Tau oligomerization: a role for tau aggregation intermediates linked to neurodegeneration

Intracellular accumulation of filamentous tau proteins is a defining feature of neurodegenerative diseases, including Alzheimer's disease, progressive supranuclear palsy, corticobasal degeneration, Pick's disease, and frontotemporal dementia with Parkinsonism linked to chromosome 17, all known collectively as tauopathies. Tau protein is a member of microtubule (MT)-associated proteins. Tau is a highly soluble and natively unfolded protein dominated by a random coil structure in solution. It is believed that aberrant modifications of tau, including phosphorylation, truncation, and conformational changes, induce filamentous aggregation. However, the mechanism underlying the conversion of tau protein from a soluble state to one of insoluble aggregates still remains elusive. The importance of tau aggregation intermediates (e.g. tau dimer, tau multimer, and granular tau oligomer) in disease pathogenesis was suggested by recent studies. Here, we review the latest developments in tracking the structural changes of tau protein and discuss the utility improving our understanding of tau aggregation pathway leading to human tauopathies.

Multifocal granulomatous hepatitis caused by Actinobacillus pleuropneumoniae serotype 2 in slaughter pigs

In a survey of 66 894 slaughter pigs, 11 animals from three farms were found to have multifocal granulomatous lesions in the liver, caused by Actinobacillus pleuropneumoniae serotype 2. The lesions consisted of epithelioid cells and multinucleated giant cells, with asteroid bodies and discernible gram-negative bacteria. Lymph nodes and spleen were occasionally affected. The results suggested that haematogenous spread had occurred from pre-existing pulmonary infections.

Complementary Distributions of Amyloid-β and Neprilysin in the Brains of Dogs and Cats

Neprilysin is an amyloid-β-degrading enzyme localized in the brain parenchyma. The involvement of neprilysin in the pathogenesis of Alzheimer's disease has recently received much attention. We examined the localization of neprilysin and amyloid-β, as well as the activity of neprilysin, in the brains of dogs and cats of various ages to clarify the relationship between neprilysin activity and amyloid-β deposition. The distribution of neprilysin was almost identical in dogs and cats, being high in the striatum, globus pallidus, and substantia nigra, but very low in the cerebral cortex. The white matter and hippocampus were negative. Neprilysin activity in the brain regions in dogs and cats was ranked from high to low as follows: thalamus/striatum > cerebral cortex > hippocampus > white matter. Amyloid-β deposition was first detected at 7 and 10 years of age in dogs and cats, respectively, and both the quantity and frequency of deposition increased with age. In both species, amyloid-β deposition appeared in the cerebral cortex and the hippocampus. In summary, the localization of neprilysin and neprilysin activity, and that of amyloid-β, were complementary in the brains of dogs and cats.

Chemosensitivity of patients with recurrent esophageal cancer receiving perioperative chemotherapy

Perioperative chemotherapy (CT) and chemoradiotherapy are widely used for advanced esophageal cancer. We evaluated the chemosensitivity of patients displaying recurrent esophageal cancer after esophagectomy with perioperative CT. From the database at National Cancer Center Hospital in Tokyo, we extracted recurrent esophageal cancer cases after perioperative CT and evaluated the effectiveness of the first CT against the recurrent disease according to the duration between termination of the original perioperative CT and recurrence with treatment-free intervals (TFIs) <or=6 and >6 months. Systemic CT for their recurrent disease was performed for 30 esophageal cancer patients after perioperative CT. All patients received 5-fluorouracil and cisplatin as perioperative CT, with relapses occurring at TFIs <or=6 months in 11 patients (eight received platinum-containing regimens and three received docetaxel for their recurrent disease) and >6 months in 19 patients (all received platinum-containing regimens). The response rate of patients experiencing a recurrence at TFIs <or=6 and >6 months was 0 and 37% (P = 0.029), the median progression-free survival was 2.8 and 4.8 months (log-rank P = 0.001) and the median overall survival was 6.1 and 10.2 months (log-rank P = 0.012), respectively. Recurrence at the TFI <or=6 months could represent resistance to CT, so regimens may need to be altered depending on a patient's specific TFI.

Establishment of fibroblast cultures

Fibroblasts are fairly easily isolated from a variety of tissues, in this case skin. The cells are fast growing and can be rapidly expanded from small samples. They are suitable for behavioral, functional, biochemical, and genomic studies. Skin fibroblast cultures are started from explants in which the epidermis is enzymatically removed to prevent contamination of the fibroblasts with epidermal cells. Alternatively, the dermis can be enzymatically dissociated to provide a suspension of fibroblasts.

Molecular chaperone-mediated tau protein metabolism counteracts the formation of granular tau oligomers in human brain

Intracellular accumulation of filamentous tau proteins is a defining feature of neurodegenerative diseases termed tauopathies. The pathogenesis of tauopathies remains largely unknown. Molecular chaperones such as heat shock proteins (HSPs), however, have been implicated in tauopathies as well as in other neurodegenerative diseases characterized by the accumulation of insoluble protein aggregates. To search for in vivo evidence of chaperone-related tau protein metabolism, we analyzed human brains with varying degrees of neurofibrillary tangle (NFT) pathology, as defined by Braak NFT staging. Quantitative analysis of soluble protein levels revealed significant positive correlations between tau and Hsp90, Hsp40, Hsp27, alpha-crystallin, and CHIP. An inverse correlation was observed between the levels of HSPs in each specimen and the levels of granular tau oligomers, the latter of which were isolated from brain as intermediates of tau filaments. We speculate that HSPs function as regulators of soluble tau protein levels, and, once the capacity of this chaperone system is saturated, granular tau oligomers form virtually unabated. This is expressed pathologically as an early sign of NFT formation. The molecular basis of chaperone-mediated protection against neurodegeneration might lead to the development of therapeutics for tauopathies. (c) 2007 Wiley-Liss, Inc.

Granulomatous Lymphadenitis and Pneumonia Associated with Actinobacillus porcitonsillarum in a Slaughter Pig

Multiple coalescing granulomatous foci were detected in the pulmonary hilar and mediastinal lymph nodes and lung of a slaughtered pig aged 6 months. Haemolytic, Gram-negative bacilli were isolated from the lymph nodes. The isolate (strain TO17214) strongly cross-reacted with sera against Actinobacillus pleuropneumoniae serotype 12 in slide agglutination tests. Comparative 16S rDNA gene sequencing analysis identified strain TO17214 as Actinobacillus porcitonsillarum. Histologically, extensive inflammation took the form of large granulomas consisting of epithelioid cells and multinucleated giant cells in the lymph nodes and lung, and Gram-negative bacilli were discernible in the centres of the lesions. Immunohistochemically, the organisms cross-reacted with polyclonal antibodies against A. pleuropneumoniae serotypes 12 and 2. The results indicated that A. porcitonsillarum, previously considered non-pathogenic, can induce multifocal granulomatous lymphadenitis accompanied by pneumonia in the growing-finishing pig.

