Uptake and killing of Leptospira interrogans and Borrelia burgdorferi, spirochetes pathogenic to humans, by reticuloendothelial cells in perfused rat liver

Characteristic features of intracellular pathogenic Leptospira in infected murine macrophages

Leptospira interrogans is a spirochaete responsible for a zoonotic disease known as leptospirosis. Leptospires are able to penetrate the abraded skin and mucous membranes and rapidly disseminate to target organs such as the liver, lungs and kidneys. How this pathogen escape from innate immune cells and spread to target organs remains poorly understood. In this paper, the intracellular trafficking undertaken by non-pathogenic Leptospira biflexa and pathogenic L. interrogans in mouse bone marrow-derived macrophages was compared. The delayed in the clearance of L. interrogans was observed. Furthermore, the acquisition of lysosomal markers by L. interrogans-containing phagosomes lagged behind that of L. biflexa-containing phagosomes, and although bone marrow-derived macrophages could degrade L. biflexa as well as L. interrogans, a population of L. interrogans was able to survive and replicate. Intact leptospires were found within vacuoles at 24 h post infection, suggesting that bacterial replication occurs within a membrane-bound compartment. In contrast, L. biflexa were completely degraded at 24 h post infection. Furthermore, L. interrogans but not L. biflexa, were released to the extracellular milieu. These results suggest that pathogenic leptospires are able to survive, replicate and exit from mouse macrophages, enabling their eventual spread to target organs.

Gene expression profiles of immune mediators and histopathological findings in animal models of leptospirosis: comparison between susceptible hamsters and resistant mice

Leptospirosis is a widespread zoonosis characterized by multiple organ failure and variable host susceptibility toward pathogenic Leptospira strains. In this study, we put the role of inflammatory mediators in parallel with bacterial burdens and organ lesions by comparing a susceptible animal model, the hamster, and a resistant one, the Oncins France 1 (OF1) mouse, both infected with virulent Leptospira interrogans serovar Icterohaemorrhagiae strain Verdun. Histological observations evidenced edema, congestion, hemorrhage, and inflammatory infiltration in the organs of hamsters, in contrast to limited changes in mice. Using reverse transcription-quantitative PCR techniques, we showed that the relative Leptospira burden progressively increased in hamster tissues, while a rapid clearance was observed in mouse tissues. The early regulation of the proinflammatory mediators interleukin-1β (IL-1β), IL-6, tumor necrosis factor alpha, and cyclo-oxygenase-2 and the chemokines gamma interferon-inducible protein 10 kDa/CXCL10 and macrophage inflammatory protein-1α/CCL3 in mouse tissues contrasted with their delayed and massive overexpression in hamster tissues. Conversely, the induction of the anti-inflammatory cytokine IL-10 was faster in the resistant than in the susceptible animal model. The role of these cytokines in the pathophysiology of leptospirosis and the implications of their differential regulation in the development of this disease are discussed.

Na/K-ATPase assay in the intact guinea pig liver submitted to in situ perfusion

We describe an assay for the enzyme Na/K-ATPase in intact guinea pig livers perfused through the portal vein with modified Hank's solution. The model uses the measurement of non-radioactive rubidium ion incorporation by liver cells, both in the absence and in the presence of the specific Na/K-ATPase inhibitor ouabain, followed by a rinsing procedure with cold saline. The concentration of Rb+ in acid-digested liver lobes was measured by atomic emission spectrometry and Na/K pump activity was calculated by the difference between the incorporation of Rb+ in the absence and in the presence of ouabain. The optimal conditions for Rb+ incorporation were: perfusion flow rate, 3 ml/min per liver; perfusion time at 37 degrees C, 60 min; rinsing time with cold saline, 5-10 min; and concentration of ouabain, 3 mM. The calculated ouabain IC(50) was 100 microM. The major advantage of this model is the possibility of testing experimental drugs affecting this enzyme in conditions close to those in the intact organ.

Leptospirosis: pathogenesis, immunity, and diagnosis

PURPOSE OF REVIEW

Leptospirosis is among the most important zoonotic diseases worldwide. Completion of the genomic sequences of leptospires has facilitated advances in diagnosis and prevention of the disease, and yielded insight into its pathogenesis. This article reviews this research, emphasizing recent progress.

RECENT FINDINGS

Leptospirosis is caused by a group of highly invasive spiral bacteria (spirochetes) that can infect both people and animals. Spirochetes can survive in the environment and host, and therefore outer membrane and secretory proteins that interact with the host are of considerable interest in leptospire research. The genetic approach to studying pathogenesis is hindered by fastidious growth of pathogenic leptospires. Integrated genomic and proteomic approaches, however, have yielded enhanced understanding of the pathogenesis of leptospirosis. Furthermore, studies of innate immune response to the organism have enhanced our understanding of host susceptibility and resistance to infection. In-silico analysis and high-throughput cloning and expression have had major impacts on efforts to develop vaccine candidates and diagnostic reagents.

SUMMARY

In the future, we must effectively utilize the wealth of genetic information to combat the disease. More studies into genetics, immune mechanisms that may be exploited to prevent leptospirosis, and pathogenesis of the disease are necessary.

