Interleukin-6, gamma interferon, and tumor necrosis factor receptors in typhoid fever related to outcome of antimicrobial therapy

One species, different diseases: the unique molecular mechanisms that underlie the pathogenesis of typhoidal Salmonella infections

Salmonella enterica is one of the most widespread bacterial pathogens found worldwide, resulting in approximately 100 million infections and over 200 000 deaths per year. Salmonella isolates, termed 'serovars', can largely be classified as either nontyphoidal or typhoidal Salmonella, which differ in regard to disease manifestation and host tropism. Nontyphoidal Salmonella causes gastroenteritis in many hosts, while typhoidal Salmonella is human-restricted and causes typhoid fever, a systemic disease with a mortality rate of up to 30% without treatment. There has been considerable interest in understanding how different Salmonella serovars cause different diseases, but the molecular details that underlie these infections have not yet been fully characterized, especially in the case of typhoidal Salmonella. In this review, we highlight the current state of research into understanding the pathogenesis of both nontyphoidal and typhoidal Salmonella, with a specific interest in serovar-specific traits that allow human-adapted strains of Salmonella to cause enteric fever. Overall, a more detailed molecular understanding of how different Salmonella isolates infect humans will provide critical insights into how we can eradicate these dangerous enteric pathogens.

Treatment of enteric fever (typhoid and paratyphoid fever) with cephalosporins

BACKGROUND

Typhoid and paratyphoid (enteric fever) are febrile bacterial illnesses common in many low- and middle-income countries. The World Health Organization (WHO) currently recommends treatment with azithromycin, ciprofloxacin, or ceftriaxone due to widespread resistance to older, first-line antimicrobials. Resistance patterns vary in different locations and are changing over time. Fluoroquinolone resistance in South Asia often precludes the use of ciprofloxacin. Extensively drug-resistant strains of enteric fever have emerged in Pakistan. In some areas of the world, susceptibility to old first-line antimicrobials, such as chloramphenicol, has re-appeared. A Cochrane Review of the use of fluoroquinolones and azithromycin in the treatment of enteric fever has previously been undertaken, but the use of cephalosporins has not been systematically investigated and the optimal choice of drug and duration of treatment are uncertain.

OBJECTIVES

To evaluate the effectiveness of cephalosporins for treating enteric fever in children and adults compared to other antimicrobials.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL, MEDLINE, Embase, LILACS, the WHO ICTRP and ClinicalTrials.gov up to 24 November 2021. We also searched reference lists of included trials, contacted researchers working in the field, and contacted relevant organizations.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in adults and children with enteric fever that compared a cephalosporin to another antimicrobial, a different cephalosporin, or a different treatment duration of the intervention cephalosporin. Enteric fever was diagnosed on the basis of blood culture, bone marrow culture, or molecular tests.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were clinical failure, microbiological failure and relapse. Our secondary outcomes were time to defervescence, duration of hospital admission, convalescent faecal carriage, and adverse effects. We used the GRADE approach to assess certainty of evidence for each outcome.

MAIN RESULTS

We included 27 RCTs with 2231 total participants published between 1986 and 2016 across Africa, Asia, Europe, the Middle East and the Caribbean, with comparisons between cephalosporins and other antimicrobials used for the treatment of enteric fever in children and adults. The main comparisons are between antimicrobials in most common clinical use, namely cephalosporins compared to a fluoroquinolone and cephalosporins compared to azithromycin. Cephalosporin (cefixime) versus fluoroquinolones Clinical failure, microbiological failure and relapse may be increased in patients treated with cefixime compared to fluoroquinolones in three small trials published over 14 years ago: clinical failure (risk ratio (RR) 13.39, 95% confidence interval (CI) 3.24 to 55.39; 2 trials, 240 participants; low-certainty evidence); microbiological failure (RR 4.07, 95% CI 0.46 to 36.41; 2 trials, 240 participants; low-certainty evidence); relapse (RR 4.45, 95% CI 1.11 to 17.84; 2 trials, 220 participants; low-certainty evidence). Time to defervescence in participants treated with cefixime may be longer compared to participants treated with fluoroquinolones (mean difference (MD) 1.74 days, 95% CI 0.50 to 2.98, 3 trials, 425 participants; low-certainty evidence). Cephalosporin (ceftriaxone) versus azithromycin Ceftriaxone may result in a decrease in clinical failure compared to azithromycin, and it is unclear whether ceftriaxone has an effect on microbiological failure compared to azithromycin in two small trials published over 18 years ago and in one more recent trial, all conducted in participants under 18 years of age: clinical failure (RR 0.42, 95% CI 0.11 to 1.57; 3 trials, 196 participants; low-certainty evidence); microbiological failure (RR 1.95, 95% CI 0.36 to 10.64, 3 trials, 196 participants; very low-certainty evidence). It is unclear whether ceftriaxone increases or decreases relapse compared to azithromycin (RR 10.05, 95% CI 1.93 to 52.38; 3 trials, 185 participants; very low-certainty evidence). Time to defervescence in participants treated with ceftriaxone may be shorter compared to participants treated with azithromycin (mean difference of -0.52 days, 95% CI -0.91 to -0.12; 3 trials, 196 participants; low-certainty evidence). Cephalosporin (ceftriaxone) versus fluoroquinolones It is unclear whether ceftriaxone has an effect on clinical failure, microbiological failure, relapse, and time to defervescence compared to fluoroquinolones in three trials published over 28 years ago and two more recent trials: clinical failure (RR 3.77, 95% CI 0.72 to 19.81; 4 trials, 359 participants; very low-certainty evidence); microbiological failure (RR 1.65, 95% CI 0.40 to 6.83; 3 trials, 316 participants; very low-certainty evidence); relapse (RR 0.95, 95% CI 0.31 to 2.92; 3 trials, 297 participants; very low-certainty evidence) and time to defervescence (MD 2.73 days, 95% CI -0.37 to 5.84; 3 trials, 285 participants; very low-certainty evidence). It is unclear whether ceftriaxone decreases convalescent faecal carriage compared to the fluoroquinolone gatifloxacin (RR 0.18, 95% CI 0.01 to 3.72; 1 trial, 73 participants; very low-certainty evidence) and length of hospital stay may be longer in participants treated with ceftriaxone compared to participants treated with the fluoroquinolone ofloxacin (mean of 12 days (range 7 to 23 days) in the ceftriaxone group compared to a mean of 9 days (range 6 to 13 days) in the ofloxacin group; 1 trial, 47 participants; low-certainty evidence).

