Distinct types of diffuse large B-cell lymphoma identified by gene expression profiling

Diffuse large B-cell lymphoma (DLBCL), the most common subtype of non-Hodgkin's lymphoma, is clinically heterogeneous: 40% of patients respond well to current therapy and have prolonged survival, whereas the remainder succumb to the disease. We proposed that this variability in natural history reflects unrecognized molecular heterogeneity in the tumours. Using DNA microarrays, we have conducted a systematic characterization of gene expression in B-cell malignancies. Here we show that there is diversity in gene expression among the tumours of DLBCL patients, apparently reflecting the variation in tumour proliferation rate, host response and differentiation state of the tumour. We identified two molecularly distinct forms of DLBCL which had gene expression patterns indicative of different stages of B-cell differentiation. One type expressed genes characteristic of germinal centre B cells ('germinal centre B-like DLBCL'); the second type expressed genes normally induced during in vitro activation of peripheral blood B cells ('activated B-like DLBCL'). Patients with germinal centre B-like DLBCL had a significantly better overall survival than those with activated B-like DLBCL. The molecular classification of tumours on the basis of gene expression can thus identify previously undetected and clinically significant subtypes of cancer.

Heterozygous embryonic lethality induced by targeted inactivation of the VEGF gene

Angiogenesis is required for a wide variety of physiological and pathological processes. The endothelial cell-specific mitogen vascular endothelial growth factor (VEGF) is a major mediator of pathological angiogenesis. Also, the expression of VEGF and its two receptors, Flt-1 and Flk-1/KDR, is related to the formation of blood vessels in mouse and rat embryos. Mice homozygous for mutations that inactivate either receptor die in utero between days 8.5 and 9.5. However, ligand(s) other than VEGF might activate such receptors. To assess the role of VEGF directly, we disrupted the VEGF gene in embryonic stem cells. Here we report the unexpected finding that loss of a single VEGF allele is lethal in the mouse embryo between days 11 and 12. Angiogenesis and blood-island formation were impaired, resulting in several developmental anomalies. Furthermore, VEGF-null embryonic stem cells exhibit a dramatically reduced ability to form tumours in nude mice.

Superplastic extensibility of nanocrystalline copper at room temperature

A bulk nanocrystalline (nc) pure copper with high purity and high density was synthesized by electrodeposition. An extreme extensibility (elongation exceeds 5000%) without a strain hardening effect was observed when the nc copper specimen was rolled at room temperature. Microstructure analysis suggests that the superplastic extensibility of the nc copper originates from a deformation mechanism dominated by grain boundary activities rather than lattice dislocation, which is also supported by tensile creep studies at room temperature. This behavior demonstrates new possibilities for scientific and technological advancements with nc materials.

In vitro and in vivo degradation of porous poly(DL-lactic-co-glycolic acid) foams

This study investigated the in vitro degradation of porous poly(DL-lactic-co-glycolic acid) (PLGA) foams during a 20-week period in pH 7.4 phosphate-buffered saline (PBS) at 37 degrees C and their in vivo degradation following implantation in rat mesentery for up to 8 weeks. Three types of PLGA 85 : 15 and three types of 50 : 50 foams were fabricated using a solvent-casting, particulate-leaching technique. The two types had initial salt weight fraction of 80 and 90%, and a salt particle size of 106-150 microm, while the third type had 90% initial weight fraction of salt in the size range 0-53 microm. The porosities of the resulting foams were 0.82, 0.89, and 0.85 for PLGA 85 : 15, and 0.73, 0.87, and 0.84 for PLGA 50 : 50 foams, respectively. The corresponding median pore diameters were 30, 50, and 17 microm for PLGA 85: 15, and 19, 17, and 17 microm for PLGA 50 : 50. The in vitro and in vivo degradation kinetics of PLGA 85: 15 foams were independent of pore morphology with insignificant variation in foam weight, thickness, pore distribution, compressive creep behavior, and morphology during degradation. The in vitro foam half-lives based on the weight average molecular weight were 11.1 +/- 1.8 (80%, 106-150 microm), 12.0 +/- 2.0 (90%, 106-150 microm), and 11.6 +/- 1.3 (90%, 0-53 microm) weeks, similar to the corresponding values of 9.4 +/- 2.2, 14.3 +/- 1.5, and 13.7 +/- 3.3 weeks for in vivo degradation. In contrast, all PLGA 50 : 50 foams exhibited significant change in foam weight, water absorption, and pore distribution after 6-8 weeks of incubation with PBS. The in vitro foam half-lives were 3.3 +/- 0.3 (80%, 106-150 microm), 3.0 +/- 0.3 (90%, 106-150 microm), and 3.2 +/- 0.1 (90%, 0-53 microm) weeks, and the corresponding in vivo half-lives were 1.9 micro 0.1, 2.2 +/- 0.2, and 2.4 +/- 0.2 weeks. The significantly shorter half-lives of PLGA 50: 50 compared to 85: 15 foams indicated their faster degradation both in vitro and in vivo. In addition, PLGA 50: 50 foams exhibited significantly faster degradation in vivo as compared to in vitro conditions due to an autocatalytic effect of the accumulated acidic degradation products in the medium surrounding the implants. These results suggest that the polymer composition and environmental conditions have significant effects on the degradation rate of porous PLGA foams.

