angle-resolved x-ray photoelectron spectroscopy that cavitands derived from resorcin[4]arenes provided with four dialkylsulfide chains form stable monolayers on gold surfaces that are well organized by self-assembly. The cavitand headgroups at the surface of the resorcin[4]arene monolayer act as molecular recognition sites for small organic molecules with remarkable selectivity for perchloroethylene (C(2)Cl(4)). Comparative thermal desorption experiments indicate binding sites with high interaction energies of C(2)Cl(4) at the surface of the resorcin[4]arene monolayers. Fast and reversible "host-guest" interactions were found by the monitoring of extremely small mass changes (in the nanogram range) with a quartz microbalance oscillator provided with gold electrodes coated by resorcin[4]arene monolayers.     

Evolution of cell recognition by viruses

Evolution of receptor specificity by viruses has several implications for viral pathogenesis, host range, virus-mediated gene targeting, and viral adaptation after organ transplantation and xenotransplantation, as well as for the emergence of viral diseases. Recent evidence suggests that minimal changes in viral genomes may trigger a shift in receptor usage for virus entry, even into the same cell type. A capacity to exploit alternative entry pathways may reflect the ancient evolutionary origins of viruses and a possible role as agents of horizontal gene transfers among cells.     

Dual activation of the Drosophila toll pathway by two pattern recognition receptors

The Toll-dependent defense against Gram-positive bacterial infections in Drosophila is mediated through the peptidoglycan recognition protein SA (PGRP-SA). A mutation termed osiris disrupts the Gram-negative binding protein 1 (GNBP1) gene and leads to compromised survival of mutant flies after Gram-positive infections, but not after fungal or Gram-negative bacterial challenge. Our results demonstrate that GNBP1 and PGRP-SA can jointly activate the Toll pathway. The potential for a combination of distinct proteins to mediate detection of infectious nonself in the fly will refine the concept of pattern recognition in insects.     

Absence of TGF-beta receptors and growth inhibitory responses in retinoblastoma cells

The responses of retinoblastoma tumor cells and normal retinal cells to various growth inhibitory factors were examined. Whereas fetal retinal cells were highly sensitive to the antimitogenic effects of transforming growth factor beta 1 (TGF-beta 1), retinoblastoma tumor cell lines were all resistant to this factor. Binding assays and affinity labeling of these cells with radioiodinated TGF-beta 1 revealed that the cells did not have TGF-beta receptors. The retinoblastoma cells lacked the three affinity-labeled proteins of 65, 95, and 300 kilodaltons typically seen in human cell lines and thus differed from normal retinal cells and from other types of neuroectodermal tumors that display the normal pattern of receptors. Loss of TGF-beta receptors, which is a rare event among tumor cells, may represent one mechanism through which these cells escape from negative control and form retinoblastomas.     

Specificity of allogeneic cell recognition by human lymphocytes in vitro

Human lymphocytes proliferate in vitro in response to foreign histocompatibility antigens that are present on allogeneic lymphocytes. Within a population of immunocompetent lymphocytes there are specific subpopulations that respond to allogeneic cells from different individuals. A means of selectively eliminating such subpopulations is suggested.     

A ribonucleotide reductase homolog of cytomegalovirus and endothelial cell tropism

Human cytomegalovirus infects vascular tissues and has been associated with atherogenesis and coronary restenosis. Although established laboratory strains of human cytomegalovirus have lost the ability to grow on vascular endothelial cells, laboratory strains of murine cytomegalovirus retain this ability. With the use of a forward-genetic procedure involving random transposon mutagenesis and rapid phenotypic screening, we identified a murine cytomegalovirus gene governing endothelial cell tropism. This gene, M45, shares sequence homology to ribonucleotide reductase genes. Endothelial cells infected with M45-mutant viruses rapidly undergo apoptosis, suggesting that a viral strategy to evade destruction by cellular apoptosis is indispensable for viral growth in endothelial cells.     

Arthritis provoked by linked T and B cell recognition of a glycolytic enzyme

The hallmark of rheumatoid arthritis (RA) is specific destruction of the synovial joints. In a mouse line that spontaneously develops a disorder with many of the features of human RA, disease is initiated by T cell recognition of a ubiquitously expressed self-antigen; once initiated, pathology is driven almost entirely by immunoglobulins. In this study, the target of both the initiating T cells and pathogenic immunoglobulins was identified as glucose-6-phosphate isomerase, a glycolytic enzyme. Thus, some forms of RA or related arthritides may develop by a mechanism fundamentally different from the currently popular paradigm of a joint-specific T cell response.     

Developmental biology of T cell receptors

T cell receptors are the antigen-recognizing elements found on the effector cells of the immune system. Two isotypes have been discovered, TCR-gamma delta and TCR-alpha beta, which appear in that order during ontogeny. The maturation of prothymocytes that colonize the thymic rudiment at defined gestational stages occurs principally within the thymus, although some evidence for extrathymic maturation also exists. The maturation process includes the rearrangement and expression of the T cell receptor genes. Determination of these mechanisms, the lineages of the cells, and the subsequent thymic selection that results in self-tolerance is the central problem in developmental immunology and is important for the understanding of autoimmune diseases.     