AUTHORS' CONCLUSIONS

Based on very low- to low-certainty evidence, ceftriaxone is an effective treatment for adults and children with enteric fever, with few adverse effects. Trials suggest that there may be no difference in the performance of ceftriaxone compared with azithromycin, fluoroquinolones, or chloramphenicol. Cefixime can also be used for treatment of enteric fever but may not perform as well as fluoroquinolones.  We are unable to draw firm general conclusions on comparative contemporary effectiveness given that most trials were small and conducted over 20 years previously. Clinicians need to take into account current, local resistance patterns in addition to route of administration when choosing an antimicrobial.

The Epigenetics of Psychosis: A Structured Review with Representative Loci

The evidence for an environmental component in chronic psychotic disorders is strong and research on the epigenetic manifestations of these environmental impacts has commenced in earnest. In reviewing this research, the focus is on three genes as models for differential methylation, MCHR1, AKT1 and TDO2, each of which have been investigated for genetic association with psychotic disorders. Environmental factors associated with psychotic disorders, and which interact with these model genes, are explored in depth. The location of transcription factor motifs relative to key methylation sites is evaluated for predicted gene expression results, and for other sites, evidence is presented for methylation directing alternative splicing. Experimental results from key studies show differential methylation: for MCHR1, in psychosis cases versus controls; for AKT1, as a pre-existing methylation pattern influencing brain activation following acute administration of a psychosis-eliciting environmental stimulus; and for TDO2, in a pattern associated with a developmental factor of risk for psychosis, in all cases the predicted expression impact being highly dependent on location. Methylation induced by smoking, a confounding variable, exhibits an intriguing pattern for all three genes. Finally, how differential methylation meshes with Darwinian principles is examined, in particular as it relates to the “flexible stem” theory of evolution.

British Infection Association Guidelines for the Diagnosis and Management of Enteric Fever in England

Enteric fever (EF) is an infection caused by the bacteria called Salmonella Typhi or Paratyphi. Infection is acquired through swallowing contaminated food or water. Most EF in England occurs in people returning from South Asia and other places where EF is common; catching EF in England is rare. The main symptom is fever, but stomach pain, diarrhoea, muscle aches, rash and other symptoms may occur. EF is diagnosed by culturing the bacteria from blood and/or stool in a microbiology laboratory. EF usually responds well to antibiotic treatment. Depending on how unwell the individual is, antibiotics may be administered by mouth or by injection. Over the past several years, there has been an overall increase in resistance to antibiotics used to treat enteric fever, in all endemic areas. Additionally, since 2016, there has been an ongoing outbreak of drug-resistant EF in Pakistan. This infection is called extensively drug-resistant, or XDR, EF and only responds to a limited number of antibiotics. Occasionally individuals develop complications of EF including confusion, bleeding, a hole in the gut or an infection of the bones or elsewhere. Some people may continue to carry the bacteria in their stool for a longtime following treatment for the initial illness. These people may need treatment with a longer course of antibiotics to eradicate infection. Travellers can reduce their risk of acquiring EF by following safe food and water practices and by receiving the vaccine at least a few weeks before travel. These guidelines aim to help doctors do the correct tests and treat patients for enteric fever in England but may also be useful to doctors and public health professionals in other similar countries.

Human Genetic Variation Influences Enteric Fever Progression

In the 21st century, enteric fever is still causing a significant number of mortalities, especially in high-risk regions of the world. Genetic studies involving the genome and transcriptome have revealed a broad set of candidate genetic polymorphisms associated with susceptibility to and the severity of enteric fever. This review attempted to explain and discuss the past and the most recent findings on human genetic variants affecting the progression of Salmonella typhoidal species infection, particularly toll-like receptor (TLR) 4, TLR5, interleukin (IL-) 4, natural resistance-associated macrophage protein 1 (NRAMP1), VAC14, PARK2/PACRG, cystic fibrosis transmembrane conductance regulator (CFTR), major-histocompatibility-complex (MHC) class II and class III. These polymorphisms on disease susceptibility or progression in patients could be related to multiple mechanisms in eliminating both intracellular and extracellular Salmonella typhoidal species. Here, we also highlighted the limitations in the studies reported, which led to inconclusive results in association studies. Nevertheless, the knowledge obtained through this review may shed some light on the development of risk prediction tools, novel therapies as well as strategies towards developing a personalised typhoid vaccine.

Change of Serum Inflammatory Cytokines Levels in Patients With Chronic Obstructive Pulmonary Disease, Pneumonia and Lung Cancer

OBJECTIVE

This study aimed to investigate the serum inflammatory cytokines levels in patients with COPD, pneumonia and lung cancer, and assess the correlation between the levels of inflammatory cytokines levels and development of these diseases.

METHODS

Two hundred thirty-two patients including 114 patients with pneumonia, 76 patients with chronic obstructive pulmonary disease (COPD) and 42 patients with lung cancer, and 62 age-matched healthy volunteers as controls were enrolled. The pro-inflammatory cytokine IL-6, IL-2, IFN-γ, TNF-α, anti-inflammatory cytokines IL-4 and IL-10 in serum were analyzed by flow cytometry microsphere array (CBA).

RESULTS

We found that the levels of TNF-α and IL-10 in patients with lung cancer, COPD and pneumonia were significantly higher than control group. The IL-6 in the lung cancer group were significantly increased compared with the controls and COPD group, pneumonia group. IFN-γ and IL-2 levels were lower in lung cancer compared with controls and COPD group, pneumonia group. TNF-α, IL-4 and IL-10 levels were increased in patients with COPD and pneumonia compared with controls. In addition, the concentrations of IFN-γ and IL-6 were increased in acute exacerbation COPD (AECOPD) group compared with stable COPD group.