Relationship of insulin-like growth factor-1 receptor and epidermal growth factor receptor expression to clinical outcomes in patients with colorectal cancer

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Background: Insulin-like growth factor-1 receptor (IGF-1R), epidermal growth factor receptor (EGFR), and HER2 have been reported to regulate tumor growth by interfering with apoptosis, cell proliferation, angiogenesis, and metastasis. However, the clinical significance of these molecules in colorectal cancer (CRC) remains undetermined. To gain further insight, we evaluated the prognostic implications of these biomarkers in patients with CRC treated with fluoropyrimidines or irinotecan. Methods: The study group comprised 91 patients who underwent surgery at National Cancer Center Hospital and subsequently received fluoropyrimidines as 1st-line chemotherapy for recurrent or residual tumors. The expressions of IGF-1R, EGFR, and HER2 in surgically removed specimens of primary lesions were analyzed immunohistochemically to determine the prognostic significance of these biomarkers. Results: IGF-1R expression (defined as >10% membranous staining) was found in 81 tumors (89%), EGFR in 77 (85%), and HER2 in 3 (3%). IGF-1R expression significantly correlated with EGFR expression (P=0.038). Overexpression (defined as >50% membranous staining) of IGF-1R was found in 48 tumors (53%), EGFR in 57 (63%), and HER2 in 2 (2%). Overexpression of IGF-1R significantly correlated with shorter survival from the start of 1st-line chemotherapy (P=0.032). Overexpression of EGFR was a significant predictive factor for a clinical response to fluoropyrimidines (P=0.037) and tended to correlate with TTP in patients given irinotecan as 2nd-line therapy (P=0.087). A multivariate analysis of potential prognostic factors showed that IGF-1R expression and worse performance status were independent predictors of poor outcomes ( Table ). Conclusions: IGF-1R and EGFR were highly positive in patients with CRC. Overexpression of IGF-1R predicts a poor outcome, and overexpression of EGFR predicts a good clinical response to fluoropyrimidines.

[Table: see text]

No significant financial relationships to disclose.

Declarative memory consolidation in humans: a prospective functional magnetic resonance imaging study

Retrieval of recently acquired declarative memories depends on the hippocampus, but with time, retrieval is increasingly sustainable by neocortical representations alone. This process has been conceptualized as system-level consolidation. Using functional magnetic resonance imaging, we assessed over the course of three months how consolidation affects the neural correlates of memory retrieval. The duration of slow-wave sleep during a nap/rest period after the initial study session and before the first scan session on day 1 correlated positively with recognition memory performance for items studied before the nap and negatively with hippocampal activity associated with correct confident recognition. Over the course of the entire study, hippocampal activity for correct confident recognition continued to decrease, whereas activity in a ventral medial prefrontal region increased. These findings, together with data obtained in rodents, may prompt a revision of classical consolidation theory, incorporating a transfer of putative linking nodes from hippocampal to prelimbic prefrontal areas.

Successful declarative memory formation is associated with ongoing activity during encoding in a distributed neocortical network related to working memory: a magnetoencephalography study

The aim of the present study was to investigate the spatio-temporal characteristics of the neural correlates of declarative memory formation as assessed by the subsequent memory effect, i.e. the difference in encoding activity between subsequently remembered and subsequently forgotten items. Different operations could account for these effects. In particular, it has been proposed that successful memory formation depends on the organization of the information at the time of encoding, an operation accomplished by the working memory system. Consequently, functional magnetic resonance imaging studies have already shown that the very same regions that are involved in certain working memory processes are also involved in declarative memory formation. Here, we used magnetoencephalography to investigate whether the subsequent memory effects in these regions are present throughout picture stimulus presentation, postulating ongoing working memory operations as an effective factor. The results showed that subsequent memory effects began to appear after about 300 ms post stimulus onset over bilateral temporal areas and left parietal regions and were sustained throughout the recording epoch (1000 ms). Roughly parallel to these effects, we identified a left frontal subsequent memory effect, which, however, was less sustained than the other effects. In addition, we revealed a late subsequent memory effect over the right occipital region, which has not been described previously in the event-related potential literature. These sustained subsequent memory effects are suggestive of working memory processes that may enable deep semantic and perceptual processing. Additionally, contextually constrained visual perception after top-down modulation may account for a more efficient encoding of the complex scene.

Lithium inhibits amyloid secretion in COS7 cells transfected with amyloid precursor protein C100

To examine the regulation of amyloid secretion in more detail, Abeta sandwich ELISAs with high sensitivity and specificity were developed. Using this technique, we measured Abeta secreted from COS7 cells transiently transfected with APP C100 in the presence of LiCl, a potent glycogen synthase kinase (GSK)-3beta inhibitor. We found that both Abetax-40 and Abetax-42 secretion were reduced by LiCl treatment in a dose-dependent manner. Diminished amyloid secretion was associated with GSK-3beta activity. These results suggest that GSK-3beta might function as a possible mediator for regulating both amyloid deposition and tau pathology in Alzheimer's disease (AD), and that lithium should be re-evaluated as a candidate reagent for preventing AD pathology.

Age-related changes in the localization of presenilin-1 in cynomolgus monkey brain

Age-related changes in PS-1 localization were examined in the brains of 22 cynomolgus monkeys ranging in age from embryonic day 87 to 35 years. In embryonic monkey brains, anti-PS-1 antibody N12, which recognizes the PS-1 N-terminal fragment (Ntf) and holo protein, stained immature neuronal cells. In juvenile monkeys, N12 stained large pyramidal neurons, cerebral neocortical neurons, and cerebellar Purkinje's cells. Cytoplasmic staining of these cells was granular in appearance. In aged monkeys, N12 stained neurons in all layers of the neocortex. In contrast, regardless of the age of the animals examined, M5, an anti-PS-1 antibody that specifically recognizes only the PS-1 C-terminal fragment (Ctf), stained neurons in all layers of the neocortex and neurons in the cerebellum. M5 also stained neuropil and white matter, and in aged monkeys, M5 stained swollen neurites of mature senile plaques. Age-related changes in PS-1 expression were further examined using Western blot analysis of mitochondrial, myelin, microsomal, nuclear, synaptosomal, and cytosol fractions isolated from 10 monkey brains ranging in age from embryonic day 87 to 32 years. In all brains, Ntf and Ctf were expressed most abundantly in the microsome fraction. The amount of PS-1 in the nuclear fraction dramatically increased with age. We conclude that the transport of PS-1 diminished with age and that PS-1 fragments accumulated in endoplasmic reticulum (ER) associated with the nuclear membrane.

Formation of filamentous tau aggregations in transgenic mice expressing V337M human tau

Formation of neurofibrillary tangles (NFTs) is the most common feature in several neurodegenerative diseases, including Alzheimer's disease (AD). Here we report the formation of filamentous tau aggregations having a beta-sheet structure in transgenic mice expressing mutant human tau. These mice contain a tau gene with a mutation of the frontotemporal dementia parkinsonism (FTDP-17) type, in which valine is substituted with methionine residue 337. The aggregation of tau in these transgenic mice satisfies all histological criteria used to identify NFTs common to human neurodegenerative diseases. These mice, therefore, provide a preclinical model for the testing of therapeutic drugs for the treatment of neurodegenerative disorders that exhibit NFTs.

