Individual-ion addressing with microwave field gradients.

Individual-qubit addressing is a prerequisite for many instances of quantum information processing. We demonstrate this capability on trapped-ion qubits with microwave near fields delivered by electrode structures integrated into a microfabricated surface-electrode trap. We describe four approaches that may be used in quantum information experiments with hyperfine levels as qubits. We implement individual control on two 25Mg+ ions separated by 4.3 µm and find spin-flip crosstalk errors on the order of 10(-3).

100-fold reduction of electric-field noise in an ion trap cleaned with in situ argon-ion-beam bombardment.

Motional heating of trapped atomic ions is a major obstacle to their use as quantum bits in a scalable quantum computer. The detailed physical origin of this heating is not well understood, but experimental evidence suggests that it is caused by electric-field noise emanating from the surface of the trap electrodes. In this study, we have investigated the role of adsorbates on the electrodes by identifying contaminant overlayers, implementing an in situ argon-ion-beam cleaning treatment, and measuring ion heating rates before and after treating the trap electrodes' surfaces. We find a 100-fold reduction in heating rate after treatment. The experiments described here are sensitive to low levels of electric-field noise in the MHz frequency range. Therefore, this approach could become a useful tool in surface science that complements established techniques.

Linien: A versatile, user-friendly, open-source FPGA-based tool for frequency stabilization and spectroscopy parameter optimization.

We present a user-friendly and versatile tool for laser frequency stabilization. Its main focus is spectroscopy locking, but the software is suitable for lock-in techniques in general as well as bare proportional-integral-derivative (PID) operation. Besides allowing for sinusoidal modulation (up to 50 MHz), triangular ramp scanning, in-phase and quadrature demodulation (1-5 f), infinite impulse response, and PID filtering, Linien features two different algorithms for automatic lock point selection; one of them performs time-critical tasks completely on field-programmable gate arrays. Linien is capable of autonomously optimizing spectroscopy parameters by means of machine learning and can measure the error signal's power spectral density. The software is built in a modular way, providing both a graphical user interface as well as a Python scripting interface. It is based on the RedPitaya STEMLab platform but may be ported to different systems.

Quantitative determination of temperature in the approach to magnetic order of ultracold fermions in an optical lattice.

We perform a quantitative simulation of the repulsive Fermi-Hubbard model using an ultracold gas trapped in an optical lattice. The entropy of the system is determined by comparing accurate measurements of the equilibrium double occupancy with theoretical calculations over a wide range of parameters. We demonstrate the applicability of both high-temperature series and dynamical mean-field theory to obtain quantitative agreement with the experimental data. The reliability of the entropy determination is confirmed by a comprehensive analysis of all systematic errors. In the center of the Mott insulating cloud we obtain an entropy per atom as low as 0.77k(B) which is about twice as large as the entropy at the Néel transition. The corresponding temperature depends on the atom number and for small fillings reaches values on the order of the tunneling energy.

Mannose receptor mediated uptake of antigens strongly enhances HLA-class II restricted antigen presentation by cultured dendritic cells.

Dendritic cells (DCs) use macropinocytosis and mannose receptor mediated endocytosis for the uptake of exogenous antigens. Here we show that the endocytosis of the mannose receptor and mannosylated antigen is distinct from that of a non-mannosylated antigen. Shortly after internalization, however, both mannosylated and non-mannosylated antigen are found in an MIIC like compartment. The mannose receptor itself does not reach this compartment, and probably releases its ligand in an earlier endosomal structure. Finally, we found that mannosylation of peptides strongly enhanced their potency to stimulate HLA class II-restricted peptide-specific T cell clones. Our results indicate that mannosylation of antigen leads to selective targeting and subsequent superior presentation by DCs which may be useful for vaccine design.

Human dendritic cells shed a functional, soluble form of the mannose receptor.

Human monocyte-derived dendritic cells (DC) use mannose receptor (MR)-mediated endocytosis for efficient antigen capture and targeting to the endosomal/lysosomal compartment. Active biosynthesis of the MR takes place in such cells. We now report that a substantial percentage (up to 20%) of these newly synthesized MR are secreted into the culture medium. The secretion of the soluble MR (sMR) was found to be proportional to the rate of synthesis. The addition of the inflammatory mediator lipopolysaccharide (LPS) to DC, known to induce maturation, strongly reduced MR synthesis, expression and shedding of the MR. The sMR is approximately 10 kDa smaller than the membrane-bound form, but contains an intact N-terminus, indicating the lack of the cytoplasmic and transmembrane region. The sMR appeared to be directly generated from the cell-bound form, indicative of proteolytic cleavage. Importantly, the sMR has maintained its mannose-binding properties since it was capable of binding a mannosylated ligand. The high amount of sMR released by DC and its ability to bind mannosylated ligand might indicate that this molecule plays a role in the transport of mannosylated proteins from the site of inflammation to other parts of the body. Whether that contributes to the generation of immune responses remains to be determined.

