Tolerization of dendritic cells by T(S) cells: the crucial role of inhibitory receptors ILT3 and ILT4

Immunoglobulin-like transcript 3 (ILT3) and ILT4 belong to a family of inhibitory receptors expressed by human monocytes and dendritic cells. We show here that CD8+CD28(-) alloantigen-specific T suppressor (TS) cells induce the up-regulation of ILT3 and ILT4 on monocytes and dendritic cells, rendering these antigen-presenting cells (APCs) tolerogenic. Tolerogenic APCs show reduced expression of costimulatory molecules and induce antigen-specific unresponsiveness in CD4+ T helper cells. Studies of human heart transplant recipients showed that rejection-free patients have circulating TS cells, which induce the up-regulation of ILT3 and ILT4 in donor APCs. These findings demonstrate an important mechanism of immune regulation.

Scrape-loading and dye transfer. A rapid and simple technique to study gap junctional intercellular communication

Gap junction-mediated intercellular communication has been recognized in cells from different tissues of various organisms and has been implicated in a variety of cellular functions and dysfunctions. Here we describe a new, direct and rapid technique with which to study this cellular phenomenon. It employs scrape-loading to introduce a low molecular weight (MW) fluorescent dye, Lucifer yellow CH (MW 457.2) into cells in culture and allows the monitoring of its transfer into contiguous cells. In communication-competent cells the dye transmission occurred within minutes after loading. The involvement of membrane junctions in Lucifer yellow transfer was verified by the concurrent loading of a high MW marker dye conjugate, rhodamine dextran (MW 10,000). Once introduced intracellularly the rhodamine dextran is unable to cross the relatively narrow membrane junctions. Chemicals of variable potency known to block junctional communication were tested in Chinese hamster V79 cells and other mammalian cells. The results showed effective blockage of the dye transfer at non-cytotoxic doses. This new technique can be applied to a wide variety of mammalian (including human) cells. In addition, it has the potential to be utilized as a rapid screening assay to detect chemicals that can modulate intercellular communication and to study their mechanism of action.

Acyl-coenzyme A:cholesterol acyltransferase

Due to its presumed role in regulating cellular cholesterol homeostasis, and in various pathophysiological conditions, acyl-coenzyme A:cholesterol acyltransferase (ACAT) has attracted much attention. Cloning the ACAT gene provides the necessary tool to advance molecular studies of this enzyme. The topics reviewed in this chapter include the pathophysiological roles of ACAT, the biochemistry and molecular biology of the ACAT protein and the ACAT gene, and the mode of regulation by sterol or nonsterol agents in mammalian cells. In addition, we present a working model linking the presumed allosteric property of ACAT with cholesterol trafficking into and out of the endoplasmic reticulum.

Elimination of metabolic cooperation in Chinese hamster cells by a tumor promoter

Wild-type Chinese hamster V79 cells (6-thioguanine-sensitive) reduce the recovery of 6-thioguanine-resistant cells when they are cultured together at high densities, through a form of intercellular communication (metabolic cooperation). Cooperation is inhibited by 12-O-tetradecanoyl phorbol-13-acetate, rescuing the 6-thioguanine-resistant cells. These results may be useful in the study of an aspect of the mechanism of tumor promotion and in assaying for promoters.

