IL-10 produced by trophoblast cells inhibits phagosome maturation leading to profound intracellular proliferation of Salmonella enterica Typhimurium

Function and therapeutic potential of Amuc_1100, an outer membrane protein of Akkermansia muciniphila: A review

The gut microbiota-derived protein Amuc_1100, a key outer membrane component of Akkermansia muciniphila, has emerged as a groundbreaking therapeutic agent with unique structural and functional properties. Amuc_1100 exerts multifaceted immune-metabolic effects through novel mechanisms, including modulation of TLR2/4 and JAK/STAT pathways. This review highlights its unique multi-component structure that enables synergistic biological activity, and its pharmacological properties, which underlies its ability to enhance intestinal barrier integrity, restore microbiota balance, and suppress systemic inflammation. Crucially, Amuc_1100 demonstrates unprecedented therapeutic versatility across both intestinal disorders (e.g., inflammatory bowel disease, antibiotic-associated diarrhea) and extraintestinal conditions-notably improving neuropsychiatric symptoms via gut-serotonin axis regulation, combating cancer through CD8+ T cell activation, and mitigating cardiotoxicity via gut-heart immune crosstalk. Emerging innovations in targeted delivery systems, including gut-retentive nano-formulations and engineered probiotic vectors, further amplify its clinical potential. We critically evaluate recent advances distinguishing Amuc_1100's mechanisms from live bacterial interventions. By synthesizing evidence from preclinical models, this work positions Amuc_1100 as a prototype for next-generation microbiome-derived therapeutics, bridging microbial ecology with precision medicine.

Amuc Prevents Liver Inflammation and Oxidative Stress in Mice Challenged with Salmonella Typhimurium

BACKGROUND

Salmonella typhimurium is a pathogen that causes gastroenteritis in humans and animals. Amuc_1100 (hereafter called Amuc), the outer membrane protein of Akkermansia muciniphila, alleviates metabolic disorders and maintains immune homeostasis.

OBJECTIVE

This study was conducted to determine whether there is a protective effect of Amuc administration.

METHODS

Male 6-wk-old C57BL6J mice were randomly allocated into 4 groups: CON (control), Amuc (gavaged with Amuc, 100 μg/d for 14 d), ST (oral administration of 1.0 × 10⁶ CFU S. typhimurium on day 7), and ST + Amuc (Amuc supplementation for 14 d, S. typhimurium administration on day 7). Serum and tissue samples were collected 14 d after treatment. Histological damage, inflammatory cell infiltration, apoptosis, and protein levels of genes associated with inflammation and antioxidant stress were analyzed. Data were analyzed by 2-way ANOVA and Duncan's multiple comparisons using SPSS software.

RESULTS

The ST group mice had 17.1% lower body weight, 1.3-3.6-fold greater organ index (organ weight/body weight for organs including the liver and spleen), 10-fold greater liver damage score, and 3.4-10.1-fold enhanced aspartate transaminase, alanine transaminase, and myeloperoxidase activities, and malondialdehyde and hydrogen peroxide concentrations compared with controls (P < 0.05). The S. typhimurium-induced abnormalities were prevented by Amuc supplementation. Furthermore, the ST + Amuc group mice had 1.44-1.89-fold lower mRNA levels of proinflammatory cytokines (interleukin [Il]6, Il1b, and tumor necrosis factor-α) and chemokines (chemokine ligand [Ccl]2, Ccl3, and Ccl8) and 27.1%-68.5% lower levels of inflammation-related proteins in the liver than ST group mice (P < 0.05).

CONCLUSIONS

Amuc treatment prevents S. typhimurium-induced liver damage partly through the toll-like receptor (TLR)2/TLR4/myeloid differentiation factor 88 and nuclear factor-κB signaling as well as nuclear factor erythroid-2 related factor signaling pathways. Thus, Amuc supplementation may be effective in treating liver injury in S. typhimurium-challenged mice.

