350 research outputs found
Role of Drosophila Rab5 during endosomal trafficking at the synapse and evoked neurotransmitter release
DNA fragility in the parallel evolution of pelvic reduction in stickleback fish
Evolution generates a remarkable breadth of living forms, but many traits evolve repeatedly, by mechanisms that are still poorly understood. A classic example of repeated evolution is the loss of pelvic hindfins in stickleback fish (Gasterosteus aculeatus). Repeated pelvic loss maps to recurrent deletions of a pelvic enhancer of the Pitx1 gene. Here, we identify molecular features contributing to these recurrent deletions. Pitx1 enhancer sequences form alternative DNA structures in vitro and increase double-strand breaks and deletions in vivo. Enhancer mutability depends on DNA replication direction and is caused by TG-dinucleotide repeats. Modeling shows that elevated mutation rates can influence evolution under demographic conditions relevant for sticklebacks and humans. DNA fragility may thus help explain why the same loci are often used repeatedly during parallel adaptive evolution
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Self-reactive human CD4 T cell clones form unusual immunological synapses
Recognition of selfβpeptide-MHC (pMHC) complexes by CD4 T cells plays an important role in the pathogenesis of many autoimmune diseases. We analyzed formation of immunological synapses (IS) in self-reactive T cell clones from patients with multiple sclerosis and type 1 diabetes. All self-reactive T cells contained a large number of phosphorylated T cell receptor (TCR) microclusters, indicative of active TCR signaling. However, they showed little or no visible pMHC accumulation or transport of TCRβpMHC complexes into a central supramolecular activation cluster (cSMAC). In contrast, influenza-specific T cells accumulated large quantities of pMHC complexes in microclusters and a cSMAC, even when presented with 100-fold lower pMHC densities. The self-reactive T cells also maintained a high degree of motility, again in sharp contrast to virus-specific T cells. 2D affinity measurements of three of these self-reactive T cell clones demonstrated a normal off-rate but a slow on-rate of TCR binding to pMHC. These unusual IS features may facilitate escape from negative selection by self-reactive T cells encountering very small amounts of self-antigen in the thymus. However, these same features may enable acquisition of effector functions by self-reactive T cells encountering large amounts of self-antigen in the target organ of the autoimmune disease
Tracing Functional Antigen-Specific CCR6+ Th17 Cells after Vaccination
BACKGROUND: The function of T helper cell subsets in vivo depends on their location, and one hallmark of T cell differentiation is the sequential regulation of migration-inducing chemokine receptor expression. CC-chemokine receptor 6 (CCR6) is a trait of tissue-homing effector T cells and has recently been described as a receptor on T helper type 17 (Th17) cells. Th17 cells are associated with autoimmunity and the defence against certain infections. Although, the polarization of Th cells into Th17 cells has been studied extensively in vitro, the development of those cells during the physiological immune response is still elusive. METHODOLOGY/PRINCIPAL FINDINGS: We analysed the development and functionality of Th17 cells in immune-competent mice during an ongoing immune response. In naΓ―ve and vaccinated animals CCR6(+) Th cells produce IL-17. The robust homeostatic proliferation and the presence of activation markers on CCR6(+) Th cells indicate their activated status. Vaccination induces antigen-specific CCR6(+) Th17 cells that respond to in vitro re-stimulation with cytokine production and proliferation. Furthermore, depletion of CCR6(+) Th cells from donor leukocytes prevents recipients from severe disease in experimental autoimmune encephalomyelitis, a model for multiple sclerosis in mice. CONCLUSIONS/SIGNIFICANCE: In conclusion, we defined CCR6 as a specific marker for functional antigen-specific Th17 cells during the immune response. Since IL-17 production reaches the highest levels during the immediate early phase of the immune response and the activation of Th17 cells precedes the Th1 cell differentiation we tent to speculate that this particular Th cell subset may represent a first line effector Th cell subpopulation. Interference with the activation of this Th cell subtype provides an interesting strategy to prevent autoimmunity as well as to establish protective immunity against infections
The Diffusion of Inclusion: An Open Polity Model of Ethnic Power Sharing
While there is a growing consensus that ethnic inclusion produces peace, less is known about what causes transitions to power sharing between ethnic groups in central governments in multiethnic states. The few studies that have addressed this question have proposed explanations stressing exclusively domestic factors. Yet, power sharing is spatially clustered, which suggests that diffusion may be at play. Inspired by studies of democratic diffusion, we study the spread of inclusive policies with an βopen polity modelβ that explicitly traces diffusion from inclusion in other states. Our findings indicate that the relevant diffusion processes operate primarily at the level of world regions rather than globally or between territorial neighbors. Thus, the more inclusive the region, the more likely a shift to power sharing becomes. Shifts away from inclusion to dominance are less common since World War II, but they are more likely in regional settings characterized by ethnic exclusion
Immunogenetic mechanisms for the coexistence of organ-specific and systemic autoimmune diseases
Phosphoinositide Regulation of Integrin Trafficking Required for Muscle Attachment and Maintenance
