The role of B cells in an early immune response to Mycobacterium bovis.

Mycobacterium tuberculosis is the main etiological agent of tuberculosis. The Bacillus Calmette-Guérin (BCG) microbes that are primarily used as a vaccine against tuberculosis also constitute the dominant infection model for studying the interaction of mycobacteria with the host cell types. The majority of interaction experiments have been conducted using macrophages and monocytes as prototype phagocyte cell types. Here, we report that M. bovis BCG infects mouse primary B cells as well as human B cell line. The complement receptors, along with B cell receptors, are engaged in the process of bacterial entry into the host B cells. Once inside the B cells, the intracellular trafficking of BCG follows the complete endocytic pathway of the ingested particles, which is in contrast to the events taking place during ingestion of BCG by macrophages. In vivo infection of mice with M. bovis BCG activated peritoneal as well as splenic B cells to produce proinflammatory cytokines. This paper further supports the evidence that B cells are involved in a host's early interactions with intracellular bacterial pathogens and participate in the induction of innate defense responses.

The Early Dendritic Cell Signaling Induced by Virulent Francisella tularensis Strain Occurs in Phases and Involves the Activation of Extracellular Signal-Regulated Kinases (ERKs) and p38 In the Later Stage.

Dendritic cells (DCs) infected by Francisella tularensis are poorly activated and do not undergo classical maturation process. Although reasons of such unresponsiveness are not fully understood, their impact on the priming of immunity is well appreciated. Previous attempts to explain the behavior of Francisella-infected DCs were hypothesis-driven and focused on events at later stages of infection. Here, we took an alternative unbiased approach by applying methods of global phosphoproteomics to analyze the dynamics of cell signaling in primary DCs during the first hour of infection by Francisella tularensis Presented results show that the early response of DCs to Francisella occurs in phases and that ERK and p38 signaling modules induced at the later stage are differentially regulated by virulent and attenuated ΔdsbA strain. These findings imply that the temporal orchestration of host proinflammatory pathways represents the integral part of Francisella life-cycle inside hijacked DCs.

Early cellular responses of germ-free and specific-pathogen-free mice to Francisella tularensis infection.

Bacteria that are highly virulent, expressing high infectivity, and able to survive nebulization, pose great risk to the human population. One of these is Francisella tularensis, the etiological agent of tularemia. F. tularensis is a subject of intense scientific interest due to the fact that vaccines for its immunoprophylaxis in humans are not yet routinely available. One of the substantial obstacles in developing such vaccines is our insufficient knowledge of processes that initiate and regulate the expression of effective protective immunity against intracellular bacteria. Here, we present data documenting the different pattern of cellular behavior occurring in an environment unaffected by microbiota using the model of germ-free mice mono-associated with F. tularensis subsp. holarctica strain LVS in comparison with a classic specific-pathogen-free murine model during early stages of infection.

Gnotobiotic mouse model's contribution to understanding host-pathogen interactions.

This brief review is dedicated to the legacy of Prof. Jaroslav Sterzl and his colleagues, who laid the foundation for gnotobiology in the former Czechoslovakia 55 years. Prof. Sterzl became one of the founders of modern Czechoslovak immunology, which was characterized by work on a wide range of problems needing to be solved. While examining the mechanisms of innate immunity, he focused his studies on the induction of antibody production by immunocompetent cells involved in adaptive immune transmission while using the model of pig fetuses and germ-free piglets and characterizing immunoglobulins in the sera of these piglets. Although not fully appreciated to this day, his experimental proof of the hypothesis focused on the common precursor of cell-forming antibodies of different isotypes was later confirmed in experiments at the gene level. Prof. Sterzl's work represented a true milestone in the development of not solely Czechoslovak but also European and global immunology. He collaborated closely with the World Health Organization for many years, serving there as leader of the Reference Laboratory for Factors of Innate Immunity.

Quantitative proteomics analysis of macrophage-derived lipid rafts reveals induction of autophagy pathway at the early time of Francisella tularensis LVS infection.

