Intestinal innate immunity and the pathogenesis of Salmonella enteritis

Establishment and evaluation of a specific antibiotic-induced inflammatory bowel disease model in rats

Physical and chemical methods for generating rat models of enteritis have been established; however, antibiotic induction has rarely been used for this purpose. The present study aimed to establish and evaluate a rat model of inflammatory bowel disease (IBD) using antibiotics. A total of 84 Sprague-Dawley (SD) rats were divided into the following groups, according to the dosage and method of administration of the antibiotics: A, control; B, low-dose clindamycin; C, medium-dose clindamycin; D, high-dose clindamycin; E, low-dose clindamycin, ampicillin and streptomycin; F, medium-dose clindamycin, ampicillin and streptomycin; and G, high-dose clindamycin, ampicillin and streptomycin. Antibiotic administration was stopped on day 7; the modeling period covered days 1-7, and the recovery period covered days 8-15. Half of the animals were dissected on day 11, with the remaining animals dissected on day 15. Food and water intake, body weight and fecal weight were recorded. Intestinal flora was analyzed via microbial culture and quantitative PCR. The content of TNF-α, IL1-β, IL-6 and C-reactive protein (CRP) was assessed in abdominal aorta blood. Colonic and rectal tissues were examined pathologically via hematoxylin-eosin staining to assess leukocyte infiltration and intestinal mucosal changes as indicators of inflammation. Rat weight, food intake, water intake and 2-h fecal weight were significantly different across the experimental groups (P = 0.040, P = 0.016, P<0.001 and P = 0.009, respectively). Microbial cultures revealed no significant differences between group A and B,C (P = 0.546,0.872) but significant differences betwenn group A and the other experimental groups (all P<0.001). Furthermore, significant differences in the levels of Bacteroides, Faecalibacterium prausnitzii and Dialister invisus on day 4 between groups A, C and F (P = 0.033, P = 0.025 and P = 0.034, respectively). Significant differences were detected in the levels of TNF-α, IL1-β, IL-6 and CRP between the groups (all P<0.001). The colonic and rectal pathological inflammation scores of the experimental groups were significantly different compared with group A (B vs. A, P = 0.002; others, all P<0.001). These findings indicated that an antibiotic-induced IBD model was successfully established in SD rats; this animal model may serve as a useful model for clinical IBD research.

Lactobacillus plantarum FNCC 0137 fermented red Moringa oleifera exhibits protective effects in mice challenged with Salmonella typhi via TLR3/TLR4 inhibition and down-regulation of proinflammatory cytokines

Background

Salmonella typhi is a foodborne pathogenic bacterium that threatens health. S. typhi infection exacerbated the antibiotic resistance problem that needs alternative strategies. Moringa oleifera possesses anti-inflammatory and antimicrobial effects. However, there is a lack of information about the pharmacological value of red M. oleifera. The fermentation of red M. oleifera leaves extract (RMOL) is expected to add to its nutritional value.

Objective

The present study aimed to evaluate non-fermented RMOL (NRMOL) and fermented RMOL (FRMOL) effects on S. typhi infection in mice.

Materials and methods

Female Balb/C mice were randomly divided into eight groups. The treatment groups were orally administered with NRMOL or FRMOL at doses 14, 42, and 84 mg/kg BW during the 28 days experimental period. Then S. typhi was introduced to mice through intraperitoneal injection except in the healthy groups. The NRMOL or FRMOL administration was continued for the next seven days. Cells that expressed CD11b⁺ TLR3⁺, CD11b⁺TLR4⁺, CD11b⁺IL-6⁺, CD11b⁺IL-17⁺, CD11b⁺TNF-a⁺, and CD4⁺CD25⁺CD62L⁺ were assessed by flow cytometry.

Results

Our result suggested that NRMOL and FRMOL extracts significantly reduced (p < 0.05) the expression of CD11b⁺TLR3⁺, CD11b⁺TLR4⁺, CD11b⁺IL-6⁺, CD11b⁺IL-17⁺, and CD11b⁺TNF-α⁺ subsets. In contrast, NRMOL and FRMOL extracts significantly increased (p < 0.05) the expression of CD4⁺CD25⁺CD62L⁺ subsets. NRMOL at dose 14 and 42 mg/kg BW was more effective compared to FRMOL in reducing the expression of CD11b⁺TLR3⁺, CD11b⁺TLR4⁺, and CD11b⁺TNF-α⁺ subsets.

