Cytokine response of porcine cell lines to Salmonella enterica serovar typhimurium and its hilA and ssrA mutants

Characterization of Porcine Monocyte-Derived Macrophages Cultured in Serum-Reduced Medium

The aim of this study was to establish a cell culture system for the generation of porcine monocyte-derived macrophages (MDMs) under reduced-serum conditions. Cultures based on either the Nu-Serum™ Growth Medium Supplement (NUS) or a conventional fetal bovine serum (FBS) were compared, which included the assessment of FBS from two different providers (FBS1 and FBS2). The data obtained confirmed the significant impact of culture conditions on in vitro-generated MDMs. The MDMs cultured under reduced-serum conditions showed increased levels of IL-1β and CD86 mRNA and a proinflammatory cytokine profile, characterized by the increased mRNA expression of IL-23p19, CXCL10, and CCL5. Phagocytic and respiratory burst activities were not adversely affected. Surprisingly, the difference between the two FBSs was much more pronounced than the effect of the reduced-serum supplement. The FBS1 culture conditions gave rise to macrophages with higher surface levels of CD14, CD16, and CD163, a lower CD80 mRNA expression, and an increased induction of IL-10 gene expression. In contrast, none of these trends were observed in macrophage cultures supplemented with FBS2. Instead, the FBS2 culture showed increased levels of IL-1b and CD86 mRNA. In conclusion, reduced-serum culture is a useful tool for in vitro porcine MDM generation, in line with the current research trend of reducing FBS use in biological research.

Cytokine expression by CD163+ monocytes in healthy and Actinobacillus pleuropneumoniae-infected pigs

Distinct monocyte subpopulations have been previously described in healthy pigs and pigs experimentally infected with Actinobacillus pleuropneumoniae (APP). The CD163+ subpopulation of bone marrow (BM), peripheral blood (PB) and lung monocytes was found to play an important role in the inflammatory process. The inflammation is accompanied by elevation of inflammatory cytokines. The aim of the study was to evaluate the contribution of CD163+ monocytes and macrophages to cytokine production during APP-induced lung inflammation. Cytokine production was assessed by flow cytometry (FC) and quantitative PCR (qPCR) in CD163+ monocytes and by qPCR, immunohistochemistry/fluorescence in lungs and tracheobronchial lymph nodes (TBLN). Despite the systemic inflammatory response after APP infection, BM and PB CD163+ monocytes did not express elevated levels of a wide range of cytokines compared to control pigs. In contrast, significant amounts of IL-1β, IL-6, IL-8 and TNF-α were produced in lung lesions and IL-1β in the TBLN. At the protein level, TNF-α was expressed by both CD163+ monocytes and macrophages in lung lesions, whereas IL-1β, IL-6 and IL-8 expression was found only in CD163+ monocytes; no CD163+ macrophages were found to produce these cytokines. Furthermore, the quantification of CD163+ monocytes expressing the two cytokines IL-1β and IL-8 that were most elevated was performed. In lung lesions, 36.5% IL-1β positive CD163+ monocytes but only 18.3% IL-8 positive CD163+ monocytes were found. In conclusion, PB and BM CD163+ monocytes do not appear to contribute to the elevated cytokine levels in plasma. On the other hand, CD163+ monocytes contribute to inflammatory cytokine expression, especially IL-1β at the site of inflammation during the inflammatory process.

The Role of Antibodies Against the Crude Capsular Extract in the Immune Response of Porcine Alveolar Macrophages to In Vitro Infection of Various Serovars of Glaesserella (Haemophilus) parasuis

