Roles for T and NK cells in the innate immune response to Shigella flexneri

Immunoinformatics Approach to Design a Multi-Epitope Vaccine against Cutaneous Leishmaniasis

Cutaneous Leishmaniasis (CL), a neglected vector-borne disease caused by protozoan parasite Leishmania major (L. major), is a major public health concern, and the development of new strategies to reduce the disease incidence has become a top priority. Advances in immunoinformatics and in-silico epitope prediction could be a promising approach to designing a finest vaccine candidate. In this study, we aimed to design a peptide-based vaccine against CL using computational tools and identified ten B-cell-derived T-cell epitopes from the glycoprotein gp63 of L. major. All of the potential immunodominant epitopes were used to design a vaccine construct along with a linker and an adjuvant at the N-terminal for enhancing its immunogenicity. Additionally, many characteristics of the proposed vaccine were examined, and it was confirmed to be non-allergenic, non-toxic, and thermally stable. To assess the vaccine interaction with the innate immune toll-like receptor-4 (TLR-4), a 3D structure of the vaccine construct was developed. Molecular docking and molecular dynamic simulation were used to confirm the binding and to assess the stability of the vaccine-TLR4 complex and interactions, respectively. In conclusion, our multi-epitope vaccine will provide a gateway to analyze the protein function of a potential vaccine candidate against CL.

Innate immune response to peritoneal bacterial infection

Spontaneous and secondary peritoneal infections, mostly of bacterial origin, easily spread to cause severe sepsis. Cellular and humoral elements of the innate immune system are constitutively present in peritoneal cavity and omentum, and play an important role in peritonitis progression and resolution. This review will focus on the description of the anatomic characteristics of the peritoneal cavity and the composition and function of such innate immune elements under both steady-state and bacterial infection conditions. Potential innate immune-based therapeutic interventions in bacterial peritonitis alternative or adjunctive to classical antibiotic therapy will be briefly discussed.

Time-Course Transcriptome Analysis of Lungs From Mice Infected With Hypervirulent Klebsiella pneumoniae via Aerosolized Intratracheal Inoculation

Hypervirulent Klebsiella pneumoniae (hvKp) can cause life-threatening community-acquired infections among healthy young individuals and is thus of concern for global dissemination. In this study, a mouse model of acute primary hvKp pneumonia was established via aerosolized intratracheal (i.t.) inoculation, laying the foundation for conducting extensive studies related to hvKp. Subsequently, a time-course transcriptional profile was created of the lungs from the mouse model at 0, 12, 24, 48 and 60 hours post-infection (hpi) using RNA Sequencing (RNA-Seq). RNA-Seq data were analyzed with the use of Mfuzz time clustering, weighted gene co-expression network analysis (WGCNA) and Immune Cell Abundance Identifier for mouse (ImmuCellAI-mouse). A gradual change in the transcriptional profile of the lungs was observed that reflected expected disease progression. At 12 hpi, genes related to acute phase inflammatory response increased in expression and lipid metabolism appeared to have a pro-inflammatory effect. At 24 hpi, exacerbation of inflammation was observed and active IFN-γ suggested that signaling promoted activation and recruitment of macrophages occurred. Genes related to maintaining the structural integrity of lung tissues showed a sustained decrease in expression after infection and the decrease was especially marked at 48 hpi. TNF, IL-17, MAPK and NF-kB signaling pathways may play key roles in the immunopathogenesis mechanism at all stages of infection. Natural killer (NK) cells consistently decreased in abundance after infection, which has rarely been reported in hvKp infection and could provide a new target for treatment. Genes Saa1 and Slpi were significantly upregulated during infection. Both Saa1, which is associated with lipopolysaccharide (LPS) that elicits host inflammatory response, and Slpi, which encodes an antimicrobial protein, have not previously been reported in hvKp infections and could be important targets for subsequent studies. To t our knowledge, this paper represents the first study to investigate the pulmonary transcriptional response to hvKp infection. The results provide new insights into the molecular mechanisms underlying the pathogenesis of hvKp pulmonary infection that can contribute to the development of therapies to reduce hvKp pneumonia.

A Novel Design of Multi-epitope Peptide Vaccine Against Pseudomonas aeruginosa

Background:

As an opportunistic pathogen, Pseudomonas aeruginosa causes many different hazardous infections. The high mortality rate resulting from infection with this antibiotic-resistant pathogen has made it a major challenge in clinical treatment; it has been listed as the most harmful bacterium to humans by the WHO. So far, no vaccine has been approved for P. aeruginosa.

Objective:

Infections performed by bacterial attachment and colonization with type IV pili (T4P), known as the most essential adhesive vital for adhesion, while pilQ is necessary for the biogenesis of T4P, also outer membrane proteins of a pathogen is also effective in stimulating the immune system; in this regard, pilQ, OprF, and OprI, are excellent candidate antigens for production of an effective vaccine against P. aeruginosa.

Methods:

In this research, various bioinformatics methods were employed in order to design a new multiepitope peptide vaccine versus P. aeruginosa. Since T CD4+ cell immunity is important in eradicating P. aeruginosa, OprF, OprI, and pilQ antigens were analyzed to determine Helper T cell Lymphocyte (HTL) epitopes by many different immunoinformatics servers. One of the receptor agonists 2 (TLR2), a segment of the Por B protein from Neisseria meningitides was used as an adjuvant in order to stimulate an effective cellular immune response, and suitable linkers were used to connect all the above mentioned parts. In the vaccine construct, linear B cell epitopes were also identified.

Results:

Conforming the bioinformatics forecasts, the designed vaccine possesses high antigenicity and is not allergen.

Conclusion:

In this regard, the designed vaccine candidate is strongly believed to possess the potential of inducing cellular and humoral immunity against P. aeruginosa.

Novel Therapeutic Approaches to Familial HLH (Emapalumab in FHL)

Primary Hemophagocytic lymphohistiocytosis (pHLH) is a rare, life-threatening, hyperinflammatory disorder, characterized by uncontrolled activation of the immune system. Mutations affecting several genes coding for proteins involved in the cytotoxicity machinery of both natural killer (NK) and T cells have been found to be responsible for the development of pHLH. So far, front-line treatment, established on the results of large international trials, is based on the use of glucocorticoids, etoposide ± cyclosporine, followed by allogeneic hematopoietic stem cell transplantation (HSCT), the sole curative treatment for the genetic forms of the disease. However, despite major efforts to improve the outcome of pHLH, many patients still experience unfavorable outcomes, as well as severe toxicities; moreover, treatment-refractory or relapsing disease is a major challenge for pediatricians/hematologists. In this article, we review the epidemiology, etiology and pathophysiology of pHLH, with a particular focus on different cytokines at the origin of the disease. The central role of interferon-γ (IFNγ) in the development and maintenance of hyperinflammation is analyzed. The value of emapalumab, a novel IFNγ-neutralizing monoclonal antibody is discussed. Available data support the use of emapalumab for treatment of pHLH patients with refractory, recurrent or progressive disease, or intolerance to conventional therapy, recently, leading to FDA approval of the drug for these indications. Additional data are needed to define the role of emapalumab in front-line treatment or in combination with other drugs.

