Investigation on the resolution of a micro cone beam CT scanner scintillating detector using Monte Carlo methods

The impact of several physical quantities on the spatial resolution of an X-ray scintillating pixel detector for a micro cone beam CT (µCBCT) is investigated and discussed. The XtremeCT from SCANCO Medical AG was simulated using the EGSnrc/EGS++ Monte Carlo (MC) framework and extensively benchmarked in a previous work. The resolution of the detector was determined by simulating a titanium knife-edge to obtain the edge spread function (ESF) and the modulation transfer function (MTF). Propagation of the scintillation light through the scintillator and its coupling into the fiber optics system was taken into account. The contribution of particles scattered in the main scanner components to the detector signal is very low and does not affect the spatial resolution of the detector. The resolution obtained from the energy deposition in the scintillator without any blurring due to the propagation of the scintillation light into the fiber optics array was 31 µm. By assuming isotropic light propagation in the scintillator, the resolution degraded to 360 µm. A simple light propagation model taking into account the impact of the scintillator's columnar microstructures was developed and compared with the MANTIS Monte Carlo simulation package. By reducing the width of the model's light propagation kernel by a factor of 2 compared to the isotropic case, the detector resolution can be improved to 83 µm, which corresponds well to the measured resolution of 86 µm. The resolution of the detector is limited mainly by the propagation of the scintillation light through the scintillator layer. It offers the greatest potential to improve the resolution of the µCBCT imaging system.

Bone micro-architecture and determinants of strength in the radius and tibia: age-related changes in a population-based study of normal adults measured with high-resolution pQCT

SUMMARY

We recruited a population-based sample of 58 males and 74 females aged 20-79 from a primary care medical practice to provide normative and descriptive data for high-resolution peripheral quantitative computed tomography (pQCT) parameters. Important effects of ageing and contrasts in the effects of sex on the micro-architecture and strength of upper and lower limb bones were revealed.

INTRODUCTION

The advent of high-resolution pQCT scanners has permitted non-invasive assessment of structural data on cortical and trabecular bone.

METHODS

We investigated age-related changes in pQCT and finite element (FE) modelling parameters at the distal radius and distal tibia in a population-based cross-sectional study of 58 males and 74 females aged 20-79 years. Linear regression models including quadratic terms for age were used for inference.

RESULTS

Age-related changes and sex differences were generally similar for pQCT parameters at the radius and tibia. At each site, mean values for bone density, cortical thickness and trabecular micro-architecture (number, separation and thickness) were lower (trabecular separation higher) in women than men. Changes with age were most apparent for bone density and cortical thickness, which declined with age, in contrast to trabecular micro-architecture parameters which were not significantly associated with age (p > 0.05) in either sex. Cortical bone density and thickness declined faster in women than men after age 50 and trabecular bone density was consistently lower in women. FE-analysis predicted failure load decreased with age and percentage of load carried by trabecular bone increased (p < 0.05).

CONCLUSIONS

These data show contrasts in the effects of sex on the micro-architecture and strength of upper and lower limb bones with ageing. The faster decline in cortical bone thickness and density in women than men after age 50 and consistently lower trabecular bone density in women have implications for the excess risks of wrist and hip fractures in women.

Innate immune receptors on neutrophils and their role in chronic lung disease

Neutrophils, the prototypic cells of the innate immune system, are recruited to infected sites to protect the human body from invading pathogens. To accomplish this function, neutrophils sense pathogens and endogenous damage-associated molecules via innate immune receptors, such as Toll-like receptors (TLRs) and other pattern recognition receptors. This defence function is essential for the pulmonary microenvironment where the host is faced with millions of particles and pathogens inhaled daily. Chronic lung diseases, such as cystic fibrosis or chronic obstructive pulmonary disease are characterized by a neutrophil accumulation and chronic bacterial colonization of the airways. Consequently, insights into the role of TLRs on neutrophils in chronic lung diseases are of high relevance for further diagnostic and therapeutic approaches. Here we summarize and discuss recent advances in the expression, regulation and functional role of TLRs on neutrophils in chronic lung diseases.

Accelerated Telomere Shortening and Telomere Abnormalities in Radiosensitive Cell Lines

We examined telomere maintenance in cells of 11 primary fibroblast cell lines with differing genetic defects that confer sensitivity to ionizing radiation. These included cell lines derived from patients with ataxia telangiectasia, Nijmegen breakage syndrome, Fanconi anemia, defective Artemis, DNA ligase I and DNA ligase IV, an immunodeficient patient with a defect in DNA double-strand break repair, and a patient diagnosed with xeroderma pigmentosum who, in addition, showed severe clinical sensitivity to ionizing radiation. Our results, based on Southern blot, flow-FISH and Q-FISH (quantitative FISH) measurements, revealed an accelerated rate of telomere shortening in most cell lines derived from the above patients compared to cell lines from normal individuals or a cell line isolated from a heterozygotic parent of one radiosensitive patient. This accelerated telomere shortening was accompanied by the formation of chromatin bridges in anaphase cells, indicative of the early loss of telomere capping function and in some cases low levels of chromosome abnormalities in metaphase cells. We also analyzed telomere maintenance in mouse embryonic stem cells deficient in Brca1, another defect that confers radiosensitivity. Similarly, these cells showed accelerated telomere shortening and mild telomere dysfunction in comparison to control cells. Our results suggest that mechanisms that confer sensitivity to ionizing radiation may be linked with mechanisms that cause telomere dysfunction.

