Helicobacter pylori-induced homotypic phagosome fusion in human monocytes is independent of the bacterial vacA and cag status

Following reports that a VacA+cag+ toxigenic but not a VacA-cag- non-toxigenic Helicobacter pylori strain induced homotypic phagosome fusion in murine macrophages, we addressed that phenomenon in human cells. Mononuclear phagocytes and epitheloid cells were challenged with H. pylori strains of different vacA and cag genotypes and with VacA- and Cag- isogenic mutants, and chased in the absence or presence of signal transduction modulators. Electron microscopy revealed that, in monocytes: (i) homotypic phagosome fusion was frequently induced by all live H. pylori strains investigated but not by exogenous VacA; (ii) phagosomes containing bacteria fused, but not those containing latex beads; (iii) fusion resulted in communal compartments resembling giant multivesicular bodies; and (iv) formation of these compartments was blocked by inhibiting the host cell regulators PI 3-kinase, phospholipase C and p42 MAP kinase. Whereas some internalized bacteria remained viable 1 h after uptake, none survived a 24 h period. In contrast to monocytes, infected epitheloid cells rarely developed communal compartments. In combination, these results demonstrate that, in human monocytes, the H. pylori-induced homotypic phagosome fusion depends on neither the vacuolating cytotoxin VacA nor the cag pathogenicity island of H. pylori and does not result in prolonged intracellular survival.

Intracellular survival of Brucella spp. in human monocytes involves conventional uptake but special phagosomes

Brucella spp. are facultative intracellular parasites of various mammals, including humans, typically infecting lymphoid as well as reproductive organs. We have investigated how B. suis and B. melitensis enter human monocytes and in which compartment they survive. Peripheral blood monocytes readily internalized nonopsonized brucellae and killed most of them within 12 to 18 h. The presence of Brucella-specific antibodies (but not complement) increased the uptake of bacteria without increasing their intracellular survival, whereas adherence of the monocytes or incubation in Ca(2+)- and Mg(2+)-free medium reduced the uptake. Engulfment of all Brucella organisms (regardless of bacterial viability or virulence) initially resulted in phagosomes with tightly apposed walls (TP). Most TP were fully fusiogenic and matured to spacious phagolysosomes containing degraded bacteria, whereas some TP (more in monocyte-derived macrophages, HeLa cells, and CHO cells than in monocytes) remained tightly apposed to intact bacteria. Immediate treatment of infected host cells with the lysosomotropic base ammonium chloride caused a swelling of all phagosomes and a rise in the intraphagosomal pH, abolishing the intracellular survival of Brucella. These results indicate that (i) human monocytes readily internalize Brucella in a conventional way using various phagocytosis-promoting receptors, (ii) the maturation of some Brucella phagosomes is passively arrested between the steps of acidification and phagosome-lysosome fusion, (iii) brucellae are killed in maturing but not in arrested phagosomes, and (iv) survival of internalized Brucella depends on an acidic intraphagosomal pH and/or close contact with the phagosomal wall.

Leishmania-host-cell interaction: complexities and alternative views

Leishmania are protozoan parasites that infect various mammalian species, including humans. It is generally thought that random attachment of the flagellated promastigotes to mononuclear phagocytes initiates their uptake via circumferential pseudopods. Intracellularly, the promastigotes become located in phagolysosomes in which they transform to and survive as 'aflagellated' amastigotes that hide their shortened flagellum within the flagellar pocket. Unrestricted replication of these amastigotes is assumed to cause the eventual burst of the host cell, thereby releasing the infectious parasites. Here, Mike Rittig and Christian Bogdan review a large body of literature containing potentially important but poorly appreciated findings, which together with recent results, argue for Leishmania-host-cell interactions that are much more complex than generally thought.