In Glässer’s disease outbreaks, Glaesserella (Haemophilus) parasuis has to overcome the non-specific immune system in the lower respiratory tract, the alveolar macrophages. Here we showed that porcine alveolar macrophages (PAMs) were able to recognize and phagocyte G. parasuis with strain-to-strain variability despite the presence of the capsule in virulent (serovar 1, 5, 12) as well in avirulent strains (serovar 6 and 9). The capsule, outer membrane proteins, virulence-associated autotransporters, cytolethal distending toxins and many other proteins have been identified as virulence factors of this bacterium. Therefore, we immunized pigs with the crude capsular extract (cCE) from the virulent G. parasuis CAPM 6475 strain (serovar 5) and evaluated the role of the anti-cCE/post-vaccinal IgG in the immune response of PAMs to in vitro infection with various G. parasuis strains. We demonstrated the specific binding of the antibodies to the cCE by Western-blotting assay and immunoprecipitation as well as the specific binding to the strain CAPM 6475 in transmission electron microscopy. In the cCE, we identified several virulence-associated proteins that were immunoreactive with IgG isolated from sera of immunized pigs. Opsonization of G. parasuis strains by post-vaccinal IgG led to enhanced phagocytosis of G. parasuis by PAMs at the first two hours of infection. Moreover, opsonization increased the oxidative burst and expression/production of both pro- and anti-inflammatory cytokines. The neutralizing effects of these antibodies on the antioxidant mechanisms of G. parasuis may lead to attenuation of its virulence and pathogenicity in vivo. Together with opsonization of bacteria by these antibodies, the host may eliminate G. parasuis in the infection site more efficiently. Based on these results, the crude capsular extract is a vaccine candidate with immunogenic properties.

Maternal Exposure Results in Long-Term Deoxynivalenol Persistence in Piglets' Plasma and Modulates the Immune System

Deoxynivalenol (DON)-contaminated feed represents a serious problem for pigs due to their high sensitivity to its toxicological effects. The aim of the present study was to evaluate the impact of intrauterine DON exposure on the immune system of piglets. Pure DON was intravenously administered to sows at the end of gestation (during the last 2–3 days of gestation, one dose of 300 µg per day). The plasma concentration of DON was analyzed using liquid chromatography combined with high-resolution Orbitrap-based mass spectrometry (LC–MS/MS (HR)) and selected immune parameters were monitored six times in piglets from birth to 18 weeks. DON was found in the plasma of 90% of newborn piglets at a mean concentration of 6.28 ng/mL and subsequently, at one, three, and seven weeks after birth with decreasing concentrations. Trace amounts were still present in the plasma 14 weeks after birth. Flow cytometry revealed a significant impact of DON on T lymphocyte subpopulations during the early postnatal period. Lower percentages of regulatory T cells, T helper lymphocytes, and their double positive CD4+CD8+ subset were followed by increased percentages of cytotoxic T lymphocytes and γδ T cells. The capacity to produce pro-inflammatory cytokines was also significantly lower after intrauterine DON exposure. In conclusion, this study revealed a long-term persistence of DON in the plasma of the piglets as a consequence of short-term intrauterine exposure, leading to altered immune parameters.

Expression of Cytokines in Porcine Iris, Retina and Choroidal Tissues Stimulated by Microbe-associated Molecular Patterns

PURPOSE

The innate immune system is strongly implicated in the pathogenesis of uveitis. This study was designed to clarify the responses of the innate immune system in uveal tissues.

MATERIALS AND METHODS

We utilized quantitative, real-time RT-PCR to measure mRNA of innate immune system receptors from porcine iris, choroid, and retina tissues. We used RT-PCR for cytokines to evaluate the responses of these tissues to specific ligands or extracts of whole bacteria that activate the innate immune system. We used ELISA for IL-6 on selected choroidal supernatants to confirm that the mRNA measurement correlated with protein levels.

RESULTS

In each of the studied tissues, we detected the expression of important receptors belonging to the innate immune system including dectin-1, TLR4, TLR8, and NOD2. Relative mRNA expression was generally lower in the retina compared to iris or choroid. All three tissues demonstrated upregulation of cytokine mRNA in response to a range of ligands that activate the innate immune system. The measurement of IL-6 protein was consistent with results based on mRNA. Notably, the expression of mRNA for IL-23 was more pronounced than IL-12 in all three tissues after stimulation with various innate immune system ligands.

CONCLUSIONS

These data provide evidence of a potent innate immune response intrinsic to uveal tissues. Specific innate immune system ligands as well as bacterial extracts enhanced the production of several inflammatory cytokines. Furthermore, the observation of higher upregulation of IL-23 mRNA, compared to IL-12 in response to innate immune stimuli, suggested that a local TH17 response might be more robust than a local TH1 response in uveal tissues. Our results expand the understanding as to how the innate immune system may contribute to uveitis.

