Bacillary angiomatosis in a German patient with AIDS

Evidence of a leading role for VEGF in Bartonella henselae-induced endothelial cell proliferations

Bartonella henselae causes the vasculoproliferative disorders bacillary angiomatosis (BA) and bacillary peliosis (BP). The pathomechanisms of these tumorous proliferations are unknown. Our results suggest a novel bacterial two-step pathogenicity strategy, in which the pathogen triggers growth factor production for subsequent proliferation of its own host cells. In fact, B. henselae induces host cell production of the angiogenic factor vascular endothelial growth factor (VEGF), leading to proliferation of endothelial cells. The presence of B. henselae pili was associated with host cell VEGF production, as a Pil- mutant of B. henselae was unable to induce VEGF production. In turn, VEGF-stimulated endothelial cells promoted the growth of B. henselae. Immunohistochemistry for VEGF in specimens from patients with BA or BP revealed increased VEGF expression in vivo. These findings suggest a novel bacteria-dependent mechanism of tumour growth.

Formation of stress fibres in human endothelial cells infected with Bartonella bacilliformis is associated with altered morphology, impaired migration and defects in cell morphogenesis

Bartonella bacilliformis, a Gram-negative, flagellated bacterium, infects human erythrocytes (haematic phase) and endothelial cells (tissue phase), resulting in a biphasic disease. In the tissue phase of disease (verruga peruana), infection leads to infection of endothelial cells and a pronounced proliferation of these cells, resulting in characteristic skin eruptions of papules and nodules. We have studied the properties of endothelial cells infected in vitro. Extensive cytoskeletal remodelling of endothelial cells occurred after infection in vitro with B. bacilliformis. The cells became spindle shaped and contained arrays of actin stress fibres orientated parallel to the long axis of the cell. Cell-cell contacts were disrupted, along with the distribution of the plasma membrane marker protein, PECAM-1, which participates in cell-cell junctions. The prominent stress fibres terminated in an increased number of focal contacts, which were studied using immunofluorescent staining for paxillin, a cytoplasmic protein that localizes in the focal adhesions. These morphological changes are consistent with activation of intracellular Rho by B. bacilliformis. Formation of stress fibres and the increased number of focal adhesions could be prevented by preincubation of the endothelial cells with C3 exoenzyme, which inactivates intracellular Rho by ADP ribosylation. Endothelial cell motility was greatly diminished in infected cells and the cells did not respond effectively to a stimulus that would evoke motility. In addition, infection of endothelial cells interfered with their ability to form networks of capillary tubes when suspended within three-dimensional collagen matrices. If the properties of infected endothelial cells in vivo are similar, the infected cells will probably not participate effectively in angiogenesis.

Interaction of Bartonella henselae with endothelial cells results in rapid bacterial rRNA synthesis and replication

Bartonella henselae is a slow-growing microorganism and the causative pathogen of bacillary angiomatosis in man. Here, we analysed how interaction of B. henselae with endothelial cells might affect bacterial growth. For this purpose, bacterial rRNA production and ribosome content was determined by fluorescence in situ hybridization (FISH) using rRNA-targeted fluorescence-labelled oligonucleotide probes. B. henselae grown on agar plates showed no detectable rRNA content by means of FISH, whereas B. henselae co-cultured with endothelial cells showed a rapid increase of rRNA production within the first 18 h after inoculation. The increased rRNA synthesis was paralleled by a approximately 1000-fold intracellular bacterial replication, whereas bacteria grown on agar base showed only a approximately 10-fold replication within the first 48 h of culture. Pretreatment of host cells with paraformaldehyde prevented adhesion, invasion, intracellular replication and bacterial rRNA synthesis of B. henselae. In contrast, inhibition of host cell protein synthesis by cycloheximide did not affect bacterial adhesion and invasion, but prevented intracellular replication although bacterial rRNA content was increased. Inhibition of actin polymerization by cytochalasin D did not affect adhesion, invasion, increased rRNA content or intracellular replication of B. henselae. These results demonstrate that rRNA synthesis and replication of B. henselae is promoted by viable host cells with intact de novo protein synthesis.

Isolation, sequencing and expression of Bartonella henselae omp43 and predicted membrane topology of the deduced protein

The infection of and interaction of human endothelial cells with Bartonella henselae is one of the most interesting aspects of Bartonella -associated disease. The gene encoding the 43 kDa B. henselae outer membrane protein (Omp43) that binds endothelial cells was cloned and sequenced. Sequence analysis revealed an open reading frame of 1206 nucleotides coding for a protein of 402 amino acids. Analysis of the deduced amino acid sequence shows 38% identity over the entire sequence to the Brucella spp. In addition to this Omp2b porin also shows a signal sequence and peptidase cleavage site. Cleavage of the signal peptide results in a mature 380 amino acid polypeptide with a predicted molecular weight of 42 kDa. Omp43 was expressed in Escherichia coli as a fusion protein. Purified recombinant Omp43 at concentrations of 11 and 2.75 microg/ml bound to intact human umbilical vein endothelial cells. Membrane topology analysis predicts that Omp43 exists as a 16 stranded beta barrel protein, similar to that predicted for the Omp2b Brucella abortus porin. Characterization and expression of the gene encoding Omp43 should provide a tool for further investigation of the role of adherence to endothelial cells in the pathogenesis of B. henselae.