Pregnancy impairs the innate immune resistance to Salmonella typhimurium leading to rapid fatal infection

Composition, Diversity and Sex-Related Differences in Intestinal Microbiota in Captive African Penguins (Spheniscus demersus)

An understanding of the microbial communities in African penguins (Spheniscus demersus) could provide valuable information for saving this endangered species. The objective of this study was to investigate the composition, diversity and sex-related differences in the intestinal microbiota of captive African penguins. Fecal samples were collected from 21 captive adult African penguins reared in the same conditions at Shanghai Zoo. The results show that Proteobacteria, Actinobacteria and Firmicutes were the predominant bacteria in the intestinal microbiota of the captive African penguins. No difference was found in microbial diversity between female and male African penguins, as shown by their similar alpha and beta diversities. However, a notable sex-related difference was found between their microbial compositions. Female African penguins have a higher abundance of Pseudomonas and a lower abundance of Kocuria than males. A functional prediction indicates that the "mRNA surveillance pathway", "Polyketide sugar unit biosynthesis", "Wnt signaling pathway", "Lysosome" and "Cell cycle" pathways were significantly enriched in the microbiota of female African penguins. In conclusion, the present study indicates that the compositions and predicted functions of the intestinal microbiota are significantly different between the sexes. Our data suggest that the intestinal microbiota of female African penguins are more unstable than the intestinal microbiota of males in captivity.

Roles of natural resistance-associated macrophage protein-1 in modulating bacterial distribution and immune responses during Salmonella enterica serovar Typhimurium infection in murine pregnancy

PROBLEM

Salmonella enterica serovar Typhimurium (S.Tm) infection in Nramp1+/+ mice during pregnancy can lead to profound bacterial growth in the feto-placental unit and adverse pregnancy outcomes, including fetal loss, maternal illness and death. The kinetics and mechanisms by which S.Tm gains entry within individual feto-placental unit, and disseminates through tissues leading to placental resorption and fetal demise remain unclear.

METHOD OF STUDY

Mice were systemically infected with S.Tm. Bacterial burden within spleen and individual placentas, and placental/fetal resorptions were quantified. Flow cytometric analysis of immune cell types in the spleen and individual placentas was performed. Cytokine expression in maternal serum was determined through cytometric bead array.

RESULTS

Systemic infection with S.Tm resulted in preferential bacterial proliferation in placentas compared to the spleen in Nramp1+/+ mice. At 24 h post-infection, the mean infection rate of individual placentas per mouse was ∼50%, increasing to >75% by 72 h post-infection, suggesting that initial infection in few sites progresses to rapid spread of infection through the uterine milieu. This correlated with a steady increase in placental/fetal resorption rates. Placental infection was associated with local increased neutrophil percentages, whereas numbers and percentages in the spleen remained unchanged, suggesting dichotomous modulation of inflammation between the systemic compartment and the feto-maternal interface. Reduced survival rates of pregnant mice during infection correlated with decreased serum IFN-γ but increased IL-10 levels relative to non-pregnant controls.

CONCLUSION

Pregnancy compromises host resistance conferred by Nramp1 against S.Tm through compartment-specific regulation of maternal and placental cellular responses, and modulation of systemic cytokine expression.

IFN-alpha receptor deficiency enhances host resistance to oral Salmonella enterica serovar Typhimurium infection during murine pregnancy

PROBLEM

Maternal tolerance during pregnancy increases the risk of infection with certain intracellular pathogens. Systemic Salmonella enterica serovar Typhimurium (S.Tm) infection during pregnancy in normally resistant 129X1/SvJ mice leads to severe placental infection, as well as fetal and maternal deaths. However, the effect of oral infection with S.Tm in pregnant mice and the roles of infection-induced inflammation and cell death pathways in contributing to susceptibility to infection are unclear.

METHOD OF STUDY

Non-pregnant and pregnant C57BL/6J wild-type (WT) and cell death pathway-altered mice (IFNAR1^-/- , Caspase-1, 11^-/- , RIP3^-/- ) were infected orally with S.Tm. Host survival and fetal resorption were determined. Bacterial burden in mesenteric lymph nodes (MLNs), spleen, liver, and placentas was enumerated at various time points post-infection. Serum cytokine expression was measured through cytometric bead array.

RESULTS

Oral infection of WT mice with S.Tm on days 9-10 of gestation resulted in systemic dissemination of the bacteria, substantial placental colonization, and fetal loss 5 days post-infection. Histopathological examination of the placentas indicated that infection-induced widespread focal necrosis and neutrophil infiltration throughout the spongiotrophoblast (SpT) layer. In the non-pregnant state, IFNAR1^-/- mice exhibited increased survival following oral S.Tm infection relative to Caspase-1, 11^-/- , RIP3^-/- , and WT mice. The increased resistance to S.Tm infection in IFNAR1^-/- mice was seen during pregnancy as well, with decreased bacterial burden within MLNs, spleen, and placenta, which correlated with the decreased resorptions relative to WT and Caspase-1, 11^-/- mice.

CONCLUSION

Oral S.Tm exposure leads to placental infection, inflammation, and resorption, whereas IFNAR1 deficiency enhances host resistance both in the non-pregnant and pregnant states.