A novel receptor involved in T-cell activation

Optimal T-cell activation and T-cell expansion require triggering by T-cell antigen receptors and co-stimulatory signals provided by accessory cells. A major co-stimulatory pathway involves crosslinking the CD28 molecule on T cells by its ligands CD80 or CD86 expressed on antigen-presenting cells. But recent studies on CD28-deficient mice have indicated that CD28 is not required for all T-cell responses and that additional T-cell co-stimulatory pathways exist. Here we describe a novel glycoprotein, of relative molecular mass 70,000 (M(r) 70K), designated SLAM, that belongs to the immunoglobulin gene superfamily, which is involved in T-cell stimulation. SLAM is constitutively expressed on peripheral-blood CD45ROhigh memory T cells, T-cell clones, immature thymocytes, and a proportion of B cells, and is rapidly induced on naive T cells after activation. Engagement of SLAM enhances antigen-specific proliferation and cytokine production by T cells carrying the CD4 antigen (CD4+). Particularly, the production of interferon-gamma (IFN-gamma) is strongly upregulated, even in T helper type 2 (Th2) CD4+ T-cell clones, whereas no induction of interleukin (IL)-4 or IL-5 production was observed in Th1 clones. In addition, the engagement of SLAM induces directly the proliferation of CD4+ T-cell clones and preactivated T cells, in the absence of any other stimuli, and without CD28 involvement. Thus SLAM is a novel receptor on T cells that, when engaged, potentiates T-cell expansion in a CD28-independent manner and induces a Th0/Th1 cytokine production profile.

BCL-6, a POZ/zinc-finger protein, is a sequence-specific transcriptional repressor

Approximately 40% of diffuse large cell lymphoma are associated with chromosomal translocations that deregulate the expression of the BCL6 gene by juxtaposing heterologous promoters to the BCL-6 coding domain. The BCL6 gene encodes a 95-kDa protein containing six C-terminal zinc-finger motifs and an N-terminal POZ domain, suggesting that it may function as a transcription factor. By using a DNA sequence selected for its ability to bind recombinant BCL-6 in vitro, we show here that BCL-6 is present in DNA-binding complexes in nuclear extracts from various B-cell lines. In transient transfectin experiments, BCL6 can repress transcription from promoters linked to its DNA target sequence and this activity is dependent upon specific DNA-binding and the presence of an intact N-terminal half of the protein. We demonstrate that this part of the BCL6 molecule contains an autonomous transrepressor domain and that two noncontiguous regions, including the POZ motif, mediate maximum transrepressive activity. These results indicate that the BCL-6 protein can function as a sequence-specific transcriptional repressor and have implications for the role of BCL6 in normal lymphoid development and lymphomagenesis.

B cell lymphoma-associated chromosomal translocation involves candidate oncogene lyt-10, homologous to NF-kappa B p50

A B cell lymphoma-associated chromosomal translocation, t(10;14)(q24;q32), juxtaposes the immunoglobulin C alpha 1 locus to a novel gene, lyt-10. The normal lyt-10 cDNA codes for a 98 kd protein which displays amino-terminal homology with the rel (DNA-binding) domain of the NF-kappa B-rel family of transcription factors and carboxy-terminal homology with the NF-kappa B p50 precursor protein, including the putative proteolytic cleavage domain (poly-G) and the ankyrin-like repeat domains. The lyt-10 protein can bind to kappa B sequences in vitro, although with different specificity from NF-kappa B p50, and in vitro DNA-binding is activated by removal of the ankyrin domain. Chromosomal translocation generates an lyt-10-C alpha 1 fusion gene coding for a protein that retains the rel effector domain, lacks the ankyrin regulatory domain, and binds kappa B sequences in vitro, suggesting its constitutive activation in vivo. Analogous rearrangements of the lyt-10 gene have been found in an additional three cases of lymphoid neoplasia. The lyt-10 gene defines a new subfamily (rel/poly-G/ankyrin) of NF-kappa B-rel transcription factors with potential for oncogenic activation in human cancer.

Chromosomal translocations cause deregulated BCL6 expression by promoter substitution in B cell lymphoma