CONCLUSION

In conclusion, elevated TNF-α and IL-10 levels in serum may be related with lung diseases including lung cancer, COPD and pneumonia. Additionally, IFN-γ and IL-6 might be potential biomarkers for the further deterioration of lung disease patients. The increased concentrations of IFN-γ and IL-6 might be used to predict the exacerbation of COPD.

Complex adaptive immunity to enteric fevers in humans: lessons learned and the path forward

Salmonella enterica serovar Typhi (S. Typhi), the causative agent of typhoid fever, and S. Paratyphi A and B, causative agents of paratyphoid fever, are major public health threats throughout the world. Although two licensed typhoid vaccines are currently available, they are only moderately protective and immunogenic necessitating the development of novel vaccines. A major obstacle in the development of improved typhoid, as well as paratyphoid vaccines is the lack of known immunological correlates of protection in humans. Considerable progress has been made in recent years in understanding the complex adaptive host responses against S. Typhi. Although the induction of S. Typhi-specific antibodies (including their functional properties) and memory B cells, as well as their cross-reactivity with S. Paratyphi A and S. Paratyphi B has been shown, the role of humoral immunity in protection remains undefined. Cell mediated immunity (CMI) is likely to play a dominant role in protection against enteric fever pathogens. Detailed measurements of CMI performed in volunteers immunized with attenuated strains of S. Typhi have shown, among others, the induction of lymphoproliferation, multifunctional type 1 cytokine production, and CD8(+) cytotoxic T-cell responses. In addition to systemic responses, the local microenvironment of the gut is likely to be of paramount importance in protection from these infections. In this review, we will critically assess current knowledge regarding the role of CMI and humoral immunity following natural S. Typhi and S. Paratyphi infections, experimental challenge, and immunization in humans. We will also address recent advances regarding cross-talk between the host's gut microbiota and immunization with attenuated S. Typhi, mechanisms of systemic immune responses, and the homing potential of S. Typhi-specific B- and T-cells to the gut and other tissues.

Salmonella-host interactions - modulation of the host innate immune system

Salmonella enterica (S. enterica) are Gram-negative bacteria that can invade a broad range of hosts causing both acute and chronic infections. This phenotype is related to its ability to replicate and persist within non-phagocytic host epithelial cells as well as phagocytic dendritic cells and macrophages of the innate immune system. Infection with S. enterica manifests itself through a broad range of clinical symptoms and can result in asymptomatic carriage, gastroenteritis, systemic disease such as typhoid fever and in severe cases, death (1). Exposure to S. enterica serovars Typhi and Paratyphi exhibits clinical symptoms including diarrhea, fatigue, fever, and temperature fluctuations. Other serovars such as the non-typhoidal Salmonella (NTS), of which there are over 2,500, are commonly contracted as, but not limited to, food-borne sources causing gastrointestinal symptoms, which include diarrhea and vomiting. The availability of complete genome sequences for many S. enterica serovars has facilitated research into the genetic determinants of virulence for this pathogen. This work has led to the identification of important bacterial components, including flagella, type III secretion systems, lipopolysaccharides, and Salmonella pathogenicity islands, all of which support the intracellular life cycle of S. enterica. Studies focusing on the host-pathogen interaction have provided insights into receptor activation of the innate immune system. Therefore, characterizing the host-S. enterica interaction is critical to understand the pathogenicity of the bacteria in a clinically relevant context. This review outlines salmonellosis and the clinical manifestations between typhoidal and NTS infections as well as discussing the host immune response to infection and the models that are being used to elucidate the mechanisms involved in Salmonella pathogenicity.

Limited role for ASC and NLRP3 during in vivo Salmonella Typhimurium infection

Background

The inflammasome is an intracellular protein complex triggered by exposure to intracellular pathogens, its components or other endogenous proteins. It leads to the activation of and subsequent release of proinflammatory cytokines such as IL-1β and IL-18. S. Typhimurium is a Gram-negative intracellular bacterium, which is known to trigger inflammasome assembly via recognition by the cytosolic receptors, NLRP3 and NLRC4 (which act via the adaptor protein, ASC) to induce cell death and cytokine release. We sought to characterize the role of ASC and NLRP3 in two different murine models (typhoid and colitis) of systemic Salmonella infection.

Results

Release of the inflammasome cytokine IL-18 was hampered in Asc^−/− but not Nlrp3^−/− mice (background C57BL/6) during S. Typhimurium infection. Unexpectedly, neither ASC nor NLRP3 played a significant role in host defense against S. Typhimurium infection, as reflected by equal bacterial counts in WT, Asc^−/− and Nlrp3^−/− mice at all time points, in both the typhoid and colitis models. Proinflammatory cytokine levels (TNF-α, IL-6) and the extent of hepatic and splenic pathology did not differ between groups in the typhoid model. In the colitis model small differences were seen with regard to splenic and hepatic inflammation, although this was IL-18 independent.

Conclusions

IL-18 release was reduced in Asc^−/− but not Nlrp3^−/− mice during S. Typhimurium infection. Despite this reduction, bacterial counts, cytokine levels and histological inflammation did not differ between wild-type and knockout mice in either model. Our results reveal a limited role for ASC and NLRP3 during in vivo S. Typhimurium infection despite its role in cytokine maturation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-014-0030-7) contains supplementary material, which is available to authorized users.

Same species, different diseases: how and why typhoidal and non-typhoidal Salmonella enterica serovars differ

Human infections by the bacterial pathogen Salmonella enterica represent major disease burdens worldwide. This highly ubiquitous species consists of more than 2600 different serovars that can be divided into typhoidal and non-typhoidal Salmonella (NTS) serovars. Despite their genetic similarity, these two groups elicit very different diseases and distinct immune responses in humans. Comparative analyses of the genomes of multiple Salmonella serovars have begun to explain the basis of the variation in disease manifestations. Recent advances in modeling both enteric fever and intestinal gastroenteritis in mice will facilitate investigation into both the bacterial- and host-mediated mechanisms involved in salmonelloses. Understanding the genetic and molecular mechanisms responsible for differences in disease outcome will augment our understanding of Salmonella pathogenesis, host immunity, and the molecular basis of host specificity. This review outlines the differences in epidemiology, clinical manifestations, and the human immune response to typhoidal and NTS infections and summarizes the current thinking on why these differences might exist.