Salmonella Enteritidis foodborne infection induces altered placental morphometrics in the murine model

INTRODUCTION

Salmonella foodborne disease during pregnancy causes a significant fetal loss in domestic livestock and preterm birth, chorioamnionitis and miscarriage in humans. These complications could be associated with alterations in placental structure. This study was aimed to determine how a low dose of Salmonella Enteritidis during late gestation affects placental histomorphometric in mice.

METHODS

We used a self-limiting enterocolitis murine model. BALB/c pregnant animals received a low dose of Salmonella Enteritidis (3-4 x 10² CFU/mouse) on gestational day (GD) 15. At day 3 post infection bacterial loads, serum cytokines expression and placental histomorphometrics parameters were analyzed.

RESULTS

We found that a sub-lethal infection with Salmonella induced a significant drop in fetal weight -to-placental weight-ratio and an increase in the placental coefficient. After bacterial inoculation maternal organs were colonized, inducing placental morphometric alterations, including increased placental thickness, reduced surface area, and diminished major and minor diameters. Also, foci of necrosis accompanied by acute leukocyte infiltration in decidual zone, reduction of vascular spaces and vascular congestion in labyrinth zone, were also evident in placentas from infected females on GD 18. Our data shows that placentas from infected mothers are phenotypically different from control ones. Furthermore, expression of IFN-gamma and IL-6 was up regulated in response to Salmonella in maternal serum.

DISCUSSION

Our findings demonstrate that a low dose of Salmonella during late gestation alters the placental morphometry leading to negative consequences on pregnancy outcome such as significant reduction in fetal body weight.

Preconceptual Priming Overrides Susceptibility to Escherichia coli Systemic Infection during Pregnancy

Maternal sepsis is a leading cause of morbidity and mortality during pregnancy. Escherichia coli is a primary cause of bacteremia in women and occurs more frequently during pregnancy. Several key outstanding questions remain regarding how to identify women at highest infection risk and how to boost immunity against E. coli infection during pregnancy. Here, we show that pregnancy-induced susceptibility to E. coli systemic infection extends to rodents as a model of human infection. Mice infected during pregnancy contain >100-fold-more recoverable bacteria in target tissues than nonpregnant controls. Infection leads to near complete fetal wastage that parallels placental plus congenital fetal invasion. Susceptibility in maternal tissues positively correlates with the number of concepti, suggesting important contributions by expanded placental-fetal target tissue. Remarkably, these pregnancy-induced susceptibility phenotypes are also efficiently overturned in mice with resolved sublethal infection prior to pregnancy. Preconceptual infection primes the accumulation of E. coli-specific IgG and IgM antibodies, and adoptive transfer of serum containing these antibodies to naive recipient mice protects against fetal wastage. Together, these results suggest that the lack of E. coli immunity may help discriminate individuals at risk during pregnancy, and that overriding susceptibility to E. coli prenatal infection by preconceptual priming is a potential strategy for boosting immunity in this physiological window of vulnerability.IMPORTANCE Pregnancy makes women especially vulnerable to infection. The most common cause of bloodstream infection during pregnancy is by a bacterium called Escherichia coli This bacterium is a very common cause of bloodstream infection, not just during pregnancy but in all individuals, from newborn babies to the elderly, probably because it is always present in our intestine and can intermittently invade through this mucosal barrier. We first show that pregnancy in animals also makes them more susceptible to E. coli bloodstream infection. This is important because many of the dominant factors likely to control differences in human infection susceptibility can be property controlled for only in animals. Despite this vulnerability induced by pregnancy, we also show that animals with resolved E. coli infection are protected against reinfection during pregnancy, including having resistance to most infection-induced pregnancy complications. Protection against reinfection is mediated by antibodies that can be measured in the blood. This information may help to explain why most women do not develop E. coli infection during pregnancy, enabling new approaches for identifying those at especially high risk of infection and strategies for preventing infection during pregnancy.

Sex Steroids Induce Membrane Stress Responses and Virulence Properties in Pseudomonas aeruginosa

Molecular mechanisms by which sex steroids interact with P. aeruginosa to modulate its virulence have yet to be reported. Our work provides the first characterization of a steroid-induced membrane stress mechanism promoting P. aeruginosa virulence, which includes the release of proinflammatory outer membrane vesicles, resulting in inflammation, host tissue damage, and reduced bacterial clearance. We further demonstrate that at nanomolar (physiological) concentrations, male and female sex steroids promote virulence in clinical strains of P. aeruginosa based on their dynamic membrane fluidic properties. This work provides, for the first-time, mechanistic insight to better understand and predict the P. aeruginosa related response to sex steroids and explain the interindividual patient variability observed in respiratory diseases such as cystic fibrosis that are complicated by gender differences and chronic P. aeruginosa infection.

Estrogen, a major female sex steroid hormone, has been shown to promote the selection of mucoid Pseudomonas aeruginosa in the airways of patients with chronic respiratory diseases, including cystic fibrosis. This results in long-term persistence, poorer clinical outcomes, and limited therapeutic options. In this study, we demonstrate that at physiological concentrations, sex steroids, including testosterone and estriol, induce membrane stress responses in P. aeruginosa. This is characterized by increased virulence and consequent inflammation and release of proinflammatory outer membrane vesicles promoting in vivo persistence of the bacteria. The steroid-induced P. aeruginosa response correlates with the molecular polarity of the hormones and membrane fluidic properties of the bacteria. This novel mechanism of interaction between sex steroids and P. aeruginosa explicates the reported increased disease severity observed in females with cystic fibrosis and provides evidence for the therapeutic potential of the modulation of sex steroids to achieve better clinical outcomes in patients with hormone-responsive strains.