Isolates of Salmonella typhimurium circumvent NLRP3 inflammasome recognition in macrophages during the chronic phase of infection

Inflammasome signaling results in cell death and release of cytokines from the IL-1 family, which facilitates control over an infection. However, some pathogens such as Salmonella typhimurium (ST) activate various innate immune signaling pathways, including inflammasomes, yet evade these cell death mechanisms, resulting in a chronic infection. Here we investigated inflammasome signaling induced by acute and chronic isolates of ST obtained from different organs. We show that ST isolated from infected mice during the acute phase displays an increased potential to activate inflammasome signaling, which then undergoes a protracted decline during the chronic phase of infection. This decline in inflammasome signaling was associated with reduced expression of virulence factors, including flagella and the Salmonella pathogenicity island I genes. This reduction in cell death of macrophages induced by chronic isolates had the greatest impact on the NLRP3 inflammasome, which correlated with a reduction in caspase-1 activation. Furthermore, rapid cell death induced by Casp-1/11 by ST in macrophages limited the subsequent activation of cell death cascade proteins Casp-8, RipK1, RipK3, and MLKL to prevent the activation of alternative forms of cell death. We observed that the lack of the ability to induce cell death conferred a competitive fitness advantage to ST only during the acute phase of infection. Finally, we show that the chronic isolates displayed a significant attenuation in their ability to infect mice through the oral route. These results reveal that ST adapts during chronic infection by circumventing inflammasome recognition to promote the survival of both the host and the pathogen.

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.

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-27 amplifies cytokine responses to Gram-negative bacterial products and Salmonella typhimurium infection

Cytokine responses from monocytes and macrophages exposed to bacteria are of particular importance in innate immunity. Focusing on the impact of the immunoregulatory cytokine interleukin (IL)-27 on control of innate immune system responses, we examined human immune responses to bacterial products and bacterial infection by E. coli and S. typhimurium. Since the effect of IL-27 treatment in human myeloid cells infected with bacteria is understudied, we treated human monocytes and macrophages with IL-27 and either LPS, flagellin, or bacteria, to investigate the effect on inflammatory signaling and cytokine responses. We determined that simultaneous stimulation with IL-27 and LPS derived from E. coli or S. typhimurium resulted in enhanced IL-12p40, TNF-α, and IL-6 expression compared to that by LPS alone. To elucidate if IL-27 manipulated the cellular response to infection with bacteria, we infected IL-27 treated human macrophages with S. typhimurium. While IL-27 did not affect susceptibility to S. typhimurium infection or S. typhimurium-induced cell death, IL-27 significantly enhanced proinflammatory cytokine production in infected cells. Taken together, we highlight a role for IL-27 in modulating innate immune responses to bacterial infection.

Prostaglandins D2 and E2 have opposite effects on alveolar macrophages infected with Histoplasma capsulatum

Prostaglandin E₂ (PGE₂) suppresses macrophage effector mechanisms; however, little is known about the function of PGD₂ in infected alveolar macrophages (AMs). Using serum-opsonized Histoplasma capsulatum (Ops-H. capsulatum) in vitro, we demonstrated that AMs produced PGE₂ and PGD₂ in a time-dependent manner, with PGE₂ levels exceeding those of PGD₂ by 48 h postinfection. Comparison of the effects of both exogenous PGs on AMs revealed that PGD₂ increased phagocytosis and killing through the chemoattractant receptor-homologous molecule expressed on Th2 lymphocytes receptor, whereas PGE₂ had opposite effects, through E prostanoid (EP) receptor 2 (EP2)/EP4-dependent mechanisms. Moreover, PGD₂ inhibited phospholipase C-γ (PLC-γ) phosphorylation, reduced IL-10 production, and increased leukotriene B4 receptor expression. In contrast, exogenous PGE₂ treatment reduced PLC-γ phosphorylation, p38 and nuclear factor κB activation, TNF-α, H₂O₂, and leukotriene B₄, but increased IL-1β production. Using specific compounds to inhibit the synthesis of each PG in vitro and in vivo, we found that endogenous PGD₂ contributed to fungicidal mechanisms and controlled inflammation, whereas endogenous PGE₂ decreased phagocytosis and killing of the fungus and induced inflammation. These findings demonstrate that, although PGD₂ acts as an immunostimulatory mediator to control H. capsulatum infection, PGE₂ has immunosuppressive effects, and the balance between these two PGs may limit collateral immune damage at the expense of microbial containment.