Stereological measures of trabecular bone structure: comparison of 3D micro computed tomography with 2D histological sections in human proximal tibial bone biopsies

Stereology applied on histological sections is the 'gold standard' for obtaining quantitative information on cancellous bone structure. Recent advances in micro computed tomography (microCT) have made it possible to acquire three-dimensional (3D) data non-destructively. However, before the 3D methods can be used as a substitute for the current 'gold standard' they have to be verified against the existing standard. The aim of this study was to compare bone structural measures obtained from 3D microCT data sets with those obtained by stereology performed on conventional histological sections using human tibial bone biopsies. Furthermore, this study forms the first step in introducing the proximal tibia as a potential bone examination location by peripheral quantitative CT and CT. Twenty-nine trabecular bone biopsies were obtained from autopsy material at the medial side of the proximal tibial metaphysis. The biopsies were embedded in methylmetacrylate before microCT scanning in a Scanco microCT 40 scanner at a resolution of 20 x 20 x 20 microm3, and the 3D data sets were analysed with a computer program. After microCT scanning, 16 sections were cut from the central 2 mm of each biopsy and analysed with a computerized method. Trabecular bone volume (BV/TV) and connectivity density (CD) were estimated in both modalities, whereas trabecular bone pattern factor (TBPf) was estimated on the histological sections only. Trabecular thickness (Tb.Th), number (Tb.N) and separation (Tb.Sp), and structure model index (SMI) were estimated with the microCT method only. Excellent correlations were found between the two techniques for BV/TV (r = 0.95) and CD (r = 0.95). Additionally, an excellent relationship (r = 0.95) was ascertained between TBPf and SMI. The study revealed high correlations between measures of bone structure obtained from conventional 2D sections and 3D microCT data. This indicates that 3D microCT data sets can be used as a substitute for conventional histological sections for bone structural evaluations.

Vr2: a new apple scab resistance gene

Reports from several European countries of the breakdown of the Vf resistance, the most frequently used source of resistance in breeding programs against apple scab, emphasize the urgency of diversifying the basis of apple scab resistance and pyramiding different apple scab resistances with the use of their associated molecular markers. GMAL 2473 is an apple scab resistant selection thought to carry the resistance gene Vr. We report the identification by BSA of three AFLP markers and one RAPD marker associated with the GMAL 2473 resistance gene. SSRs associated with the resistance gene were found by (1) identifying the linkage group carrying the apple scab resistance and (2) testing the SSRs previously mapped in the same region. One such SSR, CH02c02a, mapped on linkage group 2, co-segregates with the resistance gene. GAML 2473 was tested with molecular markers associated with other apple scab resistance genes, and accessions carrying known apple scab resistance genes were tested with the SSR linked to the resistance gene found in GMAL 2473. The results indicate that GMAL 2473 does not carry Vr, and that a new apple scab resistance gene, named Vr2, has been identified.

Creating a saturated reference map for the apple (Malus x domestica Borkh.) genome

The availability of a high quality linkage map is essential for the detection and the analysis of quantitative traits. Such a map should cover a significant part of the genome, should be densely populated with markers, and in order to gain the maximum advantage should be transferable to populations or cultivars other than the ones on which it has been constructed. An apple genetic linkage map has been constructed on the basis of a segregating population of the cross between the cultivars Fiesta and Discovery. A total of 840 molecular markers, 475 AFLPs, 235 RAPDs, 129 SSRs and 1 SCAR, were used for the two parental maps constructed with JoinMap and spanning 1,140 cM and 1,450 cM, respectively. Large numbers of codominant markers, like SSRs, enable a rapid transfer of the map to other populations or cultivars, allowing the investigation of any chosen trait in another genetic background. This map is currently the most advanced linkage map in apple with regard to genome coverage and marker density. It represents an ideal starting point for future mapping projects in Malus since the stable and transferable SSR frame of the map can be saturated quickly with dominant AFLP markers.

Mapping Quantitative Field Resistance Against Apple Scab in a 'Fiesta' x 'Discovery' Progeny

ABSTRACT Breeding of resistant apple cultivars (Malus x domestica) as a disease management strategy relies on the knowledge and understanding of the underlying genetics. The availability of molecular markers and genetic linkage maps enables the detection and the analysis of major resistance genes as well as of quantitative trait loci (QTL) contributing to the resistance of a genotype. Such a genetic linkage map was constructed, based on a segregating population of the cross between apple cvs. Fiesta (syn. Red Pippin) and Discovery. The progeny was observed for 3 years at three different sites in Switzerland and field resistance against apple scab (Venturia inaequalis) was assessed. Only a weak correlation was detected between leaf scab and fruit scab. A QTL analysis was performed, based on the genetic linkage map consisting of 804 molecular markers and covering all 17 chromosomes of apple. With the maximum likelihood-based interval mapping method, eight genomic regions were identified, six conferring resistance against leaf scab and two conferring fruit scab resistance. Although cv. Discovery showed a much stronger resistance against scab in the field, most QTL identified were attributed to the more susceptible parent 'Fiesta'. This indicated a high degree of homozygosity at the scab resistance loci in 'Discovery', preventing their detection in the progeny due to the lack of segregation.