Conclusion

Our findings demonstrated that NRMOL and FRMOL extracts could be promising agents for protection against S. typhi infection via modulation of TLR3/TLR4, regulatory T cells, and proinflammatory cytokines.

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.

Selenium deficiency causes apoptosis through endoplasmic reticulum stress in swine small intestine

Selenium (Se) plays a crucial role in intestinal health. However, the specific mechanism by which deficiency of Se causes intestinal damage remains unclear. This study was to explore whether Se deficiency can cause ER stress and induce apoptosis in swine small intestine. We established the Se deficiency swine model in vivo and the intestinal epithelial (IPEC-J2) cell Se deficiency model in vitro. The results of morphological observation showed that Se deficiency caused structural damage in intestinal villi and the decrease of goblet cell structure. The apoptotic characteristics such as nucleolar condensation, mitochondrial swelling, and apoptotic bodies were observed in the IPEC-J2 cells. The results of acridine orange/ethidium bromide and mitochondrial membrane potential fluorescence staining in vitro showed that there were more apoptotic cells in the Se-deficiency group than that in the control group. The protein and/or mRNA expression levels of Bax, Bcl-2, caspase 3, caspase 8, caspase 9, cytc, PERK, ATF6, IRE, XBP1, CHOP, GRP78, which are related to ER stress-apoptosis pathway, were significantly increased in the Se-deficient group which compared with the control group in vivo and in vitro were consistent. These results indicated that Se deficiency induced ER stress and increased the apoptosis in swine small intestine and IPEC-J2 cells and then caused the damage in swine small intestinal tissue. Besides, the results of gene expressions in our experiment proved that ER stress induced by Se deficiency promoted apoptosis. These results filled the blank in the mechanism of Se deficiency-induced intestinal injury in swine.

Molecular determinants of peaceful coexistence versus invasiveness of non-Typhoidal Salmonella: Implications in long-term side-effects

The genus Salmonella represents a wide range of strains including Typhoidal and Non-Typhoidal Salmonella (NTS) isolates that exhibit illnesses of varied pathophysiologies. The more frequent NTS ensues a self-limiting enterocolitis with rare occasions of bacteremia or systemic infections. These self-limiting Salmonella strains are capable of subverting and dampening the host immune system to achieve a more prolonged survival inside the host system thus leading to chronic manifestations. Notably, emergence of new invasive NTS isolates known as invasive Non-Typhoidal Salmonella (iNTS) have worsened the disease burden significantly in some parts of the world. NTS strains adapt to attain persister phenotype intracellularly and cause relapsing infections. These chronic infections, in susceptible hosts, are also capable of causing diseases like IBS, IBD, reactive arthritis, gallbladder cancer and colorectal cancer. The present understanding of molecular mechanism of how these chronic infections are manifested is quite limited. The current work is an effort to review the prevailing knowledge emanating from a large volume of research focusing on various forms of NTS infections including those that cause localized, systemic and persistent disease. The review will further dwell into the understanding of how this pathogen contributes to the associated long term sequelae.

Molecular Screening of Salmonella sp. from fecal sample of Sparrows (Passer domesticus) in Yogyakarta, Indonesia

Wild birds is one of the reservoir agent of some of various zoonotic diseases. The study was aim to see the potential of sparrow as the reservoir agent of Salmonella sp. using polymerase chain reaction (PCR) method. We detected the invA gene of Salmonella sp. from faecal sample of sparrows (Passer domesticus) in local area of Yogyakarta, Indonesia. A total of 30 faecal dropping samples were collected from sparrows. DNA was extracted from the faecal samples, then amplified by PCR for the target genes. The amplicons were electrophorized to see the visualization of DNA on the agarose gel. The result showed the prevalence of the positive result of Salmonella sp. was 3,3%. The study indicated that sparrows can spread zoonotic pathogens and this necessitates monitoring for the epidemiologic status of these pathogens among birds, also applying the appropriate intervention measures to prevent the transmission of zoonotic diseasesfrom birds to humans.