Immunosuppressive properties of CD95L-transduced "killer" hybrids created by fusing donor- and recipient-derived dendritic cells

Allogeneic immune responses, which are initiated by dendritic cells (DCs) of both donor and host origins, remain a major obstacle in organ transplantation. Presentation of intact major histocompatibility complex (MHC) molecules by allogeneic DCs and allogeneic peptides by syngeneic DCs leads to complex allogeneic immune responses. This study reports a novel strategy designed to suppress both pathways. A stable DC line XS106 (A/J mouse origin) was transfected with CD95L cDNA and fused with splenic DCs purified from allogeneic BALB/c mice. The resulting "killer" DC-DC hybrids: (1) expressed CD95L and MHC class I and class II molecules of both A/J and BALB/c origins, while maintaining otherwise characteristic surface phenotypes of mature DCs; (2) inhibited MHC class I- and class II-restricted mixed leukocyte reactions between the parental strains by triggering apoptosis of alloreactive T cells; and (3) abolished delayed-type hypersensitivity responses of A/J (and BALB/c) mice to BALB/c-associated (and A/J-associated) alloantigens when injected intravenously into A/J (and BALB/c) mice. The onset of graft-versus-host disease in (BALB/c x A/J) F1 hosts receiving A/J-derived hematopoietic cell transplantation was suppressed significantly (P <.001) by killer DC-DC hybrid treatment. These results form both technical and conceptual frameworks for clinical applications of CD95L-transduced killer hybrids created between donor DCs and recipient DCs in the prevention of allogeneic immune responses following organ transplantation.

The event-related potentials elicited by content and function words during the reading of sentences by patients with schizophrenia

Thought disorder is one of the main symptoms observed in schizophrenia and has been investigated in terms of language dysfunction. The purpose of the present study was to find whether there were any differences in identifying and processing between content (semantic) and function (syntax) words, and to elucidate whether semantic or syntax is more impaired for the schizophrenics. Event-related potentials were recorded in 13 patients with schizophrenia and 14 healthy controls, while they silently read three sets of passages. Event-related potentials were recorded for content words (noun, verb) and function words (auxiliary verb, particle) separately. For the healthy control group, the mean amplitude of P200 for the content word class was greater than for the function word class with fronto-central dominance. In contrast, no such difference was found for the schizophrenics mainly due to the reduction of P200 amplitude of the content words. Larger P200 for the content than the function word class suggests that greater resources were used to identify the content words. Lack of this difference found in patients with schizophrenia suggested that the disturbances in the semantics may be more attributable to the linguistic impairment than those in the syntax.

[Analysis of mouse model exhibiting neurofibrillary changes]

Dysfunction and filamentous microtubule-binding tau protein are key markers of neurodegenerative pathologies, including the pathology and neural degeneration associated with Alzheimer's disease (AD). Immunocytochemical studies of NFT-bearing neurons showed that NFTs are composed of ubiquitin and phosphorylation-dependent tau. Congo-red birefringency and thioflavin-S reactivity in NFT-bearing neurons also demonstrated that the tau aggregation forms a beta-sheet structure. Discovery of the molecular mechanisms of NFT formation may lead to more insight about events occurring during neurodegeneration. In frontotemporal dementia parkinsonism 17 (FTDP17), genetic studies indicated that tau is a causative gene, and mutation is found in exons and introns of tau gene. A patient who possesses this mutation exhibits pathologically NFT and clinically personality change and cognitive dysfunction. Then, we produced the Tg mice expressing human longest tau with missense mutation V337M. In the present study, neurons of hippocampus and cerebral cortex in our Tg mice showed phosphorylated and ubiquitinated tau aggregations with a beta-sheet structure. This was demonstrated by Congo-red and thioflavin-S positive staining, a histological criterion used to identify NFTs observed in neurodegenerative disorders. The mice also displayed altered behaviors that were associated with NFT formation. Thus, V337M mice provide a first animal model exhibiting altered behavior due to NFTs.

Development of a Langerhans cell-targeted gene therapy format using a dendritic cell-specific promoter

Langerhans cells (LC), which are a skin-specific member of the dendritic cell (DC) family of antigen presenting cells, play critical roles in the initiation of cellular immune responses in the skin. We developed a LC-targeted gene therapy format in this study, aimed at the establishment of in situ protocols for genetic manipulation of LC function. Dectin-2 is a unique C-type lectin that is expressed selectively by DC, including epidermal LC. A 3.2 kb 5' flanking fragment isolated from the mouse dectin-2 gene, termed the dectin-2 promoter (pDec2), exhibited significant transcriptional activities in epidermal-derived DC lines of the XS series, but not in any of the tested non-DC lines. When pDec2-driven luciferase gene (pDec2-Luc) or enhanced green fluorescence protein gene (pDec2-EGFP) was delivered to mouse skin using the gene gun, expression of the corresponding gene product was observed in the epidermal compartment almost exclusively by the IA+ population (ie LC). LC in the gene gun-treated sites showed features of mature DC and they migrated to the draining lymph node, suggesting that LC-targeted gene expression may lead to the development of immune responses. In fact, EGFP-specific cellular immune responses became detectable after gene gun-mediated delivery of pDec2-EGFP plasmid. These results introduce a new concept that LC function can be genetically manipulated in situ by the combination of gene gun-mediated DNA delivery and a DC-specific promoter.

Recent advances in dendritic cell vaccines for cancer treatment

Dendritic cells (DC) are special subsets of antigen presenting cells characterized by their unique abilities to efficiently take up, process, and present various forms of antigens to immunologically naive T cells. Recent advances in the understanding of molecular mechanisms regulating the functions of DC have allowed the investigators to "design" innovative DC-based vaccine formats for the treatment of cancer patients. In this article, we will review the most advanced DC vaccine strategies, focusing on three major areas: a) new ex vivo protocols for DC loading with tumor-associated antigens (TAA), b) genetic approaches to load skin-resident Langerhans cells (LC) with TAA, and c) chemokine-mediated LC entrapment and in situ loading of LC with TAA at the entrapment sites. We believe that these new classes of DC vaccine strategies will soon become applicable to the treatment of patients with malignant tumors.

A new galloylglucoside from Cleyera ochnacea DC

A new galloylglucoside, 3-hydroxy-5-methylphenol 1-O-beta-D-(6'-galloyl)glucopyranoside (1) was isolated from Cleyera ochnacea DC. (Theaceae). Its structure was elucidated on the basis of chemical and spectral analysis. Compound 1 showed inhibitory activity against rat cerebellar nitric oxide synthase (NOS).