Francisella tularensis is a highly infectious intracellular pathogen that has evolved an efficient strategy to subvert host defense response to survive inside the host. The molecular mechanisms regulating these host-pathogen interactions and especially those that are initiated at the time of the bacterial entry via its attachment to the host plasma membrane likely predetermine the intracellular fate of pathogen. Here, we provide the evidence that infection of macrophages with F. tularensis leads to changes in protein composition of macrophage-derived lipid rafts, isolated as detergent-resistant membranes (DRMs). Using SILAC-based quantitative proteomic approach, we observed the accumulation of autophagic adaptor protein p62 at the early stages of microbe-host cell interaction. We confirmed the colocalization of the p62 with ubiquitinated and LC3-decorated intracellular F. tularensis microbes with its maximum at 1 h postinfection. Furthermore, the infection of p62-knockdown host cells led to the transient increase in the intracellular number of microbes up to 4 h after in vitro infection. Together, these data suggest that the activation of the autophagy pathway in F. tularensis infected macrophages, which impacts the early phase of microbial proliferation, is subsequently circumvented by ongoing infection.

B cell subsets are activated and produce cytokines during early phases of Francisella tularensis LVS infection.

Francisella tularensis, a facultative intracellular Gram-negative bacterium, causes the illness tularemia. The infection of mice with live vaccine strain is considered to be a model of human tularemia. F. tularensis infects predominantly such phagocytic cells as macrophages or neutrophils, but it also infects non-phagocytic hepatocytes, epithelial cells, and murine and human B cell lines. Based on work with the murine tularemia model, we report here that F. tularensis LVS infects peritoneal CD19(+) cells - exclusively B-1a cells - early after intraperitoneal infection in vivo. The peritoneal and consequently spleen CD19(+) cells are activated by the F. tularensis LVS infection to express the activation markers from MHC class II, CD25, CD54, CD69, and the co-stimulatory molecules CD80 and CD86. As early as 12 h post-infection, the peritoneal CD19(+) cells produce IFN-γ, IL-1ß, IL-4, IL-6, IL-12, IL-17, IL-23, and TNF-α. The spleen CD19(+) cells respond to infection with some delay. Moreover, the F. tularensis infected A20 B cell line activates CD3(+) spleen cells isolated from naïve mice. Thus, the data presented here suggest that B cells have all the attributes to actively participate in the induction and regulation of the adaptive immune response during early stages of F. tularensis infection.

Specific antibodies protect gamma-irradiated mice against Francisella tularensis infection.

The role of antibodies in the course of Francisella tularensis (F. tularensis) infection is still a subject of debate. The understanding of the poorly described role of humoral immunity is more than important for the effort to develop effective prophylactic procedure against the infection with Francisella virulent strains. We utilized the model of gamma-irradiated mice for the studies of the protective role of anti-F. tularensis antibodies in order to partially eliminate cellular responses. The model of gamma-irradiated mice can also demonstrate the responses of immunocompromised host to intracellular bacterial infection. The gamma-irradiation by doses greater than 3 Gy completely impairs the resistance to infection and causes a disbalance of cytokine production in mice. In this study, we demonstrate that passive transfer of immune sera protected irradiated mice against subsequent infection with strains of F. tularensis subsp. holarctica. Naïve mice of BALB/c or C3H/CBi strains were subjected to passive transfer of sera obtained from immunized mice with live vaccine strain (LVS) F. tularensis LVS, F. tularensis subsp. holarctica strain 15, heat-killed F. tularensis LVS, or heat-killed strain 15 two hours before infection with lethal doses of LVS or strain 15. The passive transfer of sera obtained from immunized mice conferred full protection of naïve unirradiated as well as sublethally irradiated mice against low lethal doses of infection with F. tularensis LVS or strain 15, in all variants of the experiments. In addition, the passively protected mice that survived the primary infection with F. tularensis LVS were protected also against further secondary challenge with a highly virulent strain of F. tularensis subsp. tularensis SchuS4. Moreover, the first evidence of combination of successful passive transfer of immunity by specific antisera and subsequent active immunization of immunocompromised animals is demonstrated. In summary, we demonstrate that B cell-mediated effector responses together with the induction of T cell-mediated immunity both play an important role in naïve and also in immunocompromised mice and this fact it would be appropriate to take into the account in the design of new vaccines.