Fibroblasts as host cells in latent leishmaniosis

Intracellular parasites are known to persist lifelong in mammalian hosts after the clinical cure of the disease, but the mechanisms of persistence are poorly understood. Here, we show by confocal laser microscopy that in the draining lymph nodes of mice that had healed a cutaneous infection with Leishmania major, 40% of the persisting parasites were associated with fibroblasts forming the reticular meshwork of the lymph nodes. In vitro, both promastigotes and amastigotes of L. major infected primary skin or lymph node fibroblasts. Compared with macrophages, cytokine-activated fibroblasts had a reduced ability to express type 2 nitric oxide synthase and to kill intracellular L. major. These data identify fibroblasts as an important host cell for Leishmania during the chronic phase of infection and suggest that they might serve as safe targets for the parasites in clinically latent disease.

Studies on the pathogenesis and treatment of Lyme arthritis

Lyme arthritis is one of the most common clinical manifestations of Lyme borreliosis. It is caused by an intraarticular infection with Borrelia (B.) burgdorferi. A small number of bacteria are liable to provoke severe arthritis by inducing mechanisms (including the induction of cytokines and chemokines) that amplify the inflammatory response. The cellular immune response against B. burgdorferi is characterised by a predominant T helper cell type 1 (Th1) pattern that appears to be inadequate to overcome the infection. In most cases, Lyme arthritis may be cured by antibiotic therapy. A brief summary of current recommendations for the treatment of Lyme arthritis in adults and children is given in this article. However, about 10% of Lyme arthritis patients do not respond sufficiently to antibiotic treatment. Two not mutually exclusive pathogenetic concepts of these treatment-resistant cases will be discussed in the present study: persistent infection and infection-induced immunopathology.

Phagocytosis of microorganisms by means of overshooting pseudopods: where do we stand?

During the endocytic uptake of particulate material such as microorganisms, the transition from the engulfment step to the internalization step of phagocytosis may be disturbed. Thus, the pseudopods flanking the particles do not close to a phagosome, but lie on top of each other. This uncoupling of pseudopod extension and phagosome formation provides useful information about the regular course of phagocytosis. Experimental models on the phenomena of coiling and overlapping phagocytosis have so far been established with legionellas, spirochetes, trypanosomatids, fungal cells, and zymosan.

The mannose receptor mediates uptake of pathogenic and nonpathogenic mycobacteria and bypasses bactericidal responses in human macrophages

The mannose receptor (MR) is involved in the phagocytosis of pathogenic microorganisms. Here we investigated its role in the bactericidal functions of human monocyte-derived macrophages (MDMs), using (i) trimannoside-bovine serum albumin (BSA)-coated latex beads and zymosan as particulate ligands of the MR, and (ii) mannan and mannose-BSA as soluble ligands. We show that phagocytosis of mannosylated latex beads did not elicit the production of O2-. Zymosan, which is composed of alpha-mannan and beta-glucan, was internalized by the MR and a beta-glucan receptor, but the production of O2- was triggered only by phagocytosis through the beta-glucan receptor. Activation and translocation of Hck, a Src family tyrosine kinase located on lysosomes, has previously been used as a marker of fusion between lysosomes and phagosomes in human neutrophils. In MDMs, Hck was activated and recruited to phagosomes containing zymosan later than LAMP-1 and CD63. Phagosomes containing mannosylated latex beads fused with LAMP-1 and CD63 vesicles but not with the Hck compartment, and the kinase was not activated. We also demonstrate that the MR was unable to distinguish between nonpathogenic and pathogenic mycobacteria, as they were internalized at similar rates by this receptor, indicating that this route of entry cannot be considered as a differential determinant of the intracellular fate of mycobacteria. In conclusion, MR-dependent phagocytosis is coupled neither to the activation of NADPH oxidase nor to the maturation of phagosomes until fusion with the Hck compartment and therefore constitutes a safe portal of entry for microorganisms.

