The lipopolysaccharide outer core of Yersinia enterocolitica serotype O:3 is required for virulence and plays a role in outer membrane integrity

Lipopolysaccharide (LPS) of Yersinia enterocolitica O:3 has an inner core linked to both the O-antigen and to an outer core hexasaccharide that forms a branch. The biological role of the outer core was studied using polar and non-polar mutants of the outer core biosynthetic operon. Analysis of O-antigen- and outer core-deficient strains suggested a critical role for the outer core in outer membrane properties relevant in resistance to antimicrobial peptides and permeability to hydrophobic agents, and indirectly relevant in resistance to killing by normal serum. Wild-type bacteria but not outer core mutants killed intragastrically infected mice, and the intravenous lethal dose was approximately 10(4)-fold higher for outer core mutants. After intragastric infection, outer core mutants colonized Peyer's patches and invaded mesenteric lymph nodes, spleen and liver, and induced protective immunity against wild-type bacteria. In mice co-infected intragastrically with an outer core mutant-wild type mixture, both strains colonized Peyer's patches similarly during the first 2 days, but the mutant was much less efficient in colonizing deeper organs and was cleared faster from Peyer's patches. The results demonstrate that outer core is required for Y. enterocolitica O:3 full virulence, and strongly suggest that it provides resistance against defence mechanisms (most probably those involving bactericidal peptides).     

Intestinal uptake of fluorescent microspheres in young and aged mice

Rhodamine B-labeled synthetic latex particles (microspheres), 1.8 micron in diameter, were administered by gavage 5 days per week to young (24 days) and aged (18 months) mice. After 25 days (19 gavages), the particles were assayed in solubilized tissues by depositing them on filters and counting under fluorescence microscopy. Aged mice exhibited significantly more fluorescent particle accumulation in Peyer's patches but significantly less in lungs than young mice. Mesenteric lymph nodes and Peyer's patch-free intestinal segments contained measurable latex, but differences between young and aged animals were not significant. Liver contained only trace amounts of latex, and spleen and kidney were latex free in both young and aged animals. Nonquantitative observations on KOH-glycerol-cleared whole Peyer's patches and slices of liver, lung, and mesenteric lymph node were similar.     

Changes in antigen distribution and lymphocyte migration pattern after peroral immunization

The migration pattern of lymphoid cells in long-term p.o. immunized and control mice using the transfer of 51Cr-labelled cells from spleen, Peyer's patches and mesenteric or peripheral lymph nodes was studied. There are no differences between the homing activity of spleen of PLN cells to different organs of recipient animals. Peyer's patch cells from SRBC-fed mice home significantly more to the gut of antigen-fed mice; also the MLN cells from these mice exhibit a higher localization in the gut of SRBC-fed mice. There were no differences between the localization of antigen (SRBC) in different organs of SRBC-fed and control mice. The clearance of this antigen was higher in SRBC-fed animals.     

In vitro and in vivo expression studies of yopE from Yersinia enterocolitica using the gfp reporter gene

The Yersinia outer protein YopE belongs to the translocated effector proteins of pathogenic yersiniae. We constructed various truncated yopE genes fused to gfp (encoding the green fluorescent protein) to study yopE gene expression and YopE-GFP translocation of Y. enterocolitica in cell culture and mouse infection models. The hybrid gene fusions were co-expressed in Y. enterocolitica (i) on a low-copy plasmid in the presence of the virulence plasmid pYV08 (in trans configuration) and (ii) after co-integration by homologous recombination of a yopE-gfp-carrying suicide plasmid into pYV08 (co-integrate configuration). After 30min of infection of HEp-2 cell monolayers, extracellularly located yersiniae began to emit green fluorescence after excitation. In contrast, internalized bacteria were weakly fluorescent. Translocation of YopE-GFP into HEp-2 cells by attached yersiniae was visualized by optical sectioning of fluorescent HEp-2 cells using confocal laser scanning microscopy and was confirmed by immunoprecipitation of cytosolic YopE-GFP from selectively solubilized HEp-2 cells. The co-translocation of other Yops was not significantly impaired by YopE-GFP as shown by YopH/YopE-mediated suppression of the oxidative burst of infected neutrophils. The time course of yopE-gfp expression (in trans as well as in the co-integrate configuration) in the HEp-2 cell infection model as well as after in vitro induction was studied using a highly sensitive CCD camera and a flow cytometer. Similar results were obtained with a YopE-LUC (firefly luciferase) protein fusion as reporter. After intraperitoneal, intravenous and orogastrical infection of Balb/c mice with the recombinant yersiniae strains, green fluorescing bacteria could be visualized microscopically in the peritoneum, the spleen, the liver and in the Peyer's patches. However, only weakly fluorescent yersiniae were observed in the intestinal lumen. These results were quantified by flow cytometric measurements. The application of gfp as a reporter gene turned out to be promising for the study of protein translocation by protein type III secretion systems and differential virulence gene expression in vivo.     