A proteomic view of the host-pathogen interaction: The host perspective.

The host-pathogen interaction represents a complex and dynamic biological system. The outcome of this interaction is dependent on the microbial pathogen properties to establish infection and the ability of the host to control infection. Although bacterial pathogens have evolved a variety of strategies to subvert host defense functions, several general mechanisms have been shown to be shared among these pathogens. As a result, host effectors that are critical for pathogen entry, survival and replication inside the host cells have become a new paradigm for antimicrobial targeting. This review focuses on the potential utility of a proteomics approach in defining the host-pathogen interaction from the host's perspective.

Synthesis and Decontamination Effect on Chemical and Biological Agents of Benzoxonium-Like Salts.

Benzoxonium chloride belongs to the group of quaternary ammonium salts, which have been widely used for decades as disinfectants because of their high efficacy, low toxicity, and thermal stability. In this study, we have prepared the C10-C18 set of benzoxonium-like salts to evaluate the effect of their chemical and biological decontamination capabilities. In particular, biocidal activity against a panel of bacterial strains including Staphylococcus aureus in biofilm form was screened. In addition, the most promising compounds were successfully tested against Francisella tularensis as a representative of potential biological warfare agents. From a point of view of chemical warfare protection, the efficiency of BOC-like compounds to degrade the organophosphate simulant fenitrothion was examined. Notwithstanding that no single compound with universal effectiveness was identified, a mixture of only two compounds from this group would be able to satisfactorily cover the proposed decontamination spectrum. In addition, the compounds were evaluated for their cytotoxicity as a basic safety parameter for potential use in practice. In summary, the dual effect on chemical and biological agents of benzoxonium-like salts offer attractive potential as active components of decontamination mixtures in the case of a terrorist threat or chemical or biological accidents.

Activation of B cell apoptotic pathways in the course of Francisella tularensis infection.

Francisella tularensis is a facultative intracellular, gram-negative bacterium that induces apoptosis in macrophages and B cells. Here we show apoptotic pathways that are activated in the Ramos human B cell line in the course of F. tularensis infection. Live bacteria F. tularensis FSC200 activate caspases 8, 9 and 3, as well as Bid; release cytochrome c and apoptosis-inducing factor from mitochondria; and induce depolarization of mitochondrial membrane potential in the Ramos cell line, thus leading these cells to apoptosis. Unlike live bacteria, killed F. tularensis FSC200 bacteria activated only caspase 3, and did not cause apoptosis of Ramos cells as measured by annexin V. Killed bacteria also caused accumulation of anti-apoptotic protein Bclx(L) in mitochondrial membranes. Thus, live F. tularensis activates both caspase pathways (receptor-mediated and intrinsic) as well as caspase-independent mitochondrial death.

Proteome analysis of an attenuated Francisella tularensis dsbA mutant: identification of potential DsbA substrate proteins.

Francisella tularensis (F. tularensis) is highly infectious for humans via aerosol route and untreated infections with the highly virulent subsp. tularensis can be fatal. Our knowledge regarding key virulence determinants has increased recently but is still somewhat limited. Surface proteins are potential virulence factors and therapeutic targets, and in this study, we decided to target three genes encoding putative membrane lipoproteins in F. tularensis LVS. One of the genes encoded a protein with high homology to the protein family of disulfide oxidoreductases DsbA. The two other genes encoded proteins with homology to the VacJ, a virulence determinant of Shigella flexneri. The gene encoding the DsbA homologue was verified to be required for survival and replication in macrophages and importantly also for in vivo virulence in the mouse infection model for tularemia. Using a combination of classical and shotgun proteome analyses, we were able to identify several proteins that accumulated in fractions enriched for membrane-associated proteins in the dsbA mutant. These proteins are substrate candidates for the DsbA disulfide oxidoreductase as well as being responsible for the virulence attenuation of the dsbA mutant.

Targeted Mass Spectrometry Analysis of Clostridium perfringens Toxins.