Rab11 family expression in the human placenta: Localization at the maternal-fetal interface

Rab proteins are a family of small GTPases involved in a variety of cellular processes. The Rab11 subfamily in particular directs key steps of intracellular functions involving vesicle trafficking of the endosomal recycling pathway. This Rab subfamily works through a series of effector proteins including the Rab11-FIPs (Rab11 Family-Interacting Proteins). While the Rab11 subfamily has been well characterized at the cellular level, its function within human organ systems is still being explored. In an effort to further study these proteins, we conducted a preliminary investigation of a subgroup of endosomal Rab proteins in a range of human cell lines by Western blotting. The results from this analysis indicated that Rab11a, Rab11c(Rab25) and Rab14 were expressed in a wide range of cell lines, including the human placental trophoblastic BeWo cell line. These findings encouraged us to further analyse the localization of these Rabs and their common effector protein, the Rab Coupling Protein (RCP), by immunofluorescence microscopy and to extend this work to normal human placental tissue. The placenta is a highly active exchange interface, facilitating transfer between mother and fetus during pregnancy. As Rab11 proteins are closely involved in transcytosis we hypothesized that the placenta would be an interesting human tissue model system for Rab investigation. By immunofluorescence microscopy, Rab11a, Rab11c(Rab25), Rab14 as well as their common FIP effector RCP showed prominent expression in the placental cell lines. We also identified the expression of these proteins in human placental lysates by Western blot analysis. Further, via fluorescent immunohistochemistry, we noted abundant localization of these proteins within key functional areas of primary human placental tissues, namely the outer syncytial layer of placental villous tissue and the endothelia of fetal blood vessels. Overall these findings highlight the expression of the Rab11 family within the human placenta, with novel localization at the maternal-fetal interface.

Interleukin-10 Production by T and B Cells Is a Key Factor to Promote Systemic Salmonella enterica Serovar Typhimurium Infection in Mice

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a Gram-negative bacterium that produces disease in numerous hosts. In mice, oral inoculation is followed by intestinal colonization and subsequent systemic dissemination, which leads to severe pathogenesis without the activation of an efficient anti-Salmonella immune response. This feature suggests that the infection caused by S. Typhimurium may promote the production of anti-inflammatory molecules by the host that prevent efficient T cell activation and bacterial clearance. In this study, we describe the contribution of immune cells producing the anti-inflammatory cytokine interleukin-10 (IL-10) to the systemic infection caused by S. Typhimurium in mice. We observed that the production of IL-10 was required by S. Typhimurium to cause a systemic disease, since mice lacking IL-10 (IL-10-/-) were significantly more resistant to die after an infection as compared to wild-type (WT) mice. IL-10-/- mice had reduced bacterial loads in internal organs and increased levels of pro-inflammatory cytokines in serum at 5 days of infection. Importantly, WT mice showed high bacterial loads in tissues and no increase of cytokines in serum after 5 days of S. Typhimurium infection, except for IL-10. In WT mice, we observed a peak of il-10 messenger RNA production in ileum, spleen, and liver after 5 days of infection. Importantly, the adoptive transfer of T or B cells from WT mice restored the susceptibility of IL-10-/- mice to systemic S. Typhimurium infection, suggesting that the generation of regulatory cells in vivo is required to sustain a systemic infection by S. Typhimurium. These findings support the notion that IL-10 production from lymphoid cells is a key process in the infective cycle of S. Typhimurium in mice due to generation of a tolerogenic immune response that prevents bacterial clearance and supports systemic dissemination.