Intranasal Immunization of Mice with Multiepitope Chimeric Vaccine Candidate Based on Conserved Autotransporters SigA, Pic and Sap, Confers Protection against Shigella flexneri

Shigellosis is a diarrheal disease and the World Health Organization prompts the development of a vaccine against Shigella flexneri. The autotransporters SigA, Pic and Sap are conserved among Shigella spp. We previously designed an in silico vaccine with immunodominat epitopes from those autotransporters, and the GroEL protein of S. typhi as an adjuvant. Here, we evaluated the immunogenicity and protective efficacy of the chimeric multiepitope protein, named rMESF, in mice against lethal infection with S. flexneri. rMESF was administered to mice alone through the intranasal (i.n.) route or accompanied with Complete Freund’s adjuvant (CFA) intradermically (i.d.), subcutaneously (s.c.), and intramuscular (i.m.), as well as with Imject alum (i.m.). All immunized mice increased IgG, IgG1, IgG2a, IgA and fecal IgA titers compared to PBS+CFA and PBS+alum control groups. Furthermore, i.n. immunization of mice with rMESF alone presented the highest titers of serum and fecal IgA. Cytokine levels (IFN-γ, TNF-α, IL-4, and IL-17) and lymphocyte proliferation increased in all experimental groups, with the highest lymphoproliferative response in i.n. mice immunized with rMESF alone, which presented 100% protection against S. flexneri. In summary, this vaccine vests protective immunity and highlights the importance of mucosal immunity activation for the elimination of S. flexneri.

Vaccination With Mouse Dendritic Cells Loaded With an IpaD-IpaB Fusion Provides Protection Against Shigellosis

Diarrheal diseases are a major cause of morbidity and mortality worldwide. They are most prevalent in settings with inadequate sanitation, poor hygiene and contaminated water. An important diarrheal pathogen in such settings is Shigella. No commercially available vaccine exists against shigellosis and immunity to the pathogen is serotype-restricted. We have previously shown that a polypeptide fusion of the Type Three Secretion Apparatus (T3SA) proteins IpaB and IpaD (named DBF) was efficacious as a vaccine against Shigella. Vaccination using different administration routes indicated that protection conferred by DBF did not fully correlate with antibodies. To define the immune responses involved in protection, we studied cellular responses to intranasal immunization with the DBF and the adjuvant dmLT. We found dendritic cell (DC) activation at the nasal associated lymphoid tissue (NALT). Activation markers CD86 and MHCII significantly increase in cells from immunized mice. Antigen exposure in vitro further confirmed the upregulation of CD80 and CD40 in primary dendritic cells. Animals immunized with antigen-primed dendritic cells were protected against Shigella infection, at levels comparable to the efficacy of immunization with the protein vaccine formulation. Therefore, we show that antigen-primed DCs are enough to provide immunity, and propose a mechanism of protection against Shigella spp. based on DC-mediated antigen presentation to T cells.

Nanonized tetracycline cures deadly diarrheal disease 'shigellosis' in mice, caused by multidrug-resistant Shigella flexneri 2a bacterial infection

We reported earlier about nano-formulation of tetracycline through its entrapment within calcium-phosphate nano-particle (CPNP) and about killing of pathogenic bacterium Shigella flexnari 2a, resistant to tetracycline (and 9 other antibiotics), by the nanonized antibiotic (Tet-CPNP). Here, we report on therapeutic role of Tet-CPNP against deadly diarrheal disease 'shigellosis' in mice, caused by Shigella infection. Our findings revealed that occurrence of mushy-stool excretion, colon-length shortening, weight-loss and bacterial colonization in gastrointestinal tract of mice due to shigellosis was significantly reduced by Tet-CPNP treatment. Histo- and immuno-logical studies showed that changes in morphology and level of inflammatory cytokines TNF-α, IL-1β and IFN-γ in intestinal tissue of Shigella-infected mice were reverted to almost normal features by Tet-CPNP treatment. Bulk tetracycline had no anti-shigellosis action. Thus, nanonization of tetracycline rejuvenated the old, cheap, broad-spectrum antibiotic from obsolescence (due to resistance generation), making it highly beneficial for diarrhea-prone developing countries with limited health-care budgets.

Natural killer cells as a therapeutic tool for infectious diseases - current status and future perspectives

Natural Killer (NK) cells are involved in the host immune response against infections due to viral, bacterial and fungal pathogens, all of which are a significant cause of morbidity and mortality in immunocompromised patients. Since the recovery of the immune system has a major impact on the outcome of an infectious complication, there is major interest in strengthening the host response in immunocompromised patients, either by using cytokines or growth factors or by adoptive cellular therapies transfusing immune cells such as granulocytes or pathogen-specific T-cells. To date, relatively little is known about the potential of adoptively transferring NK cells in immunocompromised patients with infectious complications, although the anti-cancer property of NK cells is already being investigated in the clinical setting. This review will focus on the antimicrobial properties of NK cells and the current standing and future perspectives of generating and using NK cells as immunotherapy in patients with infectious complications, an approach which is promising and might have an important clinical impact in the future.

A clinically parameterized mathematical model of Shigella immunity to inform vaccine design

We refine and clinically parameterize a mathematical model of the humoral immune response against Shigella, a diarrheal bacteria that infects 80-165 million people and kills an estimated 600,000 people worldwide each year. Using Latin hypercube sampling and Monte Carlo simulations for parameter estimation, we fit our model to human immune data from two Shigella EcSf2a-2 vaccine trials and a rechallenge study in which antibody and B-cell responses against Shigella′s lipopolysaccharide (LPS) and O-membrane proteins (OMP) were recorded. The clinically grounded model is used to mathematically investigate which key immune mechanisms and bacterial targets confer immunity against Shigella and to predict which humoral immune components should be elicited to create a protective vaccine against Shigella. The model offers insight into why the EcSf2a-2 vaccine had low efficacy and demonstrates that at a group level a humoral immune response induced by EcSf2a-2 vaccine or wild-type challenge against Shigella′s LPS or OMP does not appear sufficient for protection. That is, the model predicts an uncontrolled infection of gut epithelial cells that is present across all best-fit model parameterizations when fit to EcSf2a-2 vaccine or wild-type challenge data. Using sensitivity analysis, we explore which model parameter values must be altered to prevent the destructive epithelial invasion by Shigella bacteria and identify four key parameter groups as potential vaccine targets or immune correlates: 1) the rate that Shigella migrates into the lamina propria or epithelium, 2) the rate that memory B cells (B_M) differentiate into antibody-secreting cells (ASC), 3) the rate at which antibodies are produced by activated ASC, and 4) the Shigella-specific B_M carrying capacity. This paper underscores the need for a multifaceted approach in ongoing efforts to design an effective Shigella vaccine.