Hyperexpression of CD40 ligand by B and T cells in human lupus and its role in pathogenic autoantibody production

We investigated the role of the costimulatory molecules, CD40 and its ligand CD40L, in the pathogenesis of human SLE. In comparison to normal subjects or patients in remission, PBMC from active lupus patients had a 21-fold increase in the frequency of CD40L-expressing, CD4+T cells. However, the expression of CD40L induced in either lupus or normal T cells by mitogenic stimulation could be down-regulated equally well by CD40 molecules on autologous B cells. Active lupus patients also had a 22-fold increase in percentage of CD8+ T cells expressing CD40L, consistent with their unusual helper activity in SLE. Surprisingly, patients with active lupus had a 20.5-fold increase in B cells that spontaneously expressed high levels of CD40L, as strongly as their T cells. Although lupus patients in remission had low levels of CD40L+ cells in the range of normal subjects, mitogen-induced upregulation of CD40L expression in the T and B cells was markedly greater than normal, suggesting an intrinsic defect. A mAb to CD40L blocked significantly the ability of lymphocytes from lupus patients with active and established disease to produce the pathogenic variety of antinuclear autoantibodies in vitro, bolstering the possibility of anti-CD40L immunotherapy for lupus. Future studies on the hyperexpression of CD40L could elucidate a regulatory defect in the pathogenic T and B cells of lupus.

Purification and biochemical characterization of human pluripotent hematopoietic colony-stimulating factor

Pluripotent hematopoietic colony-stimulating factor (pluripotent CSF), a protein that is constitutively produced by the human bladder carcinoma cell line 5637, has been purified from low serum (0.2% fetal calf serum)-containing conditioned medium. The purification involved sequential ammonium sulfate precipitation, ion-exchange chromatography, gel filtration, and reversed-phase high-performance liquid chromatography. The purified protein has a molecular weight of 18,000 in NaDodSO4/polyacrylamide gel electrophoresis, both by the silver staining technique and by elution of biological activity from a corresponding gel slice, and has an isoelectric point of 5.5. Pluripotent CSF supports the growth of human mixed colonies, granulocyte-macrophage colonies, and early erythroid colonies and induces differentiation of the human promyelocytic leukemic cell line HL-60 and the murine myelomonocytic leukemic cell line WEHI-3B (D+). The specific activity of the purified pluripotent CSF in the granulocyte-macrophage colony assay is 1.5 X 10(8) units/mg of protein.

A novel polymorphism in the MCP-1 gene regulatory region that influences MCP-1 expression

Two novel polymorphisms in the distal regulatory region of the MCP-1 gene were identified by directly sequencing PCR amplified genomic DNA. These polymorphisms are located at positions -2518 (G or A) and -2076 (A or T) relative to the major transcriptional start site of the gene. To examine the effect of these polymorphisms on MCP-1 transcription, polymorphic variants of the MCP-1 distal regulatory region were placed upstream of a luciferase reporter gene and transfected into A172 cells. IL-1beta-induced luciferase activity was significantly greater from cells transfected with constructs containing G at position -2518. The polymorphism at -2076 did not affect MCP-1 transcription. IL-1beta-treated peripheral blood mononuclear cells from individuals heterozygous or homozygous for G at -2518 produced more MCP-1 than cells from individuals homozygous for A at -2518. These data identify a polymorphism in the MCP-1 distal regulatory region that affects the level of MCP-1 expression in response to an inflammatory stimulus.