Coiling phagocytosis of trypanosomatids and fungal cells

Coiling phagocytosis has previously been studied only with the bacteria Legionella pneumophila and Borrelia burgdorferi, and the results were inconsistent. To learn more about this unconventional phagocytic mechanism, the uptake of various eukaryotic microorganisms by human monocytes, murine macrophages, and murine dendritic cells was investigated in vitro by video and electron microscopy. Unconventional phagocytosis of Leishmania spp. promastigotes, Trypanosoma cruzi trypomastigotes, Candida albicans hyphae, and zymosan particles from Saccharomyces cerevisiae differed in (i) morphology (rotating unilateral pseudopods with the trypanosomatids, overlapping bilateral pseudopods with the fungi), (ii) frequency (high with Leishmania; occasional with the fungi; rare with T. cruzi), (iii) duration (rapid with zymosan; moderate with the trypanosomatids; slow with C. albicans), (iv) localization along the promastigotes (flagellum of Leishmania major and L. aethiopica; flagellum or posterior pole of L. donovani), and (v) dependence on complement (strong with L. major and L. donovani; moderate with the fungi; none with L. aethiopica). All of these various types of unconventional phagocytosis gave rise to similar pseudopod stacks which eventually transformed to a regular phagosome. Further video microscopic studies with L. major provided evidence for a cytosolic localization, synchronized replication, and exocytic release of the parasites, extending traditional concepts about leishmanial infection of host cells. It is concluded that coiling phagocytosis comprises phenotypically similar consequences of various disturbances in conventional phagocytosis rather than representing a single separate mechanism.

Detection of Borrelia burgdorferi by polymerase chain reaction in synovial membrane, but not in synovial fluid from patients with persisting Lyme arthritis after antibiotic therapy

OBJECTIVES

To identify possible sites of bacterial persistence in patients with treatment resistant Lyme arthritis. It was determined whether Borrelia burgdorferi DNA may be detectable by polymerase chain reaction (PCR) in synovial membrane (SM) when PCR results from synovial fluid (SF) had become negative after antibiotic therapy.

METHODS

Paired SF and SM specimens and urine samples from four patients with ongoing or recurring Lyme arthritis despite previous antibiotic therapy were investigated. A PCR for the detection of B burgdorferi DNA was carried out using primer sets specific for the ospA gene and a p66 gene of B burgdorferi.

RESULTS

In all four cases, PCR with either primer set was negative in SF and urine, but was positive with at least one primer pair in the SM specimens. In all patients arthritis completely resolved after additional antibiotic treatment.

CONCLUSIONS

These data suggest that in patients with treatment resistant Lyme arthritis negative PCR results in SF after antibiotic therapy do not rule out the intraarticular persistence of B burgdorferi DNA. Therefore, in these patients both SF and SM should be analysed for borrelial DNA by PCR as positive results in SM are strongly suggestive of ongoing infection.

Coiling phagocytosis discriminates between different spirochetes and is enhanced by phorbol myristate acetate and granulocyte-macrophage colony-stimulating factor

The mechanisms involved in coiling phagocytosis are not yet known, and it is not even clear whether this phenomenon is either an incidental event or a specific response. Therefore, the phagocytic uptake of Borrelia burgdorferi and other spirochetes by human monocytes in vitro was used to investigate the involvement of both sides--microbes and phagocytes--in coiling phagocytosis. As seen with electron microscopy, morphologically similar Borrelia, Leptospira and Treponema strains induced markedly different frequencies of coiling phagocytosis. The monocytes used coiling phagocytosis for both live (motile) and killed (nonmotile) B. burgdorferi, but pseudopod coils were observed neither with fragmented B. burgdorferi nor with cell-free supernatant from B. burgdorferi cultures. Investigation of the relationship of coiling phagocytosis with other pseudopod-based cellular mechanisms revealed that the use of bioreagents that inhibit conventional phagocytosis also inhibited coiling phagocytis but did not affect membrane ruffling. Bioreagents that increase membrane ruffling did not affect phagocytosis of B. burgdorferi, except for granulocyte-macrophage colony-stimulating factor and phorbol myristate acetate, which increased coiling phagocytosis selectively. These results demonstrate that coiling phagocytosis is not induced by microbial motility, viability, or a certain morphology and that it is not a random event. Rather, it is a selective uptake mechanism actively driven by the phagocytes. However, whether coiling phagocytosis represents an independent alternative to conventional phagocytosis or, alternatively, a fault in conventional phagocytosis remains to be determined.