Direct control of germline stem cell division and cyst growth by neural insulin in Drosophila

Stem cells reside in specialized niches that provide signals required for their maintenance and division. Tissue-extrinsic signals can also modify stem cell activity, although this is poorly understood. Here, we report that neural-derived Drosophila insulin-like peptides (DILPs) directly regulate germline stem cell division rate, demonstrating that signals mediating the ovarian response to nutritional input can modify stem cell activity in a niche-independent manner. We also reveal a crucial direct role of DILPs in controlling germline cyst growth and vitellogenesis.     

Direct ubiquitination of pattern recognition receptor FLS2 attenuates plant innate immunity

Innate immune responses are triggered by the activation of pattern-recognition receptors (PRRs). The Arabidopsis PRR FLAGELLIN-SENSING 2 (FLS2) senses bacterial flagellin and initiates immune signaling through association with BAK1. The molecular mechanisms underlying the attenuation of FLS2 activation are largely unknown. We report that flagellin induces recruitment of two closely related U-box E3 ubiquitin ligases, PUB12 and PUB13, to FLS2 receptor complex in Arabidopsis. BAK1 phosphorylates PUB12 and PUB13 and is required for FLS2-PUB12/13 association. PUB12 and PUB13 polyubiquitinate FLS2 and promote flagellin-induced FLS2 degradation, and the pub12 and pub13 mutants displayed elevated immune responses to flagellin treatment. Our study has revealed a unique regulatory circuit of direct ubiquitination and turnover of FLS2 by BAK1-mediated phosphorylation and recruitment of specific E3 ligases for attenuation of immune signaling.     

Wnt5a control of cell polarity and directional movement by polarized redistribution of adhesion receptors

Mechanisms by which Wnt pathways integrate the organization of receptors, organelles, and cytoskeletal proteins to confer cell polarity and directional cell movement are incompletely understood. We show that acute responses to Wnt5a involve recruitment of actin, myosin IIB, Frizzled 3, and melanoma cell adhesion molecule into an intracellular structure in a melanoma cell line. In the presence of a chemokine gradient, this Wnt-mediated receptor-actin-myosin polarity (W-RAMP) structure accumulates asymmetrically at the cell periphery, where it triggers membrane contractility and nuclear movement in the direction of membrane retraction. The process requires endosome trafficking, is associated with multivesicular bodies, and is regulated by Wnt5a through the small guanosine triphosphatases Rab4 and RhoB. Thus, cell-autonomous mechanisms allow Wnt5a to control cell orientation, polarity, and directional movement in response to positional cues from chemokine gradients.     

Control of excitatory and inhibitory synapse formation by neuroligins

The normal function of neural networks depends on a delicate balance between excitatory and inhibitory synaptic inputs. Synapse formation is thought to be regulated by bidirectional signaling between pre- and postsynaptic cells. We demonstrate that members of the Neuroligin family promote postsynaptic differentiation in cultured rat hippocampal neurons. Down-regulation of neuroligin isoform expression by RNA interference results in a loss of excitatory and inhibitory synapses. Electrophysiological analysis revealed a predominant reduction of inhibitory synaptic function. Thus, neuroligins control the formation and functional balance of excitatory and inhibitory synapses in hippocampal neurons.     

Regulation of the polarity protein Par6 by TGFbeta receptors controls epithelial cell plasticity

The transition of cells from an epithelial to a mesenchymal phenotype is a critical event during morphogenesis in multicellular organisms and underlies the pathology of many diseases, including the invasive phenotype associated with metastatic carcinomas. Transforming growth factor beta (TGFbeta) is a key regulator of epithelial-to-mesenchymal transition (EMT). However, the molecular mechanisms that control the dissolution of tight junctions, an early event in EMT, remain elusive. We demonstrate that Par6, a regulator of epithelial cell polarity and tight-junction assembly, interacts with TGFbeta receptors and is a substrate of the type II receptor, TbetaRII. Phosphorylation of Par6 is required for TGFbeta-dependent EMT in mammary gland epithelial cells and controls the interaction of Par6 with the E3 ubiquitin ligase Smurf1. Smurf1, in turn, targets the guanosine triphosphatase RhoA for degradation, thereby leading to a loss of tight junctions. These studies define how an extracellular cue signals to the polarity machinery to control epithelial cell morphology.     

B细胞活化因子及调节性T细胞在免疫性血小板减少症发病中的作用

目的 了解B细胞活化因子(BAFF)及调节性T(Treg)细胞在免疫性血小板减少症(ITP)发病中的作用.方法 采集34例ITP及28例健康对照者外周血,用流式细胞术检测外周血Treg细胞数,ELISA检测血浆BAFF水平.结果 ITP患者外周血Treg细胞/CD4+细胞比值低于对照者[(1.55±1.13)％ vs (2.73±0.83)％,P＜0.01],而血浆BAFF水平高于对照者[(1 426.14±1 280.67) μg/L vs (644.29±307.97) μg/L,P＜0.01].结论 BAFF与Treg细胞可能存在相互作用,从而参与ITP发病.