Body composition, bone mass and microstructural analysis in GH-transgenic mice reveals that skeletal changes are specific to bone compartment and gender

Experimental and clinical studies suggest that high serum levels of growth hormone (GH) increase cortical but not trabecular bone. We studied body composition and bone structure in transgenic mice (MT-bGH) with systemic overexpression of GH. Body composition was examined with dual-energy X-ray absorptiometry (DXA), ashing, and chemical analysis, and the femora with DXA and micro computerized tomography. The absolute fat and bone tissue contents were significantly higher in GH transgenic mice vs controls (P < or = 0.05), but no significant difference was noted when normalizing the values to body weight. Male transgenics displayed no change in apparent (volumetric) femoral bone density, relative cortical area and trabecular bone volume fraction. Female transgenic mice demonstrated an increase in apparent femoral density and in trabecular bone volume fraction (+130%; P < or = 0.01). The mineralized tissue matrix density was decreased in male and female transgenic mice (P < or = 0.05). The results show that chronic GH excess affects trabecular bone in a gender-specific manner and that bone changes depend on the compartment investigated.

[Not Available]

To the bougeoisie in the last quarter of the 19th century, the housing problem seemed to be the key problem regarding the "social issue" (Soziale Frage). This was the background on which a number of Swiss cities undertook extensive surveys of the living conditions towards the end of the century. These surveys, which were methodologically based on the quantifying and therefore objective instruments of statistics, also attracted attention in other European states. Scientific hygiene supplied its values as the seemingly objective material criteria for the surveys. These values consisted among others of the limiting value "Luftkubus" (air volume), the natural human need for air expressed in exact numbers, as well as the rules for social behaviour in connection with this value. Together they justified "sanitary living", which a closer examination reveals as being a scientifically constructed bourgeois reality. This reality was guarded by sanitary officials, who were under the municipal sanitary authorities' supervision. These officials disposed of the means of criminal law in their struggle against "unsanitary living". The obligation to maintain health mandated by the public authorities ultimately aimed at integrating the workers into the Swiss bourgeois state and ensuring and increasing national power in modern industrial society.

A biomechanical enigma: why are tibial fractures not more frequent in the elderly?

Epidemiology revealed that diaphyseal fractures of the tibia affect young people, particularly young men; no increase was noticed for the elderly. This indicates that osteoporosis does not lead to increased bone fragility. Obviously, this is a biomechanical enigma. Torque measurements were carried out on human cadaveric tibiae and revealed a great correlation between the polar moment of inertia of the cortical bone at the tibial isthmus and the ultimate torque at failure (r = 0.83) and a lesser correlation between the cross-sectional density at the isthmus and the torque at failure (r = 0.57). Therefore, the size is more important than the degree of osteoporosis. We can speculate that endosteal resorption due to osteoporosis is compensated for by periosteal apposition and therefore does not lead to bone weakness.

Applications of micro-CT and MR microscopy to study pre-clinical models of osteoporosis and osteoarthritis

There is a tremendous unmet therapeutic need for the treatment of osteoporosis and osteoarthritis. The ovariectomized rat and the guinea pig are widely used animal models for the evaluation of new therapeutics for osteoporosis and osteoarthritis, respectively. We have utilized X-ray micro-CT techniques to quantitatively evaluate the differences in trabecular bone in the rat proximal tibia following ovariectomy and treatment with estrogen (17-B-estradiol). Results demonstrate a loss of trabecular bone and architecture following ovariectomy (p < 0.001), and a marked inhibition of trabecular bone loss in the estrogen treated group (p < 0.001). A similar change in architecture can be visualized in images obtained by high resolution MR microscopy. In addition, a good correlation was observed between the values of trabecular bone fraction (BV/TV) in the rat tibiae as obtained from 3-dimensional micro-CT data and 2-dimensional static histomorphometry (r = 0.89, 0.73, 0.79 for sham, OVX, and treated groups, respectively). Micro-CT images were also obtained from a set of lumbar vertebrae from sham operated and ovariectomized rats. Significant bone loss can be measured as early as 8 weeks following ovariectomy (p < 0.005). Micro-CT and MR images were also obtained to study age related changes in the stifle joint of the guinea pig. Significant boney changes can be seen in the tibia and femur from the animals at various ages. Changes in cartilage and joint space can also be visualized in the images. The utility of micro-CT imaging in evaluating the mouse skeletal system is illustrated by obtaining morphological and architectural details from high resolution images of the mouse hind limb and proximal tibia, respectively. The results demonstrate the advantages that multi-dimensional imaging techniques can offer in evaluating bone and joint related changes in animal models of osteoporosis and osteoarthritis.

Role of gammaENaC subunit in lung liquid clearance and electrolyte balance in newborn mice. Insights into perinatal adaptation and pseudohypoaldosteronism

Genetic evidence supports a critical role for the epithelial sodium channel (ENaC) in both clearance of fetal lung liquid at birth and total body electrolyte homeostasis. Evidence from heterologous expression systems suggests that expression of the alphaENaC subunit is essential for channel function, whereas residual channel function can be measured in the absence of beta or gamma subunits. We generated mice without gammaENaC (gammaENaC -/-) to test the role of this subunit in neonatal lung liquid clearance and total body electrolyte balance. Relative to controls, gammaENaC (-/-) pups showed low urinary [K+] and high urinary [Na+] and died between 24 and 36 h, probably from hyperkalemia (gammaENaC -/- 18.3 mEq/l, control littermates 9.7 mEq/l). Newborn gammaENaC (-/-) mice cleared lung liquid more slowly than control littermates, but lung water at 12 h (wet/dry = 5.5) was nearly normal (wet/dry = 5.3). This study suggests that gammaENaC facilitates neonatal lung liquid clearance and is critical for renal Na+ and K+ transport, and that low level Na+ transport may be sufficient for perinatal lung liquid absorption but insufficient to maintain electrolyte balance by the distal nephron. The gammaENaC (-/-) newborn exhibits a phenotype that resembles the clinical manifestations of human neonatal PHA1.