Borrelia burgdorferi induces chemokines in human monocytes

Lyme disease is clinically and histologically characterized by strong inflammatory reactions that contrast the paucity of spirochetes at lesional sites, indicating that borreliae induce mechanisms that amplify the inflammatory response. To reveal the underlying mechanisms of chemoattraction and activation of responding leukocytes, we investigated the induction of chemokines in human monocytes exposed to Borrelia burgdorferi by a dose-response and kinetic analysis. Lipopolysaccharide (LPS) derived from Escherichia coli was used as a positive control stimulus. The release of the CXC chemokines interleukin-8 (IL-8) and GRO-alpha and the CC chemokines MIP-1alpha, MCP-1, and RANTES was determined by specific enzyme-linked immunosorbent assays, and the corresponding gene expression patterns were determined by Northern blot analysis. The results showed a rapid and strong borrelia-inducible gene expression which was followed by the release of chemokines with peak levels after 12 to 16 h. Spirochetes and LPS were comparably effective in stimulating IL-8, GRO-alpha, MCP-1, and RANTES expression, whereas MIP-1alpha production preceded and exceeded chemokine levels induced by LPS. Unlike other bacteria, the spirochetes themselves did not bear or release factors with intrinsic chemotactic activity for monocytes or neutrophils. Thus, B. burgdorferi appears to be a strong inducer of chemokines which may, by the attraction and activation of phagocytic leukocytes, significantly contribute to inflammation and tissue damage observed in Lyme disease.

Hydroxyurea for treatment of unresectable and recurrent meningiomas. I. Inhibition of primary human meningioma cells in culture and in meningioma transplants by induction of the apoptotic pathway

Meningiomas, which invade intracranial bone structures and the adjacent connective tissue, are frequently unresectable because of their aggressive and recalcitrant growth behavior. They have a high recurrence rate, and in approximately 10% of these tumors there is an increased risk of malignancy. Significant morbidity and mortality rates associated with recurrent meningiomas demand nonsurgical approaches. To date, adjuvant hormonal treatment has not proven beneficial. The anticancer drug hydroxyurea was therefore tested for its potential use in the treatment of meningiomas. Early-passaged cell cultures were established from 20 different meningiomas. The addition of 5 x 10(-4) and 10(-3) M hydroxyurea over a period of 5 to 9 days resulted in a remarkable decrease in cell proliferation and even blocked tumor cell growth when compared with untreated cells. A significant arrest of meningioma cell growth in the S phase of the cell cycle was revealed on DNA flow cytometry. Electron micrographs of hydroxyurea-treated tumor cells showed ultrastructural features consistent with apoptosis, and light microscopy demonstrated DNA fragmentation by in situ DNA strand break labeling. Short-term treatment of meningioma cell cultures with hydroxyurea for 24 to 48 hours resulted in discrete oligonucleosomal fragments (DNA ladder), another characteristic sign of apoptosis. In addition to the in vitro studies, tissue from five different meningiomas was transplanted into nude mice followed by treatment with 0.5 mg/g body weight hydroxyurea over 15 days. In situ DNA strand break labeling demonstrated DNA fragmentation in distinct regions with different tumor cell densities in all hydroxyurea-treated meningioma transplants. These data provide evidence that hydroxyurea is a powerful inhibitor of meningioma cell growth, most likely by causing apoptosis in the tumor cells. Thus, hydroxyurea may be a suitable chemotherapeutic agent for the long-term treatment of unresectable or semi- to malignant meningiomas, or for preventing recurrent growth of meningiomas after resection.