Cellular and cytokine responses to Salmonella enterica serotype Typhi proteins in patients with typhoid fever in Bangladesh

We assessed interferon-gamma (IFN-γ) responses via enzyme-linked immunosorbent spot (ELISPOT) to a number of S. Typhi antigens in samples from humans with S. Typhi bacteremia and typhoid fever in Bangladesh. Compared with responses in healthy endemic zone controls, there were significantly increased IFN-γ responses at the time of clinical presentation (acute phase) and at convalescence 14–28 days later. The majority (80–90%) of IFN-γ expressing T cells were CD4+. We observed a significant increase in interleukin-17 (IL-17) positive CD4 + T cells at convalescent versus acute stage of infection using an intracellular cytokine staining assay. We also found that stimulated peripheral blood mononuclear cells (PBMCs) produced significantly increased levels of a number of cytokines at the convalescent versus acute phase of infection, including IFN-γ, MIP-1β, sCD40L, TNF-β, IL-13, and IL-9. These results suggest that S. Typhi antigens induce a predominantly Th1 response, but that elevations in other cytokines may be modulatory.

Host specificity of bacterial pathogens

Most pathogens are able to infect multiple hosts but some are highly adapted to a single-host species. A detailed understanding of the basis of host specificity can provide important insights into molecular pathogenesis, the evolution of pathogenic microbes, and the potential for pathogens to cross the species barrier to infect new hosts. Comparative genomics and the development of humanized mouse models have provided important new tools with which to explore the basis of generalism and specialism. This review will examine host specificity of bacterial pathogens with a focus on generalist and specialist serovars of Salmonella enterica.

The systemic immune state of super-shedder mice is characterized by a unique neutrophil-dependent blunting of TH1 responses

Host-to-host transmission of a pathogen ensures its successful propagation and maintenance within a host population. A striking feature of disease transmission is the heterogeneity in host infectiousness. It has been proposed that within a host population, 20% of the infected hosts, termed super-shedders, are responsible for 80% of disease transmission. However, very little is known about the immune state of these super-shedders. In this study, we used the model organism Salmonella enterica serovar Typhimurium, an important cause of disease in humans and animal hosts, to study the immune state of super-shedders. Compared to moderate shedders, super-shedder mice had an active inflammatory response in both the gastrointestinal tract and the spleen but a dampened T(H)1 response specific to the secondary lymphoid organs. Spleens from super-shedder mice had higher numbers of neutrophils, and a dampened T cell response, characterized by higher levels of regulatory T cells (T(regs)), fewer T-bet(+) (T(H)1) T cells as well as blunted cytokine responsiveness. Administration of the cytokine granulocyte colony stimulating factor (G-CSF) and subsequent neutrophilia was sufficient to induce the super-shedder immune phenotype in moderate-shedder mice. Similar to super-shedders, these G-CSF-treated moderate-shedders had a dampened T(H)1 response with fewer T-bet(+) T cells and a loss of cytokine responsiveness. Additionally, G-CSF treatment inhibited IL-2-mediated TH1 expansion. Finally, depletion of neutrophils led to an increase in the number of T-bet(+) T(H)1 cells and restored their ability to respond to IL-2. Taken together, we demonstrate a novel role for neutrophils in blunting IL-2-mediated proliferation of the TH1 immune response in the spleens of mice that are colonized by high levels of S. Typhimurium in the gastrointestinal tract.

Host-pathogen interaction in invasive Salmonellosis

Salmonella enterica infections result in diverse clinical manifestations. Typhoid fever, caused by S. enterica serovar Typhi (S. Typhi) and S. Paratyphi A, is a bacteremic illness but whose clinical features differ from other Gram-negative bacteremias. Non-typhoidal Salmonella (NTS) serovars cause self-limiting diarrhea with occasional secondary bacteremia. Primary NTS bacteremia can occur in the immunocompromised host and infants in sub-Saharan Africa. Recent studies on host-pathogen interactions in Salmonellosis using genome sequencing, murine models, and patient studies have provided new insights. The full genome sequences of numerous S. enterica serovars have been determined. The S. Typhi genome, compared to that of S. Typhimurium, harbors many inactivated or disrupted genes. This can partly explain the different immune responses both serovars induce upon entering their host. Similar genome degradation is also observed in the ST313 S. Typhimurium strain implicated in invasive infection in sub-Saharan Africa. Virulence factors, most notably, type III secretion systems, Vi antigen, lipopolysaccharide and other surface polysaccharides, flagella, and various factors essential for the intracellular life cycle of S. enterica have been characterized. Genes for these factors are commonly carried on Salmonella Pathogenicity Islands (SPIs). Plasmids also carry putative virulence-associated genes as well as those responsible for antimicrobial resistance. The interaction of Salmonella pathogen-associated molecular patterns (PAMPs) with Toll-like receptors (TLRs) and NOD-like receptors (NLRs) leads to inflammasome formation, activation, and recruitment of neutrophils and macrophages and the production of pro-inflammatory cytokines, most notably interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, and interferon-gamma (IFN)-γ. The gut microbiome may be an important modulator of this immune response. S. Typhimurium usually causes a local intestinal immune response, whereas S. Typhi, by preventing neutrophil attraction resulting from activation of TLRs, evades the local response and causes systemic infection. Potential new therapeutic strategies may lead from an increased understanding of infection pathogenesis.