Cloning of the gamma-aminobutyric acid (GABA) rho 1 cDNA: a GABA receptor subunit highly expressed in the retina

Type A gamma-aminobutyric acid (GABAA) receptors are a family of ligand-gated chloride channels that are the major inhibitory neurotransmitter receptors in the nervous system. Molecular cloning has revealed diversity in the subunits that compose this heterooligomeric receptor, but each previously elucidated subunit displays amino acid similarity in conserved structural elements. We have used these highly conserved regions to identify additional members of this family by using the polymerase chain reaction (PCR). One PCR product was used to isolate a full-length cDNA from a human retina cDNA library. The mature protein predicted from this cDNA sequence in 458 amino acids long and displays between 30 and 38% amino acid similarity to the previously identified GABAA subunits. This gene is expressed primarily in the retina but transcripts are also detected in the brain, lung, and thymus. Injection of Xenopus oocytes with RNA transcribed in vitro produces a GABA-responsive chloride conductance and expression of the cDNA in COS cells yields GABA-displaceable muscimol binding. These features are consistent with our identification of a GABA subunit, GABA rho 1, with prominent retinal expression that increases the diversity and tissue specificity of this ligand-gated ion-channel receptor family.

Costimulatory molecule-deficient dendritic cell progenitors (MHC class II+, CD80dim, CD86-) prolong cardiac allograft survival in nonimmunosuppressed recipients

We have shown previously that granulocyte-macrophage colony-stimulating factor-stimulated mouse bone marrow-derived MHC class II+ dendritic cell (DC) progenitors that are deficient in cell surface expression of the costimulatory molecules B7-1 (CD80) and B7-2 (CD86) can induce alloantigen-specific T-cell anergy in vitro. To test the in vivo relevance of these findings, 2 x 10(6) B10 (H2b) mouse bone marrow-derived DC progenitors (NLDC 145+, MHC class II+, B7-1dim, B7-2-/dim) that induced T-cell hyporesponsiveness in vitro were injected systemically into normal C3H (H2k) recipients. Seven days later, the mice received heterotopic heart transplants from B10 donors. No immunosuppressive treatment was given. Median graft survival time was prolonged significantly from 9.5 to 22 days. Median graft survival time was also increased, although to a lesser extent (16.5 days), in mice that received third-party (BALB/c; H2d) DC progenitors. Ex vivo analysis of host T-cell responses to donor and third-party alloantigens 7 days after the injection of DC progenitors (the time of heart transplant) revealed minimal anti-donor mixed leukocyte reaction and cytotoxic T lymphocyte reactivity. These responses were reduced substantially compared with those of spleen cells from animals pretreated with "mature" granulocyte-macrophage colony-stimulating factor + interleukin-4-stimulated DC (MHC class IIbright, B7-1+, B7-2bright), many of which rejected their heart grafts in an accelerated fashion. Among the injected donor MHC class II+ DC progenitors that migrated to recipient secondary lymphoid tissue were cells that appeared to have up-regulated cell surface B7-1 and B7-2 molecule expression. This observation may explain, at least in part, the temporary or unstable nature of the hyporesponsiveness induced by the DC progenitors in nonimmunosuppressed recipients.

Revealing the maximum strength in nanotwinned copper

The strength of polycrystalline materials increases with decreasing grain size. Below a critical size, smaller grains might lead to softening, as suggested by atomistic simulations. The strongest size should arise at a transition in deformation mechanism from lattice dislocation activities to grain boundary-related processes. We investigated the maximum strength of nanotwinned copper samples with different twin thicknesses. We found that the strength increases with decreasing twin thickness, reaching a maximum at 15 nanometers, followed by a softening at smaller values that is accompanied by enhanced strain hardening and tensile ductility. The strongest twin thickness originates from a transition in the yielding mechanism from the slip transfer across twin boundaries to the activity of preexisting easy dislocation sources.

