The VirB type IV secretion system of Bartonella henselae mediates invasion, proinflammatory activation and antiapoptotic protection of endothelial cells

Bartonella henselae is an arthropod-borne zoonotic pathogen causing intraerythrocytic bacteraemia in the feline reservoir host and a broad range of clinical manifestations in incidentally infected humans. Remarkably, B. henselae can specifically colonize the human vascular endothelium, resulting in inflammation and the formation of vasoproliferative lesions known as bacillary angiomatosis and bacillary peliosis. Cultured human endothelial cells provide an in vitro system to study this intimate interaction of B. henselae with the vascular endothelium. However, little is known about the bacterial virulence factors required for this pathogenic process. Recently, we identified the type IV secretion system (T4SS) VirB as an essential pathogenicity factor in Bartonella, required to establish intraerythrocytic infection in the mammalian reservoir. Here, we demonstrate that the VirB T4SS also mediates most of the virulence attributes associated with the interaction of B. henselae during the interaction with human endothelial cells. These include: (i) massive rearrangements of the actin cytoskeleton, resulting in the formation of bacterial aggregates and their internalization by the invasome structure; (ii) nuclear factor kappaB-dependent proinflammatory activation, leading to cell adhesion molecule expression and chemokine secretion, and (iii) inhibition of apoptotic cell death, resulting in enhanced endothelial cell survival. Moreover, we show that the VirB system mediates cytostatic and cytotoxic effects at high bacterial titres, which interfere with a potent VirB-independent mitogenic activity. We conclude that the VirB T4SS is a major virulence determinant of B. henselae, required for targeting multiple endothelial cell functions exploited by this vasculotropic pathogen.     

A methylcellulose microculture assay for the in vitro assessment of drug toxicity on granulocyte/macrophage progenitors (CFU-GM)

In a recent prevalidation study, the use of a methylcellulose colony-forming unit-granulocyte/macrophage (CFU-GM) macroassay for two independent in vitro tests (human and murine cell based) was suggested for quantifying the potential haematotoxicity of xenobiotics. In this paper, we describe the transfer of the macroassay to a 96-well plate microassay, in which the linearity of the response was studied (both in terms of CFU-GM and optical density [OD] versus the number of cells cultured), and the inhibitory concentration (IC) values for doxorubicin, 5-fluorouracil and taxol were determined and compared with those obtained by using the original macroassay. Fresh murine bone marrow and human umbilical cord blood mononuclear cells were used as a source of myeloid progenitors. The cells were cultured in methylcellulose containing granulocyte/macrophage-colony-stimulating factor, and in the presence of increasing drug concentrations. The cloning capacity of the progenitors was measured both as the number of colonies counted manually (CFU-GM), and as OD evaluated with an automated plate reader in an MTT test. Our results show that, in the microassay, up to 20 colonies/well could be easily counted, and that this range (20 to zero) gave a regression line from which IC values were calculated, which were very close to those obtained by using the macroassay (where the range of colony numbers was from 100 to zero). The test did not give good results when the OD (instead of the colony count) was used as the endpoint, because, although a high coefficient of determination was obtained, the OD values ranged from 0.6 to zero and the IC values determined were not comparable to those obtained by manual counts. The use of the microassay dramatically reduces the quantity of methylcellulose needed, and permits hundreds of cultures to be processed in the same experiment, contributing to significant reductions in both the work involved and the cost. A further important benefit is a reduction of the amount of drug needed for testing, which is crucial for screening new molecules, when many different toxicological tests have to be carried out. The microassay is therefore a useful and reproducible tool for screening compounds (chemicals, drugs and xenobiotics) for potential haematotoxicity directly on human myeloid progenitors, and could contribute significantly to reducing the use of animals in toxicity testing.     

The deletion of the succinate dehydrogenase gene KlSDH1 in Kluyveromyces lactis does not lead to respiratory deficiency

We have isolated a Kluyveromyces lactis mutant unable to grow on all respiratory carbon sources with the exception of lactate. Functional complementation of this mutant led to the isolation of KlSDH1, the gene encoding the flavoprotein subunit of the succinate dehydrogenase (SDH) complex, which is essential for the aerobic utilization of carbon sources. Despite the high sequence conservation of the SDH genes in Saccharomyces cerevisiae and K. lactis, they do not have the same relevance in the metabolism of the two yeasts. In fact, unlike SDH1, KlSDH1 was highly expressed under both fermentative and nonfermentative conditions. In addition to this, but in contrast with S. cerevisiae, K. lactis strains lacking KlSDH1 were still able to grow in the presence of lactate. In these mutants, oxygen consumption was one-eighth that of the wild type in the presence of lactate and was normal with glucose and ethanol, indicating that the respiratory chain was fully functional. Northern analysis suggested that alternative pathway(s), which involves pyruvate decarboxylase and the glyoxylate cycle, could overcome the absence of SDH and allow (i) lactate utilization and (ii) the accumulation of succinate instead of ethanol during growth on glucose.     