Inflammasomes Coordinate Pyroptosis and Natural Killer Cell Cytotoxicity to Clear Infection by a Ubiquitous Environmental Bacterium

Defective neutrophils in patients with chronic granulomatous disease (CGD) cause susceptibility to extracellular and intracellular infections. Microbes must first be ejected from intracellular niches to expose them to neutrophil attack, so we hypothesized that inflammasomes detect certain CGD pathogens upstream of neutrophil killing. Here, we identified one such ubiquitous environmental bacterium, Chromobacterium violaceum, whose extreme virulence was fully counteracted by the NLRC4 inflammasome. Caspase-1 protected via two parallel pathways that eliminated intracellular replication niches. Pyroptosis was the primary bacterial clearance mechanism in the spleen, but both pyroptosis and interleukin-18 (IL-18)-driven natural killer (NK) cell responses were required for liver defense. NK cells cleared hepatocyte replication niches via perforin-dependent cytotoxicity, whereas interferon-γ was not required. These insights suggested a therapeutic approach: exogenous IL-18 restored perforin-dependent cytotoxicity during infection by the inflammasome-evasive bacterium Listeria monocytogenes. Therefore, inflammasomes can trigger complementary programmed cell death mechanisms, directing sterilizing immunity against intracellular bacterial pathogens.

Diarrhoea and smoking: an analysis of decades of observational data from Bangladesh

BACKGROUND

Although cigarette smoking affects all biological systems of the human body including the gastrointestinal tract, there is a lack of evidence regarding its effect on the severity of diarrhoeal disease and whether a dose-response relationship exists. We therefore tested for the presence of specific causative pathogens for infectious diarrhoea, assessed the independent effect of smoking on its severity and tested whether any dose-response relationship existed while controlling for subjects' age, sociodemographic characteristics and presence of causative pathogens in an urban setting in Bangladesh.

METHODS

A total of 20,757 patients aged 15 years and above with diarrhoea were enrolled into the Diarrhoeal Disease Surveillance System, managed by the International Centre for Diarrhoeal Disease Research, Bangladesh, from 1993 to 2012. We collected data on individuals' current daily consumption of cigarettes and bidis (traditional hand-rolled cigarettes) and conducted an ordered logistic regression to determine the effect of smoking on diarrhoeal disease severity and whether a dose-response relationship exists.

RESULTS

We identified 19 % of patients with diarrhoea as smokers, of whom 52 % smoked 1-9 cigarettes per day. While 97 % of smokers were male, 41 % were aged 15-30 years of age. Smokers were found to have a significantly lower severity of diarrhoeal disease (OR: 0.92, 95 % CI: 0.85-0.99, p = 0.025) after adjusting for age, wealth quintile, illiteracy and the presence of specific causative pathogens (Vibrio cholerae and Shigella). We observed no dose-response relationship between the number of cigarettes smoked per day and disease severity when adjusting for the same covariates. Smokers were more frequently infected with Shigella (7 vs. 6 %, p < 0.001) and less often with Vibrio cholerae (22 vs. 26 %, p < 0.001) than their non-smoking counterparts.

CONCLUSIONS

The aetiology and severity of diarrhoeal disease differed between smokers and non-smokers in our sample. However, we found no dose-response relationship between disease severity and the number of cigarettes smoked per day.

Shigella manipulates host immune responses by delivering effector proteins with specific roles

The intestinal epithelium deploys multiple defense systems against microbial infection to sense bacterial components and danger alarms, as well as to induce intracellular signal transduction cascades that trigger both the innate and the adaptive immune systems, which are pivotal for bacterial elimination. However, many enteric bacterial pathogens, including Shigella, deliver a subset of virulence proteins (effectors) via the type III secretion system (T3SS) that enable bacterial evasion from host immune systems; consequently, these pathogens are able to efficiently colonize the intestinal epithelium. In this review, we present and select recently discovered examples of interactions between Shigella and host immune responses, with particular emphasis on strategies that bacteria use to manipulate inflammatory outputs of host-cell responses such as cell death, membrane trafficking, and innate and adaptive immune responses.

Advances in experimental systems to study hepatitis C virus in vitro and in vivo

Hepatitis C virus (HCV) represents a global health concern affecting over 185 million people worldwide. Chronic HCV infection causes liver fibrosis and cirrhosis and is the leading indication for liver transplantation. Recent advances in the field of direct-acting antiviral drugs (DAAs) promise a cure for HCV in over 90% of cases that will get access to these expensive treatments. Nevertheless, the lack of a protective vaccine and likely emergence of drug-resistant viral variants call for further studies of HCV biology. With chimpanzees being for a long time the only non-human in vivo model of HCV infection, strong efforts were put into establishing in vitro experimental systems. The initial models only enabled to study specific aspects of the HCV life cycle, such as viral replication with the subgenomic replicon and entry using HCV pseudotyped particles (HCVpp). Subsequent development of protocols to grow infectious HCV particles in cell-culture (HCVcc) ignited investigations on the full cycle of HCV infection and the virus-host interactions required for virus propagation. More recently, small animal models permissive to HCV were generated that allowed in vivo testing of novel antiviral therapies as well as vaccine candidates. This review provides an overview of the currently available in vitro and in vivo experimental systems to study HCV biology. Particular emphasis is given to how these model systems furthered our understanding of virus-host interactions, viral pathogenesis and immunological responses to HCV infection, as well as drug and vaccine development.

Co-administration of rIpaB domain of Shigella with rGroEL of S. Typhi enhances the immune responses and protective efficacy against Shigella infection

Shigella species cause severe bacillary dysentery in humans and are associated with high morbidity and mortality. The Invasion plasmid antigen (IpaB) protein, which is conserved across all Shigella spp., induces macrophage cell death and is required to invade host cells. The present study evaluates the immunogenicity and protective efficacy of the recombinant (r) domain region of IpaB (rIpaB) of S. flexneri. rIpaB was administered either alone or was co-administered with the rGroEL (heat shock protein 60) protein from S. Typhi as an adjuvant in a mouse model of intranasal immunization. The IpaB domain region (37 kDa) of S. flexneri was amplified from an invasion plasmid, cloned, expressed in BL21 Escherichia coli cells and purified. Immunization with the rIpaB domain alone stimulated both humoral and cell-mediated immune responses. Furthermore, robust antibody (IgG, IgA) and T-cell responses were induced when the rIpaB domain was co-administered with rGroEL. Antibody isotyping revealed higher IgG1 and IgG2a antibody titers and increased interferon-gamma (IFN-γ) secretion in the co-administered group. Immunization of mice with the rIpaB domain alone protected 60%-70% of the mice from lethal infection by S. flexneri, S. boydii and S. sonnei, whereas co-administration with rGroEL increased the protective efficacy to 80%-85%. Organ burden and histopathological studies also revealed a significant reduction in lung infection in the co-immunized mice compared with mice immunized with the rIpaB domain alone. This study emphasizes that the co-administration of the rIpaB domain and rGroEL protein improves immune responses in mice and increases protective efficacy against Shigella infection. This is also the first report to evaluate the potential of the GroEL (Hsp 60) protein of S. Typhi as an adjuvant molecule, thereby overcoming the need for commercial adjuvants.