Molecular selection in apple for resistance to scab caused by Venturia inaequalis

Large-scale marker-assisted selection requires highly reproducible, consistent and simple markers. The use of genetic markers is important in woody plant breeding in general, and in apple in particular, because of the high level of heterozygosity present in Malus species. We present here the transformation of two RAPD markers, which we found previously to be linked to the major scab resistance gene Vf, into more reliable and reproducible markers that can be applied directly to apple breeding. We give an example of how the use of such markers can speed up selection for the introduction of scab resistance genes into the same plant, reducing labour and avoiding time-consuming test crosses. We discuss the nature and relationship of the scab resistance gene Vf to the one present in Nova Easygro, thought to be Vr.

Resolution dependency of microstructural properties of cancellous bone based on three-dimensional mu-tomography

Micro-computed tomography (microCT) is an emerging technique for the non-destructive assessment and analysis of the three-dimensional cancellous bone architecture. However, the procedures the procedures and applications used to quantify bone structures are not yet standardized. The aim of this study was to provide more insight in the resolution-dependency of microstructural properties of three-dimensional trabecular bone. Ten iliac crest bone biopsies were measured using a newly devised microCT system providing a nominal isotropic resolution of 14 microns. To study the resolution dependency the measured data were reconstructed on reduced image arrays with reduction factors ranging from 2 to 20. To assess the structural properties, morphometric parameters were computed based on a truly three-dimensional approach. The results showed a strong resolution dependency of the structural properties and that, if very precise results are needed, only the highest resolution will predict the correct values. Nevertheless, since the properties either decrease or increase monotonously up to a nominal resolution of about 175 microns, the values appear to be restorable using a suitable calibration procedure.

A microtomographic system for the nondestructive evaluation of bone architecture

Microtomography (micro-computed-tomography, mu-CT) is a method to image and quantify trabecular bone. It has the capability to address the role of trabecular architecture on the mechanical properties of bone and to study trabecular bone remodeling. The system described in this work is based on a compact fan-beam type tomograph that can work in spiral scanning or multislice mode. An X-ray tube with a microfocus is used as a source, a CCD-array as a detector. Samples with diameters from a few millimeters to a maximum of 14 mm can be measured, typically, bone biopsies with a diameter of 8 mm and a length of approximately 10 mm are measured. Spatial resolution is 28 microns. Usually the volume of interest contains 4 x 4 x 4 mm3 and is represented in 14 x 14 x 14 microns3 voxels. 3D stereological indices are extracted according to the standard definitions used in histomorphometry. Triangular surface representation is effected with an extended marching cube algorithm and forms a convenient basis for finite element analysis. Microtomographic measurements may be employed to "calibrate" lower-dose, lower-resolution images in vivo as well as to nondestructively assess unprocessed surgical bone biopsy specimens. These specimens remain intact for mechanical or histological testing.

Abnormal B lymphocyte development, activation, and differentiation in mice that lack or overexpress the CD19 signal transduction molecule

CD19-deficient mice were generated to examine the role of CD19 in B cell growth regulation in vivo. Deletion of CD19 had no deleterious effects on the generation of B cells in the bone marrow, but there was a significant reduction in the number of B cells in peripheral lymphoid tissues. B cells from CD19-deficient mice exhibited markedly decreased proliferative responses to mitogens, and serum immunoglobulin levels were also significantly decreased. In contrast, mice that overexpressed CD19 had significant defects in early B cell development in the bone marrow, augmented mitogenic responses, and increased serum immunoglobulin levels. These experiments indicate that CD19 functions to define signaling thresholds for cell surface receptors that regulate B lymphocyte selection, activation, and differentiation.

Inhibition of natural killer cell-mediated bone marrow graft rejection by allogeneic major histocompatibility complex class I, but not class II molecules

The role of major histocompatibility complex (MHC) class I and class II molecules in natural killer (NK) cell-mediated rejection of allogeneic, semisyngeneic and MHC-matched bone marrow grafts was investigated. The use of beta 2-microglobulin (beta 2m) -/- and beta 2m +/- mice as bone marrow donors to MHC-mismatched recipients allowed an analysis of whether the presence of semi-syngeneic and allogeneic MHC class I gene products would be triggering, protective or neutral, in relation to NK cell-mediated rejection. Loss of beta 2m did not allow H-2b bone marrow cells to escape from NK cell-mediated rejection in allogeneic (BALB/c) or semi-allogeneic (H-2Dd transgenic C57BL/6) mice. On the contrary, it led to stronger rejection, as reflected by the inability of a larger bone marrow cell inoculum to overcome rejection by the H-2-mismatched recipients. In H-2-matched recipients, loss of beta 2m in the graft led to a switch from engraftment to rejection. At the recipient level, loss of beta 2m led to loss of the capability to reject H-2-matched beta 2m-deficient as well as allogeneic grafts. When MHC class II-deficient mice were used as donors, the response was the same as that against donors of normal MHC phenotype: allogeneic and semi-syngeneic grafts were rejected by NK cells, while syngeneic grafts were accepted. These data suggest a model in which allogeneic class I molecules on the target cell offer partial protection, while certain syngeneic class I molecules give full protection from NK cell-mediated rejection of bone marrow cells. There was no evidence for a role of MHC class II molecules in this system.