Molecular morphology of neuronal apoptosis: Analysis of caspase 3 activation during postnatal development of mouse cerebellar cortex

We have used the mammalian post-natal cerebellar cortex as a model to dissect out the molecular morphology of neuronal apoptosis in a well-defined population of central neurons: the cerebellar granule cells. By immunocytochemistry, in situ labeling of apoptotic cells, and analysis of cerebellar slices following particle-mediated gene transfer (biolistics), we have studied the relationship of cell death and cleavage of caspase 3, a key molecule in the execution of apoptosis, and monitored caspase 3 activation in living cells. Our results demonstrate the existence of caspase dependent and independent apoptotic pathways affecting the cerebellar granule cells at different stages of their life. Apoptosis of proliferating precursors and young pre-migratory cells occurs in the absence of caspase 3 cleavage, whereas cell death of post-mitotic post-migratory neurons is directly linked to caspase 3 activation. Data obtained from cerebellar cortex can be generalized to outline a more comprehensive picture of the cellular and molecular mechanisms of neuronal death not only in development, but also in a number of pathological conditions leading to neuronal loss.     

First Microsatellite Loci of Red Mullet (<Emphasis Type="Italic">Mullus barbatus</Emphasis>) and Their Application to Genetic Structure Analysis of Adriatic Shared Stock

In order to study the genetic structure of the Adriatic shared stock of red mullet (Mullus barbatus), we developed a set of dinucleotide microsatellite markers. A dinucleotide-enriched genomic library was obtained, and 6 polymorphic dinucleotide loci were successfully optimized. The markers showed high expected heterozygosity (from 0.68 to 0.92) and allele number (from 12 to 33); thus they appear to be suitable for detecting genetic differences in the population of red mullet. Four Adriatic samples were subsequently analyzed for microsatellite variation, and the results showed subtle but statistically significant genetic differentiation, indicating that the Adriatic red mullet may group into local, genetically isolated populations. No correlation between geographic distance and genetic differentiation was observed. In addition, the evidence of recent bottlenecks in the Adriatic samples indicates that the observed population subdivision might reflect random local allelic variations, generated by reproductive success, survival rates, or fishing pressure.     

Abnormal splicing of ABCA1 pre-mRNA in Tangier disease due to a IVS2 +5G>C mutation in ABCA1 gene

Two point mutations of ABCA1 gene were found in a patient with Tangier disease (TD): i) G>C in intron 2 (IVS2 +5G>C) and ii) c.844 C>T in exon 9 (R282X). The IVS2 +5G>C mutation was also found in the brother of another deceased TD patient, but not in 78 controls and 33 subjects with low HDL. The IVS2 +5G>C mutation disrupts ABCA1 pre-mRNA splicing in fibroblasts, leading to three abnormal mRNAs: devoid of exon 2 (Ex2-/mRNA), exon 4 (Ex4-/mRNA), or both these exons (Ex2-/Ex4-/mRNA), each containing a translation initiation site. These mRNAs are expected either not to be translated or generate short peptides. To investigate the in vitro effect of IVS2 +5G>C mutation, we constructed two ABCA1 minigenes encompassing Ex1-Ex3 region, one with wild-type (WTgene) and the other with mutant (MTgene) intron 2. These minigenes were transfected into COS1 and NIH3T3, two cell lines with a different ABCA1 gene expression. In COS1 cells, WTgene pre-mRNA was spliced correctly, while the splicing of MTgene pre-mRNA resulted in Ex2-/mRNA. In NIH3T3, no splicing of MTgene pre-mRNA was observed, whereas WTgene pre-mRNA was spliced correctly. These results stress the complexity of ABCA1 pre-mRNA splicing in the presence of splice site mutations.     

Effective genetic vaccination with a widely shared endogenous retroviral tumor antigen requires CD40 stimulation during tumor rejection phase

Endogenous retrovirus (ERV) products are recognized by T lymphocytes in mice and humans. As these Ags are preferentially expressed by neoplastic tissues, they might represent an ideal target for active immunization by genetic vaccination. However, i.m. inoculation of plasmid DNA encoding mouse gp70 or p15E, two products of the env gene of an endogenous murine leukemia virus, elicited a weak Ag-specific T lymphocyte response and resulted in partial protection from challenge with mouse tumors possessing these Ags. Depletion experiments showed that CD8(+), but not CD4(+), T lymphocytes were crucial for the antitumor activity of the vaccines. Systemic administration of agonistic anti-CD40 mAb increased the therapeutic potential of genetic vaccination, but only when given during the tumor rejection phase and not at the time of immunization. This effect correlated with a dramatic increase in the number of ERV-specific CD8(+) T lymphocytes. Adjuvant activity of CD40 agonists thus seems to be relevant to enhance the CD8(+) T cell-dependent response in tumor-bearing hosts, suggesting that sustaining tumor-specific T lymphocyte survival in subjects undergoing vaccination might be a key event in the successful vaccination with weak tumor Ags.     

Molecular interaction and enzymatic activity of macrophage migration inhibitory factor with immunorelevant peptides

Disulfide reduction is an important step in antigen processing for HLA class II restricted T cell responses. Migration inhibitory factor (MIF) is a member of the thioredoxin family and has been classically defined as a cytokine. Using enzyme-linked immunosorbent assay and CD analysis, here we describe the binding to MIF of two peptides, hepatitis B surface antigen (HBsAg) and insulin B (InsB) with high affinity for HLA class II allo-types, HLA-DP2 and HLA-DQ8, respectively. At neutral pH, cysteinylated InsB was a substrate for MIF thiol reductase activity, as assessed by mass spectroscopy/electrospray analysis. Finally, a biologically active form of MIF co-immunopurified with mature forms of HLA DP2/15, and a peptide derived from the HLA-DP beta1 helix could be used for affinity purification of MIF. The possibility that MIF participates in class II antigen presentation and/or as a chaperone is discussed.