Effects of antigen-feeding on intestinal and systemic immune responses. I. priming of precursor cytotoxic T cells by antigen feeding.

The ability of antigens administered by the intestinal route to alter the cytotoxic T lymphocyte (CTL) population in intestinal and extraintestinal sites was examined by feeding mice tumor cells bearing H-2 or non-H-2 gene-coded cell surface alloantigenic differences. Peyer's patches from mice fed tumor cells differing at H-2 demonstrated a 12-fold increase in specific CTL activity over controls after stimulation of culture but the precursor CTL population in Peyer's patches was not expanded by feeding mice cells bearing minor H gene coded alloantigenic differences. In contrast, the precursor CTL pool in spleen was increased both in mice fed cells bearing alloantigenic differences coded for by H-2 and non-H-2 gene loci. The precursor CTL population in mesenteric lymph nodes (MN) was not expanded significantly by tumor cell feeding. Feeding was nearly as effective as i.p. priming at expanding the Peyer's patch precursor CTL population when tumor cells bearing H-2 differences were used, whereas i.p. priming was more effective than feeding in expanding the precursor CTL population in spleen.     

Early response to rotavirus infection involves massive B cell activation

Rotavirus is an acute enteric pathogen which induces severe diarrhea in infants and children. To determine the immune response to rotavirus in vivo, we used a mouse model of rotavirus infection. We observed dramatic increases in the sizes of both Peyer's patches and mesenteric lymph nodes, but not spleen, between 1 and 6 days after infection with a homologous strain of murine rotavirus, EC wild type. Histological analysis showed large increases in the numbers of lymphocytes in these same tissues in rotavirus-infected mice. Flow cytometric analysis confirmed the increase in numbers of lymphocytes and revealed a large increase in the percentage of activated B, but not T, lymphocytes in both Peyer's patches and mesenteric lymph nodes of rotavirus-infected mice compared with control mice. Fragment cultures from these tissues established at 3-4 days postinfection contain rotavirus-specific IgM but not IgA Ab. A similar degree of lymphoid hyperplasia and percentage of activated B cells were observed in rotavirus-infected TCR knockout mice. Taken together, our findings show that rotavirus infection, in the context of a normal immune response, induces a large increase in the percentages of activated B cells in the absence of any detectable increase in the percentage of activated T cells, implicating a T cell-independent B cell response as the primary mechanism for initial rotavirus clearance.     

Differential effects of vasoactive intestinal peptide, substance P, and somatostatin on immunoglobulin synthesis and proliferations by lymphocytes from Peyer's patches, mesenteric lymph nodes, and spleen

We examined the effect of vasoactive intestinal peptide, substance P, and somatostatin on concanavalin A (1 microgram/ml)-induced lymphocyte proliferation and immunoglobulin (IgA, IgM, and IgG) synthesis by cells from spleens, Peyer's patches, and mesenteric lymph nodes. These neuropeptides (10(-7) to 10(-12) M) modulated immune responses in a dose-dependent manner. For a comparative study, neuropeptides were used at 10(-8) M concentration. Both vasoactive intestinal peptide and somatostatin significantly decreased DNA synthesis (30 to 50%), whereas substance P increased synthesis (40%) in lymphocytes from all organs tested. IgA synthesis was significantly altered by all of the neuropeptides tested, whereas IgM synthesis was less affected and IgG synthesis was virtually unchanged. Somatostatin inhibited IgA (20 to 50%) and IgM (10 to 30%) synthesis in lymphocytes from all three organs. Substance P increased IgA synthesis in mesenteric lymph nodes (50%), spleens (70%), and Peyer's patches (300%). It also increased IgM synthesis in Peyer's patches (20%) and spleens (30%), but was without effect on IgM synthesis in mesenteric lymph nodes. Vasoactive intestinal peptide increased the IgA response in mesenteric lymph nodes (20%) and spleens (30%), but inhibited IgA synthesis in lymphocytes from Peyer's patches (60%). Interestingly, in Peyer's patches, IgM synthesis was increased by vasoactive intestinal peptide (80%), whereas it was unchanged in mesenteric lymph nodes and spleen. Thus, not only did these neuropeptides have different effects on the production of different immunoglobulin isotypes, but their effect was also organ-specific. Because neuropeptides which are abundant in the intestine can modulate IgA and other immunoglobulin synthesis in vitro, they may play a significant regulatory role in mucosal immune responses in vivo.     