Targeted proteomics recently proved to be a technique for the detection and absolute quantification of proteins not easily accessible to classical bottom-up approaches. Due to this, it has been considered as a high fidelity tool to detect potential warfare agents in wide spread kinds of biological and environmental matrices. Clostridium perfringens toxins are considered to be potential biological weapons, especially the epsilon toxin which belongs to a group of the most powerful bacterial toxins. Here, the development of a target mass spectrometry method for the detection of C. perfringens protein toxins (alpha, beta, beta2, epsilon, iota) is described. A high-resolution mass spectrometer with a quadrupole-Orbitrap system operating in target acquisition mode (parallel reaction monitoring) was utilized. Because of the lack of commercial protein toxin standards recombinant toxins were prepared within Escherichia coli. The analysis was performed using proteotypic peptides as the target compounds together with their isotopically labeled synthetic analogues as internal standards. Calibration curves were calculated for each peptide in concentrations ranging from 0.635 to 1101 fmol/µL. Limits of detection and quantification were determined for each peptide in blank matrices.

Innate Immune Recognition: Implications for the Interaction of Francisella tularensis with the Host Immune System.

The intracellular bacterial pathogen Francisella tularensis causes serious infectious disease in humans and animals. Moreover, F. tularensis, a highly infectious pathogen, poses a major concern for the public as a bacterium classified under Category A of bioterrorism agents. Unfortunately, research has so far failed to develop effective vaccines, due in part to the fact that the pathogenesis of intracellular bacteria is not fully understood and in part to gaps in our understanding of innate immune recognition processes leading to the induction of adaptive immune response. Recent evidence supports the concept that immune response to external stimuli in the form of bacteria is guided by the primary interaction of the bacterium with the host cell. Based on data from different Francisella models, we present here the basic paradigms of the emerging innate immune recognition concept. According to this concept, the type of cell and its receptor(s) that initially interact with the target constitute the first signaling window; the signals produced in the course of primary interaction of the target with a reacting cell act in a paracrine manner; and the innate immune recognition process as a whole consists in a series of signaling windows modulating adaptive immune response. Finally, the host, in the strict sense, is the interacting cell.

Entry of Francisella tularensis into Murine B Cells: The Role of B Cell Receptors and Complement Receptors.

Francisella tularensis, the etiological agent of tularemia, is an intracellular pathogen that dominantly infects and proliferates inside phagocytic cells but can be seen also in non-phagocytic cells, including B cells. Although protective immunity is known to be almost exclusively associated with the type 1 pathway of cellular immunity, a significant role of B cells in immune responses already has been demonstrated. Whether their role is associated with antibody-dependent or antibody-independent B cell functions is not yet fully understood. The character of early events during B cell-pathogen interaction may determine the type of B cell response regulating the induction of adaptive immunity. We used fluorescence microscopy and flow cytometry to identify the basic requirements for the entry of F. tularensis into B cells within in vivo and in vitro infection models. Here, we present data showing that Francisella tularensis subsp. holarctica strain LVS significantly infects individual subsets of murine peritoneal B cells early after infection. Depending on a given B cell subset, uptake of Francisella into B cells is mediated by B cell receptors (BCRs) with or without complement receptor CR1/2. However, F. tularensis strain FSC200 ΔiglC and ΔftdsbA deletion mutants are defective in the ability to enter B cells. Once internalized into B cells, F. tularensis LVS intracellular trafficking occurs along the endosomal pathway, albeit without significant multiplication. The results strongly suggest that BCRs alone within the B-1a subset can ensure the internalization process while the BCRs on B-1b and B-2 cells need co-signaling from the co receptor containing CR1/2 to initiate F. tularensis engulfment. In this case, fluidity of the surface cell membrane is a prerequisite for the bacteria's internalization. The results substantially underline the functional heterogeneity of B cell subsets in relation to F. tularensis.

Study of antitumor effect of selected vanadium and molybdenum organometallic complexes in human leukemic T-cells.