Minimal Concentrations of Deoxynivalenol Reduce Cytokine Production in Individual Lymphocyte Populations in Pigs

Deoxynivalenol (DON) is a mycotoxin frequently found in cereals, and pigs are one of the most sensitive farm species to DON. The aim of this study was to determine the effects of DON in very low doses on peripheral blood mononuclear cells (PBMC) and on particular lymphocyte subpopulations. The cells were exposed to 1, 10 and 100 ng/mL of DON and lymphocyte viability, proliferation, and cytokine (Interleukin (IL)-1β, IL-2, IL-8, IL-17, Interferon (IFN) γ and tumor necrosis factor (TNF) α production were studied. Cells exposed to DON for 5 days in concentrations of 1 and 10 ng/mL showed higher viability compared to control cells. After 18 h of DON (100 ng/mL) exposure, a significantly lower proliferation after mitogen stimulation was observed. In contrast, an increase of spontaneous proliferation induced by DON (100 ng/mL) was detected. After DON exposure, the expression of cytokine genes decreased, with the exception of IL-1β and IL-8, which increased after 18 h exposure to 100 ng/mL of DON. Among lymphocyte subpopulations, helper T-cells and γδ T-cells exhibiting lower production of IL-17, IFNγ and TNFα were most affected by DON exposure (10 ng/mL). These findings show that subclinical doses of DON lead to changes in immune response.

IPEC-1 variable immune response to different serovars of Salmonella enterica subsp. enterica

Salmonella is a genus of Gram-negative bacteria in the Enterobacteriaceae family causing various illnesses. The ability of the different serovars of Salmonella enterica subsp. enterica to infect a host and to induce pathology relies in part on their cellular and molecular interactions with the intestinal epithelium. In the current study, an in vitro approach using non-polarized or polarized IPEC-1 porcine intestinal epithelial cells were used in order to assess the relation between adhesion, invasion, and induction of the immune response as a function of the serotype of Salmonella. Five serovars, Choleraesuis (host-adapted), Typhimurium (ubiquitous), Typhisuis (host-restricted), which are relevant for pig infection, and Dublin and Gallinarum, which are host-restricted or host-adapted, were studied. A strong variation was observed in the percentages of adhesion and invasion amongst the S. enterica serovars used to interact with the non-polarized and polarized cells. Subsequently, differences were identified between serovars in terms of immune response induced. Serovars Typhimurium and Typhisuis induced a strong innate immune response four and half hours after the beginning of cell stimulation while Choleraesuis, Gallinarum, and Dublin did not. A strong inflammatory response could limit the spread of the porcine serovars to the gut while, with a weak response, bacteria may not be constrained by the immune response enabling severe systemic diseases. Different repertoires of adhesion factors and of secreted protein effectors between Salmonella serovars interacting with IPEC-1 cells probably explains the differences in their early pathogenic behaviours.

The Salmonella type-3 secretion system-1 and flagellar motility influence the neutrophil respiratory burst

Neutrophils are innate immune response cells designed to kill invading microorganisms. One of the mechanisms neutrophils use to kill bacteria is generation of damaging reactive oxygen species (ROS) via the respiratory burst. However, during enteric salmonellosis, neutrophil-derived ROS actually facilitates Salmonella expansion and survival in the gut. This seeming paradox led us to hypothesize that Salmonella may possess mechanisms to influence the neutrophil respiratory burst. In this work, we used an in vitro Salmonella-neutrophil co-culture model to examine the impact of enteric infection relevant virulence factors on the respiratory burst of human neutrophils. We report that neutrophils primed with granulocyte-macrophage colony stimulating factor and suspended in serum containing complement produce a robust respiratory burst when stimulated with viable STm. The magnitude of the respiratory burst increases when STm are grown under conditions to induce the expression of the type-3 secretion system-1. STm mutants lacking the type-3 secretion system-1 induce less neutrophil ROS than the virulent WT. In addition, we demonstrate that flagellar motility is a significant agonist of the neutrophil respiratory burst. Together our data demonstrate that both the type-3 secretion system-1 and flagellar motility, which are established virulence factors in enteric salmonellosis, also appear to directly influence the magnitude of the neutrophil respiratory burst in response to STm in vitro.