Factors associated with encephalopathy in patients with Salmonella enterica serotype Typhi bacteremia presenting to a diarrheal hospital in Dhaka, Bangladesh

To characterize clinical correlates of typhoid fever-associated encephalopathy, we performed a retrospective chart review of patients with Salmonella enterica serotype Typhi bacteremia who were hospitalized at the International Centre for Diarrhoeal Disease Research, Bangladesh, from February of 2009 to June of 2011. Of 207 patients bacteremic with Salmonella Typhi who were ≥ 5 years of age, we identified 43 (21%) patients with encephalopathy. Univariate analysis revealed that patients with encephalopathy more often presented at ages of 10-24 years and had severe dehydration, low oxygen saturation, high respiratory rate, low leukocyte count, low platelet count, and Widal flagellar H agglutinin (TH) titer ≥ 1:640 compared with typhoid patients without encephalopathy. Multivariate analysis using logistic regression showed that age, dehydration, leukocyte count, and Widal TH titer were independently associated with encephalopathy. Our findings suggest that age, severity of disease, and immune responses are associated with encephalopathy during Salmonella Typhi bacteremia, perhaps reflecting the impact of prominent inflammatory responses.

Molecular and cellular characterization of a Salmonella enterica serovar Paratyphi a outbreak strain and the human immune response to infection

Enteric fever is an invasive life-threatening systemic disease caused by the Salmonella enterica human-adapted serovars Typhi and Paratyphi. Increasing incidence of infections with Salmonella enterica serovar Paratyphi A and the spreading of its antibiotic-resistant derivates pose a significant health concern in some areas of the world. Herein, we describe a molecular and phenotypic characterization of an S. Paratyphi A strain accounted for a recent paratyphoid outbreak in Nepal that affected at least 37 travelers. Pulsed-field gel electrophoresis analysis of the outbreak isolates revealed one genetic clone (pulsotype), confirming a single infecting source. Genetic profiling of the outbreak strain demonstrated the contribution of specific bacteriophages as a prime source of genetic diversity among clinical isolates of S. Paratyphi A. Phenotypic characterization in comparison with the S. Paratyphi A ATCC 9150 reference sequenced strain showed differences in flagellar morphology and increased abilities of the outbreak strain with respect to its motility, invasion into nonphagocytic cells, intracellular multiplication, survival within macrophages, and higher induction of interleukin-8 (IL-8) secreted by host cells. Collectively, these differences suggest an enhanced virulence potential of this strain and demonstrate an interesting phenotypic variation among S. Paratyphi A isolates. In vivo profiling of 16 inflammatory cytokines in patients infected with the outbreak strain revealed a common profile of a remarkable gamma interferon (IFN-γ) induction together with elevated concentrations of tumor necrosis factor alpha (TNF-α), IL-6, IL-8, IL-10, and IL-15, but not IL-12, which was previously demonstrated as elevated in nontyphoidal Salmonella infections. This apparent profile implies a distinct immune response to paratyphoid infections.

A Salmonella Typhimurium-Typhi genomic chimera: a model to study Vi polysaccharide capsule function in vivo

The Vi capsular polysaccharide is a virulence-associated factor expressed by Salmonella enterica serotype Typhi but absent from virtually all other Salmonella serotypes. In order to study this determinant in vivo, we characterised a Vi-positive S. Typhimurium (C5.507 Vi⁺), harbouring the Salmonella pathogenicity island (SPI)-7, which encodes the Vi locus. S. Typhimurium C5.507 Vi⁺ colonised and persisted in mice at similar levels compared to the parent strain, S. Typhimurium C5. However, the innate immune response to infection with C5.507 Vi⁺ and SGB1, an isogenic derivative not expressing Vi, differed markedly. Infection with C5.507 Vi⁺ resulted in a significant reduction in cellular trafficking of innate immune cells, including PMN and NK cells, compared to SGB1 Vi⁻ infected animals. C5.507 Vi⁺ infection stimulated reduced numbers of TNF-α, MIP-2 and perforin producing cells compared to SGB1 Vi⁻. The modulating effect associated with Vi was not observed in MyD88^−/− and was reduced in TLR4^−/− mice. The presence of the Vi capsule also correlated with induction of the anti-inflammatory cytokine IL-10 in vivo, a factor that impacted on chemotaxis and the activation of immune cells in vitro.

Pathogens of the genus Salmonella are closely related yet cause distinct diseases and have different host-range. Salmonella Typhi causes a systemic disease called typhoid fever specifically in humans, and is commonly modelled using a surrogate host-pathogen combination, namely Salmonella Typhimurium infection in mice. However, key virulence mechanisms of S. Typhi depend on the Vi polysaccharide capsule that is not expressed by S. Typhimurium. In order to study the function of the Vi capsule we characterised a S. Typhimurium/S. Typhi chimera that expresses the Vi polysaccharide in a regulated manner similar to that previously described in S. Typhi. The impact of Vi expression on immune cell populations in the spleen and mesenteric lymph nodes, and the pattern of intracellular cytokine response was determined 24 hours after i.v or i.g inoculation. Infection of mice with S. Typhimurium expressing Vi polysaccharide resulted in a blunted response in recruitment of NK and PMN cells. This was reflected in a blunted proinflammatory cytokine response, but a striking increase in the anti-inflammatory cytokine IL-10. IL-10 was expressed in macrophage, dendritic cells and NK cells in the mouse spleen, specifically in response to infection with S. Typhimurium expressing Vi polysaccharide. Indeed, neutralisation of this IL-10 production lead to increased migration and activation of splenocytes in vitro. This model can be used to develop Vi based vaccines as well as to study the impact of Vi expression on pathogenesis.

Immunology of gut mucosal vaccines

Understanding the mechanisms underlying the induction of immunity in the gastrointestinal mucosa following oral immunization and the cross-talk between mucosal and systemic immunity should expedite the development of vaccines to diminish the global burden caused by enteric pathogens. Identifying an immunological correlate of protection in the course of field trials of efficacy, animal models (when available), or human challenge studies is also invaluable. In industrialized country populations, live attenuated vaccines (e.g. polio, typhoid, and rotavirus) mimic natural infection and generate robust protective immune responses. In contrast, a major challenge is to understand and overcome the barriers responsible for the diminished immunogenicity and efficacy of the same enteric vaccines in underprivileged populations in developing countries. Success in developing vaccines against some enteric pathogens has heretofore been elusive (e.g. Shigella). Different types of oral vaccines can selectively or inclusively elicit mucosal secretory immunoglobulin A and serum immunoglobulin G antibodies and a variety of cell-mediated immune responses. Areas of research that require acceleration include interaction between the gut innate immune system and the stimulation of adaptive immunity, development of safe yet effective mucosal adjuvants, better understanding of homing to the mucosa of immunologically relevant cells, and elicitation of mucosal immunologic memory. This review dissects the immune responses elicited in humans by enteric vaccines.