Presenilin 1 regulates beta-catenin-mediated transcription in a glycogen synthase kinase-3-independent fashion

Presenilin 1 (PS1) is linked with Alzheimer's disease but exhibits functional roles regulating growth and development. For instance, PS1 binds to beta-catenin and modulates beta-catenin signaling. In the current study, we observed that knockout of PS1 inhibited beta-catenin-mediated transcription by 35%, as shown by a luciferase reporter driven by the hTcf-4 promoter. Overexpressing wild-type PS1 increased beta-catenin-mediated transcription by 37.5%, and overexpressing PS1 with mutations associated with Alzheimer's disease decreased beta-catenin-mediated transcription by 66%. To examine whether regulation of beta-catenin by PS1 requires phosphorylation by glycogen synthase kinase 3beta (GSK 3beta), we examined whether inhibiting GSK 3beta activity overcomes the inhibition of beta-catenin transcription induced by mutant PS1 constructs. Cells expressing wild-type or mutant PS1 were treated with LiCl, which inhibits GSK 3beta, or transfected with beta-catenin constructs that lack the GSK 3beta phosphorylation sites. Neither treatment overcame PS1-mediated inhibition of beta-catenin signaling, suggesting that regulation of beta-catenin by PS1 was not affected by the activity of GSK 3beta. To investigate how PS1 might regulate beta-catenin signaling, we determined whether PS1 interacts with other elements of the beta-catenin signaling cascade, such as the Tcf-4 transcription factor. Coimmunoprecipitation studies showed binding of PS1 and hTcf-4, and examining nuclear isolates indicated that nuclear hTcf-4 was decreased in cells expressing mutant PS1. These data show that PS1 interacts with multiple components of the beta-catenin signaling cascade and suggest that PS1 regulates beta-catenin in a manner independent of GSK 3beta activity.

Novel neuronal nitric oxide synthase (nNOS) selective inhibitor, aplysinopsin-type indole alkaloid, from marine sponge Hyrtios erecta

Two novel aplysinopsin-type indole alkaloids, 1 and 2, and three known indole alkaloids were isolated from the marine sponge Hyrtios erecta. These compounds exhibited selective inhibitory activity against the neuronal isozyme of nitric oxide synthase (nNOS). Furthermore, new quinolone 7 was also isolated from the same marine sponge. The chemical structures of these new compounds were elucidated on the basis of spectroscopic analysis.

Regulation by two CatR proteins that differ in binding affinity to catB promoters expressing two cat gene clusters

We isolated the two LysR-type regulatory proteins CatR1 and CatR2, which regulate the expression of cat1 and cat2 gene clusters, respectively, required for catechol degradation in the bacterium Frateuria sp. ANA-18. In a gel mobility shift assay using CatR1 and the DNA fragment containing the catB1 promoter region, the formation of two complexes, complex 1-1 (C1-1) and complex 1-2 (C1-2), was observed in the presence of cis,cis-muconate. On the other hand, CatR2 and the DNA fragment containing the catB2 promoter region formed only complex 2-2 (C2-2) at a lower concentration of cis,cis-muconate than that at which C1-1 and C1-2 were formed. As the concentration of cis,cis-muconate decreased, the production of the muconate cycloisomerase isozyme MC II encoded by catB2 decreased as well as that of MC I encoded by catB1. However, the amount of MC II synthesized was larger than that of MC I at low concentrations. On the basis of these results, we concluded that the catB2 promoter was activated at low concentrations of cis,cis-muconate.

New insights on how metals disrupt amyloid beta-aggregation and their effects on amyloid-beta cytotoxicity

Amyloid-beta protein (A beta) aggregates in the brain to form senile plaques. By using thioflavin T, a dye that specifically binds to fibrillar structures, we found that metals such as Zn(II) and Cu(II) normally inhibit amyloid beta-aggregation. Another method for detecting A beta, which does not distinguish the types of aggregates, showed that these metals induce a non-beta-sheeted aggregation, as reported previously. Secondary structural analysis and microscopic studies revealed that metals induced A beta to make non-fibrillar aggregates by disrupting beta-sheet formation. These non-fibrillar A beta aggregates displayed much weaker Congo Red birefringence, and in separate cell culture experiments, were less toxic than self beta-aggregates, as demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. The toxicity of soluble A beta was enhanced in the presence of Cu(II), which suggests the previously hypothesized role of A beta in generating oxidative stress. Finally, under an acidic condition, similar to that in the inflammation associated with senile plaques, beta-aggregation was robustly facilitated at one specific concentration of Zn(II) in the presence of heparin. However, because a higher concentration of Zn(II) virtually abolished this abnormal phenomenon, and at normal pH any concentrations strongly inhibit beta-aggregation and its associated cytotoxicity, including its anti-oxidative nature we suggest that Zn(II) has an overall protective effect against beta-amyloid toxicity.

Identification of a human homologue of the dendritic cell-associated C-type lectin-1, dectin-1

Previously we identified the novel type II lectin receptor, dectin-1, that is expressed preferentially by murine antigen presenting dendritic cells (DC) and is involved in co-stimulation of T cells by DC. To identify the human homologue (DECTIN-1), we employed degenerative PCR amplification of mRNA isolated from DC and subsequent cDNA cloning. DECTIN-1 is a type II lectin receptor with high homology to type II lectin receptors expressed by natural killer (NK) cells. It contains an immunoreceptor tyrosine-based activation motif within the cytoplasmic domain. Human DECTIN-1 mRNA is expressed predominantly by peripheral blood leukocytes and preferentially by DC. The mRNA likely encodes a 33 kDa glycoprotein. In human epidermis, the protein is expressed selectively by Langerhans cells, which are an epidermal subset of DC. A truncated form of DECTIN-1 RNA (termed T beta) encodes for a polypeptide lacking almost the entire neck domain, which is required for accessibility of the carbohydrate recognition domain to ligands. Genome analysis showed the deleted amino acid sequence in T beta to be encoded by an exon, indicating that T beta RNA is produced by alternative splicing. DECTIN-1 gene maps to chromosome 12, between p13.2 and p12.3, close to the NK gene complex (12p13.1 to p13.2) which contains genes for NK lectin receptors. Our results indicate that human DECTIN-1 shares many features with mouse dectin-1, including the generation of neck domain-lacking isoforms, which may down-regulate the co-stimulatory function of dectin-1.

Involvement of cyclin dependent kinase5 activator p25 on tau phosphorylation in mouse brain

P35 or its truncated fragment p25 is required for cyclin dependent kinase (Cdk)5 activation. It has been reported that p25 is accumulated in the brain of Alzheimer's disease (AD) patients and that p25/Cdk5 induces high phosphorylation of tau and apoptosis in cultured neurons (Nature 402 (1999) 615). Our investigation of AD brain did not show specific accumulation of p25. Exposure to Ca ionophore (A23187) at 10(-6) M induced p25 accumulation in rat primary hippocampal neurons, causing neuronal death without showing hyperphosphorylation of tau. Transgenic mice expressing p25 showed the accumulation of p25 but neither hyperphosphorylation of tau nor neuronal death was shown in these mice. The feature of these mice was the progression of cell growth in pituitary gland. These results suggest that overexpression of p25 lead to the activation of cell cycle but not to the direct phosphorylation of tau.