Analysis of the capacity of Salmonella enterica Typhimurium to infect the human Placenta

INTRODUCTION

Salmonella species are gram-negative facultative intracellular bacteria that are common causes of foodborne illness in North America. Infections by Salmonella during pregnancy are a significant cause of fetal loss in domestic livestock, and fetal and maternal mortality in mice. Furthermore, Salmonella infection is associated with miscarriage, stillbirth and preterm birth in pregnant women. Despite these collective associations, the extent to which Salmonella can infect the human placenta has not been investigated.

METHODS

Human placental villous explants from several gestational ages were exposed to Salmonella enterica serovar Typhimurium (STm) ex vivo. Infection was assessed by colony forming unit assay and whole mount immunofluorescence (WMIF).

RESULTS

Viable bacteria were recovered from placental villous explants of all gestational ages tested, but the bacterial burden was highest in 1st trimester explants. Bacterial numbers did not change appreciably with time post-infection in explants from any gestational age examined, suggesting that STm does not proliferate in placental villi. Exposure of villous explants to STm strains defective for the type III secretion systems revealed that Salmonella pathogenicity island 1 is essential for optimal invasion. In contrast to placental explants, STm infected and proliferated within villous cytotrophoblast cells isolated from term placentas. WMIF demonstrated that STm was restricted primarily to the syncytiotrophoblast layer in infected placentas.

DISCUSSION

Our study demonstrates that STm can invade into the syncytiotrophoblast but does not subsequently proliferate. Thus, the syncytiotrophoblast may function as a barrier to STm infection of the fetus.

IL-10 producing B cells rescue mouse fetuses from inflammation-driven fetal death and are able to modulate T cell immune responses

Understanding the mechanisms leading to fetal death following maternal subclinical infections is crucial to develop new therapeutic strategies. Here we addressed the relevance of IL-10 secreting B cells (B10) in the maintenance of the immune balance during gestation. µMT females lacking mature B cells presented normal pregnancies, although their fetuses were smaller and their Treg pool did not expand as in B cell sufficient controls. Pregnant µMT females were more susceptible to LPS despite having less Treg; their fetuses died at doses compatible with pregnancy in WT animals. Adoptive transfer of IL-10 negative B effector cells or B cells from IL-10 deficient mice did not modify this outcome. The transfer of B10 cells or application of recombinant murine IL-10 reduced the fetal loss, associated with a normalization of Treg numbers and cytokine modulation at the feto-maternal interface. B cell-derived IL-10 suppressed the production of IL-17A and IL-6 by T cells and promoted the conversion of naïve cells into Treg. B10 cells are required to restore the immune balance at the feto-maternal interface when perturbed by inflammatory signals. Our data position B cells in a central role in the maintenance of the balance between immunity and tolerance during pregnancy.

Type I interferons differentially modulate maternal host immunity to infection by Listeria monocytogenes and Salmonella enterica serovar Typhimurium during pregnancy

PROBLEM

IFN-alpha receptor deficiency (IFNAR^-/- ) enhances immunity to Listeria monocytogenes (LM) and Salmonella enterica serovar Typhimurium (ST) in the non-pregnant state by inhibiting pathogen-induced immune cell death. However, the roles of IFNAR signaling in modulating immunity to infection during pregnancy are not well understood.

METHOD OF STUDY

C57BL/6J wild-type (WT) and IFNAR^-/- mice were infected systemically with LM or ST. Bacterial burden in spleen and individual placentas was enumerated at day 3 post-infection. Immune cell numbers and percentages were quantified in spleen and individual placentas, respectively, through flow cytometry. Cytokine expression in serum, spleen, and individual placentas was measured through cytometric bead array.

RESULTS

IFNAR^-/- mice exhibited decreased splenic monocyte numbers in non-pregnant and pregnant state, and an altered distribution of placental immune cell types in the non-infected state. IFNAR^-/- mice controlled LM infection more effectively than WT mice even during pregnancy. This correlated with enhanced serum IL-12 expression, despite reduced splenic monocyte numbers relative to WT controls. In contrast, pregnant IFNAR^-/- mice unlike their non-pregnant counterparts exhibited increased susceptibility to ST infection, which was associated with decreased serum IL-12 expression.

CONCLUSION

Type I IFN responses differentially impact host resistance to LM and ST infection during pregnancy through modulation of immune cell distribution and cytokine responses.