A cystic fibrosis bronchial epithelial cell line: immortalization by adeno-12-SV40 infection

An immortalized cell line was created from a primary culture of bronchial epithelia isolated from a patient with cystic fibrosis. The culture was transformed with a hybrid virus, adeno-12-SV40, which has been used successfully on a number of different human epithelial tissues. The transformed bronchial epithelial cells have the following characteristics. (1) Cyclic adenosine monophosphate (cAMP) is stimulated by beta-adrenergic agonists. (2) Outwardly rectifying Cl- channels are present on the apical cell membrane. These channels can be activated by depolarizing voltages but not by protein kinase A or C. (3) Keratin is present by immunofluorescence, and this is consistent with the epithelial origin of the cells. (4) The SV40 large T antigen is present as demonstrated by immunofluorescence. (5) Multiple karyotype analyses show modal chromosome number to be 80 to 90. There are an average of four chromosome 7 per cell. (6) The phenylalanine508 deletion in the gene coding for the cystic fibrosis transmembrane regulator is present on at least one chromosome. The cells can be grown in multiple passages, contain the abnormal regulation of the secretory Cl- channel, and should be an appropriate substrate for studies of the mutant cystic fibrosis transmembrane regulatory protein and its interaction with the Cl- channel.

Corneal epithelial wound healing

One of the important functions of the cornea is to maintain normal vision by refracting light onto the lens and retina. This property is dependent in part on the ability of the corneal epithelium to undergo continuous renewal. Epithelial renewal is essential because it enables this tissue to act as a barrier that protects the corneal interior from becoming infected by noxious environmental agents. Furthermore, the smooth optical properties of the corneal epithelial surface are sustained through this renewal process. The rate of renewal is dependent on a highly integrated balance between the processes of corneal epithelial proliferation, differentiation, and cell death. One experimental approach to characterize these three aspects of the renewal process has been to study the kinetics and dynamics of corneal re-epithelialization in a wound-healing model. This effort has employed in vivo and in vitro studies. From such studies it is evident that the appropriate integration and coordination of corneal epithelial proliferation, adhesion, migration, and cell demise is dependent on the actions of a myriad of cytokines. Our goal here is to provide an overview into how these mediators and environmental factors elicit control of cellular proliferation, adhesion, migration, and apoptosis. To this end we review the pertinent literature dealing with the receptor and the cell signaling events that are responsible for mediating cytokine control of corneal epithelial renewal. It is our hope that a better appreciation can be obtained about the complexity of the control processes that are responsible for assuring continuous corneal epithelial renewal in health and disease.

In vitro degradation of thin poly(DL-lactic-co-glycolic acid) films

This study was designed to investigate the in vitro degradation of thin poly(DL-lactic-co-glycolic acid) (PLGA) films for applications in retinal pigment epithelium transplantation and guided tissue regeneration. PLGA films of copolymer ratios of 75:25 and 50:50 were manufactured with thickness levels of 10 microm (thin) and 100 microm (thick). Degradation of the films occurred during sample processing, and thin films with a higher surface area to volume ratio degraded faster. Sample weight loss, molecular weight loss, dimensional, and morphological changes were analyzed over a 10-week period of degradation in 0.2 M of phosphate-buffered saline (PBS), pH 7.4, at 37 degrees C. All PLGA films degraded by heterogeneous bulk degradation. Sample weights remained relatively constant for the first several weeks and then decreased dramatically. The molecular weights of PLGA films decreased immediately upon placement in PBS and continued to decrease throughout the time course. PLGA 50:50 films degraded faster than 75:25 films due to their higher content of hydrophilic glycolic units. The results also demonstrated that thick films degrade faster than corresponding thin films with the same composition. This was attributed to the greater extent of the autocatalytic effect, which further was confirmed by heterogeneous gel permeation chromatograms. These studies suggest that the degradation rate of thin films can be engineered by varying film thicknesses.