This work describes cytotoxic effect of non-platinum metal-based compounds on the human T-leukemic cells with different p53 status (p53 wild-type MOLT-4 and p53-deficient Jurkat cells). The cytotoxic and apoptosis-inducing effect of the vanadium complex [(η(5)-C5H5)2V(5-NH2-phen)]OTf (V1) and molybdenum complex [(η(3)-C3H5)Mo(CO)2(phen)Cl] (Mo1) were studied using flow cytometry, spectrophotometry and Western blotting. We found that the cytotoxic effect of both tested complexes after 24 h is higher against the both examined cell lines than that of cis-platin (cis-DDP). At later investigated time intervals of 48 and 72 h, the cytotoxic effect of the cis-DDP increased but the values of the cytotoxicity of the tested V1 and Mo1 complexes remained unchanged, with the cytotoxicity of V1 comparable to that of cis-DDP. Furthermore we observed that the apoptotic process was induced by the activation of the caspases 9 (intrinsic pathway) and 8 (extrinsic pathway) in cells exposed to evaluated complexes. In case of the p53 wild-type MOLT-4 cells, the expression of the tumor-suppressor protein p53 and its form phosphorylated at the serine 15 increased after both V1 and Mo1 treatment, similar to the effect of cis-DDP.

Membrane rafts: a potential gateway for bacterial entry into host cells.

Pathogenic bacteria have developed various mechanisms to evade host immune defense systems. Invasion of pathogenic bacteria requires interaction of the pathogen with host receptors, followed by activation of signal transduction pathways and rearrangement of the cytoskeleton to facilitate bacterial entry. Numerous bacteria exploit specialized plasma membrane microdomains, commonly called membrane rafts, which are rich in cholesterol, sphingolipids and a special set of signaling molecules which allow entry to host cells and establishment of a protected niche within the host. This review focuses on the current understanding of the raft hypothesis and the means by which pathogenic bacteria subvert membrane microdomains to promote infection.

Interaction of B cells with intracellular pathogen Francisella tularensis.

Immunity to Francisella tularensis is largely mediated by T lymphocytes but an important role of B lymphocytes in early stage of infection was previously uncovered. We wanted to find out if F. tularensis is able to infect B cells and/or influence them by direct contact. To investigate this possibility we infected B cell lines from mouse (A20) or humans (Ramos RA-1), or primary mouse spleen cells, with F. tularensis LVS and F. tularensis FSC200 in vitro. In all cases, we detected bacteria on the cell surface and inside the B cells using transmission electron microscopy. More than 20% cells were infected by microbes after 24h. The number of bacteria, determined by CFU, increased about 1 log during 24h. Infection with live bacteria led to apoptosis of Ramos cells and mouse CD19(+) spleen cells. Approximately 30% of cells were apoptotic after 24h and 70% after 48 h, independently of the F. tularensis strain, while only 10% of non-infected cell were apoptotic at either time point. Apoptosis was confirmed by Western blot using anti-PARP antibodies. Thus, this study demonstrates unique phenomenon - namely, the ability of the intracellular pathogen F. tularensis to invade and induce apoptosis in B cells.

The alteration of immune reactions in inbred BALB/c mice following low-level sarin inhalation exposure.

To study the influence of low-level sarin inhalation exposure on immune functions, inbred BALB/c mice were exposed to low concentrations of sarin for 60 min in the inhalation chamber. The evaluation of immune functions was carried out using phenotyping of CD3 (T lymphocytes), CD4 (helper T lymphocytes), CD8 (cytotoxic T lymphocytes), and CD19 cells (B lymphocytes) in the lungs, blood, and spleen, lymphoproliferation of spleen cells stimulated in vitro by various mitogens (concanavalin A, lipopolysaccharides), phagocyte activity of peritoneal and alveolar macrophages, production of N-oxides by peritoneal macrophages, and the measurement of the natural killer cell activity at 1 wk following sarin exposure. The results were compared to the values obtained from control mice exposed to pure air instead of sarin. The results indicate that low doses of sarin are able to alter the reaction of immune system at one week following exposure to sarin. While the numbers of CD3 cells in the lungs, blood, and spleen were slightly decreased, an increase in CD19 cells was observed, especially in the lungs and blood. The reduced proportion of T lymphocytes is caused by decay of CD4-positive T cells. Lymphoproliferation was significantly decreased regardless of the mitogen and sarin concentration used. The production of N-oxides by peritoneal macrophages was stimulated after exposure to the highest dose of sarin, whereas their ability to phagocytize the microbes was increased after exposure to the lowest dose of sarin. The natural killer cell activity was significantly higher in the case of inhalation exposure of mice to the highest level of sarin. Thus, not only organophosphorus insecticides but also nerve agents such as sarin are able to alter immune functions even at a dose that does not cause clinically manifested disruption of cholinergic nervous system in the case of inhalation exposure. Nevertheless, the alteration of immune functions following the inhalation exposure to a symptomatic concentration of sarin seems to be more pronounced.