Muscles must maintain cell compartmentalization when remodeled during development and use. How spatially restricted adhesions are regulated with muscle remodeling is largely unexplored. We show that the myotubularin (mtm) phosphoinositide phosphatase is required for integrin-mediated myofiber attachments in Drosophila melanogaster, and that mtm-depleted myofibers exhibit hallmarks of human XLMTM myopathy. Depletion of mtm leads to increased integrin turnover at the sarcolemma and an accumulation of integrin with PI(3)P on endosomal-related membrane inclusions, indicating a role for Mtm phosphatase activity in endocytic trafficking. The depletion of Class II, but not Class III, PI3-kinase rescued mtm-dependent defects, identifying an important pathway that regulates integrin recycling. Importantly, similar integrin localization defects found in human XLMTM myofibers signify conserved MTM1 function in muscle membrane trafficking. Our results indicate that regulation of distinct phosphoinositide pools plays a central role in maintaining cell compartmentalization and attachments during muscle remodeling, and they suggest involvement of Class II PI3-kinase in MTM-related disease
Diversification of βT Cell Responses to Carboxy-terminal Determinants within the 65-kD Heat-shock Protein Is Involved in Regulation of Autoimmune Arthritis
The T cell response to the 65-kD mycobacterial heat-shock protein (Bhsp65) has been implicated in the pathogenesis of autoimmune arthritis. Adjuvant arthritis (AA) induced in the Lewis rat (RT-1l) by injection of Mycobacterium tuberculosis serves as an experimental model for human rheumatoid arthritis (RA). However, the immunological basis of regulation of acute AA, or of susceptibility/resistance to AA is not known. We have defined the specificity of the proliferative T cell responses to Bhsp65 during the course of AA in the Lewis rat. During the early phase of the disease (6β9 d after onset of AA), Lewis rats raised T cell responses to many determinants within Bhsp65, spread throughout the molecule. Importantly, in the late phase of the disease (8β10 wk after onset of AA), there was evidence for diversification of the T cell responses toward Bhsp65 carboxy-terminal determinants (BCTD) (namely, 417β431, 441β455, 465β479, 513β527, and 521β535). Moreover, arthritic rats in the late phase of AA also raised vigorous T cell responses to those carboxy-terminal determinants within self(rat) hsp65 (Rhsp65) that correspond in position to the above BCTD. These results suggest that the observed diversification is possibly triggered in vivo by induction of self(Rhsp65)-reactive T cells. Interestingly, another strain of rat, the Wistar Kyoto (WKY/NHsd) rat (RT-1l), with the same major histocompatibility complex class II molecules as the Lewis rat, was found to be resistant to AA. In WKY rats, vigorous responses to the BCTD, to which the Lewis rat responded only in the late phase of AA, were observed very early, 10 d after injection of M. tuberculosis. Strikingly, pretreatment with the peptides comprising the set of BCTD, but not its amino-terminal determinants, provided significant protection to naive Lewis rats from subsequent induction of AA. Thus, T cell responses to the BCTD are involved in regulating inflammatory arthritis in the Lewis rat and in conferring resistance to AA in the WKY rat. These results have important implications in understanding the pathogenesis of RA and in devising new immunotherapeutic strategies for this disease
Vaccine-elicited receptor-binding site antibodies neutralize two New World hemorrhagic fever arenaviruses
While five arenaviruses cause human hemorrhagic fevers in the Western Hemisphere, only Junin virus (JUNV) has a vaccine. The GP1 subunit of their envelope glycoprotein binds transferrin receptor 1 (TfR1) using a surface that substantially varies in sequence among the viruses. As such, receptor-mimicking antibodies described to date are type-specific and lack the usual breadth associated with this mode of neutralization. Here we isolate, from the blood of a recipient of the live attenuated JUNV vaccine, two antibodies that cross-neutralize Machupo virus with varying efficiency. Structures of GP1βFab complexes explain the basis for efficient cross-neutralization, which involves avoiding receptor mimicry and targeting a conserved epitope within the receptor-binding site (RBS). The viral RBS, despite its extensive sequence diversity, is therefore a target for cross-reactive antibodies with activity against New World arenaviruses of public health concern
Membrane Protein Location-Dependent Regulation by PI3K (III) and Rabenosyn-5 in Drosophila Wing Cells
The class III phosphatidylinositol-3 kinase (PI3K (III)) regulates intracellular vesicular transport at multiple steps through the production of phosphatidylinositol-3-phosphate (PI(3)P). While the localization of proteins at distinct membrane domains are likely regulated in different ways, the roles of PI3K (III) and its effectors have not been extensively investigated in a polarized cell during tissue development. In this study, we examined in vivo functions of PI3K (III) and its effector candidate Rabenosyn-5 (Rbsn-5) in Drosophila wing primordial cells, which are polarized along the apical-basal axis. Knockdown of the PI3K (III) subunit Vps15 resulted in an accumulation of the apical junctional proteins DE-cadherin and Flamingo and also the basal membrane protein Ξ²-integrin in intracellular vesicles. By contrast, knockdown of PI3K (III) increased lateral membrane-localized Fasciclin III (Fas III). Importantly, loss-of-function mutation of Rbsn-5 recapitulated the aberrant localization phenotypes of Ξ²-integrin and Fas III, but not those of DE-cadherin and Flamingo. These results suggest that PI3K (III) differentially regulates localization of proteins at distinct membrane domains and that Rbsn-5 mediates only a part of the PI3K (III)-dependent processes
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