Acute pancreatitis affects non-parenchymal liver cells by a mechanism dependent on platelet-activating factor

BACKGROUND/AIM

During acute experimental pancreatitis, inflammatory mediators/cytokines are released by the pancreas and enter the portal venous system, reaching the liver. We investigate some aspects of the liver cell function under conditions of acute pancreatitis and the effect of in vivo treatment with a selective platelet-activating factor (PAF) antagonist.

METHODS

Cells were isolated from Wistar rats 24 h after induction of acute pancreatitis by retrograde injection of sodium taurocholate into the main pancreatic duct. The non-parenchymal cell population was separated by Percoll gradient and the adherent cell population (Kupffer cells) obtained. The cells were cultured for 24 h and supernatants assayed for nitrite by Griess reaction and for tumour necrosis factor (TNF) by bioassay in L929 cells. The microbicidal activity was evaluated by killing of Candida albicans. The PAF antagonist WEB2170 (10 mg/kg i.v.) was administered 30 min before induction of pancreatitis.

RESULTS

We found that liver cells produce nitric oxide (NO) only under lipopolysaccharide stimulation and that WEB-2170 treatment reduces the NO production by liver cells in the pancreatitis group only. Cells from both groups produced TNF spontaneously, and the levels were further increased after lipopolysaccharide stimulation. WEB-2170 treatment did not affect the TNF levels. Moreover, killing of C. albicans by Kupffer cells wassignificantly increased by the PAF antagonist.

CONCLUSION

These results suggest that PAF released during acute pancreatitis upregulates the NO production by non-parenchymal liver cells and inhibits Kupffer cell microbicidal activity which could explain the increased bacterial dissemination observed in acute pancreatitis.

Chlamydia pneumoniae replicates in Kupffer cells in mouse model of liver infection

AIM: To develop an animal model of liver infection with Chlamydia pneumoniae (C. pneumoniae) in intraperitoneally infected mice for studying the presence of chlamydiae in Kupffer cells and hepatocytes.

METHODS: A total of 80 BALB/c mice were inoculated intraperitoneally with C. pneumoniae and sacrificed at various time points after infection. Chlamydiae were looked for in liver homogenates as well as in Kupffer cells and hepatocytes separated by liver perfusion with collagenase. C. pneumoniae was detected by both isolation in LLC-MK2 cells and fluorescence in situ hybridization (FISH). The releasing of TNFA-α by C. pneumoniae in vitro stimulated Kupffer cells was studied by enzyme-linked immunosorbent assay.

RESULTS: C. pneumoniae isolation from liver homogenates reached a plateau on d 7 after infection when 6 of 10 animals were positive, then decreased, and became negative by d 20. C. pneumoniae isolation from separated Kupffer cells reached a plateau on d 7 when 5 of 10 animals were positive, and became negative by d 20. The detection of C. pneumoniae in separated Kupffer cells by FISH, confirmed the results obtained by culture. Isolated hepatocytes were always negative. Stimulation of Kupffer cells by alive C. pneumoniae elicited high TNF-α levels.

CONCLUSION: A productive infection by C. pneumoniae may take place in Kupffer cells and C. pneumoniae induces a local pro-inflammatory activity. C. pneumoniae is therefore, able to act as antigenic stimulus when localized in the liver. One could speculate that C. pneumoniae infection, involving cells of the innate immunity such as Kupffer cells, could also trigger pathological immune reactions involving the liver, as observed in human patients with primary biliary cirrhosis.

Production of reactive oxygen species and expression of inducible nitric oxide synthase in rat isolated Kupffer cells stimulated by Leptospira interrogans and Borrelia burgdorferi

AIM: To evaluate the production of reactive oxygen species (ROS) and the expression of inducible nitric oxide synthase (iNOS) in rat isolated Kupffer cells (KCs) stimulated by Leptospira interrogans and Borrelia burgdorferi.

METHODS: Rat Kupffer cells were separated by perfusion of the liver with 0.05% collagenase, and purified by Percoll gradients. Purified Kupffer cells were tested in vitro with alive L.interogans and B. burgdorferi preparations. The production of ROS was determined by chemiluminescence, whereas iNOS protein expression was evaluated by Western blot assay using anti-iNOS antibodies.

RESULTS: B. burgdorferi and to a less extent L. interrogans induced ROS production with a peak 35 min after infection. The chemiluminescence signal progressively diminished and was undetectable by 180 min of incubation. Leptospirae and borreliae induced an increased iNOS expression in Kupffer cells that peaked at 6 hours and was still evident 22 h after infection.

CONCLUSION: Both genera of spirochetes induced ROS and iNOS production in rat Kupffer cells. Since the cause of liver damage both in leptospiral as well as in borrelial infections are still unknown, we suggest that leptospira and borrelia damage of the liver can be initially mediated by oxygen radicals, and is then maintained at least in part by nitric oxide.