Translation initiation control by heme-regulated eukaryotic initiation factor 2alpha kinase in erythroid cells under cytoplasmic stresses

Cytoplasmic stresses, including heat shock, osmotic stress, and oxidative stress, cause rapid inhibition of protein synthesis in cells through phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha) by eIF2alpha kinases. We have investigated the role of heme-regulated inhibitor (HRI), a heme-regulated eIF2alpha kinase, in stress responses of erythroid cells. We have demonstrated that HRI in reticulocytes and fetal liver nucleated erythroid progenitors is activated by oxidative stress induced by arsenite, heat shock, and osmotic stress but not by endoplasmic reticulum stress or nutrient starvation. While autophosphorylation is essential for the activation of HRI, the phosphorylation status of HRI activated by different stresses is different. The contributions of HRI in various stress responses were assessed with the aid of HRI-null reticulocytes and fetal liver erythroid cells. HRI is the only eIF2alpha kinase activated by arsenite in erythroid cells, since HRI-null cells do not induce eIF2alpha phosphorylation upon arsenite treatment. HRI is also the major eIF2alpha kinase responsible for the increased eIF2alpha phosphorylation upon heat shock in erythroid cells. Activation of HRI by these stresses is independent of heme and requires the presence of intact cells. Both hsp90 and hsc70 are necessary for all stress-induced HRI activation. However, reactive oxygen species are involved only in HRI activation by arsenite. Our results provide evidence for a novel function of HRI in stress responses other than heme deficiency.

Mutations in a novel cochlear gene cause DFNA9, a human nonsyndromic deafness with vestibular dysfunction

DFNA9 is an autosomal dominant, nonsyndromic, progressive sensorineural hearing loss with vestibular pathology. Here we report three missense mutations in human COCH (previously described as Coch5b2), a novel cochlear gene, in three unrelated kindreds with DFNA9. All three residues mutated in DFNA9 are conserved in mouse and chicken Coch, and are found in a region containing four conserved cysteines with homology to a domain in factor C, a lipopolysaccharide-binding coagulation factor in Limulus polyphemus. COCH message, found at high levels in human cochlear and vestibular organs, occurs in the chicken inner ear in the regions of the auditory and vestibular nerve fibres, the neural and abneural limbs adjacent to the cochlear sensory epithelium and the stroma of the crista ampullaris of the vestibular labyrinth. These areas correspond to human inner ear structures which show histopathological findings of acidophilic ground substance in DFNA9 patients.

Manufacture of porous biodegradable polymer conduits by an extrusion process for guided tissue regeneration

We have fabricated porous, biodegradable tubular conduits for guided tissue regeneration using a combined solvent casting and extrusion technique. The biodegradable polymers used in this study were poly(DL-lactic-co-glycolic acid) (PLGA) and poly(L-lactic acid) (PLLA). A polymer/salt composite was first prepared by a solvent casting process. After drying, the composite was extruded to form a tubular construct. The salt particles in the construct were then leached out leaving a conduit with an open-pore structure. PLGA was studied as a model polymer to analyze the effects of salt weight fraction, salt particle size, and processing temperature on porosity and pore size of the extruded conduits. The porosity and pore size were found to increase with increasing salt weight fraction. Increasing the salt particle size increased the pore diameter but did not affect the porosity. High extrusion temperatures decreased the pore diameter without altering the porosity. Greater decrease in molecular weight was observed for conduits manufactured at higher temperatures. The mechanical properties of both PLGA and PLLA conduits were tested after degradation in vitro for up to 8 weeks. The modulus and failure strength of PLLA conduits were approximately 10 times higher than those of PLGA conduits. Failure strain was similar for both conduits. After degradation for 8 weeks, the molecular weights of the PLGA and PLLA conduits decreased to 38% and 43% of the initial values, respectively. However, both conduits maintained their shape and did not collapse. The PLGA also remained amorphous throughout the time course, while the crystallinity of PLLA increased from 5.2% to 11.5%. The potential of seeding the conduits with cells for transplantation or with biodegradable polymer microparticles for drug delivery was also tested with dyed microspheres. These porous tubular structures hold great promise for the regeneration of tissues which require tubular scaffolds such as peripheral nerve, long bone, intestine, or blood vessel.

Cl- channels in CF: lack of activation by protein kinase C and cAMP-dependent protein kinase

Secretory chloride channels can be activated by adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase in normal airway epithelial cells but not in cells from individuals with cystic fibrosis (CF). In excised, inside-out patches of apical membrane of normal human airway cells and airway cells from three patients with CF, the chloride channels exhibited a characteristic outwardly rectifying current-voltage relation and depolarization-induced activation. Channels from normal tissues were activated by both cAMP-dependent protein kinase and protein kinase C. However, chloride channels from CF patients could not be activated by either kinase. Thus, gating of normal epithelial chloride channels is regulated by both cAMP-dependent protein kinase and protein kinase C, and regulation by both kinases is defective in CF.