Hydroxyurea for treatment of unresectable and recurrent meningiomas. II. Decrease in the size of meningiomas in patients treated with hydroxyurea

In this paper the authors present the first evidence that meningiomas respond to treatment with hydroxyurea. Hydroxyurea was administered as an adjunct chemotherapeutic treatment in patients with recurrent and unresectable meningiomas. Hydroxyurea was used because experimental data demonstrated that it inhibits growth of cultured human meningioma cells and meningioma transplants in nude mice by inducing apoptosis. The authors therefore treated four selected patients with hydroxyurea. All patients had undergone multiple gross resections and all except one received radiotherapy. Three patients with recurrent Grade I meningiomas assessed according to World Health Organization (WHO) guidelines received hydroxyurea because of an increased tumor growth rate, documented by magnetic resonance (MR) imaging, within a 6- or 12-month interval. A fourth patient with a malignant meningioma (WHO Grade III) began a course of treatment with hydroxyurea immediately after his sixth palliative operation without waiting for another relapse to be demonstrated on MR imaging. Because of their location and invasive growth behavior none of the meningiomas could have been removed completely by surgical intervention. All patients received hydroxyurea at a dosage level of 1000 to 1500 mg/day (approximately 20 mg/kg/day). In a man with a large sphenoid wing meningioma invading the right cavernous sinus and the temporal base, the intracranial tumor mass was reduced by 60% during 6 months of treatment. A woman with a large ball-shaped meningioma of the right sphenoid wing invading the cavernous sinus exhibited a 74% decrease of the initial tumor volume in 10 months of treatment with oral hydroxyurea. Serial MR images obtained monthly revealed that the process of size reduction was continuous and proportionate. The shrinkage of the tumor was accompanied by a complete remission of symptomatic trigeminal neuralgia after 2 months and by improved abducent paresis after 5 months. The third patient had a slowly growing meningioma that exhibited a 15% reduction in mass when reassessed after 5 months of hydroxyurea treatment. The fourth patient with the malignant meningioma in the left cerebellopontine angle has had no recurrence for 24 months. Long-term treatment with hydroxyurea may result in full remission of tumors in meningioma patients. The preliminary data indicate that hydroxyurea provides true medical treatment in patients with unresectable and recurrent meningiomas, replacing palliative surgery and radiotherapy in the management of this disease.

An optimized PCR leads to rapid and highly sensitive detection of Borrelia burgdorferi in patients with Lyme borreliosis

The present study aimed at developing an optimized PCR protocol fro the sensitive and specific detection of all three Borrelia burgdorferi genospecies pathogenic to humans in Lyme borreliosis patients. A rapid DNA extraction method using alkaline lysis was introduced and was found to be superior to other DNA extraction methods. Nested PCR was performed with primer sets targeting the plasmid-located ospA gene and a chromosomal gene segment encoding a 66-kDa protein (p66). In spiked synovial fluid (SF) fewer than three borreliae/sample were detected. The specificities of the amplicons were confirmed by Southern blot analysis with PCR-derived probes. Urine, cerebrospinal fluid (CSF), and SF specimens from 57 patients with Lyme borreliosis and from 58 controls were examined. In clinical samples the diagnostic sensitivity of PCR was 85% with SF samples, 79% with urine samples, and 91% with paired SF-urine samples from patients with Lyme arthritis and was 79% with CSF samples, 45% with urine samples, and 87% with paired CSF-urine specimens from neuroborreliosis patients. One patient each with neuroborreliosis and with Lyme arthritis had PCR-positive urine samples only. In 17% of all cases both primer sets yielded positive results, while the other patients were positive with only one primer set. Among these, more positive results were obtained with the p66 gene primer than with the ospA primer. The specificity exceeded 99%. We conclude that DNA from B. burgdorferi sensu lato species can sensitively and specifically be detected with the optimized PCR method described. At least two different primer sets should be used, and whenever possible, urine and CSF or SF should be analyzed in parallel to achieve maximum sensitivity of the test. This protocol, therefore, considerably enhances the diagnostic power of PCR in patients with B. burgdorferi infection.

Phagocytes from both vertebrate and invertebrate species use "coiling" phagocytosis

Coiling phagocytosis has been observed previously only by chance, and there has been no systematic investigation of this uptake mechanism. Therefore, a comparative electron microscopical study was performed. Different human and murine cell populations, phagocytes from various vertebrate and invertebrate species, and predatory amoebae were incubated with Borrelia burgdorferi, one of the microbes known to induce coiling phagocytosis, to study the uptake mechanisms used. In this model, coiling phagocytosis was observed with both vertebrate and invertebrate species but not with amoebae. With cells from humans and mice, this uptake mechanism was restricted to phagocytic cells of myeloid origin. The coiled membrane gaps did not give rise to phagosomes; instead, membrane fusion was followed by membrane dissipation. Thus, coiling of B. burgdorferi apparently is an alternative uptake mechanism used by metazoan phagocytes, involving special membrane processing. However, coiling phagocytosis may show different features with different microbes.