New classification of moricizine and propafenone based on electrophysiologic and electrocardiographic data from isolated rabbit heart

Because the classification of propafenone and moricizine is not clear, we measured in 20 specifically equipped isolated rabbit hearts QRS duration, QT interval, action potential duration at 90% of repolarization (APD90), effective refractory period (ERP), conduction time (CT), and rise velocity (Rv) of the monophasic action potentials (AP) during exposure to moricizine and propafenone in comparison with procainamide. Propafenone and procainamide prolonged APD90 and JT. All drugs increased ERP. Propafenone demonstrated marked tonic sodium channel block. Onset of use-dependent kinetics (tau on), defined as change in Rv as fraction per beat at 300 ms cycle length (CL), were 0.047 +/- 0.004/beat for procainamide, 0.050 +/- 0.004/beat for propafenone, and 0.022 +/- 0.003/beat for miricizine. Recovery kinetics, defined as recovery of Rv after cessation of pacing, had a time constant of 5.3 +/- 0.7 s for procainamide, 6.3 +/- 0.8 s for propafenone, and 25.0 +/- 1.3 s for moricizine. Based on these data, moricizine must be classified as a Ic agent, whereas propafenone demonstrates pronounced tonic sodium channel block, in addition to its phasic block, which is similar to class Ia kinetics.

DNA markers linked to Malus floribunda 821 scab resistance

Breeding resistant apple plants is an alternative way to control fungal pathogens reducing the environmental impact due to the use of pesticides. The breeding of apple cultivars resistant to Venturia inaequalis could be much improved by marker-assisted selection. A molecular marker closely linked to the resistance locus called Vf could replace selection based on infection studies. To find such molecular markers, DNA of progenies from crossings of a resistant and a susceptible apple tree was subject to bulked segregant analysis. Two markers were found with a genetic distance of 10.6% and 19.7% recombination frequency to the Vf locus.

Improved renal function in mouse kidney allografts lacking MHC class I antigens

The immunological responses that lead to rejection of organ and tissue transplants are triggered by the recognition of proteins encoded within the MHC. The relative contributions of responses directed toward MHC class I compared with class II in the loss of functional integrity of vascularized organ grafts have been difficult to define. The recent development of technologies which allow the generation of mice in which specific genes have been altered by gene targeting offers a new approach to addressing this question. We examine here the rejection of kidney allografts from mice lacking native MHC class I Ag. These mice were obtained from embryonic stem cells in which the beta 2 microglobulin (beta 2m) gene had been disrupted by homologous recombination. We found a significant improvement in function of renal allografts from MHC class I-deficient donors compared with allografts from donors with normal MHC class I expression. Surprisingly, the improved function of the MHC class I-deficient grafts was not associated with differences in mononuclear inflammatory cell infiltration of these grafts nor in differences in alloreactive proliferative or cytotoxic T cell responses. However, we did find differences in alloantibody response between the groups. Recipients of control allografts produced antibodies against both donor MHC class I and II, whereas recipients of MHC class I-deficient grafts formed alloantibodies primarily against donor MHC class II Ag. These studies confirm that immune responses directed toward donor MHC class I alloantigens contribute to kidney transplant dysfunction in this model. Also, these findings suggest that, at least for renal transplants, genetic manipulations which reduce MHC class I expression may be effective in overcoming some of the effects of MHC incompatibility.

Improved renal function in mouse kidney allografts lacking MHC class I antigens

The immunological responses that lead to rejection of organ and tissue transplants are triggered by the recognition of proteins encoded within the MHC. The relative contributions of responses directed toward MHC class I compared with class II in the loss of functional integrity of vascularized organ grafts have been difficult to define. The recent development of technologies which allow the generation of mice in which specific genes have been altered by gene targeting offers a new approach to addressing this question. We examine here the rejection of kidney allografts from mice lacking native MHC class I Ag. These mice were obtained from embryonic stem cells in which the beta 2 microglobulin (beta 2m) gene had been disrupted by homologous recombination. We found a significant improvement in function of renal allografts from MHC class I-deficient donors compared with allografts from donors with normal MHC class I expression. Surprisingly, the improved function of the MHC class I-deficient grafts was not associated with differences in mononuclear inflammatory cell infiltration of these grafts nor in differences in alloreactive proliferative or cytotoxic T cell responses. However, we did find differences in alloantibody response between the groups. Recipients of control allografts produced antibodies against both donor MHC class I and II, whereas recipients of MHC class I-deficient grafts formed alloantibodies primarily against donor MHC class II Ag. These studies confirm that immune responses directed toward donor MHC class I alloantigens contribute to kidney transplant dysfunction in this model. Also, these findings suggest that, at least for renal transplants, genetic manipulations which reduce MHC class I expression may be effective in overcoming some of the effects of MHC incompatibility.

Identification of apple cultivars using RAPD markers

Eleven apple cultivars were differentiated using randomly amplified polymorphic DNA (RAPD) markers obtained by the polymerase chain reaction (PCR). The variability of the technique and of the origin of the DNA extract was analyzed. A set of bands consistent in their presence or absence was chosen to create a differentiating band pattern. A key is proposed by which one can differentiate apple cultivars using commercially available prime.

Major histocompatibility complex class I-restricted T cells are required for resistance to Mycobacterium tuberculosis infection

Mice with a targeted disruption in the beta 2-microglobulin (beta 2m) gene, which lack major histocompatibility complex class I molecules and consequently fail to develop functional CD8 T cells, provided a useful model for assessing the role of class I-restricted T cells in resistance to infection with virulent Mycobacterium tuberculosis. Of mutant beta 2m-/-mice infected with virulent 10(6) M. tuberculosis, 70% were dead or moribund after 6 weeks, while all control mice expressing the beta 2m gene remained alive for > 20 weeks. Granuloma formation occurred in mutant and control mice, but far greater numbers of tubercle bacilli were present in the lungs of mutant mice than in controls, and caseating necrosis was seen only in beta 2m-/-lungs. In contrast, no differences were seen in the course of infection of mutant and control mice with an avirulent vaccine strain, bacille Calmette-Guérin (BCG). Immunization with BCG vaccine prolonged survival of beta 2m-/-mice after challenge with M. tuberculosis for 4 weeks but did not protect them from death. These data indicate that functional CD8 T cells, and possibly T cells bearing gamma delta antigen receptor, are a necessary component of a protective immune response to M. tuberculosis in mice.