GATA DNA-binding protein expressed in mouse I-10 Leydig testicular tumor cells

A nuclear extract of the mouse I-10 Leydig tumor cell line was analyzed by gel mobility shift assay with a combination of antibodies for various mammalian GATA proteins. Antibodies for GATA-4 caused a super-shift of the DNA-protein complex, which is formed through GATA-4 binding to an oligonucleotide with a typical GATA motif, while ones for GATA-1, GATA-2, GATA-3, and GATA-6 did not. These results indicated that I-10 cells express GATA-4 protein. Western blotting analysis of cellular proteins also demonstrated the presence of GATA-4 protein, the size of which corresponds to that of the rat orthologous protein transiently expressed in Cos-1 cells. A significant level of GATA-4 expression in I-10 cells would be advantageous for studying the roles of this protein, especially in view of gonadal function. We further examined the binding site preference of GATA-4 expressed in I-10 cells. GATA-4 showed broad sequence specificity similar to GATA-6, the order of binding core site preference being GATA > GATT > GATC, and adenine was favored on both sides of the core for strong binding. Thus the conserved zinc finger domain of GATA proteins is suggested to contribute to the binding sequence preference. GATA-4 expressed in I-10 cells was not susceptible to proteolysis coupled with cAMP signaling.

Induction of hepatocellular carcinoma with high metastatic potential in WS/Shi rats: discovery of an inbred strain highly susceptible to the liver carcinogen N-nitrosomorpholine

We investigated the susceptibility of three inbred strains of rats to the hepatocarcinogen, N-nitrosomorpholine (NNM), to establish a spontaneous metastatic model of hepatocellular carcinoma (HCC). WS/Shi. SD/gShi, and F344/DuCrj rats were given 0.02% NNM in drinking water for 8 weeks and thereafter left without any treatment. The experiment ceased at week 20, because mortality markedly increased after this time point in WS/Shi rats. Liver weight was highest in WS/Shi rats among the three strains examined. The incidence of HCC was 15/15 (100%) in WS/Shi rats, 1/16 (6%) in SD/gShi rats, and 13/16 (81%) in F344/DuCrj rats surviving after NNM treatment. Metastasis to the lung was observed in HCC-bearing rats at an incidence of 13/15 (87%) in WS/Shi, 1/1 in SD/gShi, and 6/13 (46%) in F344/DuCrj. Four-week administration of NNM resulted in a significantly higher BrdU-labeling index of hepatocytes in WS/Shi rats than in the other strains. These findings indicated that WS/Shi is the most sensitive strain to NNM and may be the most suitable strain for use as a spontaneous metastatic model of HCC among the strains of rats examined in the present study.

New technologies to prevent and treat contact hypersensitivity responses

Allergic contact dermatitis is a common inflammatory skin disease caused by T cells that recognize environmental and industrial allergens (i.e., haptens). Langerhans' cells (LC), which are skin-specific and "immature" members of the dendritic cell (DC) family of antigen-presenting cells, play crucial roles in the induction of contact hypersensitivity (CH) responses. Upon exposure to haptens, LC migrate from the epidermis to draining lymph nodes, mature into T cell-stimulatory DC, and activate hapten-reactive T cells. Therefore, CH responses should be preventable at the sensitization phase by interfering with one of these changes that occur in LC. Our objective is to develop new technologies for the prevention and treatment of allergic contact dermatitis. In this article, we will introduce three technologies that we have recently developed. First, using a phage display strategy, we have identified a 12-mer peptide (termed "peptide 1") that binds and blocks the function of hyaluronan (HA), which is known to serve as an adhesive substrate for LC migration. Local injection of peptide 1 in mice before topical application of DNFB blocked almost completely the emigration of LC from the epidermis to the draining lymph node, where antigen presentation takes place. Peptide 1 represents a new strategy that is designed to inhibit the initial event of CH. Second, we have established an in vitro experimental system to study the terminal maturation of LC during antigen-specific interaction with T cells. This experimental system, which employs a long-term LC line and T cell clones, should provide a unique tool for the identification of new immunosuppressive agents that block LC terminal maturation selectively. Finally, under the hypothesis that LC, which are engineered to overexpress a death ligand, would deliver apoptotic signals instead of activation signals to T cells, we created a "killer" LC clone by introducing CD95L cDNA into our long-term LC line XS106. In vivo administration of DNFB-pulsed killer LC into mice, either before or after sensitization, resulted in marked suppression of CH responses to DNFB. The killer LC technology represents an entirely new immunosuppressive therapy that is designed to eliminate only the pathogenic T cells.

Involvement of iNOS in postischemic heart dysfunction of stroke-prone spontaneously hypertensive rats

We investigated the possible contribution of inducible nitric oxide synthase (iNOS) to postischemic heart dysfunction and injuries in stroke-prone spontaneously hypertensive rats (SHRSP). SHRSP, 13-14 wk of age, had significantly higher systolic blood pressure and greater heart weight than age-matched Wistar-Kyoto rats (WKY). Permanent occlusion of the left anterior descending coronary artery (LAD) caused significant and long-lasting increases in the activity and mRNA expression of myocardial iNOS in SHRSP compared with WKY. However, there was no significant difference in the LAD occlusion-induced expression of interleukin-1beta mRNA between SHRSP and WKY. Hemodynamic deterioration and myocardial fibrosis were also observed in SHRSP at 4 wk after LAD occlusion. Continuous administration of 2-amino-5,6-dihydro-6-methyl-4H-1,2-thiazin (AMT) completely blocked the LAD occlusion-induced increase in the myocardial iNOS activity of SHRSP. Moreover, postischemic heart dysfunction and injuries were also significantly ameliorated by 2-amino-5,6-dihydro-6-methyl-4H-1,2-thiazin (AMT). These results suggest that the increased activity of myocardial iNOS plays a pivotal role in the development of postischemic cardiac dysfunction and injuries in SHRSP with the hypertensive and hypertrophic heart.

Dendritic cells phagocytose and are activated by Treponema pallidum

Cell-mediated immune processes play a prominent role in the clinical manifestations of syphilis, a sexually transmitted disease of humans caused by spirochetal bacterium Treponema pallidum. The immune cell type that initiates the early immune response to T. pallidum thus far has not been identified. However, dendritic cells (DCs) are the first immune-competent cells to encounter antigens within skin or mucous membranes, the principal sites of early syphilitic infection. In the present study, immature DC line XS52, derived from murine skin, was utilized to examine T. pallidum-DC interactions and subsequent DC activation (maturation). Electron microscopy revealed that T. pallidum was engulfed by DCs via both coiling and conventional phagocytosis and was delivered to membrane-bound vacuoles. The XS52 DC line expressed surface CD14 and mRNA for Toll-like receptors 2 and 4, molecules comprising important signaling components for immune cell activation by bacterial modulins. Both T. pallidum and a synthetic lipopeptide (corresponding to the 47-kDa major membrane lipoprotein) activated the XS52 DC line, as indicated by the secretion of interleukin-12 (IL-12), IL-1beta, tumor necrosis factor alpha, and IL-6 and elevated surface expression of CD54. The combined data support the contention that DCs stimulated by T. pallidum and/or its proinflammatory membrane lipoproteins are involved in driving the cellular immune processes that typify syphilis.