Borrelia burgdorferi-induced ultrastructural alterations in human phagocytes: a clue to pathogenicity?

A chronic infection with the spirochaete Borrelia burgdorferi typically results in a multistage, multisystem illness. Thus, Lyme borreliosis may provide an interesting model to study the pathomechanisms of microbial persistence. In the present investigation, human peripheral blood monocytes, polymorphonuclear leukocytes, and synovial macrophages were incubated with B. burgdorferi and examined by light and electron microscopy. It was found that incubation with the spirochaetes induced distinct features in the phagocytes. Features which may be related to the pathogenesis of Lyme disease included the segmental uptake of spirochaetes with leaky lysosomes, the invagination of large membrane areas, the extra-lysosomal degradation of internalized B. burgdorferi cells and, finally, the formation of mononuclear syncytial cells and homotypic cell clusters. Features of unknown relevance were the occurrence of two types of cytoplasmic inclusion bodies and exocytic vesicles. These novel findings suggest that reactive alterations of the phagocytes may contribute to the pathogenesis of Lyme borreliosis, which could help to focus future histopathological studies. Moreover, these results may provide new insights into the pathogenesis of other infectious diseases characterized similarly by microbial persistence.

Innervation of the ciliary process vasculature and epithelium by nerve fibers containing catecholamines and neuropeptide Y

The ciliary processes (CPs) in the rat were investigated for the presence of neuropeptide Y (NPY)-like immunoreactivity and for histofluorescence indicating catecholamine (CAM)-ergic innervation in the rat, rabbit and cynomolgus monkey. Special attention was paid to those CP vessel segments which in previous studies showed distinct reactions on application of CAM or NPY, and on the respective sections of the CP epithelium. In the rat and cynomolgus monkey most CAM-ergic nerve fibers concentrated along the terminal arterioles and the epithelium of the anteriormost portion of the major CPs. In comparison, the rabbit displayed most intense CAM-ergic innervation along the terminal arterioles and the epithelium of both the iridial processes and the anterior portion of the major CPs. The NPY-ergic nerve fibers built up a dense subepithelial nervous plexus in the anterior portion of the rat CPs, diminishing towards the posterior CPs. Also, many NPY-ergic fibers were found along the terminal arterioles of the anterior CPs. The findings demonstrate that CAM- and NPY-ergic nerve fibers preferentially supply vasculature and epithelium of the anterior ciliary processes, suggesting a crucial function of these structures for the precise regulation of aqueous humor formation.

Coiling phagocytosis is the preferential phagocytic mechanism for Borrelia burgdorferi

The uptake mechanism for the spirochete Borrelia burgdorferi, the causative agent of Lyme disease, was investigated by electron microscopy for human and murine phagocytes. Spirochetes of both a low- and a high-passage strain were preferentially internalized by coiling rather than by conventional phagocytosis. The spirochetes engulfed by coiling phagocytosis were found to disintegrate in an organelle exclusion zone without evident participation of lysosomes. Preincubation of B. burgdorferi with monoclonal antibody to the spirochetal OspA enhanced phagocytosis in general but did not consistently influence the uptake mechanism. Quantitative and kinetic differences concerning the phagocytic rate and mechanism were evident between cells from different lineages, different human individuals, and mice and humans. In general, when few phagocytes participated in spirochete uptake, the active cells displayed a high ratio of coiling versus conventional phagocytosis. These results suggest that coiling phagocytosis of B. burgdorferi plays a critical role in the control of spirochetal infection. More detailed studies on the molecular basis of this phagocytic mechanism may lead to new insights into the pathogenesis of Lyme borreliosis, a disease which is frequently characterized by the host's inability to eliminate the pathogenic spirochete.