Prolongation of life in an experimental model of aging in Drosophila melanogaster.

(R)-Deprenyl, the archetypical monoamine oxidase-B inhibitor, has been shown to increase life-span in a number of species. Although many theories for this effect have been suggested, for example, an increase in superoxide dismutase (SOD) activity, the mechanism of action has yet to be elucidated. To investigate this phenomenon, we have examined the effects of (R)-deprenyl, and some aliphatic propargylamines, in an experimental aging model in Drosophila melanogaster. Both wild-type Oregon-R type flies, as well as a SOD knock-out mutant strain were used. Flies obtained from a series of paired mates were divided equally among treatment groups. In all studies, flies were treated for the duration of life following adult emergence. The aging model consists of substitution of sucrose with galactose in the regular food media of the flies. Initial experiments confirmed that such a substitution resulted in a significant (p < 0.01, Breslow test) reduction in mean and maximal life-span of flies, an effect not due to nutrient deprivation. Inclusion of (R)-deprenyl and the aliphatic propargylamines in the media, at average daily doses in the range 0.5-1 ng/fly/day, led to a significant increase in mean and maximal life-span of galactose-treated, but not control flies. This effect was seen in both wild-type and mutant flies.

Effect of IL-6 on proliferation and IG production of human EBV-transformed cell lines in serum free culture media.

To optimalize growth and Ig production of EBV transformed B cells for large scale tissue culture, we analyzed five stable monoclonal EBV-B cell lines for their responsiveness to interleukin (IL)-6 in standard medium with 5% FCS and in several serum-free media. As we previously demonstrated these cell lines were found to be heterogeneous with regard to their production of Il-1, Il-6 and lymphotoxin. We could not demonstrate an effect of Il-6 on proliferation on any of the cell lines in either standard medium with 5% FCS or in any of the serum-free culture media. In standard medium, cell lines capable of Il-6 production showed a slight elevation of Ig production in response to exogenous Il-6. Only one cell line, that did not secrete any of the lymphokines tested, responded strongly to Il-6 with a 12 times elevated IgM production. In contrast, in serum-free medium supplemented with Bovine Serum Albumin (BSA), Il-6 raised Ig secretion of all cell lines. This study shows that in some serum-free culture media EBV cell lines can be propagated as well as in standard medium with FCS. Responsiveness of these cells to cytokines is heterogeneous and is at least partially influenced by the culture medium used.

Get into the groove! Targeting antigens to MHC class II.

The activation of MHC class II-restricted helper T cells is paramount to adaptive immune responses. Vaccine development could therefore benefit from improved ways of targeting antigens into MHC class II molecules. In recent years, the natural pathways of MHC class II antigen presentation have been exploited to achieve this goal. First, antigenic proteins and peptides have been modified to facilitate receptor-mediated uptake by professional antigen-presenting cells. Second, DNA constructs containing specific targeting sequences have been used to direct endogenously synthesized antigens to the MHC class II compartments. Both strategies proved to be highly effective. We review these data and describe how this knowledge is currently applied to the design of vaccines that activate helper T cells in vivo.

Chronic schistosomiasis: dendritic cells generated from patients can overcome antigen-specific T cell hyporesponsiveness.

Chronic infection with helminths is associated with down-regulated antigen-specific T cell responses. In order to determine whether schistosome-specific T cells are present, yet functionally unresponsive, or absent in the periphery of chronically infected persons, autologous granulocyte-macrophage colony-stimulating factor and dendritic cells (DC) derived from interleukin (IL)-4 were used as highly efficient antigen-presenting cells (APC). Peripheral blood mononuclear cells (PBMC) from persons harboring Schistosoma haematobium infection and hyporesponsive to parasite antigen were cocultured with autologous DC in the presence of adult worm antigen (AWA). In contrast to PBMC alone, DC-supplemented cultures responded to AWA by proliferation and by IL-4 and IL-5 production and, in some patients, by production of interferon-gamma. Thus, schistosome-specific T helper cells are present in the periphery but are functionally hyporesponsive during active infection with schistosomes. Cytokine responses representing the Th1 and (more importantly) Th2 types can be restored in vitro when DC are used as APC.

Human epidermal Langerhans cells lack functional mannose receptors and a fully developed endosomal/lysosomal compartment for loading of HLA class II molecules.