Immunological Tolerance, Pregnancy, and Preeclampsia: The Roles of Semen Microbes and the Father

Although it is widely considered, in many cases, to involve two separable stages (poor placentation followed by oxidative stress/inflammation), the precise originating causes of preeclampsia (PE) remain elusive. We have previously brought together some of the considerable evidence that a (dormant) microbial component is commonly a significant part of its etiology. However, apart from recognizing, consistent with this view, that the many inflammatory markers of PE are also increased in infection, we had little to say about immunity, whether innate or adaptive. In addition, we focused on the gut, oral and female urinary tract microbiomes as the main sources of the infection. We here marshall further evidence for an infectious component in PE, focusing on the immunological tolerance characteristic of pregnancy, and the well-established fact that increased exposure to the father's semen assists this immunological tolerance. As well as these benefits, however, semen is not sterile, microbial tolerance mechanisms may exist, and we also review the evidence that semen may be responsible for inoculating the developing conceptus (and maybe the placenta) with microbes, not all of which are benign. It is suggested that when they are not, this may be a significant cause of PE. A variety of epidemiological and other evidence is entirely consistent with this, not least correlations between semen infection, infertility and PE. Our view also leads to a series of other, testable predictions. Overall, we argue for a significant paternal role in the development of PE through microbial infection of the mother via insemination.

CXCR3 blockade protects against Listeria monocytogenes infection-induced fetal wastage

Mammalian pregnancy requires protection against immunological rejection of the developing fetus bearing discordant paternal antigens. Immune evasion in this developmental context entails silenced expression of chemoattractant proteins (chemokines), thereby preventing harmful immune cells from penetrating the maternal-fetal interface. Here, we demonstrate that fetal wastage triggered by prenatal Listeria monocytogenes infection is driven by placental recruitment of CXCL9-producing inflammatory neutrophils and macrophages that promote infiltration of fetal-specific T cells into the decidua. Maternal CD8+ T cells with fetal specificity upregulated expression of the chemokine receptor CXCR3 and, together with neutrophils and macrophages, were essential for L. monocytogenes-induced fetal resorption. Conversely, decidual accumulation of maternal T cells with fetal specificity and fetal wastage were extinguished by CXCR3 blockade or in CXCR3-deficient mice. Remarkably, protection against fetal wastage and in utero L. monocytogenes invasion was maintained even when CXCR3 neutralization was initiated after infection, and this protective effect extended to fetal resorption triggered by partial ablation of immune-suppressive maternal Tregs, which expand during pregnancy to sustain fetal tolerance. Together, our results indicate that functionally overriding chemokine silencing at the maternal-fetal interface promotes the pathogenesis of prenatal infection and suggest that therapeutically reinforcing this pathway represents a universal approach for mitigating immune-mediated pregnancy complications.

Salmonella enterica serovar Enteritidis enterocolitis during late stages of gestation induces an adverse pregnancy outcome in the murine model

Foodborne diseases caused by Salmonella enterica serovar Enteritidis (S. Enteritidis) are a significant health problem. Pregnancy, state of immunological tolerance, is a predisposing condition for the development of infections with intracellular pathogens. Salmonella species can cause pregnancy complications such as chorioamnionitis, transplacental fetal infection, pre term labor, abortions, neonatal and maternal septicemia. However, the specific mechanisms by which Salmonella infections trigger these alterations are not clear. In the present work, using a self-limiting enterocolitis murine model, we show that the ingestion of a low dose of S. Enteritidis at late stages of pregnancy (day 15 of gestation) is sufficient to induce massive maternal infection. We found that Salmonella infection leads to 40% of pre term delivery, 33% of abortion and fetal growth restriction. Placental dysfunction during S. Enteritidis enterocolitis was confirmed through cellular infiltration and hypoxia markers (MPO activity and COX-1 and COX-2 expression, respectively). Apoptosis in placental tissue due to Salmonella infection was also evident at day 18 of gestation when investigated by morphometric procedure, DNA fragmentation and Fas/FasL expression. Also, the expression of IFN-γ, TNF-α, IL-17 and IL-10 was up regulated in response to Salmonella not only in placenta, but also in amniotic fluid and maternal serum. Altogether, our results demonstrate that S. Enteritidis enterocolitis during late stages of gestation causes detrimental effect on pregnancy outcome.

Sequential gene expression profiling in the mouse spleen during 14 d feeding with Lactobacillus brevis KB290

Some lactic acid bacteria play an important role in the immune system with potential benefits to the host. However, detailed mechanisms of immune modulation exerted by probiotics remain to be clarified. Since immune response changes in a time-related manner in some cases, we monitored changes in mRNA levels in the spleen of mice during 14 d feeding with Lactobacillus brevis KB290 (KB290). Female BALB/c mice, aged 9 weeks, commenced a diet containing KB290 (3 × 109 colony-forming units/g) or starch for a period of 1, 4, 7 or 14 d. Cytotoxic activity of the resulting splenocytes against YAC-1 cells was measured using flow cytometry. The activity was found to be significantly higher in the treated group on days 1 and 7. The highest activity appeared on day 4, but was not statistically significantly different. Gene expression profiles were analysed using DNA microarray. Gene Ontology (GO) terms related to the immune process were significantly enriched in the up-regulated gene set on days 1, 4 and 7, and GO terms related to the cellular process were enriched in the down-regulated gene set on days 4 and 7. Although the up-regulated genes involved in antigen processing and presentation for stimulation of CD8+ cytotoxic T cells were not observed on day 14, some genes involved in T-cell and natural killer cell activation remained up-regulated until day 14. For the majority of the genes tested, RT-PCR analysis was used to verify the results obtained from the DNA microarray analysis. The sequential gene expression profiling reflected changes in cytotoxic activity during KB290 feeding.