The BCL6 gene codes for a zinc-finger transcription factor and is involved in chromosomal rearrangements in 30-40% of diffuse large-cell lymphoma (DLCL). These rearrangements cluster within the 5' regulatory region of BCL6 spanning its first non-coding exon. To determine the functional consequences of these alterations, we have analyzed the structure of the rearranged BCL6 alleles and their corresponding RNA and protein species in two DLCL biopsies and one tumor cell line which carried the t(3;14)(q27;q32) translocation involving the BCL6 and immunoglobulin heavy-chain (IgH) loci. In all three cases, the breakpoints were mapped within the IgH switch region and the BCL6 first intron, leading to the juxtaposition of part of the IgH locus upstream and in the same transcriptional orientation to the BCL6 coding exons. An analysis of cDNA clones showed that these recombinations generate chimeric IgH-BCL6 transcripts which initiated from IgH germline transcript promoters (I mu or I gamma 3), but retain a normal BCL6 coding domain. In the tumor cell line, the chimeric I gamma 3-BCL6 allele, but not the germline BCL6 gene, was transcriptionally active and produced a normal BCL6 protein. These findings indicate that t(3;14) translocations alter BCL6 expression by promoter substitution and imply that the consequence of these alterations is the deregulated expression of a normal BCL6 protein.

Roles of acyl-coenzyme A:cholesterol acyltransferase-1 and -2

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) is an intracellular enzyme that produces cholesteryl esters in various tissues. In mammals, two ACAT genes (ACAT1 and ACAT2) have been identified. Together, these two enzymes are involved in storing cholesteryl esters as lipid droplets, in macrophage foam-cell formation, in absorbing dietary cholesterol, and in supplying cholesteryl esters as part of the core lipid for lipoprotein synthesis and assembly. The key difference in tissue distribution of ACAT1 and ACAT2 between humans, mice and monkeys is that, in adult human liver (including hepatocytes and bile duct cells), the major enzyme is ACAT1, rather than ACAT2. There is compelling evidence implicating a role for ACAT1 in macrophage foam-cell formation, and for ACAT2 in intestinal cholesterol absorption. However, further studies at the biochemical and cell biological levels are needed in order to clarify the functional roles of ACAT1 and ACAT2 in the VLDL or chylomicron synthesis/assembly process.

Immunological quantitation and localization of ACAT-1 and ACAT-2 in human liver and small intestine

By using specific anti-ACAT-1 antibodies in immunodepletion studies, we previously found that ACAT-1, a 50-kDa protein, plays a major catalytic role in the adult human liver, adrenal glands, macrophages, and kidneys but not in the intestine. Acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity in the intestine may be largely derived from a different ACAT protein. To test this hypothesis, we produced specific polyclonal anti-ACAT-2 antibodies that quantitatively immunodepleted human ACAT-2, a 46-kDa protein expressed in Chinese hamster ovary cells. In hepatocyte-like HepG2 cells, ACAT-1 comprises 85-90% of the total ACAT activity, with the remainder attributed to ACAT-2. In adult intestines, most of the ACAT activity can be immunodepleted by anti-ACAT-2. ACAT-1 and ACAT-2 do not form hetero-oligomeric complexes. In differentiating intestinal enterocyte-like Caco-2 cells, ACAT-2 protein content increases by 5-10-fold in 6 days, whereas ACAT-1 protein content remains relatively constant. In the small intestine, ACAT-2 is concentrated at the apices of the villi, whereas ACAT-1 is uniformly distributed along the villus-crypt axis. In the human liver, ACAT-1 is present in both fetal and adult hepatocytes. In contrast, ACAT-2 is evident in fetal but not adult hepatocytes. Our results collectively suggest that in humans, ACAT-2 performs significant catalytic roles in the fetal liver and in intestinal enterocytes.

Transcriptional repression of Stat6-dependent interleukin-4-induced genes by BCL-6: specific regulation of iepsilon transcription and immunoglobulin E switching