Langerhans cells (LC) represent the dendritic cell (DC) lineage in the epidermis. They capture and process antigens in the skin and subsequently migrate to the draining lymph nodes to activate naive T cells. Efficient uptake and processing of protein antigens by LC would, therefore, seem a prerequisite. We have now compared the capacity of human epidermal LC, blood-derived DC and peripheral blood mononuclear cells to endocytose and present (mannosylated) antigens to antigen-specific T cells. Moreover, we have determined the expression of mannose receptors, and the composition of the intracellular endosomal/lysosomal MHC class II-positive compartment. The results indicate that LC have poor endocytic capacity and do not exploit mannose receptor-mediated endocytosis pathways. Furthermore, the composition of the class II compartment in LC is distinct from that in other antigen-presenting cells and is characterized by the presence of relatively low levels of lysosomal markers. These results underscore the unique properties of LC and indicate that LC are relatively inefficient in antigen uptake, processing and presentation. This may serve to avoid hyper-responsiveness to harmless protein antigens that are likely to be frequently encountered in the skin due to (mechanical) skin damage.

Strongly increased efficiency of altered peptide ligands by mannosylation.

Altered peptide ligands (APL) have the potential to modulate pathogenic T cell reactivity. High concentrations of APL, however, are required to achieve efficient blocking of the T cell response. We have therefore investigated whether improved delivery of APL to professional antigen-presenting cells (APC) can lead to more efficient application of such peptides. For this purpose APL were bis-mannosylated in order to facilitate their uptake by mannose receptor-positive dendritic cells (DC) in vitro. We present evidence that a 100- to 1000-fold lower concentration of bis-mannosylated APL was sufficient for complete blocking of the proliferative T cell response against the agonist peptide compared to the non-mannosylated APL. Moreover, bis-mannosylated APL were similarly effective in the inhibition of the T cell response against whole protein antigens. In contrast, unrelated, bis-mannosylated class II binding peptides were ineffective, indicating that the increased efficiency of the mannosylated APL was not due to competition for binding to class II molecules. Furthermore, a strong increase in the efficiency of presentation of APL was also observed when macrophages and peripheral blood mononuclear cells were used as APC. Thus, bis-mannosylation of APL greatly increases their potency to inhibit proliferative T cell responses. Moreover, it is likely that the use of bis-mannosylated APL will result in preferential presentation by mannose receptor-positive, professional APC. These results may be of relevance for more effective use of APL for immunoregulation in vivo.

Heterogeneity in both cytokine production and responsiveness of a panel of monoclonal human Epstein-Barr virus-transformed B-cell lines.

To optimize growth and Ig production of in vitro-cultured Epstein-Barr virus (EBV)-transformed B cells, a panel of six monoclonal EBV B-cell lines was analyzed for autocrine growth factor production and responsiveness to various cytokines. Three cell lines produced Il-I and four produced Il-6, although differences concerning the amount of lymphokines produced were observed. Interestingly a considerable tumor necrosis factor beta (lymphotoxin) activity was found in supernatants of all cell lines. One IgM-producing cell line that did not secrete either Il-1 or Il-6 was exceptional in its ability to respond to the addition of rIl-6 with a 5- to 10-times elevated IgM production. In contrast, cell lines in the panel capable of Il-6 production showed only a minimal elevation of Ig production on addition of exogenous Il-6. Ig production was slightly less in some cell lines when Il-6 was neutralized. Antibodies against lymphotoxin or Il-6 did not influence growth rate of the cell lines significantly, implying that neither Il-6 nor lymphotoxin had an autostimulatory effect on the analyzed cell lines. This study demonstrates a heterogeneity regarding the amount and type of lymphokines produced by long-term monoclonal EBV cell lines, which may account for the diverse responses exhibited by these cells towards exogenously added lymphokines.

Mannose receptor-mediated uptake of antigens strongly enhances HLA class II-restricted antigen presentation by cultured dendritic cells.

Dendritic cells (DC) efficiently take up antigens by macropinocytosis and mannose receptor-mediated endocytosis. Here we show that endocytosis of mannose receptor-antigen complexes takes place via small coated vesicles, while non-mannosylated antigens were mainly present in larger vesicles. Shortly after internalization the mannose receptor and its ligand appeared in the larger vesicles. Within 10 min, the mannosylated and non-mannosylated antigens co-localized with typical markers for major histocompatibility complex class II-enriched compartments and lysosomes. In contrast, the mannose receptor appeared not to reach these compartments, suggesting that it releases its ligand in an earlier endosomal structure. Moreover, we demonstrate that mannosylation of protein antigen and peptides resulted in a 200-10,000-fold enhanced potency to stimulate HLA class II-restricted peptide-specific T cell clones compared to non-mannosylated peptides. Our results indicate that mannosylation of antigen leads to selective targeting and subsequent superior presentation by DC which may be applicable in vaccine design.