Conventional NK cells can produce IL-22 and promote host defense in Klebsiella pneumoniae pneumonia

It was reported that host defense against pulmonary Klebsiella pneumoniae infection requires IL-22, which was proposed to be of T cell origin. Supporting a role for IL-22, we found that Il22(-/-) mice had decreased survival compared with wild-type mice after intratracheal infection with K. pneumoniae. Surprisingly, however, Rag2(-/-) mice did not differ from wild-type mice in survival or levels of IL-22 in the lungs postinfection with K. pneumoniae. In contrast, K. pneumoniae-infected Rag2(-/-)Il2rg(-/-) mice failed to produce IL-22. These data suggested a possible role for NK cells or other innate lymphoid cells in host defense and production of IL-22. Unlike NK cell-like innate lymphoid cells that produce IL-22 and display a surface phenotype of NK1.1(-)NKp46(+)CCR6(+), lung NK cells showed the conventional phenotype, NK1.1(+)NKp46(+)CCR6(-). Mice depleted of NK cells using anti-asialo GM1 showed decreased survival and higher lung bacterial counts, as well as increased dissemination of K. pneumoniae to blood and liver, compared with control-treated mice. NK cell depletion also led to decreased production of IL-22 in the lung. Within 1 d postinfection, although there was no increase in the number of lung NK cells, a subset of lung NK cells became competent to produce IL-22, and such cells were found in both wild-type and Rag2(-/-) mice. Our data suggest that, during pulmonary infection of mice with K. pneumoniae, conventional NK cells are required for optimal host defense, which includes the production of IL-22.

Characterization of a novel fusion protein from IpaB and IpaD of Shigella spp. and its potential as a pan-Shigella vaccine

Shigellosis is an important disease in the developing world, where about 90 million people become infected with Shigella spp. each year. We previously demonstrated that the type three secretion apparatus (T3SA) proteins IpaB and IpaD are protective antigens in the mouse lethal pulmonary model. In order to simplify vaccine formulation and process development, we have evaluated a vaccine design that incorporates both of these previously tested Shigella antigens into a single polypeptide chain. To determine if this fusion protein (DB fusion) retains the antigenic and protective capacities of IpaB and IpaD, we immunized mice with the DB fusion and compared the immune response to that elicited by the IpaB/IpaD combination vaccine. Purification of the DB fusion required coexpression with IpgC, the IpaB chaperone, and after purification it maintained the highly α-helical characteristics of IpaB and IpaD. The DB fusion also induced comparable immune responses and retained the ability to protect mice against Shigella flexneri and S. sonnei in the lethal pulmonary challenge. It also offered limited protection against S. dysenteriae challenge. Our results show the feasibility of generating a protective Shigella vaccine comprised of the DB fusion.

Agglutinating secretory IgA preserves intestinal epithelial cell integrity during apical infection by Shigella flexneri

Shigella flexneri, by invading intestinal epithelial cells (IECs) and inducing inflammatory responses of the colonic mucosa, causes bacillary dysentery. Although M cells overlying Peyer's patches are commonly considered the primary site of entry of S. flexneri, indirect evidence suggests that bacteria can also use IECs as a portal of entry to the lamina propria. Passive delivery of secretory IgA (SIgA), the major immunoglobulin secreted at mucosal surfaces, has been shown to protect rabbits from experimental shigellosis, but no information exists as to its molecular role in maintaining luminal epithelial integrity. We have established that the interaction of virulent S. flexneri with the apical pole of a model intestinal epithelium consisting of polarized Caco-2 cell monolayers resulted in the progressive disruption of the tight junction network and actin depolymerization, eventually resulting in cell death. The lipopolysaccharide (LPS)-specific agglutinating SIgAC5 monoclonal antibody (MAb), but not monomeric IgAC5 or IgGC20 MAbs of the same specificity, achieved protective functions through combined mechanisms, including limitation of the interaction between S. flexneri and epithelial cells, maintenance of the tight junction seal, preservation of the cell morphology, reduction of NF-κB nuclear translocation, and inhibition of proinflammatory mediator secretion. Our results add to the understanding of the function of SIgA-mediated immune exclusion by identifying a mode of action whereby the formation of immune complexes translates into maintenance of the integrity of epithelial cells lining the mucosa. This novel mechanism of protection mediated by SIgA is important to extend the arsenal of effective strategies to fight against S. flexneri mucosal invasion.

Applying mathematical tools to accelerate vaccine development: modeling Shigella immune dynamics

We establish a mathematical framework for studying immune interactions with Shigella, a bacteria that kills over one million people worldwide every year. The long-term goal of this novel approach is to inform Shigella vaccine design by elucidating which immune components and bacterial targets are crucial for establishing Shigella immunity. Our delay differential equation model focuses on antibody and B cell responses directed against antigens like lipopolysaccharide in Shigella’s outer membrane. We find that antibody-based vaccines targeting only surface antigens cannot elicit sufficient immunity for protection. Additional boosting prior to infection would require a four-orders-of-magnitude increase in antibodies to sufficiently prevent epithelial invasion. However, boosting anti-LPS B memory can confer protection, which suggests these cells may correlate with immunity. We see that IgA antibodies are slightly more effective per molecule than IgG, but more total IgA is required due to spatial functionality. An extension of the model reveals that targeting both LPS and epithelial entry proteins is a promising avenue to advance vaccine development. This paper underscores the importance of multifaceted immune targeting in creating an effective Shigella vaccine. It introduces mathematical models to the Shigella vaccine development effort and lays a foundation for joint theoretical/experimental/clinical approaches to Shigella vaccine design.