Menstrual blood-derived stromal cells modulate functional properties of mouse and human macrophages

Menstrual blood-derived stromal cells (MenSCs) are emerging as a strong candidate for cell-based therapies due to their immunomodulatory properties. However, their direct impact on innate immune populations remains elusive. Since macrophages play a key role in the onset and development of inflammation, understanding MenSCs implication in the functional properties of these cells is required to refine their clinical effects during the treatment of inflammatory disorders. In this study, we assessed the effects that MenSCs had on the recruitment of macrophages and other innate immune cells in two mouse models of acute inflammation, a thioglycollate (TGC)-elicited peritonitis model and a monobacterial sepsis model. We found that, in the TGC model, MenSCs injection reduced the percentage of macrophages recruited to the peritoneum and promoted the generation of peritoneal immune cell aggregates. In the sepsis model, MenSCs exacerbated infection by diminishing the recruitment of macrophages and neutrophils to the site of infection and inducing defective bacterial clearance. Additional in vitro studies confirmed that co-culture with MenSCs impaired macrophage bactericidal properties, affecting bacterial killing and the production of reactive oxygen intermediates. Our findings suggest that MenSCs modulate the macrophage population and that this modulation must be taken into consideration when it comes to future clinical applications.

Effect of dietary oridonin supplementation on growth performance, gut health, and immune response of broilers infected with Salmonella pullorum

Background

The effects of dietary supplementation of oridonin (ORI) on growth performance, cecal microbiota, epithelium development and antioxidant and immune parameters of broilers infected with S. pullorum were studied. A total of 300 1-d-old male chicks were selected and divided into 5 trial groups (6 replicates of 10 chickens): 1) nonchallenge control chicks (CON), 2) chicks treated with Salmonella Challenged Control (SCC), 3) chicks treated with S. pullorum challenge and 50 mg/kg ORI (O1), 4) chicks treated with S. pullorum challenge and 80 mg/kg ORI (O2), and 5) chicks treated with S. pullorum challenge and 100 mg/kg ORI (O3).

Results

The results showed that S. pullorum had no effect on the feed intake (FI), body weight gain (BWG) or feed conversion ratio (FCR) of broilers compared with the values measured for the CON group (P > 0.05). However, compared with the characteristics of CON, S. pullorum showed effects on the counts of Salmonella and Lactobacillus at 7 d and at 14 d (P < 0.05), on jejunal development at 7 d (P < 0.05), and on jejunal immunoglobulin A (IgA) concentration at 7 d (P < 0.05). The addition of 100 mg/kg ORI had the greatest effect on the counts of Lactobacillus and Salmonella in cecal content (P < 0.05), malonaldehyde (MDA) content in the jejunum (P < 0.05), villi height of the small intestine, and IgA concentrations in the jejunum (P < 0.05).

Conclusions

The results suggest that ORI can improve Salmonella-induced immune responses and protect intestinal health, not only through its immune inhibitory properties but also through its multi-protective effects on gut health.

Identification of a novel gene in ROD9 island of Salmonella Enteritidis involved in the alteration of virulence-associated genes expression

Salmonella enterica subsp. I serovar Enteritidis (S. Enteritidis), one of the causative agents for non-typhoidal gastrointestinal diseases in humans is an intracellular bacterium and mechanism for its invasion into host cells is critical to cause infection. The virulence of the pathogen is explained by the expression of genes located on its pathogenicity islands, mostly encoded under SPI-1 and SPI-2. However, S. Typhimurium SL1344, despite sharing ∼98% of its genome with S. Enteritidis P125109, lacks few regions of differences (ROD) that are hypothesized to impart virulence potential to S. Enteritidis. In this study, we created different mutants in the ROD9 island of S. Enteritidis, also referred as SPI-19 and identified a novel locus, SEN1005, encoding a hypothetical protein that is involved in its pathogenesis. ΔSEN1005 displayed significantly reduced entry into cultured epithelial cells as well as uptake by macrophages and failed to cause acute colitis in C57BL/6 mice at day 3 post-infection (p.i.). Additionally, the global transcriptome analysis revealed a highly repressed SPI-1 and other down-regulated genes responsible for flagellar assembly, chemotaxis and motility in the mutant which correlated with decreased invasion and abated inflammation as compared to the wild-type. Therefore, our findings revealed that ΔSEN1005 was attenuated in vitro as well as in vivo and we propose this hypothetical protein to play a role in altering the expression of genes involved in Salmonella virulence.