Bone marrow-derived dendritic cell progenitors (NLDC 145+, MHC class II+, B7-1dim, B7-2-) induce alloantigen-specific hyporesponsiveness in murine T lymphocytes

The functional maturation of dendritic cells (DC) and other antigen-presenting cells is believed to reflect the upregulation of cell surface major histocompatibility complex (MHC) class II and other T cell co-stimulatory molecules, especially the CD28 ligands B7-1 (CD80) and B7-2 (CD86). In this study, we propagated cells exhibiting characteristics of DC precursors from the bone marrow (BM) of B10 mice (H-2b; I-A+) in response to granulocyte-macrophage colony stimulating factor (GM-CSF). The methods used were similar to those employed previously to propagate DC progenitors from normal mouse liver. Cells expressing DC lineage markers (NLDC 145+, 33D1+, N418+) harvested from 8-10-day GM-CSF stimulated BM cell cultures were CD45+, heat-stable antigen+, CD54+, CD44+, MHC class II+, B7-1dim but B7-2- (costimulatory molecule-deficient). Supplementation of cultures with interleukin-4 (IL-4) in addition to GM-CSF however, resulted in marked upregulation of MHC class II and B7-2 expression. These latter cells exhibited potent allostimulatory activity in primary mixed leukocyte cultures. In contrast, the cells stimulated with GM-CSF alone were relatively weak stimulators and induced alloantigen-specific hyporesponsiveness in allogeneic T cells (C3H; H-2k; I-E+) detected upon restimulation in secondary MLR. This was associated with blockade of IL-2 production. Reactivity to third-party stimulators was intact. The hyporesponsiveness induced by the GM-CSF stimulated, costimulatory molecule-deficient cells was prevented by incorporation of anti-CD28 monoclonal antibody in the primary MLR and was reversed by addition of IL-2 to restimulated T cells. The findings show that MHC class II+ B7-2- cells with a DC precursor phenotype can induce alloantigen-specific hyporesponsiveness in vitro. Under the appropriate conditions, such costimulatory molecule-deficient cells could contribute to the induction of donor-specific unresponsiveness in vivo.

Hemokinin is a hematopoietic-specific tachykinin that regulates B lymphopoiesis

We report here the molecular cloning of a newly identified preprotachykinin gene, Pptc, which specifies the sequence for a new preprotachykinin protein and bioactive peptide designated hemokinin 1 (HK-1). PPT-C mRNA was detected primarily in hematopoietic cells in contrast to the previously described Ppta and Pptb genes, which are predominantly expressed in neuronal tissues. HK-1 has several biological activities that are similar to the most studied tachykinin, substance P, such as induction of plasma extravasation and mast cell degranulation. However, HK-1 also has properties that are indicative of a critical role in mouse B cell development. HK-1 stimulated the proliferation of interleukin 7-expanded B cell precursors, whereas substance P had no effect. HK-1, but not substance P, promoted the survival of freshly isolated bone marrow B lineage cells or cultured, lipopolysaccharide-stimulated pre-B cells. N-acetyl-L-trytophan-3,5-bistrifluromethyl benzyl ester, a tachykinin receptor antagonist, increased apoptosis of these cells and in vivo administration of this antagonist led to specific reductions of the B220lowCD43 population (the pre-B cell compartment) in the bone marrow and the IgMhighIgDlow population (the newly generated B cells) in the spleen. Thus, HK-1 may be an autocrine factor that is important for the survival of B cell precursors at a critical phase of development.