Phagocytosis of Treponema pallidum and reactive oxygen species production by isolated rat Kupffer cells

The in vitro phagocytosis of viable Treponema pallidum subsp. pallidum by isolated rat Kupffer cells, studied by immunofluorescence staining of Kupffer cells-associated bacteria, showed that ingestion of live, unopsonized treponemes was slow: in fact, Kupffer cells started to be positive 1 h after infection, when only 4% of the cells presented small round fluorescent inclusion-like bodies. Thereafter, the number of positive cells progressively increased with time: 7%, 17%, 36%, and 69% of Kupffer cells were positive, respectively, 2, 4, 6 and 8 h after infection. Opsonization of T. pallidum with human immune serum did not substantially modify the percentage (8%) of Kupffer cells ingesting T. pallidum 1 h after infection, whereas opsonization significantly ( P<0.01) increased phagocytosis after 2, 4 and 6 h of incubation, when 44%, 58%, and 68% of Kupffer cells were positive, respectively. At 8 h after infection of Kupffer cells by opsonized T. pallidum, 75% of the cells were positive by immunofluorescence. Heat-inactivation of T. pallidum slightly enhanced phagocytosis. In contrast, opsonization of heat-inactivated spirochetes with specific antibodies significantly ( P<0.01) increased the phagocytosis of bacteria by Kupffer cells, beginning as early as 30 min after infection, when 65% of the cells were positive by immunofluorescence. The reactive oxygen species (ROS) production by Kupffer cells following incubation with spirochetes was also determined by chemiluminescence. Treponemes induced an oxidative burst in Kupffer cells in a dose-dependent manner and the generation of ROS was already detectable 20 min after the exposure of the Kupffer cells to treponemes and peaked at 35 min of incubation. Live, as well as live and opsonized, and heat-inactivated treponemes, induced an O(2)(-) production lower than that induced by heat-inactivated and opsonized spirochetes.

Leptospira interrogans binds to the CR3 receptor on mammalian cells

Pathogenic leptospires adhere to phagocytes even in the absence of specific antibodies; we demonstrate that the CR3 integrin (known as Mac-1 or CD11b/CD18 receptor), expressed on neutrophils and CHO Mac-1 transfected cells, recognizes and binds leptospires. The I-domain of the molecule seems to be involved in the recognition and data suggest that this occurs via fibronectin absorbed at the Leptospira surface. On the other hand, since N-acetyl-D-glucosamine does not behave as antagonist of the binding, the lectin-like domain of the receptor is not involved in the recognition.

Leptospires are killed in vitro by both oxygen-dependent and -independent reactions

This study reports for the first time that leptospires are killed by H(2)O(2) and by low-molecular-weight primary granule components, which are agents normally released by neutrophils upon stimulation. Although both pathogenic and nonpathogenic strains were sensitive to H(2)O(2)-mediated killing, nonpathogenic organisms were found to be more susceptible. In addition, the killing of leptospires by H(2)O(2) was found to be independent of the presence of the neutrophil primary granule component myeloperoxidase and therefore not a consequence of halogenation reactions. We have also determined that leptospires are significantly sensitive only to primary granule components and, among those, to proteins and/or peptides of less than 30 kDa.

Rapid translocation of polarized MDCK cell monolayers by Leptospira interrogans, an invasive but nonintracellular pathogen

Pathogenic spirochetes of the genus Leptospira are a major cause of human zoonotic infectious disease worldwide. After gaining entry through the skin, the organism causes disease by hematogenously disseminating to multiple organs. The mechanism by which it penetrates the mammalian cell barriers to disseminate is not well understood. In this study, we used a low-passage-number isolate of Leptospira interrogans to elucidate the invasive potential of this spirochete. Quantification of bacteria by dark-field microscopy revealed that pathogenic spirochetes were able to translocate through polarized MDCK cell monolayers at a rate significantly greater than that of nonpathogenic Leptospira or a recognized invasive bacterial pathogen, Salmonella: In contrast to Salmonella, L. interrogans did not alter transepithelial electrical resistance during cell translocation. Both transmission and scanning electron microscopy revealed tight association of the extracellular spirochetes with the host cell plasma membrane, without membrane perturbations suggestive of cytoskeletal rearrangement. Spirochetes were not observed within intercellular junctions or membrane-bound compartments inside cells. They were found within the cytoplasm of only 8% of the counted cells. These results indicate that Leptospira is an invasive but not a facultative intracellular organism. We propose that the rapid translocation of mammalian cells by pathogenic Leptospira is a mechanism designed to evade killing by host cells that permits the organism to quickly reach the bloodstream and disseminate to multiple organs.

The role of microorganisms in biliary tract disease

The biliary tract is normally sterile, but bile-tolerant bacteria are frequently isolated from patients with cholecystitis. Since the identification of about 25 Helicobacter species, some of which may grow in bile, studies have addressed the role of these organisms in primary biliary cirrhosis, primary sclerosing cholangitis, and cholelithiasis. Most of these bacteria show the presence of Helicobacter DNA or antigens in the bile tract and in liver samples. Altogether, data from studies on biliary and hepatic diseases, as well as pancreatic disorders, suggest that bile-tolerant Helicobacter species may induce a chronic infection with possible malignant transformation.