p40 phox -Deficient Mice Exhibit Impaired Bacterial Clearance and Enhanced Pro-inflammatory Responses during Salmonella enterica serovar Typhimurium Infection

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a major cause of acute gastroenteritis in humans. During infection, reactive oxygen species (ROS), generated from NADPH oxidase (a multisubunit enzyme complex), are required for pathogen killing upon phagocytosis and for regulating pro-inflammatory signaling in phagocytic cells. Mutations in subunits forming the NADPH complex may lead to enhanced susceptibility to infection and inflammatory disease. Compared to other NADPH oxidase subunits, the function of p40^phox is relatively understudied, particularly in the context of intestinal bacterial infection. In this study, we utilized genetically engineered mice to determine the role of p40^phox in the response to S. Typhimurium infection. We show that mice lacking p40^phox are more susceptible to oral infection with S. Typhimurium, as demonstrated by significantly enhanced bacterial dissemination to spleen and liver, and development of exacerbated bacterial colitis. Moreover, we demonstrate that the increased infection and disease severity are correlated with markedly increased F4/80⁺ macrophage and Ly6G⁺ neutrophil infiltration in the infected tissues, coincident with significantly elevated pro-inflammatory cytokines (IL-1β and TNF-α) and chemoattractant molecules in the infected tissues. Functional analysis of macrophages and neutrophils further shows that p40^phox deficiency impairs bacteria- or PMA-induced intracellular ROS production as well as intracellular killing of Salmonella. These observations indicate that the p40^phox subunit of NADPH oxidase plays an essential role in suppressing intracellular multiplication of Salmonella in macrophages and in the regulation of both systemic and mucosal inflammatory responses to bacterial infection.

RCAN1 deficiency protects against Salmonella intestinal infection by modulating JNK activation

OBJECTIVE

RCAN1 (regulator of calcineurin 1) has been shown to be involved in various physiological and pathological processes. However, the biological implications of RCAN1 during gastrointestinal tract infection remain unclear. In this study, we tried to determine the role of RCAN1 in acute Salmonella infectious colitis.

METHODS

Wild type and RCAN1-deficient mice or macrophages were used to characterize the impacts of RCAN1 on intestinal inflammation, inflammatory cytokines production, animal survival, and pathogen clearance following Salmonella challenge.

RESULTS

Histologic and quantitative assessments showed increased inflammation and elevated proinflammatory cytokines production in RCAN1-deficient mice. The aberrant inflammatory response was recapitulated in primary bone marrow-derived macrophages. In addition, we reveal a novel regulatory role for RCAN1 in the proinflammatory JNK signaling both in vitro and in vivo. Further analysis showed that the increased inflammation in RCAN1-deficient mice contributed to pathogen clearance and host survival.

CONCLUSIONS

The present study demonstrates that RCAN1 deficiency protects against Salmonella intestinal infection by enhancing proinflammatory JNK signaling.

Understanding the complexities of Salmonella-host crosstalk as revealed by in vivo model organisms

Foodborne infections caused by non-typhoidal Salmonellae, such as Salmonella enterica serovar Typhimurium (ST), pose a major challenge in the developed and developing world. With constant rise of drug-resistant strains, understanding the epidemiology, microbiology, pathogenesis and host-pathogen interactions biology is a mandatory requirement to enable health systems to be ready to combat these illnesses. Patient data from hospitals, at least from some parts of the world, have aided in epidemiological understanding of ST-mediated disease. Most of the other aspects connected to Salmonella-host crosstalk have come from model systems that offer convenience, genetic tractability and low maintenance costs that make them extremely valuable tools. Complex model systems such as the bovine model have helped in understanding key virulence factors needed for infection. Simple systems such as fruit flies and Caenorhabditis elegans have aided in identification of novel virulence factors, host pathways and mechanistic details of interactions. Some of the path-breaking concepts of the field have come from mice model of ST colitis, which allows genetic manipulations as well as high degree of similarity to human counterpart. Together, they are invaluable for correlating in vitro findings of ST-induced disease progression in vivo. The current review is a compilation of various advances of ST-host interactions at cellular and molecular levels that has come from investigations involving model organisms.