Major histocompatibility complex class I-specific and -restricted killing of beta 2-microglobulin-deficient cells by CD8+ cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTLs) recognize major histocompatibility complex (MHC) class I molecules, normally composed of a heavy chain, a beta 2-microglobulin (beta 2m), and peptide antigens. beta 2m is considered essential for the assembly and intracellular transport of MHC class I molecules as well as their peptide presentation to CTLs. Contrary to this dogma, we now report the generation of allospecific and restricted CD8+ and TCR alpha beta+ CTLs (where TCR is T-cell receptor) capable of killing beta 2m-deficient cells. Such CTLs were obtained by priming mice with live allogeneic beta 2m- spleen cells or mutant lymphoma cells producing MHC class I protein but no detectable beta 2m. Although both beta 2m- and beta 2m-expressing lymphoma cells were rejected in allogeneic mice, only the former were efficient inducers of CTLs recognizing beta 2m- cells. These CTLs were MHC class I (H-2Kb or Db)-specific and CD8-dependent and did not require serum as a source of external beta 2m in the culture. They could be induced across major and minor histocompatibility barriers. The H-2-restricted CTLs generated in the latter case failed to kill the antigen-processing-deficient target RMA-S cells. The results show that MHC class I heavy chains in beta 2m- cells can be transported to the cell surface and act as antigens or antigen-presenting molecules to allospecific and MHC-restricted CTLs.

Recognition of beta 2-microglobulin-negative (beta 2m-) T-cell blasts by natural killer cells from normal but not from beta 2m- mice: nonresponsiveness controlled by beta 2m- bone marrow in chimeric mice

The role of major histocompatibility complex (MHC) class I expression in control of the sensitivity of normal cells to natural killer (NK) cells was studied by the use of mutant mice made deficient for expression of beta 2-microglobulin (beta 2m) through homologous recombination in embryonal stem cells. T-cell blasts from beta 2m-deficient (beta 2m -/-) mice were killed by NK cells from normal mice in vitro, while beta 2m +/- blasts were resistant. The beta 2m defect also affected the NK effector cell repertoire: NK cells from beta 2m -/- mice failed to kill beta 2m -/- blasts, while they retained the ability to kill the prototype NK cell target lymphoma YAC-1, although at reduced levels. The inability to recognize beta 2m -/- blasts could be transferred with beta 2m -/- bone marrow to irradiated beta 2m-expressing mice. In contrast, the development of CD8+ T cells (deficient in beta 2m -/- mice) was restored in such chimera. These results indicate that loss of MHC class I/beta 2m expression is sufficient to render normal cells sensitive to NK cells, and that the same defect in the hemopoietic system of a mouse renders its NK cells tolerant to beta 2m-deficient but otherwise normal cells. In the beta 2m -/- mice, NK cells may be selected or educated by other bone marrow cells to tolerate the MHC class I deficiency. Alternatively, the specificity may be controlled directly by the class I molecules on the NK cells themselves.

[Can sudden cardiac death be prevented by treatment with anti-arrhythmia drugs?]

Sudden cardiac death is defined as death due to a primary cardiac cause or mechanism, occurring within one hour of the onset of acute illness in a person thought to be free of, or with symptomatically mild, heart disease, or simply prehospital death. Of persons dying suddenly, 90% have coronary artery disease, less commonly, dilated cardiomyopathy or hypertrophic cardiomyopathy, preexcitation syndrome, long QT-syndrome, conduction disturbances, congenital or valvular heart disease as well as cardiac tamponade are responsible. In the USA, the incidence of sudden cardiac death is approximately 450,000 per year, in the Federal Republic of Germany the number lies at about 70,000 to 80,000. The most important risk factors for sudden cardiac death are impaired left ventricular ejection fraction, myocardial ischemia and arrhythmias. In general, sudden cardiac death is caused by ventricular fibrillation which arises mainly by degeneration of ventricular tachycardia (VT). The terminal arrhythmia, it is assumed, is precipitated by premature ventricular beats originating in an arrhythmogenic substrate. MEDICAL ANTIARRHYTHMIC TREATMENT IN PATIENTS WITH CORONARY ARTERY DISEASE AFTER MYOCARDIAL INFARCTION: STUDIES WITH CLASS I DRUGS: The results of nine large, randomized , controlled studies are available in which the mortality of patients on antiarrhythmic treatment has been studied (Table 1). Two studies each were carried out with aprindine, phenytoin, mexiletine and tocainide as well as one study with endainide, flecainide or morizicine. With the exception of the CAST study, no study showed a significant difference between treated patients and the control group with respect to mortality or incidence of sudden cardiac death. The CAST study was terminated after ten months because the administration of flecainide and encainide led to overall mortality of 7.7% vs. 3.0% in the control group and the rate of sudden cardiac death at 4.5% was significantly higher in the treatment group than the 1.2% incidence found in controls (Table 2). For nearly all of the studies described, the patient groups were not sufficiently large and subgrouping according to patient characteristics was not carried out such that possibly, inhomogeneity of the entire collective may not have been recognized precluding identification of some individuals who may have shown benefit from antiarrhythmic treatment. The necessity for treatment in many of those receiving drugs is questionable since generally the rhythm profile of the patients was not taken into consideration for the decision to treat. Proarrhythmic effects, accordingly, were also not assessed. Individual treatment and dosage adjustment by monitoring with effectiveness criteria was carried out in one study only in which, even here, criteria for effectiveness were arbitrarily capable of eliciting antiarrhythmic actions. Calculation of mortality rates was carried out on the basis of the total number of deaths in the respective groups without taking into consideration that by the end of the study, in the treatment group the medication had been discontinued in up to 40% of the patients. STUDIES WITH CLASS II DRUGS: For treatment with beta-receptor blockers there are 15 large, controlled, randomized, long-term studies available in which total mortality and the incidence of sudden cardiac death were studied.(ABSTRACT TRUNCATED AT 400 WORDS)