The BCL-6 proto-oncogene encodes a POZ/zinc-finger transcription factor that is expressed in B cells and a subset of CD4(+) T cells within germinal centers. Recent evidence suggests that BCL-6 can act as a sequence-specific repressor of transcription, but the target genes for this activity have not yet been identified. The binding site for BCL-6 shares striking homology to the sites that are the target sequence for the interleukin-4 (IL-4)-induced Stat6 (signal transducers and activators of transcription) signaling molecule. Electrophoretic mobility shift assays demonstrate that BCL-6 can bind, with different affinities, to several DNA elements recognized by Stat6. Expression of BCL-6 can repress the IL-4-dependent induction of immunoglobulin (Ig) germ line epsilon transcripts, but does not repress the IL-4 induction of CD23 transcripts. Consistent with the role of BCL-6 in modulating transcription from the germ line epsilon promoter, BCL-6(-/-) mice display an increased ability to class switch to IgE in response to IL-4 in vitro. These animals also exhibit a multiorgan inflammatory disease characterized by the presence of a large number of IgE(+) B cells. The apparent dysregulation of IgE production is abolished in BCL-6(-/-) Stat6(-/-) mice, indicating that BCL-6 regulation of Ig class switching is dependent upon Stat6 signaling. Thus, BCL-6 can modulate the transcription of selective Stat6-dependent IL-4 responses, including IgE class switching in B cells.

Homozygous deletions that simultaneously eliminate expressions of class I and class II antigens of EBV-transformed B-lymphoblastoid cells. I. Reduced proliferative responses of autologous and allogeneic T cells to mutant cells that have decreased expression of class II antigens

Mutant human B-lymphoblastoid cell lines, 721.174 and 721.180, that have greatly reduced expressions of known class I and class II HLA antigens were produced by two cycles of gamma-ray mutagenesis followed by selection for HLA antigen loss. Residual binding of monoclonal antibodies directed against class II antigens was negligible except for 10% residual binding of SB-binding antibody ILR1. However, deletion of SB was functionally complete as indicated by failure of the mutants to stimulate proliferation of SB-primed lymphocytes. Residual binding of monoclonal antibodies directed against class I "framework" determinants was reduced by 90-95%. However, the binding of monoclonal antibodies directed against beta 2-microglobulin and against the A2 epitope recognized by monoclonal antibody BB 7.2 was about 20% of normal. The identities of the residual class I-like antigens are unknown. The mutants retained full expression of the EBV-induced EBVCS antigen. Mutants 721.174 and 721.180 have lost most, but definitely not all, of their capacity to stimulate primary allogeneic and autologous lymphoproliferative responses. Therefore, the mutants still express antigens other than those that are presently known to stimulate lymphocyte proliferation. By means of studies of the present sort, and in future studies on expression of transferred HLA genes, mutants 721.174 and 721.180 promise to be useful in molecular and functional analysis of MHC-region-encoded gene products and their genetic regulation.

Training nu-support vector classifiers: theory and algorithms

The nu-support vector machine (nu-SVM) for classification proposed by Schölkopf, Smola, Williamson, and Bartlett (2000) has the advantage of using a parameter nu on controlling the number of support vectors. In this article, we investigate the relation between nu-SVM and C-SVM in detail. We show that in general they are two different problems with the same optimal solution set. Hence, we may expect that many numerical aspects of solving them are similar. However, compared to regular C-SVM, the formulation of nu-SVM is more complicated, so up to now there have been no effective methods for solving large-scale nu-SVM. We propose a decomposition method for nu-SVM that is competitive with existing methods for C-SVM. We also discuss the behavior of nu-SVM by some numerical experiments.

Towards a combined prognostic index for survival in HIV infection: the role of 'non-HIV' biomarkers

BACKGROUND

As those with HIV infection live longer, 'non-AIDS' condition associated with immunodeficiency and chronic inflammation are more common. We ask whether 'non-HIV' biomarkers improve differentiation of mortality risk among individuals initiating combination antiretroviral therapy (cART).

METHODS

Using Poisson models, we analysed data from the Veterans Aging Cohort Study (VACS) on HIV-infected veterans initiating cART between 1 January 1997 and 1 August 2002. Measurements included: HIV biomarkers (CD4 cell count, HIV RNA and AIDS-defining conditions); 'non-HIV' biomarkers (haemoglobin, transaminases, platelets, creatinine, and hepatitis B and C serology); substance abuse or dependence (alcohol or drug); and age. Outcome was all cause mortality. We tested the discrimination (C statistics) of each biomarker group alone and in combination in development and validation data sets, over a range of survival intervals, and adjusting for missing data.