Dynamic Transcriptional Regulation of Fis in Salmonella During the Exponential Phase

Fis is one of the most important global regulators and has attracted extensive research attention. Many studies have focused on comparing the Fis global regulatory networks for exploring Fis function during different growth stages, such as the exponential and stationary stages. Although the Fis protein in bacteria is mainly expressed in the exponential phase, the dynamic transcriptional regulation of Fis during the exponential phase remains poorly understood. To address this question, we used RNA-seq technology to identify the Fis-regulated genes in the S. enterica serovar Typhimurium during the early exponential phase, and qRT-PCR was performed to validate the transcriptional data. A total of 1495 Fis-regulated genes were successfully identified, including 987 Fis-repressed genes and 508 Fis-activated genes. Comparing the results of this study with those of our previous study, we found that the transcriptional regulation of Fis was diverse during the early- and mid-exponential phases. The results also showed that the strong positive regulation of Fis on Salmonella pathogenicity island genes in the mid-exponential phase transitioned into insignificant effect in the early exponential phase. To validate these results, we performed a cell infection assay and found that Δfis only exhibited a 1.49-fold decreased capacity compared with the LT2 wild-type strain, indicating a large difference from the 6.31-fold decrease observed in the mid-exponential phase. Our results provide strong evidence for a need to thoroughly understand the dynamic transcriptional regulation of Fis in Salmonella during the exponential phase.

Application of Molecular Approaches for Understanding Foodborne Salmonella Establishment in Poultry Production

Salmonellosis in the United States is one of the most costly foodborne diseases. Given that Salmonella can originate from a wide variety of environments, reduction of this organism at all stages of poultry production is critical. Salmonella species can encounter various environmental stress conditions which can dramatically influence their survival and colonization. Current knowledge of Salmonella species metabolism and physiology in relation to colonization is traditionally based on studies conducted primarily with tissue culture and animal infection models. Consequently, while there is some information about environmental signals that control Salmonella growth and colonization, much still remains unknown. Genetic tools for comprehensive functional genomic analysis of Salmonella offer new opportunities for not only achieving a better understanding of Salmonella pathogens but also designing more effective intervention strategies. Now the function(s) of each single gene in the Salmonella genome can be directly assessed and previously unknown genetic factors that are required for Salmonella growth and survival in the poultry production cycle can be elucidated. In particular, delineating the host-pathogen relationships involving Salmonella is becoming very helpful for identifying optimal targeted gene mutagenesis strategies to generate improved vaccine strains. This represents an opportunity for development of novel vaccine approaches for limiting Salmonella establishment in early phases of poultry production. In this review, an overview of Salmonella issues in poultry, a general description of functional genomic technologies, and their specific application to poultry vaccine developments are discussed.

Evaluation of in vitro and in vivo anti-inflammatory activity of biologically active phospholipids with anti-neoplastic potential in porcine model

Background

This study aims to investigate the anti-inflammatory effect of biologically active phospholipids (BAP) used in preparations for clinical practice in humans. Until date, except anti-neoplastic ability, little is known about anti-inflammatory property of the phospholipids.

Methods

While the course of bacterially induced acute pneumonia and markers of inflammation were studied in in vivo system in pigs orally supplemented with BAP, the pro- and anti-inflammatory response of lipopolysaccharide-stimulated porcine monocyte-derived macrophages to 24 h- and 48 h-treatmeant by BAP was investigated in in vitro system. In vivo, the animal health status was monitored and pro-inflammatory IL-1β and IL-8 in sera were detected by ELISA during the experiment, while bronchoalveolar lavage fluids (BALF) and the lungs were examined post-mortem. Total and differential counts of white blood cell (WBC) were determined in blood and BALF. In vitro, mRNA expression of pro-inflammatory (TNF-α, IL-1β, CXCL10) and anti-inflammatory (IL-10 and Arg1) cytokines, and level of activated caspase 1 and phosphorylated protein kinase C epsilon (pPKCϵ), were studied using qRT-PCR and Western blot, respectively. For the purposes of both systems, 6 animals were used in each of the BAP-supplemented and the control groups.

Results

In vivo, BAP had a positive influence on the course of the disease. The immunomodulatory effects of BAP were confirmed by lower levels of IL-1β, IL-8, and a lower WBC count in the supplemented group in comparison with the control group. A lower percentage of lung parenchyma was affected in the supplemented group comparing to the control group (on average, 4% and 34% of tissue, respectively). In vitro, BAP suppressed mRNA expression of mRNA for IL-10 and all pro-inflammatory cytokines tested. This down-regulation was dose- and time-dependent. Arg1 mRNA expression remained unaffected. Further dose- and time-dependent suppression of the activated caspase 1 and pPKCϵ was detected in macrophages when treated with BAP.