An attenuated strain of the facultative intracellular bacterium Francisella tularensis can escape the phagosome of monocytic cells.

The facultative intracellular bacterium Francisella tularensis is a highly virulent and contagious organism, and little is known about its intracellular survival mechanisms. We studied the intracellular localization of the attenuated human vaccine strain, F. tularensis LVS, in adherent mouse peritoneal cells, in mouse macrophage-like cell line J774A.1, and in human macrophage cell line THP-1. Confocal microscopy of infected J774A.1 cells indicated that during the first hour of infection the bacteria colocalized with the late endosomal-lysosomal glycoprotein LAMP-1, but within 3 h this colocalization decreased significantly from approximately 60% to 30%. Transmission electron microscopy revealed that >90% of bacteria were not enclosed by a phagosomal membrane after 2 h of infection, and some bacteria were in vacuoles that were only partially surrounded by a limiting membrane. Similar findings were obtained with all three host cell types. Immunoelectron microscopy performed with an F. tularensis LVS-specific polyclonal rabbit antiserum showed that the antiserum stained a thick, evenly distributed capsule-like material in bacteria grown in broth. In contrast, intracellular F. tularensis LVS cells were only marginally stained with this antiserum. Instead, most of the immunoreactive material was diffusely localized in the phagosomes or was associated with the phagosomal membrane. Our findings indicate that F. tularensis LVS is able to escape from the phagosomes of macrophages via a mechanism that may involve degradation of the phagosomal membrane.

Proteome study of Francisella tularensis live vaccine strain-containing phagosome in Bcg/Nramp1 congenic macrophages: resistant allele contributes to permissive environment and susceptibility to infection.

The phagocytosis of pathogens by macrophages classically initiates maturation of the phagosome that involves a dynamic exchange of phagosomal components with intracellular compartments of the endocytic pathway. The intracellular microorganisms have developed sophisticated mechanisms to sense environmental conditions and respond to them by phenotypic alterations that ensure their adaptation, survival and proliferation inside the cell. They have learned also to utilise host cellular components to ensure own survival. Recent results suggest that the Bcg locus/Nramp1 gene (natural resistance-associated macrophage protein 1) controls natural resistance to infection by Francisella tularensis LVS (live vaccine strain) and its effect is opposite to that observed for other Bcg/Nramp1-controlled pathogens such as several mycobacterial species, Leischmania donovani, and Salmonella typhimurium. In the case of F. tularensis LVS infection, the mutant allele of the Bcg locus (Bcg(s)/Nramp1(s)) is associated with natural resistance and, inversely, the wild type allele (Bcg(r)/Nramp1(r)) confers susceptibility. To determine whether differential allelic expression of the Bcg locus/Nramp1 gene modifies the composition of F. tularensis LVS-containing phagosomes (FCP), we have utilised an approach where we isolated FCP from infected Bcg congenic B10R (Bcg(r)/Nramp1(r)) and B10S (Bcg(s)/Nramp1(s)) macrophages of susceptible and resistant phenotype, respectively. Comparative proteomic analysis of the two phagosomal compartments with subsequent mass spectrometric analysis allowed identification of several proteins typical for FCP from B10R macrophages. They include a bacterial hypothetical 23 kDa protein, 60 kDa chaperonin GroEL, and host putative proteins that appeared to be mitochondrial ATP synthase beta-chain and NADH-ubiquinone oxidoreductase based on high cross-species homology. High abundance of the hypothetical 23 kDa protein correlates with the susceptible phenotype and, possibly, pathogenicity of F. tularensis LVS. The results demonstrate that F. tularensis LVS can exploit ion transport function of Bcg/Nramp1 to its own advantage.