concanavalin-a and Bacteremia

Intragastric inoculation of Klebsiella pneumoniae can cause invasive diseases, including necrosis of liver tissues and bacteremia. The effect of concanavalin A (ConA) on K. pneumoniae was tested. Pretreatment with ConA was able to protect mice from K. pneumoniae infection in an intragastric model. K. pneumoniae-induced mouse death and liver injury such as liver necrosis, as well as blood levels of aspartate aminotransferase and alanine aminotransferase, were inhibited in a dose-dependent manner by ConA. ConA administered intravenously as late as 24 h after K. pneumoniae inoculation was still protective. In an in vitro assay, ConA was able to bind K. pneumoniae cells directly and further agglutinate them but had no effect on their in vitro growth. Surveys of bacterial counts of ConA-treated mice revealed that the bacteria were eliminated effectively in both blood and liver tissues. Furthermore, the bactericidal activity of macrophages against K. pneumoniae was also enhanced in a dose-dependent manner by ConA in an in vitro culture. These data suggest that ConA is a potentially therapeutic agent for K. pneumoniae-induced liver infection.

Topics: Alanine Transaminase; Animals; Aspartate Aminotransferases; Bacteremia; Concanavalin A; Immunohistochemistry; Immunologic Factors; Klebsiella Infections; Klebsiella pneumoniae; Liver; Macrophages; Mice; Mice, Inbred C57BL

The cytokine response to the agent of human granulocytic ehrlichiosis (HGE) was assessed in a murine infection model and the role of gamma interferon (IFN-gamma), a cytokine that is crucial for host defenses against intracellular pathogens, was investigated by using IFN-gamma-deficient mice. The agent of HGE (aoHGE) is an obligate intracellular bacterium that survives within neutrophils: morulae (vacuoles containing HGE organisms) are evident in polymorphonuclear leukocytes of experimentally infected immunocompetent mice for 1 to 2 weeks. We now show that IFN-gamma levels increase during early infection of C3H/HeN or C57BL/6 mice with HGE bacteria. Moreover, in response to aoHGE extracts or concanavalin A, splenocytes from ehrlichia-infected mice produced more IFN-gamma and less interleukin-4 than controls, suggesting that aoHGE partially skewed the immune response towards a Th1 phenotype. Absolute concentration of morulae containing neutrophils in blood was 122 +/- 22 cells/microliter on day 8. The bacterial DNA burden was also highest on day 8 and then declined after IFN-gamma levels peaked. In contrast, IFN-gamma-deficient mice had a markedly elevated HGE bacteria burden with morulae concentration of 282 +/- 48 cells/microliter on day 5 (P = 0.004) and 242 +/- 63 cells/microliter on day 8 (P = 0.005). Rickettsemia resolved in immunocompetent and IFN-gamma deficient mice after 2 weeks, while both the immunocompetent and the IFN-gamma-deficient mice had increased serum antibodies against aoHGE antigens at this time point. These data demonstrate that the HGE agent elicits a prominent IFN-gamma response in mice and that IFN-gamma is important in controlling the degree of rickettsemia during the early phase of infection, while IFN-gamma independent mechanisms play a role at later time points.

Topics: Animals; Bacteremia; Concanavalin A; Cytokines; Disease Progression; Dose-Response Relationship, Drug; Ehrlichiosis; Enzyme-Linked Immunosorbent Assay; Female; HL-60 Cells; Humans; Immunoglobulin G; Interferon-gamma; Mice; Mice, Inbred C3H; Neutrophils; Reverse Transcriptase Polymerase Chain Reaction; Rickettsia; Spleen; T-Lymphocytes; Time Factors

Sepsis is associated with depressed T-cell functions and increased circulating levels of immunosuppressive agents. TGF-beta is a potential anti-inflammatory cytokine that can modify T-cell growth and differentiation. The up-regulation of TGF-beta and the mechanism of its action on the T-cells during septic injury have not been resolved. We hypothesized that in sepsis TGF-beta produced by macrophages acts on T-cells in a paracrine manner to suppress interleukin (IL)-2 production and proliferation. In this study, we examined the circulating TGF-beta levels in a rat model of Gram-negative bacterial sepsis, and compared the abilities of adherent and non-adherent splenocytes to produce TGF-beta. Additionally, we investigated the causal relationships of hrTGF-beta to concanavalin A (ConA)-induced T-cell responses and the intracellular mechanism of the generation of these responses in normal splenic rat T-cells. Sepsis was induced in rats by intraabdominally implanting fecal pellets containing Escherichia coli (150 CFU) and Bacteroides fragilis (10000 CFU). Adherent and non-adherent splenocytes were isolated by differential adherence using Ficoll gradient centrifugation. T-cells were purified by use of Nylon wool columns. We observed a 3-6-fold increase in the circulating levels of TGF-beta in sepsis. Western blots and ELISA determinations revealed a 2.5-3-fold increase in cell-associated TGF-beta protein levels in adherent splenic cells. Northern analyses also showed a marked increase in TGF-beta mRNA expression in adherent cells during sepsis. On the other hand, a significant change was not observed in the TGF-beta protein and mRNA expression in non-adherent splenocytes. Pretreatment of control rat T-cells with hrTGF-beta decreased both ConA-induced proliferation (by 35-40%) and IL-2 mRNA expression (by > 50%). Further, whereas incubation of control rat T-cells with either ConA or TGF-beta for 24 h resulted in a 10-15-fold increase in cAMP generation, the addition of hrTGF-beta along with ConA resulted in a 50-60-fold increase in cAMP. These results suggest that in sepsis, TGF-beta produced by splenic macrophages can act in a paracrine manner on T-cells to depress their IL-2 mRNA expression, IL-2 production and proliferation after up-regulation of cAMP which can interfere with T-cell signaling for proliferation.

Topics: Animals; Bacteremia; Bacteroides fragilis; Bacteroides Infections; Cell Adhesion; Concanavalin A; Cyclic AMP; Enzyme-Linked Immunosorbent Assay; Escherichia coli Infections; Interleukin-2; Lymphocyte Activation; Male; Rats; Rats, Sprague-Dawley; Reference Values; Spleen; T-Lymphocytes; Transcription, Genetic; Transforming Growth Factor beta

Clearance of various bacteria isolated from portal and systemic blood of mice was evaluated and compared. All portal blood strains, including Escherichia coli and enterococci were eliminated more rapidly from the circulation than were strains isolated from systemic blood, including Pseudomonas aeruginosa. With mannose-type lectin, mannose or fucose residues that mediated lectinophagocytosis were detected on the surfaces of most portal strains by agglutination tests. Blood clearance of Esch. coli H21 was inhibited by prior injection of mannose into mice, suggesting that the clearance of this strain was mediated by mannose-type lectin on the surface of tissue macrophages. However, no inhibition of clearance of any other strains was observed by the injection of mannose, galactose, or fucose into mice, nor by pre-incubation of bacteria with mannose. Blood clearance of some portal strains was significantly faster in CBA/J mice than in CBA/N mice with B cell immune deficiency, indicating that immunoglobulin was involved in their clearance. Among portal strains only enterococci showed high cell-surface hydrophobicity. These data suggest that initial bacteria blood clearance may be critical in determining whether latent portal bacteraemia progresses to systemic bacteraemia and that the rapid clearance of most strains is multifactorial.

Topics: Agglutination Tests; Animals; Bacteremia; Bacteria; Concanavalin A; Injections, Intravenous; Lectins; Liver Circulation; Male; Mannose; Mice; Mice, Inbred CBA; Surface Properties; Water