First trimester typhoid Fever with vertical transmission of salmonella typhi, an intracellular organism

We report a case in which placental abruption occurred at 16 weeks following first trimester diagnosis and treatment for typhoid fever. Unexpectedly Salmonella enterica serovar Typhi (S. Typhi) was found in fetal tissues at autopsy. Using information from the murine model of typhoid fever in pregnancy, we draw parallels between S. Typhi and L. monocytogenes to develop a plausible hypothesis to explain how this organism was able to cross the placenta in the first trimester to cause abruption, inflammation, and expulsion of the fetus and placenta. We hope that this model for understanding placental infections by the hematogenous route helps to raise awareness that organisms not typically associated with TORCH infection can nevertheless cause placental infection and pregnancy loss.

Regulatory T cells and the immune pathogenesis of prenatal infection

Pregnancy in placental mammals offers exceptional comprehensive benefits of in utero protection, nutrition, and metabolic waste elimination for the developing fetus. However, these benefits also require durable strategies to mitigate maternal rejection of fetal tissues expressing foreign paternal antigens. Since the initial postulate of expanded maternal immune tolerance by Sir Peter Medawar 60 years ago, an amazingly elaborate assortment of molecular and cellular modifications acting both locally at the maternal-placental interface and systemically have been shown to silence potentially detrimental maternal immune responses. In turn, simultaneously maintaining host defense against the infinite array of potential pathogens during pregnancy is equally important. Fortunately, resistance against most infections is preserved seamlessly throughout gestation. On the other hand, recent studies on pathogens with unique predisposition for prenatal infections have uncovered distinctive holes in host defense associated with the reproductive process. Using these infections to probe the response during pregnancy, the immune suppressive regulatory subset of maternal CD4 T cells has been increasingly shown to dictate the inter-workings between prenatal infection susceptibility and pathogenesis of ensuing pregnancy complications. Herein, the recent literature suggesting a necessity for maternal regulatory T cells (Tregs) in pregnancy-induced immunological shifts that sustain fetal tolerance is reviewed. Additional discussion is focused on how expansion of maternal Treg suppression may become exploited by pathogens that cause prenatal infections and the perilous potential of infection-induced immune activation that may mitigate fetal tolerance and inadvertently inject hostility into the protective in utero environment.

From mice to women: the conundrum of immunity to infection during pregnancy

Resistance to infection is the ability of the host to evoke a strong immune response sufficient to eliminate the infectious agent. In contrast, maternal tolerance to the fetus necessitates careful regulation of immune responses. Successful pregnancy requires the maternal host to effectively balance the opposing processes of maternal immune reactivity and tolerance to the fetus. However, this balance can be perturbed by infections which are recognized as the major cause of adverse pregnancy outcome including pre-term labor. Select pathogens also pose a serious threat of severe maternal illness. These include intracellular and chronic pathogens that have evolved immune evasive strategies. Murine models of intracellular bacteria and parasites that mimic pathogenesis of infection in humans have been developed. While human epidemiological studies provide insight into maternal immunity to infection, experimental infection in pregnant mice is a vital tool to unravel the complex molecular mechanisms of placental infection, congenital transmission and maternal illness. We will provide a comprehensive review of the pathogenesis of several infection models in pregnant mice and their clinical relevance. These models have revealed the immunological function of the placenta in responding to, and resisting infection. Murine feto-placental infection provides an effective way to evaluate new intervention strategies for managing infections during pregnancy, adverse fetal outcome and long-term effects on the offspring and mother.

Role of sex steroid hormones in bacterial-host interactions

Sex steroid hormones play important physiological roles in reproductive and nonreproductive tissues, including immune cells. These hormones exert their functions by binding to either specific intracellular receptors that act as ligand-dependent transcription factors or membrane receptors that stimulate several signal transduction pathways. The elevated susceptibility of males to bacterial infections can be related to the usually lower immune responses presented in males as compared to females. This dimorphic sex difference is mainly due to the differential modulation of the immune system by sex steroid hormones through the control of proinflammatory and anti-inflammatory cytokines expression, as well as Toll-like receptors (TLRs) expression and antibody production. Besides, sex hormones can also affect the metabolism, growth, or virulence of pathogenic bacteria. In turn, pathogenic, microbiota, and environmental bacteria are able to metabolize and degrade steroid hormones and their related compounds. All these data suggest that sex steroid hormones play a key role in the modulation of bacterial-host interactions.

Type I interferon induces necroptosis in macrophages during infection with Salmonella enterica serovar Typhimurium

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a virulent pathogen that induces rapid host death. Here we observed that host survival after infection with S. Typhimurium was enhanced in the absence of type I interferon signaling, with improved survival of mice deficient in the receptor for type I interferons (Ifnar1(-/-) mice) that was attributed to macrophages. Although there was no impairment in cytokine expression or inflammasome activation in Ifnar1(-/-) macrophages, they were highly resistant to S. Typhimurium-induced cell death. Specific inhibition of the kinase RIP1 or knockdown of the gene encoding the kinase RIP3 prevented the death of wild-type macrophages, which indicated that necroptosis was a mechanism of cell death. Finally, RIP3-deficient macrophages, which cannot undergo necroptosis, had similarly less death and enhanced control of S. Typhimurium in vivo. Thus, we propose that S. Typhimurium induces the production of type I interferon, which drives necroptosis of macrophages and allows them to evade the immune response.