Information processing by nonspiking interneurons: passive and active properties of dendritic membrane determine synaptic integration

Nonspiking interneurons control activities of postsynaptic cells without generating action potentials in the central nervous system of many invertebrates. Physiological characteristics of their dendritic membrane have been analyzed in previous studies using single electrode current- and voltage-clamp techniques. We constructed a single compartment model of an identified nonspiking interneuron of crayfish. Experimental results allowed us to simulate how the passive and active properties of the dendritic membrane influence the integrative processing of synaptic inputs. The results showed that not only the peak amplitude but also the time course of synaptic potentials were dependent on the membrane potential level at which the synaptic activity was evoked. When the synaptic input came sequentially, each individual input was still discernible at depolarized levels at which the membrane time constant was short due to depolarization-dependent membrane conductances. In contrast, synaptic potentials merged with each other to develop a sustained potential at hyperpolarized levels where the membrane behaved passively. Thus, synaptic integration in a single nonspiking interneuron depends on the value of membrane potential at which it occurs. This probably reflects the temporal resolution required for specific types of information processing.

Electrophysiological and theoretical analysis of depolarization-dependent outward currents in the dendritic membrane of an identified nonspiking interneuron in crayfish

Depolarization-dependent outward currents were analyzed using the single-electrode voltage clamp technique in the dendritic membrane of an identified nonspiking interneuron (LDS interneuron) in situ in the terminal abdominal ganglion of crayfish. When the membrane was depolarized by more than 20 mV from the resting potential (65.0 +/- 5.7 mV), a transient outward current was observed to be followed by a sustained outward current. Pharmacological experiments revealed that these outward currents were composed of 3 distinct components. A sustained component (I(s)) was activated slowly (half rise time > 5 msec) and blocked by 20 mM TEA. A transient component (I(t1)) that was activated and inactivated very rapidly (peak time < 2.5 msec, half decay time < 1.2 msec) was also blocked by 20 mM TEA. Another transient component (I(t2)) was blocked by 100 microM 4AP, activated rapidly (peak time < 10.0 msec) and inactivated slowly (half decay time > 131.8 msec). Two-step pulse experiments have revealed that both sustained and transient components are not inactivated at the resting potential: the half-maximal inactivation was attained at -21.0 mV in I(t1), and -38.0 mV in I(t2). I(s) showed no noticeable inactivation. When the membrane was initially held at the resting potential level and clamped to varying potential levels, the half-maximal activation was attained at -36.0 mV in I(s), -31.0 mV in I(t1) and -40.0 mV in I(t2). The activation and inactivation time constants were both voltage dependent. A mathematical model of the LDS interneuron was constructed based on the present electrophysiological records to simulate the dynamic interaction of outward currents during membrane depolarization. The results suggest that those membrane conductances found in this study underlie the outward rectification of the interneuron membrane as well as depolarization-dependent shaping of the excitatory synaptic potential observed in current-clamp experiments.

T cells reactive to keratinocyte antigens are generated during induction of contact hypersensitivity in mice. A model for autoeczematization in humans?

BACKGROUND

The role of keratinocytes (KC) in contact hypersensitivity (CH) has been examined more with respect to cytokine secretion and tolerance induction and less as a source of antigenic proteins to which chemical haptens can conjugate.

OBJECTIVE

To determine whether KC-derived proteins can serve as antigenic carriers for haptens such as dinitrofluorobenzene (DNFB).

METHODS

We examined the capacity of draining lymph node cells from BALB/c mice sensitized to DNFB to proliferate in response to hapten or to hapten-conjugated protein extracts derived from a KC line (DNP-Pam KC extract). Using limiting dilution microculture of these lymph node cells, we established DNP-specific T cell clones as well as DNP-Pam KC extract-reactive T cell clones. We also examined the proliferative responses of the DNP-Pam KC extract-reactive clones and of lymph node cells from mice sensitized to different haptens.

RESULTS

Lymph node cells from DNFB-sensitized mice proliferated well to hapten or to DNP-Pam KC extract. Six la(d)-restricted, alphabeta TCR-bearing, CD4+ clones were established: 4 proliferated specifically to soluble hapten (DNBS), whereas 2 proliferated in response to DNP-Pam KC extract. Surprisingly, the DNP-Pam KC extract-reactive clones proliferated as well to Pam KC extract without hapten. Lymph node cells from hapten-sensitized mice not only proliferated specifically in response to the hapten to which they were sensitized, but also proliferated to Pam KC extract without hapten.

CONCLUSIONS

T cell clones generated during the induction of (CH) in mice include those reactive to hapten as well as those reactive to KC antigens independent of hapten. Analogous mechanisms in humans might account for autoreactive events such as id reactions associated with CH and angry back syndrome during patch testing.

Induction of Th2-directed immune responses by IL-4-transduced dendritic cells in mice

Dendritic cell (DC)-based vaccines have been used to generate Th1-mediated, protective immunity against cancers and infectious microorganisms. As an attempt to develop a new vaccine protocol for the induction of Th2-directed responses, we introduced an IL-4 plasmid vector into the XS106 DC line (derived from A/J mice). Although relatively small fractions of XS106 cells exhibited apparent intracellular deposition of IL-4, they secreted biologically relevant amounts of the cytokine. IL-4-transduced XS106 DC and control XS106 DC transfected with vector alone were pulsed with KLH and injected s.c. into A/J mice. The overall magnitude of KLH-specific cellular and humoral responses was comparable between the two animal groups. However, they differed in the isotype profile albeit only transiently, with the IL-4-transduced DC group showing higher IgE and lower IgG2a responses, and in the cytokine profile, with spleen cells isolated from the IL-4-transduced DC group producing higher IL-13 and lower IL-12. Thus, delivery of IL-4 gene to relatively small numbers of DC is sufficient to modify the immunological outcome of DC-based vaccines.