Novel mechanism of miRNA-365-regulated trophoblast apoptosis in recurrent miscarriage

Clinical pregnancies increasingly end in recurrent miscarriage (RM) during the first trimester, with genetic factors shouldering the main responsibility. MicroRNAs (miRNAs) regulate gene expression in a wide array of important biological processes. We examined the potential role of dysregulated miRNAs in RM pathogenesis and trophoblast development as an approach to elucidate the molecular mechanism behind RM. miRNA profiles from clinical specimens of RM and induced abortion (IA) were compared, and several miRNAs were found to be aberrantly expressed in RM samples. Among the miRNAs, miR-365 was significantly differentially expressed in RM decidual tissues. Furthermore, our results demonstrate that miR-365 functions as an upstream regulator of MDM2/p53 expression, cell cycle progression and apoptosis in trophoblasts. Bioinformatic prediction and experimental validation assays identified SGK1 as a direct target of miR-365; consistently, its protein levels were low in decidual tissues. Additionally, functional studies revealed that SGK1 silencing elicits cell cycle arrest and apoptosis in trophoblasts and that SGK1 overexpression attenuates the effects of miR-365 on apoptosis and MDM2/p53 expression. Collectively, our data provide evidence that the up-regulation of miR-365 may contribute to RM by decreasing SGK1 expression, which suggests its potential utility as a prognostic biomarker and therapeutic target for RM.

Opposing roles of IL-10 in acute bacterial infection

Interleukin-10 (IL-10) is recognized as an anti-inflammatory cytokine that downmodulates inflammatory immune responses at multiple levels. In innate cells, production of this cytokine is usually triggered after pathogen recognition receptor (PRR) engagement by pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patters (DAMPs), as well as by other soluble factors. Importantly, IL-10 is frequently secreted during acute bacterial infections and has been described to play a key role in infection resolution, although its effects can significantly vary depending on the infecting bacterium. While the production of IL-10 might favor host survival in some cases, it may also result harmful for the host in other circumstances, as it can prevent appropriate bacterial clearance. In this review we discuss the role of IL-10 in bacterial clearance and propose that this cytokine is required to recover from infection caused by extracellular or highly pro-inflammatory bacteria. Altogether, we propose that IL-10 drives excessive suppression of the immune response upon infection with intracellular bacteria or in non-inflammatory bacterial infections, which ultimately favors bacterial persistence and dissemination within the host. Thus, the nature of the bacterium causing infection is an important factor that needs to be taken into account when considering new immunotherapies that consist on the modulation of inflammation, such as IL-10. Indeed, induction of this cytokine may significantly improve the host's immune response to certain bacteria when antibiotics are not completely effective.

Distinct innate responses are induced by attenuated Salmonella enterica serovar Typhimurium mutants

Upon bacterial infection the host cells generate a wide variety of cytokines. Genetic attenuation of bacterial physiological pathogens can be accomplished not only by disruption of normal bacterial processes, but also by the loss of the ability to redirect the host immune system. We examined nine attenuated Salmonella Typhimurium mutants for their ability to replicate as well as the cytokines produced after infection of Bone Marrow Derived Macrophages (BMDM). Infection of BMDM with attenuated Salmonella mutants led to host cytokine patterns distinct from those that followed WT infection. Surprisingly, each bacterial mutant had a unique cytokine signature. Because some of the mutants induced an IL-10 response not seen in WT, we examined the role of IL-10 on Salmonella replication. Surprisingly, addition of IL-10 before or concurrent with infection restricted growth of WT Salmonella in BMDM. Bacterial attenuation is not a single process and results in attenuated host responses, which result in unique patterns for each attenuated mutants.