Effect of Salmonella enteric Serovar Typhimurium in Pregnant Mice: A Biochemical and Histopathological Study

Background

Food borne infections caused by Salmonella enterica species are increasing globally and pregnancy poses a significant threat in developing countries, where sanitation facilities are inadequate. Thus, the present study was designed to delineate the effect of Salmonella infection during pregnancy.

Method

Pregnant, BALB/c mice were challenged orally with Salmonella enterica serovar Typhimurium on gestational day 10 and were monitored for bacterial load, hepatic injury, histopathological alterations vis-a-vis oxidant and antioxidant levels.

Results

Pregnant-Salmonella-infected mice had higher bacterial translocation in the liver, spleen as well as liver enzymes mainly aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase compared with Salmonella-infected mice. The levels of lipid peroxidation were significantly higher in all the organs of both pregnant-Salmonella-infected and Salmonella-infected mice compared with control mice. However, the activities of antioxidant enzymes (reduced glutathione, superoxide dismutase and catalase) were lower in the liver, spleen and placenta of pregnant, pregnant-Salmonella-infected and Salmonella-infected mice compared with control mice, but the decrease was more in pregnant-Salmonella-infected mice indicating depression of antioxidant defense system. Histopathologically, pregnant-Salmonella-infected mice had more architectural damage in the liver, spleen and placenta compared with other groups.

Conclusion

Pregnancy makes the host more vulnerable to typhoid fever by affecting the physiology of pivotal organs and highlighting the importance of early and prompts diagnosis so as to avoid the further materno-fetal complications.

Foxp3(+) regulatory T cells, immune stimulation and host defence against infection

The immune system is intricately regulated allowing potent effectors to expand and become rapidly mobilized after infection, while simultaneously silencing potentially detrimental responses that averts immune-mediated damage to host tissues. This relies in large part on the delicate interplay between immune suppressive regulatory CD4⁺ T (Treg) cells and immune effectors that without active suppression by Treg cells cause systemic and organ-specific autoimmunity. Although these beneficial roles have been classically described as counterbalanced by impaired host defence against infection, newfound protective roles for Treg cells against specific viral pathogens (e.g. herpes simplex virus 2, lymphocytic choriomeningitis virus, West Nile virus) have been uncovered using transgenic mice that allow in vivo Treg-cell ablation based on Foxp3 expression. In turn, Foxp3⁺ Treg cells also provide protection against some parasitic (Plasmodium sp., Toxoplasma gondii) and fungal (Candida albicans) pathogens. By contrast, for bacterial and mycobacterial infections (e.g. Listeria monocytogenes, Salmonella enterica, Mycobacterium tuberculosis), experimental manipulation of Foxp3⁺ cells continues to indicate detrimental roles for Treg cells in host defence. This variance is probably related to functional plasticity in Treg cell suppression that shifts discordantly following infection with different types of pathogens. Furthermore, the efficiency whereby Treg cells silence immune activation coupled with the plasticity in Foxp3⁺ cell activity suggest that overriding Treg-mediated suppression represents a prerequisite ‘signal zero’ that together with other stimulation signals [T-cell receptor (signal 1), co-stimulation (signal 2), inflammatory cytokines (signal 3)] are essential for T-cell activation in vivo. Herein, the importance of Foxp3⁺ Treg cells in host defence against infection, and the significance of infection-induced shifts in Treg-cell suppression are summarized.

Foxp3(+) regulatory T cell expansion required for sustaining pregnancy compromises host defense against prenatal bacterial pathogens

Although pregnancy confers unique susceptibility to infection, the pregnancy-associated immune defects that erode host defense remain largely undefined. Herein, we demonstrate that expansion of immune-suppressive Foxp3(+) regulatory T cells (Tregs) which occurs physiologically during pregnancy or when experimentally induced in transgenic mice caused enhanced susceptibility to prenatal pathogens including Listeria and Salmonella species. Reciprocally, infection susceptibility was uniformly reduced with Treg ablation. Importantly however, the sustained expansion of maternal Tregs was essential for maintaining immune tolerance to the developing fetus because even partial transient ablation of Foxp3-expressing cells fractured maternal tolerance to fetal antigen and triggered fetal resorption. Interestingly, Foxp3 cell-intrinsic defects in the immune-suppressive cytokine IL-10 alone were sufficient to override Treg-mediated infection susceptibility, while IL-10 was nonessential for sustaining pregnancy. Thus, maternal Treg expansion required for sustaining pregnancy creates naturally occurring holes in host defense that confer prenatal infection susceptibility.