Biphenotypic leukemic lymphocyte precursors in CD2+CD19+ acute lymphoblastic leukemia and their putative normal counterparts in human fetal hematopoietic tissues

During detailed immunophenotypic analyses of marrow blasts from 336 acute lymphoblastic leukemia (ALL) patients, a very small percentage of cases reactive with B-cell-directed as well as T-cell-directed monoclonal antibodies (MoAbs) were identified. Five ALL cases were biphenotypic since they coexpressed CD2 (Tp50) and CD19 (Bp95) antigens at the single-cell level. The composite immunophenotype of these biphenotypic ALL cases was [TdT+HLA-ABC+CD2+CD3-CD10+CD13-CD14-CD16-CD19+CD20+ ++-CD21-CD33-CD34+Bgp95-C mu- slg-]. Low-molecular-weight B-cell growth factor (LMW-BCGF), recombinant interleukin-2 (rIL-2), and rIL-3 stimulated the proliferative activity of biphenotypic leukemic lymphocyte precursors without inducing differentiation. In the presence of the phorbol ester TPA, leukemic blasts from two cases differentiated along the B precursor pathway to the [CD2-CD10+CD19+CD20+C mu+slg-] pre-B cell stage. Biphenotypic ALL cases did not share a common configuration and gene rearrangement pattern of the immunoglobulin heavy chain genes or T-cell receptor (TCR) genes. Three cases had rearranged C mu genes but germline TCR genes, one case showed rearrangement of both C mu and TCR genes, and the remaining case had rearranged TCR genes but germline C mu genes. All five patients attained prompt remission after standard induction chemotherapy. Three to four years after initial diagnosis, four patients are now off chemotherapy and remain alive in their first remission. One patient relapsed at 3 years, 7 months, but promptly achieved complete remission after reinduction chemotherapy and remains in second remission off chemotherapy greater than 3 years after her reinduction therapy. With two-color immunofluorescence staining techniques and multiparameter flow cytometric analyses, we identified a small population of CD2+CD19+ lymphoid cells in fetal livers (FLs) and fetal bone marrows (FBMs), which may represent the putative normal counterparts of biphenotypic ALL blasts. A CD2+CD19+ normal biphenotypic lymphoid precursor cell line, designated FL 8.2 CD2+, was established from an FL of 8-weeks of gestational age by Epstein-Barr virus (EBV)-induced blastoid transformation. The composite immunophenotype of FL 8.2 CD2+ cell line was [TdT+HLA-ABC+HLA-DR+ CD2+CD5-CD7-CD10+/-CD13-CD19+CD20-CD21+ CD22+CD33-CD34+/-Bgp95-CDw40+C mu-slgD-slgM-]. FL 8.2 CD2+ cells showed germline patterns of immunoglobulin heavy-chain joining region, heavy-chain constant region, kappa light-chain constant region genes, and TCR beta-chain genes. Cross-linking of CD2 as well as CD19 antigens on FL 8.2 CD2+ cells caused an increase of intracellular ionized calcium.(ABSTRACT TRUNCATED AT 400 WORDS)

Entamoeba histolytica ribosomal RNA genes are carried on palindromic circular DNA molecules

Highly abundant DNA fragments obtained after restriction enzyme digests of nuclear DNA of Entamoeba histolytica strain HM-1:IMSS have been cloned and characterized. Northern blot hybridization to E. histolytica rRNA and sequence analysis identified the abundant DNAs as ribosomal DNA containing species. Several overlapping clones containing these abundant DNAs were isolated from 4 different genomic libraries of E. histolytica. Alignment of the restriction maps was consistent with a circular molecule, about 24.6 kilobase pairs (kb) in size. Nuclease BA131 digestion provided additional evidence for the circular nature of this DNA. The ribosomal DNA molecule contains two large inverted repeat-regions, each at least 5.2 kb in length. Sequence analysis of clone R715 revealed homology to the large rRNA units of various eukaryotic organisms. This clone was located in both inverted repeats, suggesting two rRNA cistrons per molecule. The inverted repeats are flanked by stretches of DNA which contain tandemly reiterated sequences. Southern blot analysis of E. histolytica nuclear DNA revealed the presence of two populations of molecules. These molecules have identical arrangements of restriction sites, but differ in size (0.7 kb) in a fragment containing tandemly reiterated sequences. Analysis of E. histolytica nuclear DNA by electron microscopy also revealed circular molecules. These molecules are about 26.6 kb +/- 0.5 kb in size and contain structural features predicted by the restriction map of the extrachromosomal ribosomal DNA of E. histolytica.