Conclusions

Our results demonstrate that BAP has anti-inflammatory and immunomodulatory properties, thus emphasizing the potential of this compound as a natural healing agent.

SPI-1 encoded genes of Salmonella Typhimurium influence differential polarization of porcine alveolar macrophages in vitro

Background

Within the last decade, macrophages have been shown to be capable of differentiating toward a classically activated phenotype (M1) with a high antimicrobial potential or an alternatively activated phenotype (M2). Some pathogens are capable of interfering with differentiation in order to down-regulate the anti-microbial activity and enhance their survival in the host.

Results

To test this ability in Salmonella enterica serovar Typhimurium, we infected porcine alveolar macrophages with wild-type Salmonella Typhimurium and its isogenic mutants devoid of two major pathogenicity islands, SPI-1 and SPI-2. The induction of genes linked with M1 or M2 polarization was determined by quantification of gene expression by RT-qPCR. The ΔSPI-1 mutant induced a high, dose-dependent M1 response but a low M2 response in infected macrophages. On the other hand, wild-type Salmonella Typhimurium induced a low M1 response but a high, dose-dependent M2 response in infected macrophages. The response to ΔSPI-2 mutant infection was virtually the same as the wild-type strain.

Conclusions

We therefore propose that Salmonella Typhimurium DT104 studied here can polarize macrophages towards the less bactericidal M2 phenotype and that this polarization is dependent on the type III secretion system encoded by SPI-1.

Nipah virus infects specific subsets of porcine peripheral blood mononuclear cells

Nipah virus (NiV), a zoonotic paramyxovirus, is highly contagious in swine, and can cause fatal infections in humans following transmission from the swine host. The main viral targets in both species are the respiratory and central nervous systems, with viremia implicated as a mode of dissemination of NiV throughout the host. The presented work focused on the role of peripheral blood mononuclear cells (PBMC) in the viremic spread of the virus in the swine host. B lymphocytes, CD4-CD8-, as well as CD4+CD8- T lymphocytes were not permissive to NiV, and expansion of the CD4+CD8- cells early post infection was consistent with functional humoral response to NiV infection observed in swine. In contrast, significant drop in the CD4+CD8- T cell frequency was observed in piglets which succumbed to the experimental infection, supporting the hypothesis that antibody development is the critical component of the protective immune response. Productive viral replication was detected in monocytes, CD6+CD8+ T lymphocytes and NK cells by recovery of infectious virus in the cell supernatants. Virus replication was supported by detection of the structural N and the non-structural C proteins or by detection of genomic RNA increase in the infected cells. Infection of T cells carrying CD6 marker, a strong ligand for the activated leukocyte cell adhesion molecule ALCAM (CD166) highly expressed on the microvascular endothelial cell of the blood-air and the blood-brain barrier may explain NiV preferential tropism for small blood vessels of the lung and brain.

Effect of Saccharomyces cerevisiae var. Boulardii and β-galactomannan oligosaccharide on porcine intestinal epithelial and dendritic cells challenged in vitro with Escherichia coli F4 (K88)

Probiotic and prebiotics, often called "immune-enhancing" feed additives, are believed to deal with pathogens, preventing the need of an immune response and reducing tissue damage. In this study, we investigated if a recently developed β-galactomannan (βGM) had a similar protective role compared to Saccharomyces cerevisiae var. Boulardii (Scb), a proven probiotic, in the context of enterotoxigenic Escherichia coli (ETEC) infection. ETEC causes inflammation, diarrhea and intestinal damage in piglets, resulting in large economic loses worldwide. We observed that Scb and βGM products inhibited in vitro adhesion of ETEC on cell surface of porcine intestinal IPI-2I cells. Our data showed that Scb and βGM decreased the mRNA ETEC-induced gene expression of pro-inflammatory cytokines TNF-α, IL-6, GM-CSF and chemokines CCL2, CCL20 and CXCL8 on intestinal IPI-2I. Furthermore, we investigated the putative immunomodulatory role of Scb and βGM on porcine monocyte-derived dendritic cells (DCs) per se and under infection conditions. We observed a slight up-regulation of mRNA for TNF-α and CCR7 receptor after co-incubation of DC with Scb and βGM. However, no differences were found in DC activation upon ETEC infection and Scb or βGM co-culture. Therefore, our results indicate that, similar to probiotic Scb, prebiotic βGM may protect intestinal epithelial cells against intestinal pathogens. Finally, although these products may modulate DC activation, their effect under ETEC challenge conditions remains to be elucidated.