Cross-protection provided by live Shigella mutants lacking major antigens

The immune response elicited by Shigella infections is dominated by serotype-specific antibodies recognizing the LPS O-antigens. Although a marked antibody response to invasion plasmid antigens (Ipa-s) shared by all virulent strains is also induced, the varying level of immunity elicited by natural infections is serotype-restricted. Previous vaccines have tried to mimic and achieve this serotype-specific, infection-induced immunity. As, however, the four Shigella species can express 50 different types of O-antigens, current approaches with the aim to induce a broad coverage use a mixture of the most common O-antigens combined in single vaccines. In the current study we present data on an alternative approach to generate immunity protective against multiple serotypes. Mutants lacking both major immune-determinant structures (i.e. the Ipa and O-antigens) were not only highly attenuated, but, unlike their avirulent counterparts still expressing these antigens, elicited a protective immune response to heterologous serotypes in a murine model. Evidence is provided that protection was mediated by the enhanced immunogenic potential of minor conserved antigens. Furthermore, the rough, non-invasive double mutants triggered an immune response different from that induced by the smooth, invasive strains regarding the isotype of antibodies generated. These non-invasive, rough mutants may represent promising candidates for further development into live vaccines for the prophylaxis of bacillary dysentery in areas with multiple endemic serotypes.

Role of NK cells in host defense against pulmonary type A Francisella tularensis infection

Pneumonic tularemia is a potentially fatal disease caused by the Category A bioterrorism agent Francisella tularensis. Understanding the pulmonary immune response to this bacterium is necessary for developing effective vaccines and therapeutics. In this study, characterization of immune cell populations in the lungs of mice infected with the type A strain Schu S4 revealed a significant loss in natural killer (NK) cells over time. Since this decline in NK cells correlated with morbidity and mortality, we hypothesized these cells contribute to host defense against Schu S4 infection. Depletion of NK cells prior to Schu S4 challenge significantly reduced IFN-γ and granzyme B in the lung but had no effect on bacterial burden or disease progression. Conversely, increasing NK cell numbers with the anti-apoptotic cytokine IL-15 and soluble receptor IL-15Rα had no significant impact on Schu S4 growth in vivo. A modest decrease in median time to death, however, was observed in live vaccine strain (LVS)-vaccinated mice depleted of NK1.1+ cells and challenged with Schu S4. Therefore, NK cells do not appear to contribute to host defense against acute respiratory infection with type A F. tularensis in vivo, but they play a minor role in protection elicited by LVS vaccination.

Increased presence of effector lymphocytes during Helicobacter hepaticus-induced colitis

AIM: To identify and characterize drosophila mothers against decapentaplegic (SMAD)3-dependent changes in immune cell populations following infection with Helicobacter hepaticus (H. hepaticus).

METHODS: SMAD3^-/- (n = 19) and colitis-resistant SMAD3^+/- (n = 24) mice (8-10 wk of age) were infected with H. hepaticus and changes in immune cell populations [T lymphocytes, natural killer (NK) cells, T regulatory cells] were measured in the spleen and mesenteric lymph nodes (MsLNs) at 0 d, 3 d, 7 d and 28 d post-infection using flow cytometry. Genotype-dependent changes in T lymphocytes and granzyme B⁺ cells were also assessed after 28 d in proximal colon tissue using immunohistochemistry.

RESULTS: As previously observed, SMAD3^-/-, but not SMAD3^+/- mice, developed colitis, peaking at 4 wk post-infection. No significant changes in T cell subsets were observed in the spleen or in the MsLNs between genotypes at any time point. However, CD4⁺ and CD8⁺/CD62L^lo cells, an effector T lymphocyte population, as well as NK cells (NKp46/DX5⁺) were significantly higher in the MsLNs of SMAD3^-/- mice at 7 d and 28 d post-infection. In the colon, a higher number of CD3⁺ cells were present in SMAD3^-/- compared to SMAD3^+/– mice at baseline, which did not significantly change during infection. However, the number of granzyme B⁺ cells, a marker of cytolytic lymphocytes, significantly increased in SMAD3^-/- mice 28 d post-infection compared to both SMAD3^+/- mice and to baseline values. This was consistent with more severe colitis development in these animals.

CONCLUSION: Data suggest that defects in SMAD3 signaling increase susceptibility to H. hepaticus-induced colitis through aberrant activation and/or dysregulation of effector lymphocytes.

Broadly protective Shigella vaccine based on type III secretion apparatus proteins

Shigella spp. are food- and waterborne pathogens that cause severe diarrheal and dysenteric disease associated with high morbidity and mortality. Individuals most often affected are children under 5 years of age in the developing world. The existence of multiple Shigella serotypes and the heterogenic distribution of pathogenic strains, as well as emerging antibiotic resistance, require the development of a broadly protective vaccine. All Shigella spp. utilize a type III secretion system (TTSS) to initiate infection. The type III secretion apparatus (TTSA) is the molecular needle and syringe that form the energized conduit between the bacterial cytoplasm and the host cell to transport effector proteins that manipulate cellular processes to benefit the pathogen. IpaB and IpaD form a tip complex atop the TTSA needle and are required for pathogenesis. Because they are common to all virulent Shigella spp., they are ideal candidate antigens for a subunit-based, broad-spectrum vaccine. We examined the immunogenicity and protective efficacy of IpaB and IpaD, alone or combined, coadministered with a double mutant heat-labile toxin (dmLT) from Escherichia coli, used as a mucosal adjuvant, in a mouse model of intranasal immunization and pulmonary challenge. Robust systemic and mucosal antibody- and T cell-mediated immunities were induced against both proteins, particularly IpaB. Mice immunized in the presence of dmLT with IpaB alone or IpaB combined with IpaD were fully protected against lethal pulmonary infection with Shigella flexneri and Shigella sonnei. We provide the first demonstration that the Shigella TTSAs IpaB and IpaD are promising antigens for the development of a cross-protective Shigella vaccine.

C5a regulates NKT and NK cell functions in sepsis

Complement, NKT, and NK cells play critical roles in the first line defense against pathogens. Functional roles for both C5a receptors, that is, complement receptor C5a (C5aR) and C5a receptor-like 2 (C5L2), in sepsis have been demonstrated. However, the role of C5a in innate lymphocyte activation during sepsis remains elusive. In this article, we show that naive NKT and NK cells already express high levels of C5aR and minor levels of C5L2 mRNA, but no protein. Upon Escherichia coli-induced sepsis, we found C5aR surface expression on subpopulations of NKT and NK cells, suggesting rapid translation into C5aR protein on bacterial encounter. Importantly, significantly increased survival in the absence of C5aR, NKT, and NK cells, but not of C5L2, was associated with reduced IFN-γ and TNF-α serum levels. Sepsis induction in C5aR(+)/C5aR(-) mixed bone marrow chimeras identified cognate engagement of C5aR on NKT cells as an important factor for the recruitment of NKT cells. Furthermore, we found synergistic interaction between C5aR and TLRs enhancing the production of TNF-α and IFN-γ from NKT and NK cells in cocultures with dendritic cells. Our results identify C5aR activation as a novel pathway driving detrimental effects of NKT and NK cells during early experimental sepsis.