RESULTS

Of veterans initiating cART, 9784 (72%) had complete data. Of these, 2566 died. Subjects were middle-aged (median age 45 years), mainly male (98%) and predominantly black (51%). HIV and 'non-HIV' markers were associated with each other (P < 0.0001) and discriminated mortality (C statistics 0.68-0.73); when combined, discrimination improved (P < 0.0001). Discrimination for the VACS Index was greater for shorter survival intervals [30-day C statistic 0.86, 95% confidence interval (CI) 0.80-0.91], but good for intervals of up to 8 years (C statistic 0.73, 95% CI 0.72-0.74). Results were robust to adjustment for missing data.

CONCLUSIONS

When added to HIV biomarkers, 'non-HIV' biomarkers improve differentiation of mortality. When evaluated over similar intervals, the VACS Index discriminates as well as other established indices. After further validation, the VACS Index may provide a useful, integrated risk assessment for management and research.

Activation of acyl-coenzyme A:cholesterol acyltransferase by cholesterol or by oxysterol in a cell-free system

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) is an intracellular enzyme that catalyzes the conjugation of long chain fatty acid and cholesterol to form cholesteryl esters. It is an integral membrane protein located in the endoplasmic reticulum. Experiments performed in intact mammalian cells have shown that the rate of cholesteryl ester synthesis in intact cells, as well as the ACAT activity from cell extracts, are greatly activated by the addition of low density lipoprotein (LDL) or oxygenated sterols such as 25-hydroxycholesterol to the growth medium. However, the molecular mechanism(s) by which sterol(s) stimulate the ACAT activity remains to be elucidated. Recently, our laboratory reported the expression cloning of human ACAT cDNA (Chang, C. C. Y., Huh, H. Y., Cadigan, K. M., and Chang, T. Y. 1993) J. Biol. Chem. 268, 20747-20755). In the current study, we report the expression of human ACAT cDNA in insect Sf9 cells. Uninfected Sf9 cells do not express detectable ACAT-like activity. Infecting these cells with recombinant virus containing ACAT cDNA caused these cells to express high levels of ACAT protein and high levels of ACAT activity when assayed in vitro. The catalytic properties of ACAT expressed in these cells were found to be similar to those found in human tissue culture cells. The combination of high level of ACAT protein expression and the low level of cellular cholesterol content in the infected cells have provided us a novel opportunity to establish a simple cell-free system, whereby stimulation of ACAT by sterols can be readily demonstrated. Using this system, we have shown that cholesterol itself can serve as an ACAT activator in vitro, in addition to its role as an ACAT substrate. The current work provides the experimental basis to hypothesize that, inside mammalian cells, cholesterol itself may serve as a physiological regulator of ACAT.

Overexpression of HO-1 protects against TNF-alpha-mediated airway inflammation by down-regulation of TNFR1-dependent oxidative stress

Oxidative stresses are believed to play an important role in the induction of both cell adhesion molecules and pro-inflammatory cytokines, a key event in a variety of inflammatory processes. The enzyme heme oxygenase-1 (HO-1) functions as an antioxidant and serves to protect against tissue injury. In this study, we report that HO-1 was induced in cultured human tracheal smooth muscle cells after either treatment with a potent inducer of HO-1 activity, cobalt protoporphyrin IX, or infection with a recombinant adenovirus that carries the human HO-1 gene. Overexpression of HO-1 protected against tumor necrosis factor (TNF)-alpha-mediated airway inflammation via the down-regulation of oxidative stress, adhesion molecules, and interleukin-6 in both cultured human tracheal smooth muscle cells and the airways of mice. In addition, HO-1 overexpression inhibited TNF-alpha-induced intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression, adherence of THP-1 cells, generation of interleukin-6, p47(phox) translocation, and nuclear factor-kappaB activation. HO-1 overexpression also attenuated TNF-alpha-induced oxidative stress, which was abrogated in the presence of both the HO-1 inhibitor, zinc protoporphyrin IX, as well as a carbon monoxide scavenger. In addition, HO-1 overexpression reduced the formation of a TNFR1/c-Src/p47(phox) complex. These results suggest that HO-1 functions as a suppressor of TNF-alpha signaling, not only by inhibiting the expression of adhesion molecules and generation of interleukin-6, but also by diminishing intracellular reactive oxygen species production and nuclear factor-kappaB activation in both cultured human tracheal smooth muscle cells and the airways of mice.