Salmonella enterica serovar Typhimurium and Enteritidis infection of pigs and cytokine signalling in palatine tonsils

Pigs are considered as one of the major sources of zoonotic strains of Salmonella enterica for humans. Out of many S. enterica serovars, S. Typhimurium dominates in pigs, however, in several countries in Central Europe, S. Enteritidis is also quite frequent in pig herds. In this study we therefore compared the colonisation of pigs with S. Typhimurium and S. Enteritidis. We found that 3 weeks after infection S. Enteritidis 147 colonised the intestinal tract in higher quantities but was shed in faeces in lower quantities than S. Typhimurium 17C10. In a second experiment we found out that S. Enteritidis 147 and its SPI-1 and SPI-4 mutants increased proinflammatory cytokine (IL-1β and IL-8) signalling in the ileum 5 days post infection. On the other hand, independent of SPI-1 or SPI-4, S. Enteritidis 147 suppressed expression of IL-18, MCP1, TLR2, CD86, IL-7, IL-10 and IL-15 in the palatine tonsils. The suppression of cytokine signalling may facilitate the initial colonisation of the palatine tonsils by Salmonella. Moreover, immune suppression may also influence pig resistance to opportunistic pathogens and Salmonella infection in pigs thus may become an issue not only in terms of pork contamination but also in terms of affecting the immunological status of pig herds.

The mycotoxin deoxynivalenol potentiates intestinal inflammation by Salmonella typhimurium in porcine ileal loops

Background and Aims

Both deoxynivalenol (DON) and nontyphoidal salmonellosis are emerging threats with possible hazardous effects on both human and animal health. The objective of this study was to examine whether DON at low but relevant concentrations interacts with the intestinal inflammation induced by Salmonella Typhimurium.

Methodology

By using a porcine intestinal ileal loop model, we investigated whether intake of low concentrations of DON interacts with the early intestinal inflammatory response induced by Salmonella Typhimurium.

Results

A significant higher expression of IL-12 and TNFα and a clear potentiation of the expression of IL-1β, IL-8, MCP-1 and IL-6 was seen in loops co-exposed to 1 µg/mL of DON and Salmonella Typhimurium compared to loops exposed to Salmonella Typhimurium alone. This potentiation coincided with a significantly enhanced Salmonella invasion in and translocation over the intestinal epithelial IPEC-J2 cells, exposed to non-cytotoxic concentrations of DON for 24 h. Exposure of Salmonella Typhimurium to 0.250 µg/mL of DON affected the bacterial gene expression level of a limited number of genes, however none of these expression changes seemed to give an explanation for the increased invasion and translocation of Salmonella Typhimurium and the potentiated inflammatory response in combination with DON.

Conclusion

These data imply that the intake of low and relevant concentrations of DON renders the intestinal epithelium more susceptible to Salmonella Typhimurium with a subsequent potentiation of the inflammatory response in the gut.

Cell-mediated immune response in swine infected with Mycobacterium avium subsp. avium

The zoonotic characteristic of Mycobacterium avium subsp. avium (MAA) represents a veterinary and economic problem in infected pigs. In this study, we analysed cell-mediated immunity six months after experimental infection by measuring interferon-γ (IFN-γ) production and by performing lymphocyte transformation tests after in vitro re-stimulation with the MAA-derived antigen. At the same time, IFN-γ-producing cells were characterised by flow cytometry. In MAA-infected animals, the production of IFN-γ increased in response to the MAA antigen in the blood, spleen and mesenteric lymph nodes. Similarly, a positive antigen-driven response was detected by the proliferation assay. In contrast, IFN-γ production and proliferation was undetectable after stimulation with the MAA antigen in uninfected control animals. These results indicate that both methods can be used for the identification of individual MAA-infected pigs. Using flow cytometry, we found that double-positive CD4(+)CD8(+) lymphocytes were the major T lymphocyte subset producing IFN-γ after in vitro re-stimulation.