Salmonella Engages Host MicroRNAs To Modulate SUMOylation: a New Arsenal for Intracellular Survival

Posttranslational modifications (PTMs) can alter many fundamental properties of a protein. One or combinations of them have been known to regulate the dynamics of many cellular pathways and consequently regulate all vital processes. Understandably, pathogens have evolved sophisticated strategies to subvert these mechanisms to achieve instantaneous control over host functions. Here, we present the first report of modulation by intestinal pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) of host SUMOylation, a PTM pathway central to all fundamental cellular processes. Both in cell culture and in a mouse model, we observed that S. Typhimurium infection led to a dynamic SUMO-conjugated proteome alteration. The intracellular survival of S. Typhimurium was dependent on SUMO status as revealed by reduced infection and Salmonella-induced filaments (SIFs) in SUMO-upregulated cells. S. Typhimurium-dependent SUMO modulation was seen as a result of depletion of crucial SUMO pathway enzymes Ubc-9 and PIAS1, at both the protein and the transcript levels. Mechanistically, depletion of Ubc-9 relied on upregulation of small noncoding RNAs miR30c and miR30e during S. Typhimurium infection. This was necessary and sufficient for both down-modulation of Ubc-9 and a successful infection. Thus, we demonstrate a novel strategy of pathogen-mediated perturbation of host SUMOylation, an integral mechanism underlying S. Typhimurium infection and intracellular survival.

Coinfection with an intestinal helminth impairs host innate immunity against Salmonella enterica serovar Typhimurium and exacerbates intestinal inflammation in mice

Salmonella enterica serovar Typhimurium is a Gram-negative food-borne pathogen that is a major cause of acute gastroenteritis in humans. The ability of the host to control such bacterial pathogens may be influenced by host immune status and by concurrent infections. Helminth parasites are of particular interest in this context because of their ability to modulate host immune responses and because their geographic distribution coincides with those parts of the world where infectious gastroenteritis is most problematic. To test the hypothesis that helminth infection may negatively regulate host mucosal innate immunity against bacterial enteropathogens, a murine coinfection model was established by using the intestinal nematode Heligmosomoides polygyrus and S. Typhimurium. We found that mice coinfected with S. Typhimurium and H. polygyrus developed more severe intestinal inflammation than animals infected with S. Typhimurium alone. The enhanced susceptibility to Salmonella-induced intestinal injury in coinfected mice was found to be associated with diminished neutrophil recruitment to the site of bacterial infection that correlated with decreased expression of the chemoattractants CXCL2/macrophage inflammatory protein 2 (MIP-2) and CXCL1/keratinocyte-derived chemokine (KC), poor control of bacterial replication, and exacerbated intestinal inflammation. The mechanism of helminth-induced inhibition of MIP-2 and KC expression involved interleukin-10 (IL-10) and, to a lesser extent, IL-4 and IL-13. Ly6G antibody-mediated depletion of neutrophils reproduced the adverse effects of H. polygyrus on Salmonella infection. Our results suggest that impaired neutrophil recruitment is an important contributor to the enhanced severity of Salmonella enterocolitis associated with helminth coinfection.