Humanized nonobese diabetic-scid IL2rgammanull mice are susceptible to lethal Salmonella Typhi infection

Salmonella enterica serovar Typhi, the cause of typhoid fever, is host-adapted to humans and unable to cause disease in mice. Here, we show that S. Typhi can replicate in vivo in nonobese diabetic (NOD)-scid IL2rgamma(null) mice engrafted with human hematopoietic stem cells (hu-SRC-SCID mice) to cause a lethal infection with pathological and inflammatory cytokine responses resembling human typhoid. In contrast, S. Typhi does not exhibit net replication or cause illness in nonengrafted or immunocompetent control animals. Screening of transposon pools in hu-SRC-SCID mice revealed both known and previously unknown Salmonella virulence determinants, including Salmonella Pathogenicity Islands 1, 2, 3, 4, and 6. Our observations indicate that the presence of human immune cells allows the in vivo replication of S. Typhi in mice. The hu-SRC-SCID mouse provides an unprecedented opportunity to gain insights into S. Typhi pathogenesis and devise strategies for the prevention of typhoid fever.

Toll-like receptors and cytokines in immune responses to persistent mycobacterial and Salmonella infections

Bacterial persistence is of major concern worldwide in the control of a number of bacterial infections. The carriers who are asymptomatic act as reservoirs of the bacteria. Knowledge of the host response, of the persistence process, and of the potential of biological mediators as diagnostic markers is essential towards development of prophylactic and treatment modalities for these diseases. Immune mechanisms related to recognition and elimination of the bacteria play pivotal roles in the control of bacterial infections. The majority of the studies on bacterial infections detail the immune mechanisms in the active phase of infection, and reports on the immune status in carriers are scanty. The present review describes the role of recognition molecules (TLRs) and the immune mediators (cytokines) in bacterial persistence. It appears that the TLR-mediated induction of cytokine profiles differs in active infection and bacterial persistence, with an active Th1 response being beneficial for the clearance of a high load of bacteria and at the same time conducive for the persistence of low bacterial load. Immunomodulation aiming at stimulation of the immune responses should be carried out with care as it could give rise to a carrier state in individuals with low load of the bacteria.

The Vi-capsule prevents Toll-like receptor 4 recognition of Salmonella

The viaB locus enables Salmonella enterica serotype Typhi to reduce Toll-like receptor (TLR) dependent cytokine production in tissue culture models. This DNA region contains genes involved in the regulation (tviA), biosynthesis (tviBCDE) and export (vexABCDE) of the Vi capsule. Expression of the Vi capsule in S. Typhimurium, but not expression of the TviA regulatory protein, reduced tumour necrosis factor-alpha (TNF-alpha) and IL-6 production by murine bone-marrow derived macrophages. Production of TNF-alpha and IL-6 was dependent on expression of TLR4 as stimulation of macrophages from TLR4(-/-) mice with S. Typhimurium did not result in expression of these cytokines. Intraperitoneal infection of mice with S. Typhimurium induced expression of TNF-alpha and inducible nitric oxide synthase (iNOS) in the liver. Introduction of the cloned viaB region into S. Typhimurium reduced TNF-alpha and iNOS expression to levels observed after infection with a S. Typhimurium msbB mutant. In contrast, no differences in TNF-alpha expression between the S. Typhimurium wild type and strains expressing the Vi-capsule or carrying a mutation in msbB were observed after infection of TLR4(-/-) mice. We conclude that the Vi capsule prevents both in vitro and in vivo recognition of S. Typhimurium lipopolysaccharide by TLR4.

Serum cytokines in differentiating between viral and bacterial enterocolitis

It is difficult to distinguish clinically between bacterial and viral causes of enterocolitis. The aim of the study was to investigate if serum cytokines can distinguish bacterial from viral enterocolitis. We prospectively enrolled 147 paediatric in-patients with acute enterocolitis. Blood was taken for leucocyte count, CRP, ESR, IL-6, IL-8, IFN-alpha and TNF-alpha on the day of admission. A pathogen was identified in 115 of the 147 children, 72 of whom had a bacterial pathogen (bacterial group) and 43 rotavirus (viral group). Mean values of the serum markers IL-6, IL-8 and CRP were significantly higher in the bacterial group. Receiver-operating characteristic curves demonstrated that a cut-off of 15 pg/ml for IL-6 had a sensitivity of 0.75 and a specificity of 0.91 for bacterial diarrhoea. Comparable values for CRP at a cut-off of 13 mg/L demonstrated a sensitivity of 0.54 and a specificity of 0.72. Values for IL-8 at a cut-off of 80 pg/ml had a sensitivity of 0.46 and a specificity of 0.71. Despite the small sample size, our data suggest that serum IL-6, IL-8 and CRP are significantly elevated in children with bacterial enterocolitis. IL-6 has a higher sensitivity, specificity and positive predictive value than IL-8 and CRP. Determination of serum cytokines might be a useful way of differentiating viral from bacterial gastro-enteritis.

Expression of the kynurenine pathway enzyme tryptophan 2,3-dioxygenase is increased in the frontal cortex of individuals with schizophrenia

Markers of the kynurenine pathway were studied in postmortem frontal cortex obtained from individuals with schizophrenia and controls. Quantitative endpoint RT-PCR was used to measure mRNA transcripts. Of the two enzymes capable of catalyzing the first step in the pathway, tryptophan 2,3-dioxygenase (TDO2) and indoleamine dioxygenase (IDO), the concentration of mRNA for TDO2 was found to be elevated 1.6-fold in the schizophrenia group (P = 0.03), whereas the concentration of the mRNA for IDO was not significantly different between the schizophrenia and control groups. Immunohistochemistry showed an increased density of TDO2-immunopositive astroglial cells in the white matter of patients with schizophrenia (P = 0.04). Neurons and vessels were also immunopositive for TDO2, but there were no significant differences in labeling of these structures between the two groups. These results add to the evidence that kynurenine pathway changes might be involved in the pathogenesis of schizophrenia and the schizophrenia-like psychoses of other disorders.