Graphene-silicon Schottky diodes

We have fabricated graphene-silicon Schottky diodes by depositing mechanically exfoliated graphene on top of silicon substrates. The resulting current-voltage characteristics exhibit rectifying diode behavior with a barrier energy of 0.41 eV on n-type silicon and 0.45 eV on p-type silicon at the room temperature. The I-V characteristics measured at 100, 300, and 400 K indicate that temperature strongly influences the ideality factor of graphene-silicon Schottky diodes. The ideality factor, however, does not depend strongly on the number of graphene layers. The optical transparency of the thin graphene layer allows the underlying silicon substrate to absorb incident laser light and generate a photocurrent. Spatially resolved photocurrent measurements reveal the importance of inhomogeneity and series resistance in the devices.

Oncogenic collagen I homotrimers from cancer cells bind to α3β1 integrin and impact tumor microbiome and immunity to promote pancreatic cancer

In contrast to normal type I collagen (Col1) heterotrimer (α1/α2/α1) produced by fibroblasts, pancreatic cancer cells specifically produce unique Col1 homotrimer (α1/α1/α1). Col1 homotrimer results from epigenetic suppression of the Col1a2 gene and promotes oncogenic signaling, cancer cell proliferation, tumor organoid formation, and growth via α3β1 integrin on cancer cells, associated with tumor microbiome enriched in anaerobic Bacteroidales in hypoxic and immunosuppressive tumors. Deletion of Col1 homotrimers increases overall survival of mice with pancreatic ductal adenocarcinoma (PDAC), associated with reprograming of the tumor microbiome with increased microaerophilic Campylobacterales, which can be reversed with broad-spectrum antibiotics. Deletion of Col1 homotrimers enhances T cell infiltration and enables efficacy of anti-PD-1 immunotherapy. This study identifies the functional impact of Col1 homotrimers on tumor microbiome and tumor immunity, implicating Col1 homotrimer-α3β1 integrin signaling axis as a cancer-specific therapeutic target.

Gap junctions and the regulation of cellular functions of stem cells during development and differentiation

In multicellular organisms, the role of gap junction intercellular communication (GJIC) in the regulation of cell proliferation, cell differentiation, and apoptosis is becoming increasingly recognized as one of the major cellular functions from the start of the fertilized egg, through normal development of the embryo and fetus, to the sexual maturation of the adult and ultimately to the maintenance of health of the aging adult. Given that the function of this membrane-associated protein channel is to synchronize electrotonic or metabolic functions, differential regulation of function at the transcriptional, translational, and posttranslational levels of a family of highly evolutionarily conserved genes (connexins) needs to be considered. Both inherited mutations and environmental modulation of GJIC could, in principle, affect the function of gap junctions to control cell proliferation, cell differentiation, and apoptosis, thereby leading to a wide variety of pathologies. We review a few techniques used to characterize the ability of stem and progenitor cells to perform GJIC.