SPI-1-encoded type III secretion system of Salmonella enterica is required for the suppression of porcine alveolar macrophage cytokine expression

Genes localized at Salmonella pathogenicity island-1 (SPI-1) are involved in Salmonella enterica invasion of host non-professional phagocytes. Interestingly, in macrophages, SPI-1-encoded proteins, in addition to invasion, induce cell death via activation of caspase-1 which also cleaves proIL-1β and proIL-18, precursors of 2 proinflammatory cytokines. In this study we were therefore interested in whether SPI-1-encoded type III secretion system (T3SS) may influence proinflammatory response of macrophages. To test this hypothesis, we infected primary porcine alveolar macrophages with wild-type S. Typhimurium and S. Enteritidis and their isogenic SPI-1 deletion mutants. ΔSPI1 mutants of both serovars invaded approx. 5 times less efficiently than the wild-type strains and despite this, macrophages responded to the infection with ΔSPI1 mutants by increased expression of proinflammatory cytokines IL-1β, IL-8, TNFα, IL-23α and GM-CSF. Identical macrophage responses to that induced by the ΔSPI1 mutants were also observed to the infection with sipB but not the sipA mutant. The hilA mutant exhibited an intermediate phenotype between the ΔSPI1 mutant and the wild-type S. Enteritidis. Our results showed that the SPI-1-encoded T3SS is required not only for cell invasion but in macrophages also for the suppression of early proinflammatory cytokine expression.

Epidemiology and interaction of Salmonella enterica serovar Derby, Infantis and Typhimurium with porcine alveolar macrophages

In this study we were interested in the serovars which are frequently isolated from pigs, i.e. S. Typhimurium, S. Derby and S. Infantis. First we collected different isolates of S. Infantis and S. Derby and compared them by macrorestriction analysis. In the second part of the study we infected porcine alveolar macrophages (PAMs) with representative strains of these serovars and S. Typhimurium and determined intracellular survival, cytotoxicity and cytokine response. In S. Derby, 17 different profiles in 51 isolates have been identified and in S. Infantis, 12 different profiles in 37 isolates have been identified. Four hours post-addition of bacteria to PAMs, higher numbers of intracellular S. Typhimurium than S. Derby or S. Infantis were observed. However, within next 24h, counts of S. Typhimurium did not change while S. Derby and S. Infantis increased their counts 10 and 5 times, respectively. The apparent inability of S. Typhimurium to multiply inside PAMs was caused by its higher cytotoxicity because PAMs infected with S. Typhimurium released LDH 24h post-infection to a significantly higher level than when infected with the other two serovars. The IL-1β, IL-8, IL-12p40, IL-23p19 and TNFα response to S. Derby and S. Infantis was always higher than to S. Typhimurium and the differences among the serovars were more significant at 4 than 24h post-infection. The lower cytokine signaling but higher cytotoxicity of S. Typhimurium for macrophages correlates with the higher virulence for pigs of this serotype when compared with S. Derby or S. Infantis.

Gene expression study of two widely used pig intestinal epithelial cell lines: IPEC-J2 and IPI-2I

The intestinal epithelial cells (IEC) play an important role in the immune system of swine, protecting against infectious and non-infectious environmental insults. The IEC participate in the innate immune response of the intestine through different mechanisms such as barrier function, mucus secretion, antibacterial peptide synthesis and participation in the cytokine/chemokine networks. Most of the current knowledge of intestinal cell functions has come from studies conducted on cell cultures generated from human cancers or from classical animal models. However, because the molecular and cellular elements of the immune system have been selected over evolutionary time in response to the species-specific environment, models of immune function based on mouse and human need to be applied cautiously in pig. Few models of swine small intestine epithelium exist and these are poorly characterised. In the present study we characterised the basal expression of epithelial and immune-related genes of two pig small intestine cell lines, IPEC-J2 and IPI-2I, under different culture conditions. These data represent essential background information for future studies on pig-intestinal pathogen interactions.

The mucosal immune system: recent developments and future directions in the pig

In most animals, the mucosal immune system effectively controls expression of active immune responses to pathogen and tolerance to harmless antigens. Our understanding of the function and control of the mucosal immune system has advanced as a result of studies in rodents and humans. The discoveries of regulatory T-cells and T-helper-17 cells, and studies on the interactions between epithelial and dendritic cells, demonstrate its complexity. In pigs, some of the systems and reagents for determining the relevance of these mechanisms are present, and indicate lines for future work. However, many empirical studies of the effect of manipulation of the mucosal immune system in the pig by prebiotics, probiotics and feed additives have been carried out. Interpretation of these results needs to be made with care, since manipulation of the mucosal immune system may improve its efficiency under a specific set of environmental and husbandry conditions, but impair it under others.