Double blind comparison of ibuprofen and paracetamol for adjunctive treatment of uncomplicated typhoid fever

BACKGROUND

Antipyretics reduce the prolonged, high fever characteristic of typhoid fever. The benefits of nonsteroidal drugs in this role have not been quantified. There have been concerns about the safety of antipyretics in typhoid.

METHODS

In a double blind randomized study, 80 Vietnamese children with uncomplicated typhoid fever were randomized to receive identical syrup preparations of ibuprofen (10 mg/kg) or paracetamol (12 mg/kg) every 6 h until 36 h after defervescence. Children with a nalidixic acid-susceptible (Na) isolate of Salmonella typhi were treated with ofloxacin (15 mg/kg/day) for 3 days and those with a nalidixic acid-resistant (Na) isolate were treated for 7 days.

RESULTS

S. typhi was isolated from 36 of 40 children randomized to ibuprofen (11 isolates Na) and 37 of 40 randomized to paracetamol (13 isolates Na). The median (range) fever clearance time (hours) was shorter in the ibuprofen group than the paracetamol group (68, 4 to 260 vs. 104, 12 to 404; P = 0.055) as was the area under the temperature time curve above 37 degree C (74, 0 to 237 vs. 127, 0 to 573; P = 0.013). The differences occurred predominantly in the children infected with a NaS. typhi whose infections responded more slowly to antibiotic treatment. There were no major side effects associated with the use of either drug. There were no differences between the two treatment arms in the concentrations of circulating interleukin-6 and tumor necrosis factor alpha during the course of treatment.

CONCLUSION

The antipyretic effect of ibuprofen is superior to that of paracetamol in children with typhoid fever, particularly those with prolonged fever. Both antipyretics appeared to be safe.

The pathophysiology of falciparum malaria

Falciparum malaria is a complex disease with no simple explanation, affecting organs where the parasite is rare as well as those organs where it is more common. We continue to argue that it can best be understood in terms of excessive stimulation of normally useful pathways mediated by inflammatory cytokines, the prototype being tumor necrosis factor (TNF). These pathways involve downstream mediators, such as nitric oxide (NO) that the host normally uses to control parasites, but which, when uncontrolled, have bioenergetic failure of patient tissues as their predictable end point. Falciparum malaria is no different from many other infectious diseases that are clinically confused with it. The sequestration of parasitized red blood cells, prominent in some tissues but absent in others with equal functional loss, exacerbates, but does not change, these overriding principles. Recent opportunities to stain a wide range of tissues from African pediatric cases of falciparum malaria and sepsis for the inducible NO synthase (iNOS) and migration inhibitory factor (MIF) have strengthened these arguments considerably. The recent demonstration of bioenergetic failure in tissue removed from sepsis patients being able to predict a fatal outcome fulfils a prediction of these principles, and it is plausible that this will be demonstrable in severe falciparum malaria. Understanding the disease caused by falciparum malaria at a molecular level requires an appreciation of the universality of poly(ADP-ribose) polymerase-1 (PARP-1) and Na(+)/K(+)-ATPase and the protean effects of activation by inflammation of the former that include inactivation of the latter.

Peptide immunomodulators versus infection; an analysis

A disease gets manifested only when the host immune system is not strong enough to fight off the infective agents. A number of small peptides both from natural and synthetic origin are found to be capable of modulating the immune response. While immune adjuvants are known to strengthen the immune response and help the host not to give way to the pathogens thereby preventing their establishment, the immunosuppressors are found useful in autoimmune conditions as well as in facilitating the organ transplants. Recent understanding of immune network, however, reveals its cross connectivity with the endocrine and central nervous systems as well. Thus, the inhibition and control of disease by planned restoration of homeostatis in these systems through immunomodulation is also possible.

Salmonella typhi flagella are potent inducers of proinflammatory cytokine secretion by human monocytes

The cytokine production patterns of human peripheral blood mononuclear cells (PBMC) in response to Salmonella typhi flagella (STF) were examined in culture supernatants of PBMC stimulated with STF. Consistent with previous findings in volunteers vaccinated with aroC aroD deletion mutants of S. typhi, PBMC from volunteers immunized with the licensed live Ty21a S. typhi vaccine secreted gamma interferon following exposure to STF. Stimulation with STF induced rapid de novo synthesis of tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta), followed by IL-6 and IL-10. Trypsin treatment of STF abrogated their effects, while polymyxin B had no effect. Intracellular cytokine measurements of STF-stimulated PBMC revealed the existence of monocyte subpopulations that produce only TNF-alpha, IL-1beta or both cytokines. Moreover, STF markedly decreased the percentage of CD14(+) cells. These data demonstrate that STF are powerful monocyte activators which may have important implications for vaccine development and for understanding the pathogenesis of S. typhi infection.

Circulating immunoreactive interleukin-6 in cystic fibrosis

We measured circulating and sputum-sol concentrations of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), neutrophil elastase-alpha1-antiproteinase complex (NEAPC), and C-reactive protein (CRP) in an exacerbation, after antibiotic treatment, and in clinically stable patients with cystic fibrosis and chronic pulmonary infection with Pseudomonas aeruginosa. The aim was to determine the compartmental patterns of a proinflammatory and anti-inflammatory cytokine compared with other markers of inflammatory activity in cystic fibrosis. IL-6, NEAPC, CRP, and absolute neutrophil count were reduced after antibiotic treatment, p < 0.01. IL-6 and CRP concentrations were greater, p = 0.007, and p = 0.01, respectively, in a stable group of patients compared with those at the end of an exacerbation. IL-6 and CRP concentrations were related (r = 0.836, p < 0.0001), and both were greater than in matched control subjects (p < 0.001) at all times studied. Sputum-sol concentrations of IL-6 after treatment were positively related to FEV1 and FVC and inversely related to concentrations of neutrophil elastase. The separation between patients and healthy subjects, and the reduction of IL-6 after antibiotic treatment indicates it could be used as a marker of inflammation, but its relationship to other markers depends on the compartment in which it is measured.