The natural cytotoxicity receptor 1 contribution to early clearance of Streptococcus pneumoniae and to natural killer-macrophage cross talk

Natural killer (NK) cells serve as a crucial first line of defense against tumors, viral and bacterial infections. We studied the involvement of a principal activating natural killer cell receptor, natural cytotoxicity receptor 1 (NCR1), in the innate immune response to S. pneumoniae infection. Our results demonstrate that the presence of the NCR1 receptor is imperative for the early clearance of S. pneumoniae. We tied the ends in vivo by showing that deficiency in NCR1 resulted in reduced lung NK cell activation and lung IFNγ production at the early stages of S. pneumoniae infection. NCR1 did not mediate direct recognition of S. pneumoniae. Therefore, we studied the involvement of lung macrophages and dendritic cells (DC) as the mediators of NK-expressed NCR1 involvement in response to S. pneumoniae. In vitro, wild type BM-derived macrophages and DC expressed ligands to NCR1 and co-incubation of S. pneumoniae-infected macrophages/DC with NCR1-deficient NK cells resulted in significantly lesser IFNγ levels compared to NCR1-expressing NK cells. In vivo, ablation of lung macrophages and DC was detrimental to the early clearance of S. pneumoniae. NCR1-expressing mice had more potent alveolar macrophages as compared to NCR1-deficient mice. This result correlated with the higher fraction of NCR1-ligand^high lung macrophages, in NCR1-expressing mice, that had better phagocytic activity compared to NCR1-ligand^dull macrophages. Overall, our results point to the essential contribution of NK-expressed NCR1 in early response to S. pneumoniae infection and to NCR1-mediated interaction of NK and S. pneumoniae infected-macrophages and -DC.

Serine protease autotransporters from Shigella flexneri and pathogenic Escherichia coli target a broad range of leukocyte glycoproteins

The serine protease autotransporters of Enterobacteriaceae (SPATEs) are secreted by pathogenic Gram-negative bacteria through the autotransporter pathway. We previously classified SPATE proteins into two classes: cytotoxic (class 1) and noncytotoxic (class 2). Here, we show that Pic, a class 2 SPATE protein produced by Shigella flexneri 2a, uropathogenic and enteroaggregative Escherichia coli strains, targets a broad range of human leukocyte adhesion proteins. Substrate specificity was restricted to glycoproteins rich in O-linked glycans, including CD43, CD44, CD45, CD93, CD162 (PSGL-1; P-selectin glycoprotein ligand 1), and the surface-attached chemokine fractalkine, all implicated in leukocyte trafficking, migration, and inflammation. N-terminal sequencing of proteolytic products revealed Pic (protease involved in colonization) cleavage sites to occur before Thr or Ser residues. The purified carbohydrate sLewis-X implied in inflammation and malignancy inhibited cleavage of PSGL-1 by Pic. Exposure of human leukocytes to purified Pic resulted in polymorphonuclear cell activation, but impaired chemotaxis and transmigration; Pic-treated T cells underwent programmed cell death. We also show that the Pic-related protease Tsh/Hbp, implicated in extraintestinal infections, exhibited a spectrum of substrates similar to those cleaved by Pic. In the guinea pig keratoconjunctivitis model, a Shigella pic mutant induced greater inflammation than its parent strain. We suggest that the class-2 SPATEs represent unique immune-modulating bacterial virulence factors.

Antigen-specific CD8(+) T cells fail to respond to Shigella flexneri

CD8(+) T lymphocytes often play a primary role in adaptive immunity to cytosolic microbial pathogens. Surprisingly, CD8(+) T cells are not required for protective immunity to the enteric pathogen Shigella flexneri, despite the ability of Shigella to actively secrete proteins into the host cytoplasm, a location from which antigenic peptides are processed for presentation to CD8(+) T cells. To determine why CD8(+) T cells fail to play a role in adaptive immunity to S. flexneri, we investigated whether antigen-specific CD8(+) T cells are primed during infection but are unable to confer protection or, alternatively, whether T cells fail to be primed. To test whether Shigella is capable of stimulating an antigen-specific CD8(+) T-cell response, we created an S. flexneri strain that constitutively secretes a viral CD8(+) T-cell epitope via the Shigella type III secretion system and characterized the CD8(+) T-cell response to this strain both in mice and in cultured cells. Surprisingly, no T cells specific for the viral epitope were stimulated in mice infected with this strain, and cells infected with the recombinant strain were not targeted by epitope-specific T cells. Additionally, we found that the usually robust T-cell response to antigens artificially introduced into the cytoplasm of cultured cells was significantly reduced when the antigen-presenting cell was infected with Shigella. Collectively, these results suggest that antigen-specific CD8(+) T cells are not primed during S. flexneri infection and, as a result, afford little protection to the host during primary or subsequent infection.

Inactivated and subunit vaccines to prevent shigellosis

Shigellosis remains a formidable disease globally, with children of the developing world bearing the greatest number of infections. The need for an affordable, safe and efficacious vaccine has persisted for decades. Vaccines to prevent shigellosis can be divided into living and nonliving approaches. Several nonliving Shigella vaccines are currently at different stages of development and show substantial promise. Outlined here is an overview of multiple nonliving vaccine technologies, highlighting their current status and recent advances in testing. In addition, gaps in the knowledge base regarding immune mechanisms of protection are explored.

Interferon-gamma secretion is induced in IL-12 stimulated human NK cells by recognition of Helicobacter pylori or TLR2 ligands

Helicobacter pylori induce a chronic inflammation in the human gastric mucosa characterized by increased production of interferon-gamma (IFN-γ). The presence of natural killer (NK) cells in the human gastric mucosa and the ability of NK cells to produce IFN-γ suggest an important role of NK cells in the immune response directed towards H. pylori infection. Since NK cells previously have been shown to respond to bacterial components with IFN-γ production, we investigated the mechanisms for the recognition of H. pylori. We found that inhibition of MyD88 homodimerization resulted in decreased production of IFN-γ and that inhibition of the p38 MAPK decreased the production as well as the secretion of IFN-γ. Further studies indicated an involvement of Toll-like receptors (TLRs), in particular TLR2. Finally, we showed that the H. pylori specific membrane bound lipoprotein HpaA induced IFN-γ production from NK cells through recognition by TLR2. In conclusion, we suggest an involvement of TLR2 in the recognition of H. pylori by human NK cells and that HpaA is a TLR2 ligand important for recognition.