In vivo evaluation of poly(L-lactic acid) porous conduits for peripheral nerve regeneration

The present study provides in vivo trials of poly(L-lactic acid) (PLLA) as a porous biodegradable nerve conduit using a 10 mm sciatic nerve defect model in rats. The PLLA conduits, fabricated by an extrusion technique, had an inner diameter of 1.6 mm, an outer diameter of 3.2 mm, and a length of 12 mm. They were highly porous with an interconnected pore structure (of 83.5% porosity and 12.1 microm mean pore size). The conduits were interposed into the right sciatic nerve defect of Sprague Dawley rats using microsurgical techniques; nerve isografts served as controls. Walking track analysis was performed after conduit placement monthly through 16 weeks. At the conclusion of 6 and 16 weeks, sections from the isograft/conduit and distal nerve were harvested for histomorphometric analysis. The right gastrocnemius muscle was also harvested and its weight was determined. All conduits remained intact without breakage. Moreover, no conduit elongated during the 16 weeks of placement. Walking track analysis and gastrocnemius muscle weight demonstrated increasing regeneration over the 16 weeks in both the conduit and isograft control groups, with control values significantly greater. The nerve fiber density in the distal sciatic nerve for the PLLA conduits (0.16+/-0.07) was similar to that for the control isografts (0.19+/-0.05) at 16 weeks. The number of axons/mm2 in the distal sciatic nerve for the PLLA conduits was lower than that for the isografts (13 800+/-2500 vs. 10700+/-4700) at 16 weeks. The results for PLLA were significantly improved over those for 75:25 poly(DL-lactic-co-glycolic acid) of a previous study and suggest that PLLA porous conduits may serve as a scaffold for peripheral nerve regeneration.

Gate-voltage control of chemical potential and weak antilocalization in Bi₂Se₃

We report that Bi₂Se₃ thin films can be epitaxially grown on SrTiO₃ substrates, which allow for very large tunablity in carrier density with a back gate. The observed low field magnetoconductivity due to weak antilocalization (WAL) has a very weak gate-voltage dependence unless the electron density is reduced to very low values. Such a transition in WAL is correlated with unusual changes in longitudinal and Hall resistivities. Our results suggest a much suppressed bulk conductivity at large negative gate voltages and a possible role of surface states in the WAL phenomena.

Propagation of dendritic cell progenitors from normal mouse liver using granulocyte/macrophage colony-stimulating factor and their maturational development in the presence of type-1 collagen

Within 1 wk of liquid culture in granulocyte/macrophage colony-stimulating factor (GM-CSF), normal B10 BR (H-2k I-E+) mouse liver nonparenchymal cells (NPC) formed loosely adherent myeloid cell clusters that have been shown to contain dendritic cell (DC) progenitors in similar studies of mouse blood or bone marrow. Mononuclear cell progeny released from these clusters at and beyond 4 d exhibited distinct dendritic morphology and were actively phagocytic. After 6-10 d of culture, these cells strongly expressed CD45, CD11b, heat stable antigen, and CD44. However, the intensity of expression of the DC-restricted markers NLDC 145, 33D1, and N418, and the macrophage marker F4/80, intercellular adhesion molecule 1, and Fc gamma RII was low to moderate, whereas the cells were negative for CD3, CD45RA, and NK1.1. Splenocytes prepared in the same way also had a similar range and intensity of expression of these immunophenotypic markers. Unlike the splenic DC, however, most of the GM-CSF-propagated putative liver DC harvested at 6-10 d expressed only a low level of major histocompatibility complex (MHC) class II (I-Ek), and they failed to induce primary allogeneic responses in naive T cells, even when propagated additionally in GM-CSF and tumor necrosis alpha and/or interferon gamma-supplemented medium. However, when 7-d cultured GM-CSF-stimulated liver cells were maintained additionally for three or more days on type-1 collagen-coated plates in the continued presence of GM-CSF, they exhibited characteristics of mature DC: MHC class II expression was markedly upregulated, mixed leukocyte reaction stimulatory activity was increased, and phagocytic function was decreased. Similar observations were made when Ia+ cells were depleted from the GM-CSF-propagated cells before exposure to collagen. Further evidence that the GM-CSF-stimulated class IIdim or class II-depleted hepatic NPC were immature DC was obtained by injecting them into allogeneic B10 (H-2b I-E-) recipients. They "homed" to T cell-dependent areas of lymph nodes and spleen where they strongly expressed donor MHC class II antigen 1-5 d later. These observations provide insight into the regulation of DC maturation, and are congruent with the possibility that the migration of immature DC from normal liver and perhaps other organ allografts may help explain their inherent tolerogenicity.