A chimeric transcript containing a 16 S rRNA and a potential mRNA in chloroplasts of Euglena gracilis

The chloroplast genome of Euglena gracilis contains a supplementary gene for a 16 S rRNA (s16 S rrn gene), which is not part of a complete rrn operon. An open reading frame (ORF406) is located downstream of the s16 S rrn gene. Chloroplast RNA was hybridized with cloned DNA fragments of this region and the hybrids were analysed by electron microscopy and S1-nuclease protection experiments. The s16 S rrn gene and the ORF406 are transcribed as one continuous 3.6 kb long RNA, which starts just upstream of the 5'-end of the s16 S rrn gene. The 3'-end occurs at multiple sites within a region of 700 bases downstream of the ORF. Northern blot analysis shows that the abundance of the transcript is comparable with that of other chloroplast mRNAs.

A gene cluster in the spinach and pea chloroplast genomes encoding one CF1 and three CF0 subunits of the H+-ATP synthase complex and the ribosomal protein S2

The regions of the spinach and pea chloroplast genomes containing the ATP synthase genes atpA, atpF and atpH have been sequenced. The encoded proteins, CF1 alpha, CF0I and CF0III, are well conserved between spinach and pea, and analogous to the alpha, b and c subunits of the Escherichia coli ATP synthase complex. The atpF gene is split by a single intron, and the exon/intron boundaries have been defined by isolating and sequencing a partial cDNA clone. Two other genes, designated atpI and rps2, located upstream from atpH, have also been sequenced. They encode a 27,000 Mr hydrophobic protein analogous to the F0a subunit of E. coli ATP synthase and a basic protein analogous to the S2 protein of the E. coli 30 S ribosomal subunit. Transcriptional analysis by electron microscopy of RNA-DNA hybrids, Northern blotting and primer extension experiments shows that these genes are transcribed and processed into a complex set of transcripts, with 5' ends mapping upstream from the rps2, atpI and atpH genes.

Evidence for in vivo trans splicing of pre-mRNAs in tobacco chloroplasts

The rps12 gene codes for chloroplast ribosomal protein S12. In the tobacco chloroplast genome (156 kbp circular DNA), exons II and III of this gene are separated by an intron of 536 bases and are present in two copies in the inverted repeat region, while exon I is located in the large single copy region at a distance of 90 kb and 126 kb from the two copies of exons II and III. These three exons were artificially combined in cloned DNA fragments and hybridized with tobacco chloroplast RNA. Electron microscopic analysis of RNA-DNA hybrids showed that exon I is transcribed as part of a polycistronic RNA containing upstream and downstream sequences; the same is true for exons II and III. Exon I is shown to be transcribed separately from exons II and III. In the most abundant class of the hybridized RNA molecules, exon I was covalently linked to exon II. In these molecules the sequences downstream of exon I and upstream of exon II are not present. These data indicate that maturation of rps12 pre-mRNAs in chloroplasts of tobacco involves trans splicing.

Transfer of cloned human class I major histocompatibility complex genes into HLA mutant human lymphoblastoid cells

Three new kinds of recombinant DNA constructs were used to transfer cloned human class I HLA genes (A2 and B8) into unique HLA mutant lymphoblastoid cells: pHeBo(x): a class I gene, "x," in plasmid vector pHeBo, which contains a hygromycin resistance gene and Epstein-Barr virus oriP element that sustains extrachromosomal replication; pHPT(x): gene x in a vector with a hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene; pHPTe(x): gene x in a vector with the HPRT gene and oriP element. Cell surface class I antigen expression was strong in transferents made with class I-deficient lymphoblastoid cell line mutants .144 (A-null), .53 (B-null), and .184 (A-null, B-null). Transferents expressing HLA-A2 were recognized specifically by HLA-A2-specific cytotoxic T lymphocytes. When introduced on either of the vectors with the Epstein-Barr virus oriP element, the class I gene replicated extrachromosomally and was lost at rates of 0.2 to 0.3 per cell division. When introduced with vector pHPT (lacking Epstein-Barr virus oriP), the B8 gene was inserted at different chromosomal locations. Introduction of the HLA-B8 gene failed to restore antigen expression by HLA-B-null mutant .174, providing evidence that, unlike mutants exemplified by .53, .144, and .184, some HLA antigen loss mutants are deficient in a trans-acting function needed for class I antigen expression. Of more general interest, the results obtained with HLA class I genes in vectors that replicate extrachromosomally suggest ways of relating genic expression to chromatin structure and function and of attempting to clone functional human centromeres.

The enigma of the gene coding for ribosomal protein S12 in the chloroplasts of Nicotiana

A 2.9 kbp region from within the inverted repeat of Nicotiana chloroplast DNA hybridized with a chloroplast DNA fragment from Euglena containing the complete rps12 gene coding for ribosomal protein S12. Nucleotide sequencing within this region revealed the existance of two rps12 coding stretches interrupted by 540 bp having class II intron structure. Joining and decoding the exon regions produced a sequence of 85 amino acids colinear and 81% homologous to the S12 protein of Euglena chloroplasts and E. coli, starting from amino acid residue 38 to the stop codon. Immediately upstream of codon 38, conserved intron sequences were located. However, the 5' 37 codon of Nicotiana chloroplast rps12 could not be identified by electron microscopy of RNA-DNA hybrids within a DNA region extending 4000 bp upstream of codon 38, nor by computer search of a completely sequenced region extending for more than 9000 bp upstream of this codon. In E. coli, alteration in rps12 codons 42 or 87 causes streptomycin resistance. However, the nucleotide sequence of the identified rps12 exons in two Nicotiana chloroplast mutants resistant to streptomycin were found to be identical to that of wild type.