Salmonella enterica serovar Typhimurium lacking hfq gene confers protective immunity against murine typhoid

Salmonella enterica is an important enteric pathogen and its various serovars are involved in causing both systemic and intestinal diseases in humans and domestic animals. The emergence of multidrug-resistant strains of Salmonella leading to increased morbidity and mortality has further complicated its management. Live attenuated vaccines have been proven superior over killed or subunit vaccines due to their ability to induce protective immunity. Of the various strategies used for the generation of live attenuated vaccine strains, focus has gradually shifted towards manipulation of virulence regulator genes. Hfq is a RNA chaperon which mediates the binding of small RNAs to the mRNA and assists in post-transcriptional gene regulation in bacteria. In this study, we evaluated the efficacy of the Salmonella Typhimurium Δhfq strain as a candidate for live oral vaccine in murine model of typhoid fever. Salmonella hfq deletion mutant is highly attenuated in cell culture and animal model implying a significant role of Hfq in bacterial virulence. Oral immunization with the Salmonella hfq deletion mutant efficiently protects mice against subsequent oral challenge with virulent strain of Salmonella Typhimurium. Moreover, protection was induced upon both multiple as well as single dose of immunizations. The vaccine strain appears to be safe for use in pregnant mice and the protection is mediated by the increase in the number of CD4(+) T lymphocytes upon vaccination. The levels of serum IgG and secretory-IgA in intestinal washes specific to lipopolysaccharide and outer membrane protein were significantly increased upon vaccination. Furthermore, hfq deletion mutant showed enhanced antigen presentation by dendritic cells compared to the wild type strain. Taken together, the studies in murine immunization model suggest that the Salmonella hfq deletion mutant can be a novel live oral vaccine candidate.

Maternal immune responses to trophoblast: the contribution of the horse to pregnancy immunology

The horse has proven to be a distinctively informative species in the study of pregnancy immunology for several reasons. First, unique aspects of the anatomy and physiology of the equine conceptus facilitate approaches that are not possible in other model organisms, such as non-surgical recovery of early stage embryos and conceptuses and isolation of pure trophoblast cell populations. Second, pregnant mares make strong cytotoxic antibody responses to paternal major histocompatibility complex class I antigens expressed by the chorionic girdle cells, permitting detailed evaluation of the antigenicity of these invasive trophoblasts and how they affect the maternal immune system. Third, there is abundant evidence for local maternal cellular immune responses to the invading trophoblasts in the pregnant mare. The survival of the equine fetus in the face of strong maternal immune responses highlights the complex immunoregulatory mechanisms that result in materno-fetal tolerance. Finally, the parallels between human and horse trophoblast cell types, their gene expression, and function make the study of equine pregnancy highly relevant to human health. Here, we review the most pertinent aspects of equine reproductive immunology and how studies of the pregnant mare have contributed to our understanding of maternal acceptance of the allogeneic fetus.

Salmonella enterica serovar Typhimurium-induced placental inflammation and not bacterial burden correlates with pathology and fatal maternal disease

Food-borne infections caused by Salmonella enterica species are increasing globally, and pregnancy poses a high risk. Pregnant mice rapidly succumb to S. enterica serovar Typhimurium infection. To determine the mechanisms involved, we addressed the role of inflammation and bacterial burden in causing placental and systemic disease. In vitro, choriocarcinoma cells were a highly conducive niche for intracellular S. Typhimurium proliferation. While infection of mice with S. Typhimurium wild-type (WT) and mutant (Delta aroA and Delta invA) strains led to profound pathogen proliferation and massive burden within placental cells, only the virulent WT S. Typhimurium infection evoked total fetal loss and adverse host outcome. This correlated with substantial placental expression of granulocyte colony-stimulating factor (G-CSF), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-alpha) and increased serum inflammatory cytokines/chemokines, such as G-CSF, IL-6, CCL1, and KC, evoked by WT S. Typhimurium infection. In contrast, infection with high doses of S. Typhimurium Delta aroA, despite causing massive placental infection, resulted in reduced inflammatory cellular and cytokine response. While S. Typhimurium WT bacteria were dispersed in large numbers across all regions of the placenta, including the deeper labyrinth trophoblast, S. Typhimurium Delta aroA bacteria localized primarily to the decidua. This correlated with the widespread placental necrosis accompanied by neutrophil infiltration evoked by the S. Typhimurium WT bacteria. Thus, the ability of Salmonella to localize to deeper layers of the placenta and the nature of inflammation triggered by the pathogen, rather than bacterial burden, profoundly influenced placental integrity and host survival.

Split immunological tolerance to trophoblast

Split immunological tolerance refers to states in which an individual is capable of mounting certain types of immune responses to a particular antigenic challenge, but is tolerant of the same antigen in other compartments of the immune system. This concept is applicable to the immunological relationship between mother and fetus, and particularly relevant in equine pregnancy. In pregnant mares, antibody responses to paternal foreign Major Histocompatibility Complex class I antigens are robust, while anti-paternal cytotoxic T cell responses are diminished compared to those mounted by non-pregnant mares. Here, we compared the distribution of the major lymphocyte subsets, the percentage of lymphocytes expressing Interferon Gamma (IFNG) and Interleukin 4 (IL4) and the level of expression of the immunoregulatory transcription factor FOXP3 between pregnant and non-pregnant mares, and between peripheral blood and the endometrium during pregnancy. In a cohort of mares in which peripheral blood lymphocytes were tested during early pregnancy and in the non-pregnant state, there were only slight changes observed during pregnancy. In contrast, comparison of peripheral blood lymphocytes with lymphocytes isolated from the endometrial cups of pregnant mares revealed striking differences in lymphocyte sub-populations. The endometrial cups contained higher numbers of IFNG+ lymphocytes, and lower numbers of lymphocytes expressing IL4. The endometrial cup lymphocytes also had higher numbers of FOXP3+ cells compared to peripheral blood lymphocytes. Taken together, these results strengthen the evidence for a state of split tolerance to trophoblast, and furthermore define sharp differences in immune reactivity during equine pregnancy between peripheral blood lymphocytes and lymphocytes at the maternal-fetal interface.