Activation of focal adhesion kinase by Salmonella suppresses autophagy via an Akt/mTOR signaling pathway and promotes bacterial survival in macrophages

Autophagy has emerged as an important antimicrobial host defense mechanism that not only orchestrates the systemic immune response, but also functions in a cell autonomous manner to directly eliminate invading pathogens. Pathogenic bacteria such as Salmonella have evolved adaptations to protect themselves from autophagic elimination. Here we show that signaling through the non-receptor tyrosine kinase focal adhesion kinase (FAK) is actively manipulated by the Salmonella SPI-2 system in macrophages to promote intracellular survival. In wild-type macrophages, FAK is recruited to the surface of the Salmonella-containing vacuole (SCV), leading to amplified signaling through the Akt-mTOR axis and inhibition of the autophagic response. In FAK-deficient macrophages, Akt/mTOR signaling is attenuated and autophagic capture of intracellular bacteria is enhanced, resulting in reduced bacterial survival. We further demonstrate that enhanced autophagy in FAK^−/− macrophages requires the activity of Atg5 and ULK1 in a process that is distinct from LC3-assisted phagocytosis (LAP). In vivo, selective knockout of FAK in macrophages resulted in more rapid clearance of bacteria from tissues after oral infection with S. typhimurium. Clearance was correlated with reduced infiltration of inflammatory cell types into infected tissues and reduced tissue damage. Together, these data demonstrate that FAK is specifically targeted by S. typhimurium as a novel means of suppressing autophagy in macrophages, thereby enhancing their intracellular survival.

Salmonella enterica is a food- and water-borne pathogen that has evolved closely with vertebrate hosts. Two medically relevant serovars include S. typhimurium, which causes gastroenteritis and S. typhi, which is the causative agent of typhoid fever. Host cells can utilize a process called autophagy, normally involved in the elimination of defective proteins and organelles, to capture and degrade intracellular pathogens. Enteric Salmonella express numerous virulence factors that enable the bacterium to subvert host defense mechanisms. Here we report that Salmonella specifically activates the host molecule focal adhesion kinase (FAK) in macrophages, triggering a signaling cascade that suppresses the autophagic elimination of intracellular bacteria. A key regulator of autophagy in mammalian cells is the target of rapamycin, mTOR, which transmits inhibitory signals that downregulate the autophagic response. We show that Salmonella-induced FAK activation leads to the Akt-dependent activation of mTOR, thereby repressing autophagic signaling. Inhibition of autophagy results in increased bacterial survival, while in FAK-deficient cells, autophagy is enhanced and intracellular Salmonella are eliminated. We also show that in mice lacking macrophage-specific FAK, animals were less susceptible to oral Salmonella infection. Together, these data identify FAK as a novel regulator of autophagy in macrophages with broad implications for host survival.

Consumption of Lactobacillus casei fermented milk prevents Salmonella reactive arthritis by modulating IL-23/IL-17 expression

Reactive arthritis is the development of sterile joint inflammation as a sequel to a remote infection, often in the gut. We have previously shown that a low dose of S. enteritidis inoculated to streptomycin-pretreated mice generates a self-limiting enterocolitis suitable for studying reactive arthritis. Here we show that consumption of Lactobacillus casei prior to infection abolishes intestinal and joint inflammation triggered by Salmonella. BALB/c mice were sacrificed after infection; intestinal and joint samples were analyzed for histological changes and expression of cytokines. TNF-α was measured by ELISA and the expression of IL-1β, IL-6, IL-10, IL-17, IL-23 and TGF-β was assessed by qPCR. L. casei consumption prevented Salmonella-induced synovitis, the increment of TNF-α in knees and the increase of IL-17 expression in popliteal and inguinal lymph nodes. At intestinal level consumption of L. casei drastically diminished S. enteritidis invasiveness and shortened splenic persistence of the pathogen. Bacterial loads recovered at days 2 and 5 from Peyer's patches were 10-fold lower in mice fed with L. casei. In accordance, we found that the augment in gut permeability induced during enterocolitis was decreased in those animals. Consumption of L. casei prior to infection failed to increase anti- inflammatory molecules such as IL-10 and TGF-β in the intestine. On the other hand, consumption of L. casei abrogated the expression of TNF-α, IL-17, IL-23, IL-1β and IL-6 in cecum and mesenteric lymph nodes. These cytokines are needed for differentiation of immune cells involved in the development of reactive arthritis such as Th17 and γδ T cells. Trafficking of these inflammatory cells from the gut to the joints has been proposed as a mechanism of generation of reactive arthritis. Our results suggest that L. casei consumption prevents Salmonella-induced synovitis by altering the intestinal milieu necessary for differentiation of cells involved in the generation of joint inflammation.