Serum thrombomodulin levels in patients with typhoid fever

Elevated plasma or serum levels of thrombomodulin (TM) have been reported in some diseases. However, to our knowledge, plasma and serum levels of TM have not been investigated in febrile patients with typhoid fever. Serum TM and creatinine levels were determined in 7 male Japanese febrile patients with typhoid fever and 6 male Japanese healthy controls. The serum TM values of the patients and controls, in arbitrary units/mL, were 5.04 (SD = 1.69) and 2.93 (SD = 0.74), respectively (P < 0.025). The serum creatinine levels of the patients and controls were 0.93 (SD = 0.16) mg/dL and 0.77 (SD = 0.10) mg/dL, respectively, and the lack of any significant difference between them suggests that delayed clearance from the kidneys was not the predominant explanation for the elevated serum TM levels. Although the numbers of patients and controls were small and more studies are needed, we conclude that elevated serum TM levels during the course of a febrile infection with Salmonella serovar typhi may reflect the disease activity.

Plasma cytokines in paediatric typhoidal salmonellosis: correlation with clinical course and outcome

We evaluated the clinical profile, outcome and serial plasma interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) concentrations in 38 consecutive children (aged 6 months-14 years) admitted with culture-proven multidrug-resistant typhoid. All children received therapy for 14 days with either i.v. ceftriaxone or oral cefixime, with comparable outcome. Concentrations of IL-6 and TNF-alpha were significantly elevated in over 50% of the cases and correlated with clinical severity of illness as quantitated by the typhoid morbidity score. Sequential measurements revealed a significant decrease in IL-6 and TNF-alpha concentrations within 7 days of initiation of therapy (P<0.05). While no clear relationship was seen with time-to-defervescence, the failure rate was significantly higher in children with baseline serum IL-6 values >400 pg/ml (P<0.05). Our data suggest that plasma cytokine activity is frequently elevated in children with typhoidal salmonellosis, and IL-6 concentrations show a correlation with clinical severity and recovery from the illness.

Therapeutic aspects of typhoidal salmonellosis in childhood: the Karachi experience

We evaluated the response to therapy in a series of 876 children consecutively admitted to The Aga Khan University Hospital with culture-proven typhoid, including 281 cases infected with multi-drug-resistant (MDR) strains. Among sensitive isolates there was no significant difference in cure rates, failure rates and time to defervescence with either ampicillin or chloramphenicol. Of the 217 children with MDR typhoid who received therapy with third-generation cephalosporins, the outcome was significantly better with intravenous ceftriaxone compared with cefotaxime. Despite comparable cure rates, the time to defervescence was significantly longer among MDR strains treated with ceftriaxone versus sensitive strains (mean (SD): 7.2 (3.4) versus 6.3 (29) days; p < 0.05). Earlier recognition and introduction of appropriate second-line therapy has allowed us to reduce the case fatality rates of typhoid to under 1%. Although a 14-day course of ceftriaxone can be used successfully to treat most children hospitalized with MDR typhoid, there is a need to evaluate the role of short-course therapy or alternative therapeutic agents.

Impact of age and drug resistance on mortality in typhoid fever

The risk factors for mortality were analysed in a consecutive group of 1158 children presenting to the Aga Khan University Medical Center, Karachi, with multidrug resistant typhoid fever that had been proved on culture. There were 19 deaths, representing an overall case fatality rate of 1.6%. Multidrug resistant typhoid was associated with a more severe clinical illness and higher rates of toxicity, hepatomegaly, hypotensive shock, and death. Irrespective of drug resistance status, typhoid fever was found to be a more severe illness in young infants with significantly higher rates of diarrhoea, hypotensive shock, and mortality. Univariate analysis of admission characteristics associated with increased risk for mortality revealed significant association with younger age (p < 0.05), hypotensive shock or hypothermia (p < 0.001), obtundation (p < 0.001), seizures (p < 0.05), anaemia at admission (p < 0.005), and leucocytosis (p < 0.001). Logistic regression analysis of risk factors for mortality showed persistent association of hypothermia, toxicity, and anaemia with mortality. The data provides evidence that multidrug resistant typhoid in childhood is associated with increased risk of mortality, especially in infancy and closer attention to several risk factors for increased morbidity and case fatality rates may lead to improved outcome of treatment.

Soluble receptors for tumour necrosis factor in clinical laboratory diagnosis

Soluble tumour necrosis factor receptors (sTNF-Rs) play a role as modulators of the biological function of tumour necrosis factor-alpha (TNF-alpha) in an agonist/antagonist pattern. In various pathologic states the production and release of sTNF-Rs may mediate host response and determine the course and outcome of disease by interacting with TNF-alpha and competing with cell surface receptors. The determination of sTNF-Rs in body fluids such as plasma or serum is a new tool to gain information about immune processes and provides valuable insight into a variety of pathological conditions. Regarding its immediate clinical use, sTNF-Rs levels show high accuracy in the follow-up and prognosis of various diseases. In HIV infection and sepsis, sTNF-Rs concentrations strongly correlate with the clinical stage and the progression of disease and can be of predictive value. Determination of sTNF-Rs also gives useful information for monitoring cancer and autoimmune diseases. The information provided is often even superior to that obtained with classical disease markers, probably due to the direct involvement of the "TNF system" in the pathogenetic mechanisms in these patients. The available data imply that the measurement of sTNF-Rs, especially of the sTNF-R 75kD type, is a useful adjunct for quantification of the Th1-type immune response, similar to other immune activation markers such as neopterin and beta 2-microglobulin. Endogenous sTNF-Rs concentrations appear to reflect the activation state of the TNF-alpha/TNF receptor system.