Identification of a novel, dendritic cell-associated molecule, dectin-1, by subtractive cDNA cloning

Dendritic cells (DC) are special subsets of antigen presenting cells characterized by their potent capacity to activate immunologically naive T cells. By subtracting the mRNAs expressed by the mouse epidermus-derived DC line XS52 with the mRNAs expressed by the J774 macrophage line, we identified five novel genes that were expressed selectively by this DC line. One of these genes encoded a type II membrane-integrated polypeptide of 244 amino acids containing a putative carbohydrate recognition domain motif at the COOH-terminal end. This molecule, termed "dectin-1," was expressed abundantly at both mRNA and protein levels by the XS52 DC line, but not by non-DC lines (including the J774 macrophage line). Dectin-1 mRNA was detected predominantly in spleen and thymus (by Northern blotting) and in skin-resident DC, i.e. Langerhans cells (by reverse transcription-polymerase chain reaction). Affinity-purified antibody against dectin-1 identified a 43-kDa glycoprotein in membrane fractions isolated from the XS52 DC line and from the dectin-1 cDNA-transfected COS-1 cells. His-tagged recombinant proteins containing the extracellular domains of dectin-1 showed marked and specific binding to the surface of T cells and promoted their proliferation in the presence of anti-CD3 monoclonal antibody at suboptimal concentrations. These in vitro results suggest that dectin-1 on DC may bind to as yet undefined ligand(s) on T cells, thereby delivering T cell co-stimulatory signals. Not only do these results document the efficacy of subtractive cDNA cloning for the identification of unique genes expressed by DC, they also provide a framework for studying the physiological function of dectin-1.

Hepatocarcinogenic activity of N-butyl-N-(4-hydroxybutyl)nitrosamine in rats is not modified by sodium L-ascorbate

Male F344 and Wistar Shionogi (WS) rats were treated with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) for 20 weeks and then killed at week 36 (experiment 1). Although reduction of body weight increase was found, no effects on liver weights were noted. Formalin-fixed and paraffin-embedded liver tissues from rats killed terminally were cut and stained for glutathione S-transferase placental form (GST-P) immunohistochemically. Marked elevation of quantitative values of small GST-P positive (GST-P+) foci were apparent in both strains of rat administered BBN. In experiment 2, both sexes of F344 rats were given 0.05% BBN in the drinking water for 4 weeks and then fed diet containing 0 or 5.0% sodium L-ascorbate (SA) for 32 weeks. No body and liver weight changes were evident in any group. Quantitative values for small GST-P+ foci were increased in both sexes of rats exposed to BBN but were not modified by additional SA treatment. Thus, it was confirmed that the selective bladder carcinogen BBN also acts as a liver carcinogen. These results, from the quantitative analysis of small GST-P+ foci as end point marker lesions, indicate that the liver tumor modifying potential of test chemicals can be evaluated in rats by using an initiation/promotion protocol for urinary bladder carcinogenesis.

A role for NF-kappaB-dependent gene transactivation in sunburn

Exposure of skin to ultraviolet (UV) radiation is known to induce NF-kappaB activation, but the functional role for this pathway in UV-induced cutaneous inflammation remains uncertain. In this study, we examined whether experimentally induced sunburn reactions in mice could be prevented by blocking UV-induced, NF-kappaB-dependent gene transactivation with oligodeoxynucleotides (ODNs) containing the NF-kappaB cis element (NF-kappaB decoy ODNs). UV-induced secretion of IL-1, IL-6, TNF-alpha, and VEGF by skin-derived cell lines was inhibited by the decoy ODNs, but not by the scrambled control ODNs. Systemic or local injection of NF-kappaB decoy ODNs also inhibited cutaneous swelling responses to UV irradiation. Moreover, local UV-induced inflammatory changes (swelling, leukocyte infiltration, epidermal hyperplasia, and accumulation of proinflammatory cytokines) were all inhibited specifically by topically applied decoy ODNs. Importantly, these ODNs had no effect on alternative types of cutaneous inflammation caused by irritant or allergic chemicals. These results indicate that sunburn reactions culminate from inflammatory events that are triggered by UV-activated transcription of NF-kappaB target genes, rather than from nonspecific changes associated with tissue damage.

Familial Alzheimer's disease-associated mutations block translocation of full-length presenilin 1 to the nuclear envelope

A polyclonal antibody, M5, to the hydrophilic loop domain of human presenilin 1 (PS1) was prepared. Western blot and immunoprecipitation analyses showed that M5 specifically recognized the processed C-terminal fragment, but not the full-length PS1. Epitope mapping analysis revealed that the essential sequence for recognition of the C-terminal fragment by M5 is DPEAQRR (302-308). The recognition of the C-terminal fragment by M5 in a processing-dependent manner was further confirmed by competitive enzyme-linked immunosorbent assay using the synthetic peptide L281 (281-311), which contains the putative processing site and the preceding amino acids to the site. Although L281 contains the epitope sequence for M5, the maximum inhibition was only 14%. Immunocytochemistry using M5 combined with hL312, which recognizes both full-length PS1 and the C-terminal fragment, allowed us to distinguish the localization of the processed C-terminal fragment from that of full-length PS1. Confocal microscopy demonstrated that the full-length form of wild-type PS1 is preferentially located in the nuclear envelope, while the processed C-terminal fragment is mainly present in the endoplasmic reticulum (ER). However, PS1 with familial Alzheimer's disease-associated mutations could not translocate to the nuclear envelope, and both the full-length and processed mutants were co-localized in the ER.

Cloning of a second dendritic cell-associated C-type lectin (dectin-2) and its alternatively spliced isoforms

Using a subtractive cDNA cloning strategy, we isolated previously five novel genes that were expressed abundantly by the murine dendritic cell (DC) line XS52, but not by the J774 macrophage line. One of these genes encoded a unique, DC-associated C-type lectin, termed "dectin-1." Here we report the characterization of a second novel gene that was also expressed in a DC-specific manner. Clone 1B12 encoded a type II membrane-integrated polypeptide of 209 amino acids containing a single carbohydrate recognition domain motif in the COOH terminus. The expression pattern of this molecule, termed "dectin-2," was almost indistinguishable from that for dectin-1; that is, both were expressed abundantly at mRNA and protein levels by the XS52 DC line, but not by non-DC lines, and both were detected in spleen and thymus, as well as in skin resident DC (i.e. Langerhans cells). Interestingly, reverse transcriptase-polymerase chain reaction and immunoblotting revealed multiple bands of dectin-2 transcripts and proteins suggesting molecular heterogeneity. In fact, we isolated additional cDNA clones encoding two distinct, truncated dectin-2 isoforms. Genomic analyses indicated that a full-length dectin-2 (alpha isoform) is encoded by 6 exons, whereas truncated isoforms (beta and gamma) are produced by alternative splicing. We propose that dectin-2 and its isoforms, together with dectin-1, represent a unique subfamily of DC-associated C-type lectins.

Proteolytic processing and degradation of human presenilin-1 expressed in yeast

Numerous mutations causing early-onset familial Alzheimer's disease have been identified in the presenilin-1 gene. Presenilin-1 protein is produced as a 47 kDa holoprotein and proteolytically processed to an N-terminal 28 kDa and a C-terminal 19 kDa fragments by unidentified presenilinase in mammalian cells. We have demonstrated that this proteolytic processing also occurs in yeast. We also show that degradation of C-terminal fragment of presenilin-1 is dependent of proteasomal function. This yeast system will be a good tool to identify presenilinase and to study the role of presenilin-1 in amyloid precursor protein processing.