Tolerance to the foetal allograft?

In this review, we will detail the concept of tolerance and its history in reproductive immunology. We will then consider whether it applies to the foetal-maternal relationship and discuss the mechanisms involved in non-rejection of the foeto-placental unit.

Natural Killer cells: keepers of pregnancy in the turnstile of the environment

During early pregnancy, an orchestrated endocrine-immunological scenario of maternal adaptation toward tolerance of the semiallogeneic fetus is required. Mechanisms preventing fetal loss by protecting the immune privilege of the gravid uterus, i.e. Galectin-1 or regulatory T cells, have recently been identified. Further, the presence of a unique population of Natural Killer (NK) cells, in humans identified by their CD56(+++)Galectin (Gal)-1(+)CD16(-) phenotype in the uterine lining (decidua), has been proposed to be a pivotal aspect of maternal adaptation to pregnancy. Decidual NK (dNK) cells comprise the largest population of immune cells during the first trimester in human decidua and control trophoblast invasion and vascular remodeling through their ability to secrete an array of angiogenesis-regulating molecules, chemokines and cytokines. A wealth of environmental factors, such as smoking, altered nutrition, pollution or stress has been proposed to peril not only pregnancy, but also fetal development. Further, published evidence supports that NK cells act as sentinel cells and environmental challenges can change their phenotype, e.g. via epigenetic pathways. We here review the effect of environmental factors, largely stress perception, on NK cells and its implication for pregnancy, fetal development and general health. As NK cells may not only be passive responders to the environment, but can also be 'educated and licensed', we propose novel strategies aiming to take advantage of the versatility of NK cells in maintaining immunosurveillance and tissue homeostasis.

A safe vaccine (DV-STM-07) against Salmonella infection prevents abortion and confers protective immunity to the pregnant and new born mice

Pregnancy is a transient immuno-compromised condition which has evolved to avoid the immune rejection of the fetus by the maternal immune system. The altered immune response of the pregnant female leads to increased susceptibility to invading pathogens, resulting in abortion and congenital defects of the fetus and a subnormal response to vaccination. Active vaccination during pregnancy may lead to abortion induced by heightened cell mediated immune response. In this study, we have administered the highly attenuated vaccine strain DeltapmrG-HM-D (DV-STM-07) in female mice before the onset of pregnancy and followed the immune reaction against challenge with virulent S. Typhimurium in pregnant mice. Here we demonstrate that DV-STM-07 vaccine gives protection against Salmonella in pregnant mice and also prevents Salmonella induced abortion. This protection is conferred by directing the immune response towards Th2 activation and Th1 suppression. The low Th1 response prevents abortion. The use of live attenuated vaccine just before pregnancy carries the risk of transmission to the fetus. We have shown that this vaccine is safe as the vaccine strain is quickly eliminated from the mother and is not transmitted to the fetus. This vaccine also confers immunity to the new born mice of vaccinated mothers. Since there is no evidence of the vaccine candidate reaching the new born mice, we hypothesize that it may be due to trans-colostral transfer of protective anti-Salmonella antibodies. These results suggest that our vaccine DV-STM-07 can be very useful in preventing abortion in the pregnant individuals and confer immunity to the new born. Since there are no such vaccine candidates which can be given to the new born and to the pregnant women, this vaccine holds a very bright future to combat Salmonella induced pregnancy loss.

Selectively reduced intracellular proliferation of Salmonella enterica serovar typhimurium within APCs limits antigen presentation and development of a rapid CD8 T cell response

Ag presentation to CD8(+) T cells commences immediately after infection, which facilitates their rapid expansion and control of pathogen. This paradigm is not followed during infection with virulent Salmonella enterica serovar Typhimurium (ST), an intracellular bacterium that causes mortality in susceptible C57BL/6J mice within 7 days and a chronic infection in resistant mice (129 x 1SvJ). Infection of mice with OVA-expressing ST results in the development of a CD8(+) T cell response that is detectable only after the second week of infection despite the early detectable bacterial burden. The mechanism behind the delayed CD8(+) T cell activation was evaluated, and it was found that dendritic cells/macrophages or mice infected with ST-OVA failed to present Ag to OVA-specific CD8(+) T cells. Lack of early Ag presentation was not rescued when mice or dendritic cells/macrophages were infected with an attenuated aroA mutant of ST or with mutants having defective Salmonella pathogenicity island I/II genes. Although extracellular ST proliferated extensively, the replication of ST was highly muted once inside macrophages. This muted intracellular proliferation of ST resulted in the generation of poor levels of intracellular Ag and peptide-MHC complex on the surface of dendritic cells. Additional experiments revealed that ST did not actively inhibit Ag presentation, rather it inhibited the uptake of another intracellular pathogen, Listeria monocytogenes, thereby causing inhibition of Ag presentation against L. monocytogenes. Taken together, this study reveals a dichotomy in the proliferation of ST and indicates that selectively reduced intracellular proliferation of virulent pathogens may be an important mechanism of immune evasion.