Th17 cells are the dominant T cell subtype primed by Shigella flexneri mediating protective immunity

The T cell response to Shigella, the causative agent of bacillary dysentery, remains poorly understood. Using a murine model of infection, we report that Shigella flexneri primes predominately IL-17A- and IL-22-producing Th17 cells. Shigella-specific Th1 cells are only significantly induced on secondary infection, whereas specific Th2 and CD8(+) T cells are undetectable. Apart from Th17 cells that are primed in a MHC class II- and IL-6-dependent, but IL12/23p40-independent manner, we identified gammadelta T cells as an additional but minor source of IL-17A. Priming of IL-17A(+) gammadelta T cells is dependent on IL12/23p40, but independent of MHC-class II and IL-6. Th17 cells have emerged as important players in inflammatory, autoimmune, and infectious diseases. Among the yet unresolved questions is their role in long-term immunity to pathogens. In this study, we show that the elicited S. flexneri-specific Th17 pool gives rise to an enhanced recall response up to 12 mo after priming, suggesting the presence of a long-term memory state. The clearance of primary infection is impaired in the absence of T cells, but independently of IL-17A. However, after reinfection, IL-17A produced by S. flexneri-specific Th17 cells becomes important to ultimately restrict bacterial growth. These findings bring new insights into the adaptive immune response to Shigella infection and highlight the importance of pathogen-specific Th17 cell immunity for secondary immune protection.

Spa15 of Shigella flexneri is secreted through the type III secretion system and prevents staurosporine-induced apoptosis

Shigella flexneri is a gram-negative, facultative intracellular pathogen that invades the colonic epithelium and causes bacillary dysentery. We previously demonstrated that S. flexneri inhibits staurosporine-induced apoptosis in infected epithelial cells and that a DeltamxiE mutant is unable to inhibit apoptosis. Therefore, we hypothesized that an MxiE-regulated gene was responsible for protection of epithelial cells from apoptosis. Analysis of all MxiE-regulated genes yielded no mutants that lacked the ability to prevent apoptosis. Spa15, which is defined as a type III secretion system chaperone, was analyzed since it associates with MxiE. A Deltaspa15 mutant was unable to prevent staurosporine-induced apoptosis. C-terminal hemagglutinin-tagged spa15 was secreted by S. flexneri within 2 h in the Congo red secretion assay, and secretion was dependent on the type III secretion system. Spa15 was also secreted by Shigella in infected epithelial cells, as verified by immunofluorescence analysis. Spa15 secretion was decreased in the DeltamxiE mutant, which demonstrates why this mutant is unable to prevent staurosporine-induced apoptosis. Our data are the first to show that Spa15 is secreted in a type III secretion system-dependent fashion, and the absence of Spa15 in the Deltaspa15 mutant results in the loss of protection from staurosporine-induced apoptosis in epithelial cells. Thus, Spa15 contributes to the intracellular survival of Shigella by blocking apoptosis in the infected host cell.

Role of T cells for cytokine production and outcome in a model of acute septic peritonitis

Although it is generally accepted that early defense mechanisms are controlled by cells of the innate immune system, T cells were found to be crucial for host resistance against acute septic peritonitis. However, the mechanisms by which T cells mediate protection are not fully understood. Here, we demonstrate mice deficient for recombinase-activating gene (RAG) 1, which lack mature B and T cells, showed enhanced susceptibility and impaired bacterial clearance in a model of acute septic peritonitis. Whereas B-cell-deficient muMT mice showed no significant difference in the survival rate after peritonitis induction, T-cell-deficient Balb/c nude mice exhibited reduced survival. Importantly, analysis of cytokine production in both RAG-1-deficient and T-cell-deficient nude mice indicated strongly attenuated production of IL-12, interferon (IFN) gamma, and IL-10 during sepsis. Reduced cytokine levels were detected both in serum and in organ extracts of septic mice. Direct analysis of T cells isolated from septic mice demonstrated that T cells respond to an acute septic challenge by increased production of IFN-gamma and IL-10. Moreover, bacterial numbers in spleens of septic RAG-1-deficient mice were significantly increased as compared with controls, suggesting that T cells are engaged in the early antibacterial immune defense during sepsis, possibly via the production of IFN-gamma. In summary, these results imply that T cells contribute to protective immune responses against acute systemic infections via their ability to produce crucial immune mediators.

Rickettsiae stimulate dendritic cells through toll-like receptor 4, leading to enhanced NK cell activation in vivo

Adoptive transfer of Toll-like receptor (TLR) 4-stimulated dendritic cells (DCs) induces protective immunity against an ordinarily lethal rickettsial challenge, but the mechanism underlying this protection remains elusive. Therefore, we sought to determine the importance of TLR4 in early immunity to rickettsiae in vivo, particularly that conferred by TLR4-stimulated DCs. Rickettsial growth proceeded logarithmically in mice lacking TLR4 function, whereas in TLR4-competent mice rickettsial growth manifested a lag phase early, suggesting that TLR4 may initiate innate rickettsial immunity. TLR4-competent mice produced significant amounts of interferon (IFN)-gamma on day 1 of Rickettsia conorii infection, which was associated with significant expansion of the population of activated NK cells. Moreover, NK cells from TLR4-competent mice produced significantly higher levels of IFN-gamma and had greater cytotoxic activity than did those from TLR4-deficient mice. Last, adoptive transfer of rickettsiae-exposed, TLR4-stimulated DCs activated NK cells in vivo. Together, these data reveal an important role for DCs in recognizing rickettsiae through TLR4 and inducing early antirickettsial immunity.

NKG2D is critical for NK cell activation in host defense against Pseudomonas aeruginosa respiratory infection

Pseudomonas aeruginosa is a major cause of nosocomial respiratory infections. The eradication of P. aeruginosa from the lung involves the orchestrated actions of the pulmonary epithelium and both resident and recruited immune cells. The NKG2D receptor is constitutively expressed on the surface of circulating and tissue-resident NK cells (and other cytotoxic lymphocytes), and is capable of controlling NK cell activation and production of cytokines, such as IFN-gamma via interactions with ligands expressed on the surface of stressed cells. Previously, we demonstrated that NKG2D mediates pulmonary clearance of P. aeruginosa. In the present study, we investigated the cellular and molecular mechanisms of NKG2D-mediated clearance of P. aeruginosa using a novel transgenic mouse model of doxycycline-inducible conditional expression of NKG2D ligands (retinoic acid early transcript 1, alpha) in pulmonary epithelial cells. NKG2D ligand expression in this model increased pulmonary clearance, cellular phagocytosis, and survival following P. aeruginosa respiratory infection. Additionally, NK cell sensitivity to ex vivo LPS stimulation was greater in lung cells isolated from naive transgenic mice administered doxycycline. We also showed that NK cells are the primary source of lymphocyte-derived IFN-gamma in response to P. aeruginosa respiratory infection. Significantly, we demonstrated that NKG2D is critical to the nonredundant IFN-gamma production by pulmonary NK cells following acute P. aeruginosa infection. These results represent the principal report of NKG2D-mediated activation of lung NK cells following respiratory infection with an opportunistic pathogen and further establish the importance of NKG2D in the host response against P. aeruginosa respiratory infection.