Osteonecrosis: current perspectives on pathogenesis and treatment

Nontraumatic osteonecrosis results from impairment of circulation to the affected bone. The femoral head is affected most frequently. The underlying cause for the circulatory defect in osteonecrosis varies and may involve both local and systemic changes. Steroid use, alcohol consumption, pancreatitis, and lipid disorders appear to lead to bone death either by development of fat emboli in the microcirculature surrounding the affected bone or by fatty infiltration of the marrow. Decompression syndrome results from the presence of gaseous emboli in the microcirculature. In Legg-Calvé-Perthes disease other associated features are present such as short stature, suboptimal growth velocity, and/or hormonal imbalances, and it is likely that osteonecrosis may be secondary to systemic abnormalities, although specific factors have not been identified. Other frequently suggested pathogenic factors that play a role in the development of osteonecrosis include increased intraosseous pressures, the presence of cytotoxic cellular factors, intravascular coagulation, venous stasis, and the hyperviscosity syndrome. Some investigators have attempted, without success, to find a common etiology for all cases of osteonecrosis. In addition, patients have developed osteonecrosis without any known risk factors; this syndrome has been coined idiopathic avascular necrosis. In advanced stages of femoral head osteonecrosis, total hip arthroplasty appears to be the best therapeutic modality, particularly in older individuals.

Regulation and immunolocalization of acyl-coenzyme A: cholesterol acyltransferase in mammalian cells as studied with specific antibodies

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the formation of intracellular cholesterol esters in various tissues. We recently reported the cloning and expression of human macrophage ACAT cDNA. In the current study, we report the production of specific polyclonal antibodies against ACAT by immunizing rabbits with the recombinant fusion protein composed of glutathione S-transferase and the first 131 amino acids of ACAT protein. Immunoblot analysis showed that the antibodies cross-reacted with a 50-kDa protein band from a variety of human cell lines. These antibodies immunodepleted more than 90% of detergent-solubilized ACAT activities from six different human cell types, demonstrating that the 50-kDa protein is the major ACAT catalytic component in these cells. In multiple human tissues examined, the antibodies recognized protein bands with various molecular weights. These antibodies also cross-reacted with the ACAT protein in Chinese hamster ovary cells. Immunoblot analysis showed that the ACAT protein contents in human fibroblast cells, HepG2 cells, or Chinese hamster ovary cells were not affected by sterol in the medium, demonstrating that the main mechanism for sterol-dependent regulation of ACAT activity in these cells is not change in ACAT protein content. As revealed by indirect immunofluorescent microscopy, the ACAT protein in tissue culture cells was located in the endoplasmic reticulum. This finding, along with earlier studies, suggests that cholesterol concentration in the endoplasmic reticulum may be the major determinant for regulating ACAT activity in the intact cells.

Molecular evidence of Bartonella spp. in questing adult Ixodes pacificus ticks in California

Ticks are the vectors of many zoonotic diseases in the United States, including Lyme disease, human monocytic and granulocytic ehrlichioses, and Rocky Mountain spotted fever. Most known Bartonella species are arthropod borne. Therefore, it is important to determine if some Bartonella species, which are emerging pathogens, could be carried or transmitted by ticks. In this study, adult Ixodes pacificus ticks were collected by flagging vegetation in three sites in Santa Clara County, Calif. PCR-restriction fragment length polymorphism and partial sequencing of 273 bp of the gltA gene were applied for Bartonella identification. Twenty-nine (19.2%) of 151 individually tested ticks were PCR positive for Bartonella. Male ticks were more likely to be infected with Bartonella than female ticks (26 versus 12%, P = 0.05). None of the nine ticks collected at Baird Ranch was PCR positive for Bartonella. However, 7 (50%) of 14 ticks from Red Fern Ranch and 22 (17%) of 128 ticks from the Windy Hill Open Space Reserve were infected with Bartonella. In these infected ticks, molecular analysis showed a variety of Bartonella strains, which were closely related to a cattle Bartonella strain and to several known human-pathogenic Bartonella species and subspecies: Bartonella henselae, B. quintana, B. washoensis, and B. vinsonii subsp. berkhoffii. These findings indicate that I. pacificus ticks may play an important role in Bartonella transmission among animals and humans.