Presenilin-1 mutations downregulate the signalling pathway of the unfolded-protein response

Missense mutations in the human presenilin-1 (PS1) gene, which is found on chromosome 14, cause early-onset familial Alzheimer's disease (FAD). FAD-linked PS1 variants alter proteolytic processing of the amyloid precursor protein and cause an increase in vulnerability to apoptosis induced by various cell stresses. However, the mechanisms responsible for these phenomena are not clear. Here we report that mutations in PS1 affect the unfolded-protein response (UPR), which responds to the increased amount of unfolded proteins that accumulate in the endoplasmic reticulum (ER) under conditions that cause ER stress. PS1 mutations also lead to decreased expression of GRP78/Bip, a molecular chaperone, present in the ER, that can enable protein folding. Interestingly, GRP78 levels are reduced in the brains of Alzheimer's disease patients. The downregulation of UPR signalling by PS1 mutations is caused by disturbed function of IRE1, which is the proximal sensor of conditions in the ER lumen. Overexpression of GRP78 in neuroblastoma cells bearing PS1 mutants almost completely restores resistance to ER stress to the level of cells expressing wild-type PS1. These results show that mutations in PS1 may increase vulnerability to ER stress by altering the UPR signalling pathway.

New technologies toward dendritic cell-based cancer immunotherapies

Immunologically naive T cells are activated most efficiently or even exclusively by special subsets of antigen presenting cells, termed dendritic cells (DC). Members of the DC family have been identified in virtually all epithelial tissues that are constantly exposed to environmental antigens or infectious microbes. For example, skin is equipped with at least two members of this family, epidermal Langerhans cells (LC) and dermal DC. DC have been shown to play pathogenic roles in several different inflammatory/immunological disorders and protective roles against infectious pathogenes and cancer development. In this review article, we will overview the recent progress in the development of DC-based immunotherapies for the prevention and treatment of cancers.

Induction of antigen-specific immunosuppression by CD95L cDNA-transfected 'killer' dendritic cells

Dendritic cells (DCs) are special subsets of antigen-presenting cells characterized by their highly potent capacity to activate immunologically naive T cells. Here we report that DCs that are transfected with CD95 ligand (CD95L) cDNA, called 'killer' DCs, deliver death signals, instead of activation signals, to T cells after antigen-specific interaction. Injection of antigen-pulsed killer DCs into mice before sensitization induced antigen-specific immunosuppression. When administered after sensitization, killer DCs suppressed immune responses almost completely after subsequent challenge. Thus, killer DCs represent an entirely new immunomodulatory protocol, which may become directly applicable in preventing and even treating T cell-mediated inflammatory diseases.

Dendritic cells in genetic immunization

Both humoral and cellular immune responses are inducible by inoculation of naked plasmid DNA encoding a polypeptide antigen. This new vaccination protocol, known as genetic immunization, has been used to initiate protective immunity against a variety of infectious pathogens and tumors in experimental animals. Dendritic cells (DC) are thought to play at least three distinct roles in genetic immunization: (1) MHC class II-restricted presentation of antigens secreted by neighboring, transfected cells, (2) MHC class I-restricted "cross" presentation of antigens released by neighboring, transfected cells, and (3) direct presentation of antigens by transfected DC themselves. Several new technologies have been developed recently in an attempt to improve the overall efficacy of genetic vaccination, as well as to regulate the type and class of resulting immune responses. These technologies include modification of plasmid DNA, co-delivery of genes encoding immunoregulatory molecules, and DC targeting. We will overview some of these new technologies in genetic immunization.

Twenty-nine missense mutations linked with familial Alzheimer's disease alter the processing of presenilin 1

1. Full-length form of human presenilin 1 (PS1) is processed and an N-terminal fragment (28 KD) and C-terminal fragment (19 KD) are generated. To elucidate the possible role of presenilin mutations in Alzheimer's disease (AD), the authors analyze the effects of AD-linked mutations on PS1 processing in cultured cells. 2. Complementary DNAs encoding genes for human PS1 harboring twenty-nine missense mutations linked with familial Alzheimer's disease (FAD) were introduced into PC12 cells. Human PS1 exogenously expressed in the cells was detected by immunoblotting using a monoclonal antibody that recognized the N-terminal region of human PS1. The amounts of full-length form (48 KD) and N-terminal fragment (28 KD) of PS1 was quantified by densitometrical analysis. 3. The ratio of the N-terminal fragment to total PS1 was reduced by twenty-nine mutations. The specific effects on PS1 processing varied according to mutation. 4. These results suggest that AD-linked missense mutations of PS1 are involved in neurodegeneration via inhibition of PS1 processing.

Apoptosis in dendritic cell biology

Apoptosis or programmed cell death regulates many aspects in immunological homeostasis and, thus, controls the initiation, magnitude, duration, and termination of immune responses. Recent studies on dendritic cells (DC), including Langerhans cells (LC), have reinforced this concept by documenting that these antigen presenting cells express surface receptors and ligands that are known to mediate apoptotic cell death and that they are highly susceptible to apoptotic signals. In this review article, four major topics concerning apoptosis in the biology of DC will be overviewed: (a) molecular mechanisms of apoptosis; (b) DC apoptosis induced by various stimuli; (c) regulation of DC apoptosis; and (d) cross-priming and cross-tolerance induced by DC ingesting apoptotic bodies.

Dendritic cells undergo rapid apoptosis in vitro during antigen-specific interaction with CD4+ T cells

The terminal fate of dendritic cells (DC) remains relatively uncertain. In this study, we tested the hypothesis that DC undergo apoptosis after Ag-specific interaction with T cells. When splenic DC isolated from BALB/c mice were cocultured with HDK-1 T cells (a keyhole limpet hemocyanin (KLH)-specific CD4+ Th1 clone) in the presence of KLH, they showed conspicuous cell death as measured by propidium iodide (PI) uptake and chromatin condensation, whereas they remained relatively intact when incubated with either T cells or KLH alone. Likewise, the long term DC line XS52, which was established from BALB/c mouse epidermis, also died rapidly (within 2 h), and they exhibited characteristic DNA laddering when cocultured with HDK-1 T cells in the presence of KLH. RT-PCR and FACS analyses revealed the expression of CD95 (Fas) by XS52 DC and of CD95 ligand (CD95L) (Fas ligand) by activated HDK-1 T cells, suggesting a functional role for these molecules. In fact, anti-CD95L mAb inhibited partially (50%) T cell-mediated XS52 cell death, and coupling of surface CD95 with anti-CD95 mAb triggered significant XS52 cell death, but only in the presence of cycloheximide. Thus, ligation of CD95 (on DC) with CD95L (on T cells) is one, but not the only, mechanism by which T cells induce DC death. Finally, DC isolated from the CD95-deficient mice were found to be significantly more efficient than DC from control mice in their capacity to induce delayed type hypersensitivity responses in vivo. We propose that T cell-induced DC apoptosis serves as a unique down-regulatory mechanism that prevents the interminable activation of T cells by Ag-bearing DC.