Progesterone promotes maternal-fetal tolerance by reducing human maternal T-cell polyfunctionality and inducing a specific cytokine profile

Progesterone is a steroid hormone essential for the maintenance of human pregnancy, and its actions are thought to include promoting maternal immune tolerance of the semiallogenic fetus. We report that exposure of maternal T cells to progesterone at physiological doses induced a unique skewing of the cytokine production profile of CD4⁺ and CD8⁺ T cells, with reductions not only in potentially deleterious IFN‐γ and TNF‐α production but also in IL‐10 and IL‐5. Conversely, production of IL‐4 was increased. Maternal T cells also became less polyfunctional, focussing cytokine production toward profiles including IL‐4. This was accompanied by reduced T‐cell proliferation. Using fetal and viral antigen‐specific CD8⁺ T‐cell clones, we confirmed that this as a direct, nonantigen‐specific effect. Yet human T cells lacked conventional nuclear progesterone receptors, implicating a membrane progesterone receptor. CD4⁺ and CD8⁺ T cells responded to progesterone in a dose‐dependent manner, with subtle effects at concentrations comparable to those in maternal blood, but profound effects at concentrations similar to those at the maternal–fetal interface. This characterization of how progesterone modulates T‐cell function is important in understanding the normal biology of pregnancy and informing the rational use of progesterone therapy in pregnancies at risk of fetal loss.

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.

Obesity during pregnancy disrupts placental morphology, cell proliferation, and inflammation in a sex-specific manner across gestation in the mouse

It is well-accepted that maternal obesity affects fetal development to elevate the risk of offspring disease, but how this happens is unclear. Understanding placental alterations during gestation as a consequence of maternal obesity is critical to understanding the impact of maternal obesity on fetal programming. Here, we used histological criteria, flow cytometry, quantitative PCR, and multiplex cytokine assays to examine changes in cell proliferation and inflammation in the placenta during gestation in a mouse model of maternal high-fat diet-induced obesity. We focused on mouse mid- to late gestation (approximately human late first and third trimester) because previous literature has indicated that this is when important regulators of metabolism, including that of the brain and endocrine pancreas, are forming. These studies were undertaken in order to understand how maternal obesity changes the placenta during this period, which might suggest a causal link to later-life metabolic dysfunction. We found that labyrinth thickness and cell proliferation were decreased at both pregnancy stages in obese compared to normal weight pregnancies. Inflammation was also altered in late pregnancy with increased macrophage activation and elevated cytokine gene expression in the placenta as well as increased abundance of some cytokines in the fetal circulation in obese compared to normal weight pregnancies. These changes in macrophage activation and cytokine gene expression were of greater magnitude and significance in placentas accompanying male fetuses. These data provide insight into placental changes in obesity and identify potential links between placental inflammation and programming of offspring disease by maternal obesity.

Malaria parasite infection compromises control of concurrent systemic non-typhoidal Salmonella infection via IL-10-mediated alteration of myeloid cell function

Non-typhoidal Salmonella serotypes (NTS) cause a self-limited gastroenteritis in immunocompetent individuals, while children with severe Plasmodium falciparum malaria can develop a life-threatening disseminated infection. This co-infection is a major source of child mortality in sub-Saharan Africa. However, the mechanisms by which malaria contributes to increased risk of NTS bacteremia are incompletely understood. Here, we report that in a mouse co-infection model, malaria parasite infection blunts inflammatory responses to NTS, leading to decreased inflammatory pathology and increased systemic bacterial colonization. Blunting of NTS-induced inflammatory responses required induction of IL-10 by the parasites. In the absence of malaria parasite infection, administration of recombinant IL-10 together with induction of anemia had an additive effect on systemic bacterial colonization. Mice that were conditionally deficient for either myeloid cell IL-10 production or myeloid cell expression of IL-10 receptor were better able to control systemic Salmonella infection, suggesting that phagocytic cells are both producers and targets of malaria parasite-induced IL-10. Thus, IL-10 produced during the immune response to malaria increases susceptibility to disseminated NTS infection by suppressing the ability of myeloid cells, most likely macrophages, to control bacterial infection.