Early immune response following Salmonella enterica subspecies enterica serovar Typhimurium infection in porcine jejunal gut loops

Salmonella enterica subspecies enterica serovar Typhimurium, commonly called S. Typhimurium, can cause intestinal infections in humans and various animal species such as swine. To analyze the host response to Salmonella infection in the pig we used an in vivo gut loop model, which allows the analysis of multiple immune responses within the same animal. Four jejunal gut-loops were each inoculated with 3×10⁸ cfu of S. Typhimurium in 3 one-month-old piglets and mRNA expressions of various cytokines, chemokines, transcription factors, antimicrobial peptides, toll like and chemokine receptors were assessed by quantitative real-time PCR in the Peyer’s patch and the gut wall after 24 h. Several genes such as the newly cloned CCRL1/CCX-CKR were assessed for the first time in the pig at the mRNA level. Pro-inflammatory and T-helper type-1 (Th1) cytokine mRNA were expressed at higher levels in infected compared to non-infected control loops. Similarly, some B cell activation genes, NOD2 and toll like receptor 2 and 4 transcripts were more expressed in both tissues while TLR5 mRNA was down-regulated. Interestingly, CCL25 mRNA expression as well as the mRNA expressions of its receptors CCR9 and CCRL1 were decreased both in the Peyer’s patch and gut wall suggesting a potential Salmonella strategy to reduce lymphocyte homing to the intestine. In conclusion, these results provide insight into the porcine innate mucosal immune response to infection with entero-invasive microorganisms such as S. Typhimurium. In the future, this knowledge should help in the development of improved prophylactic and therapeutic approaches against porcine intestinal S. Typhimurium infections.

Coated fatty acids alter virulence properties of Salmonella Typhimurium and decrease intestinal colonization of pigs

Salmonella Typhimurium infections in pigs are a major source of human foodborne salmonellosis. To reduce the number of infected pigs, acidification of feed or drinking water is a common practice. The aim of the present study was to determine whether some frequently used short- (SCFA) and medium-chain fatty acids (MCFA) are able to alter virulence gene expression and to decrease Salmonella Typhimurium colonization and shedding in pigs using well established and controlled in vitro and in vivo assays. Minimal inhibitory concentrations (MIC) of 4 SCFA (formic acid, acetic acid, propionic acid and butyric acid) and 2 MCFA (caproic and caprylic acid) were determined using 54 porcine Salmonella Typhimurium field strains. MIC values increased at increasing pH-values and were two to eight times lower for MCFA than for SCFA. Expression of virulence gene fimA was significantly lower when bacteria were grown in LB-broth supplemented with sub-MIC concentrations of caproic or caprylic acid (2 mM). Expression of hilA and invasion in porcine intestinal epithelial cells was significantly lower when bacteria were grown in LB-broth containing sub-MIC concentrations of butyric acid or propionic acid (10 mM) and caproic or caprylic acid (2 mM). When given as feed supplement to pigs experimentally infected with Salmonella Typhimurium, coated butyric acid decreased the levels of faecal shedding and intestinal colonization, but had no influence on the colonization of tonsils, spleen and liver. Uncoated fatty acids, however, did not influence fecal shedding, intestinal or tonsillar colonization in pigs. In conclusion, supplementing feed with certain coated fatty acids, such as butyric acid, may help to reduce the Salmonella load in pigs.

Non-typhoidal Salmonella infections in pigs: a closer look at epidemiology, pathogenesis and control

Contaminated pork is an important source of Salmonella infections in humans. The increasing multiple antimicrobial resistance associated with pork-related serotypes such as Salmonella Typhimurium and Salmonella Derby may become a serious human health hazard in the near future. Governments try to anticipate the issue of non-typhoidal Salmonella infections in pork by starting monitoring programmes and coordinating control measures worldwide. A thorough knowledge of how these serotypes interact with the porcine host should form the basis for the development and optimisation of these monitoring and control programmes. During recent years, many researchers have focussed on different aspects of the pathogenesis of non-typhoidal Salmonella infections in pigs. The present manuscript reviews the importance of pigs and pork as a source for salmonellosis in humans and discusses commonly accepted and recent insights in the pathogenesis of non-typhoidal Salmonella infections in pigs, with emphasis on Salmonella Typhimurium, and to relate this knowledge to possible control measures.