Effect of the Salmonella pathogenicity island 2 type III secretion system on Salmonella survival in activated chicken macrophage-like HD11 cells

In order to better identify the role of the Salmonella pathogenicity island 2 (SPI-2) type III secretion system (T3SS) in chickens, we used the well-known gentamicin protection assay with activated HD11 cells. HD11 cells are a macrophage-like chicken cell line that can be stimulated with phorbol 12-myristate 13-acetate (PMA) to exhibit more macrophage-like morphology and greater production of reactive oxygen species (ROS). Activated HD11 cells were infected with a wild-type Salmonella enterica subspecies enterica serovar Typhimurium (S. Typhimurium) strain, a SPI-2 mutant S. Typhimurium strain, a wild-type Salmonella enterica subspecies enterica serovar Enteritidis (S. Enteritidis) strain, a SPI-2 mutant S. Enteritidis strain, or a non-pathogenic Escherichia coli (E. coli) strain. SPI-2 mutant strains were found to survive as well as their parent strain at all time points post-uptake (PU) by the HD11 cells, up to 24 h PU, while the E. coli strain was no longer recoverable by 3 h PU. We can conclude from these observations that the SPI-2 T3SS of S. Typhimurium and S. Enteritidis is not important for survival of Salmonella in the activated macrophage-like HD11 cell line, and that Salmonella must employ other mechanisms for survival in this environment, as E. coli is effectively eliminated.

Protective role of Akt2 in Salmonella enterica serovar typhimurium-induced gastroenterocolitis

The Salmonella effector protein SopB has previously been shown to induce activation of Akt and protect epithelial cells from apoptosis in vitro. To characterize the role of Akt2 in host defense against Salmonella enterica serovar Typhimurium infection, wild-type (WT) mice and mice lacking Akt2 (Akt2 knockout [KO] mice) were infected using a Salmonella acute gastroenteritis model. Infected Akt2 KO mice showed a more pronounced morbidity and mortality associated with higher bacterial loads in the intestines and elevated levels of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-α), gamma interferon (IFN-γ), and MCP-1, in the colons at 1 day postinfection compared to those shown in WT mice. Histopathological assessment and immunohistochemical analysis of cecal sections at 1 day postinfection revealed more severe inflammation and higher levels of neutrophil infiltration in the ceca of Akt2 KO mice. Flow cytometry analysis further confirmed an increase in the recruitment of Gr-1(+) CD11b(+) neutrophils and F4/80(+) CD11b(+) macrophages in the intestines of infected Akt2 KO mice. Additionally, enhanced levels of annexin V(+) and terminal transferase dUTP nick end labeling-positive (TUNEL(+)) apoptotic cells in the intestines of infected Akt2 KO mice were also observed, indicating that Akt2 plays an essential role in protection against apoptosis. Finally, the differences in bacterial loads and cecal inflammation in WT and Akt2 KO mice infected with WT Salmonella were abolished when these mice were infected with the sopB deletion mutant, indicating that SopB may play a role in protecting the mice from Salmonella infection through the activation of Akt2. These data demonstrate a definitive phenotypic abnormality in the innate response in mice lacking Akt2, underscoring the important protective role of Akt2 in Salmonella infection.

Lack of functional P-selectin ligand exacerbates Salmonella serovar typhimurium infection

The selectin family of adhesion molecules mediates the recruitment of immune cells to the site of inflammation, which is critical for host survival of infection. To characterize the role of selectins in host defense against Salmonella Typhimurium infection, wild-type (WT) mice and mice lacking P-selectin glycoprotein ligand-1 (PSGL-1), P-, E-, or L-selectin, or the glycosyltransferase C2GlcNAcT-I (core 2) were infected using a Salmonella acute gastroenteritis model. Mice were monitored for survival and assessed for intestinal inflammation at 1 and 4 days postinfection. Infected mice lacking core 2, PSGL-1, or P-selectin showed a more pronounced morbidity and a significantly higher mortality rate associated with higher bacterial load and proinflammatory cytokine production, including that of TNF-alpha, MCP-1, and IL-6, from the colons at 4 days postinfection as compared with WT control. Surprisingly, at 1 day postinfection, more severe inflammation and higher neutrophil infiltration were observed in the ceca of mice lacking core 2, PSGL-1, or P-selectin compared with WT control. Enhanced levels of alpha(4)beta(7)(+) and MAdCAM-1(+) cells were observed in the ceca of infected mice lacking core 2, PSGL-1, or P-selectin. Neutrophil recruitment, cecal inflammation, and mortality rates were dramatically reduced in infected P-selectin knockout mice receiving blocking mAb to alpha(4)beta(7) integrin, indicating that this alternative adhesion molecule may attempt to compensate for the loss of selectins in neutrophil recruitment. These results demonstrate a definitive phenotypic abnormality in mice lacking core 2, PSGL-1, or P-selectin, suggesting that the interaction of functional PSGL-1 with P-selectin is an important process in host defense against Salmonella infection.