Activation of human NK cells by the bacterial pathogen-associated molecular pattern muramyl dipeptide

Muramyl dipeptide (MDP) is a bacterial pathogen associated molecular pattern derived from both Gram-positive and -negative bacteria. It is a specific ligand for nuclear oligomerization domain 2, a pattern recognition receptor best characterized for its role in immunosurveillance in the gut. In this study, we demonstrate that human peripheral blood NK cells express nuclear oligomerization domain 2 and respond to MDP. NK cells naturally internalize MDP leading to direct cell activation, including signaling through NFkappaB: characterized by p50/p65 heterodimers at early stimulations times and sustained activation of p50 homodimers. Moreover, MDP synergizes with IFN-alpha and IL-12 to activate NK cells and stimulate IFN-gamma secretion, suggesting a role for accessory cells in induction of an optimal NK cell response. Although IL-12 costimulation leads to a greater IFN-gamma response by NK cells, higher levels of CD69 in response to MDP are induced in the presence of IFN-alpha, suggesting that different pathogen-induced cytokine profiles will affect downstream NK cell responses. In contrast, MDP alone or in combination with either IFN-alpha or IL-12 only poorly increases NK cell cytotoxicity. In summary, this report identifies MDP as a bacterial pathogen associated molecular pattern that activates human NK cells.

Evolutionary struggles between NK cells and viruses

Natural killer (NK) cells are well recognized for their ability to provide a first line of defence against viral pathogens and they are increasingly being implicated in immune responses against certain bacterial and parasitic infections. Reciprocally, viruses have devised numerous strategies to evade the activation of NK cells and have influenced the evolution of NK-cell receptors and their ligands. NK cells contribute to host defence by their ability to rapidly secrete cytokines and chemokines, as well as to directly kill infected host cells. In addition to their participation in the immediate innate immune response against infection, interactions between NK cells and dendritic cells shape the nature of the subsequent adaptive immune response to pathogens.

Immune reconstitution of CD56(dim) NK cells in individuals with primary HIV-1 infection treated with interleukin-2

Natural killer (NK) cells are believed to play a role in human immunodeficiency virus type 1 (HIV-1) disease progression, and NK cell levels are reduced in individuals with chronic HIV-1 infection. Interleukin (IL)-2 therapy results in an expansion of CD4(+) T cells as well as NK cells; however, little is known about the detailed effects of IL-2 therapy on NK cells in HIV-1 infection in general and in early infection in particular. Here, we investigated the effects of combined IL-2 therapy and antiretroviral therapy (ART) on the number, frequency, phenotype, and interferon (IFN)-gamma production of NK cells in individuals with early HIV-1 infection. Patients randomized to receive combined ART and IL-2 therapy predominantly expanded CD56(dim) NK cells, and the expansion was greater than in patients randomized to receive ART alone. Importantly, NK cell receptor expression and IFN-gamma production were maintained over time. This reconstitution of NK cells may be useful in helping contain viremia if patients discontinue therapy or develop drug resistance.

Molecular pathogenesis of Shigella spp.: controlling host cell signaling, invasion, and death by type III secretion

Shigella spp. are gram-negative pathogenic bacteria that evolved from harmless enterobacterial relatives and may cause devastating diarrhea upon ingestion. Research performed over the last 25 years revealed that a type III secretion system (T3SS) encoded on a large plasmid is a key virulence factor of Shigella flexneri. The T3SS determines the interactions of S. flexneri with intestinal cells by consecutively translocating two sets of effector proteins into the target cells. Thus, S. flexneri controls invasion into EC, intra- and intercellular spread, macrophage cell death, as well as host inflammatory responses. Some of the translocated effector proteins show novel biochemical activities by which they intercept host cell signal transduction pathways. An understanding of the molecular mechanisms underlying Shigella pathogenesis will foster the development of a safe and efficient vaccine, which, in parallel with improved hygiene, should curb infections by this widespread pathogen.

A role for natural killer cells in intestinal inflammation caused by infection with Salmonella enterica serovar Typhimurium

Acute gastroenteritis caused by Salmonella infection is a significant public health problem. Using a mouse model of this condition, the authors demonstrated previously that the cytokine gamma interferon (IFN-gamma) is required for a normal intestinal inflammatory response to the pathogen. In the present study, these experiments are extended to show that natural killer (NK) cells constitute an early source of intestinal IFN-gamma during Salmonella infection, and that these cells have a significant impact on intestinal inflammation. It was found that infection of mice with Salmonella increased both intestinal IFN-gamma production and the numbers of NK cells in the intestine and mesenteric lymph nodes. NK cells, along with other types of lymphocytes, produced IFN-gamma in response to the bacteria in vitro, while antibody-mediated depletion of NK cells in vivo resulted in a significant reduction in Salmonella-induced intestinal IFN-gamma expression. In a mouse strain lacking NK cells and T and B lymphocytes, intestinal production of IFN-gamma and Salmonella-induced intestinal inflammation were both significantly decreased compared with a strain deficient only in T and B cells. The authors' observations point to an important function for NK cells and NK-derived IFN-gamma in regulating the intestinal inflammatory response to Salmonella.

The inner gel component of Aloe vera suppresses bacterial-induced pro-inflammatory cytokines from human immune cells

The present study was carried out to examine the anti-inflammatory activity of the inner leaf gel component of Aloe barbadensis Miller. A simple in vitro assay was designed to determine the effect of the inner gel on bacterial-induced pro-inflammatory cytokine production, namely TNF-alpha and IL-1 beta, from peripheral blood leukocytes stimulated with Shigella flexneri or LPS. This report describes the suppression of both cytokines with a freeze-dried inner gel powder and a commercial health drink from the same source. Comparison was made with a human monocytic cell-line (THP-1 cells) and a similar trend in responses was demonstrated.

[Shigellosis or bacillary dysentery]

Shigellosis, commonly known as bacillary dysentery, is an enterobacterial disease caused by the Shigella genus, which now belongs to the Escherichia tribe, because of their genetic and phenotypic similarities. S. sonnei, flexneri, boydii and dysenteriae differ in their epidemiologic and pathogenic characteristics. S. sonnei is predominant in industrialized countries and causes the mildest disease. S. dysentery is especially dangerous because it occurs in outbreaks, sometimes in catastrophic situations, and has a high mortality rate. Shigellosis typically causes watery diarrhea followed by dysentery. It may be associated with a variety of mild to severe or even life-threatening complications. Shigellosis is a significant public health problem in developing countries where it remains a major cause of diarrhea-related morbidity and mortality, especially among children. Annual cases worldwide are estimated at 160 million. Shigellosis is a highly contagious disease of poor and crowded communities, with fecal-oral (hand-to-mouth) transmission, and an extremely low minimum infectious dose. Multidrug resistance is a serious problem. Ciprofloxacin is the first-line antibiotic, recommended for 3 days. Prevention and control should include personal hygiene, hand washing, sanitation, and water supply. No vaccine is available, but several candidates are currently being evaluated.