Interleukin-23 orchestrates mucosal responses to Salmonella enterica serotype Typhimurium in the intestine

Salmonella enterica serotype Typhimurium causes an acute inflammatory reaction in the ceca of streptomycin-pretreated mice that involves T-cell-dependent induction of gamma interferon (IFN-gamma), interleukin-22 (IL-22), and IL-17 expression (genes Ifn-gamma, Il-22, and Il-17, respectively). We investigated here the role of IL-23 in initiating these inflammatory responses using the streptomycin-pretreated mouse model. Compared to wild-type mice, the expression of IL-17 was abrogated, IL-22 expression was markedly reduced, but IFN-gamma expression was normal in the ceca of IL-23p19-deficient mice during serotype Typhimurium infection. IL-23p19-deficient mice also exhibited a markedly reduced expression of regenerating islet-derived 3 gamma, keratinocyte-derived cytokine, and reduced neutrophil recruitment into the cecal mucosa during infection. Analysis of CD3(+) lymphocytes in the intestinal mucosa by flow cytometry revealed that alphabeta T cells were the predominant cell type expressing the IL-23 receptor in naive mice. However, a marked increase in the number of IL-23 receptor-expressing gammadelta T cells was observed in the lamina propria during serotype Typhimurium infection. Compared to wild-type mice, gammadelta T-cell-receptor-deficient mice exhibited blunted expression of IL-17 during serotype Typhimurium infection, while IFN-gamma expression was normal. These data suggested that gammadelta T cells are a significant source, but not the sole source, of IL-17 in the acutely inflamed cecal mucosa of mice. Collectively, our results point to IL-23 as an important player in initiating a T-cell-dependent amplification of inflammatory responses in the intestinal mucosa during serotype Typhimurium infection.

T cells help to amplify inflammatory responses induced by Salmonella enterica serotype Typhimurium in the intestinal mucosa

Salmonella enterica serotype Typhimurium causes an acute inflammatory reaction in the ceca of streptomycin-pretreated mice. We determined global changes in gene expression elicited by serotype Typhimurium in the cecal mucosa. The gene expression profile was dominated by T-cell-derived cytokines and genes whose expression is known to be induced by these cytokines. Markedly increased mRNA levels of genes encoding gamma interferon (IFN-gamma), interleukin-22 (IL-22), and IL-17 were detected by quantitative real-time PCR. Furthermore, the mRNA levels of genes whose expression is induced by IFN-gamma, IL-22, or IL-17, including genes encoding macrophage inflammatory protein 2 (MIP-2), inducible nitric oxide synthase (Nos2), lipocalin-2 (Lcn2), MIP-1alpha, MIP-1beta, and keratinocyte-derived cytokine (KC), were also markedly increased. To assess the importance of T cells in orchestrating this proinflammatory gene expression profile, we depleted T cells by using a monoclonal antibody prior to investigating cecal inflammation caused by serotype Typhimurium in streptomycin-pretreated mice. Depletion of CD3+ T cells resulted in a dramatic reduction in gross pathology, a significantly reduced recruitment of neutrophils, and a marked reduction in mRNA levels of Ifn-gamma, Il-22, Il-17, Nos2, Lcn2, and Kc. Our results suggest that T cells play an important role in amplifying inflammatory responses induced by serotype Typhimurium in the cecal mucosa.

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

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