Alternate mucosal immune system: organized Peyer's patches are not required for IgA responses in the gastrointestinal tract

The progeny of mice treated with lymphotoxin (LT)-beta receptor (LTbetaR) and Ig (LTbetaR-Ig) lack Peyer's patches but not mesenteric lymph nodes (MLN). In this study, we used this approach to determine the importance of Peyer's patches for induction of mucosal IgA Ab responses in the murine gastrointestinal tract. Immunohistochemical analysis revealed that LTbetaR-Ig-treated, Peyer's patch null (PP null) mice possessed significant numbers of IgA-positive (IgA+) plasma cells in the intestinal lamina propria. Further, oral immunization of PP null mice with OVA plus cholera toxin as mucosal adjuvant resulted in Ag-specific mucosal IgA and serum IgG Ab responses. OVA-specific CD4+ T cells of the Th2 type were induced in MLN and spleen of PP null mice. In contrast, when TNF and LT-alpha double knockout (TNF/LT-alpha-/-) mice, which lack both Peyer's patches and MLN, were orally immunized with OVA plus cholera toxin, neither mucosal IgA nor serum IgG anti-OVA Abs were induced. On the other hand, LTbetaR-Ig- and TNF receptor 55-Ig-treated normal adult mice elicited OVA- and cholera toxin B subunit-specific mucosal IgA responses, indicating that both LT-alphabeta and TNF/LT-alpha pathways do not contribute for class switching for IgA Ab responses. These results show that the MLN plays a more important role than had been appreciated until now for the induction of both mucosal and systemic Ab responses after oral immunization. Further, organized Peyer's patches are not a strict requirement for induction of mucosal IgA Ab responses in the gastrointestinal tract.     

Qualitative and quantitative characteristics of rotavirus-specific CD8 T cells vary depending on the route of infection

CD8 T-cell response provides an important defense against rotavirus, which infects a variety of systemic locations in addition to the gut. Here we investigated the distribution, phenotype, and function of rotavirus-specific CD8 T cells in multiple organs after rotavirus infection initiated via the intranasal, oral, or intramuscular route. The highest level of virus-specific CD8 T cells was observed in the Peyer's patches of orally infected mice and in the lungs of intranasally infected animals. Very low levels of virus-specific CD8 T cells were detected in peripheral blood or spleen irrespective of the route of infection. Rotavirus-specific CD8 T cells from Peyer's patches of orally infected mice expressed high levels of CCR9, while CXCR6 and LFA-1 expression was associated with virus-specific CD8 T cells in lungs of intranasally infected mice. Oral infection induced the highest proportion of gamma interferon(-) CD107a/b(+) CD8 T cells in Peyer's patches. When equal numbers of rotavirus-specific CD8 T cells were transferred into Rag-1 knockout mice chronically infected with rotavirus, the donor cells derived from Peyer's patches of orally infected mice were more efficient than those derived from lungs of intranasally infected animals in clearing intestinal infection. These results suggest that different routes of infection induce virus-specific CD8 T cells with distinct homing phenotypes and effector functions as well as variable abilities to clear infection.     

Functional characteristics of Peyer's patch lymphoid cells. IV. Effect of antigen feeding on the frequency of antigen-specific B cells.

The frequency of B cells in Peyer's patches from normal BDF(1) and sheep red blood cell (SRBC)-fed BDF(1) mice that could respond to antigenic determinants on SRBC and trinitrophenyl (TNP) was determined using an in vitro system of limiting dilution analysis. In normal mice, one B cell in 1.9 x 10(4) Peyer's patch cells could be induced to an anti-SRBC response and one B cell in 3.6 x 10(4) Peyer's patch cells could be induced to an anti-TNP response. The frequency of B cells capable of responding to SRBC in normal mice was similar in Peyer's patches and spleen. However, after feeding mice SRBC for 3 weeks, there was a 6-fold reduction in the frequency of B cells in Peyer's patches capable of responding to SRBC but no change in the frequency of B cells capable of responding to TNP. The average clone size of Peyer's patch B cells responding to SRBC was similar in normal and SRBC-fed mice. Although antigen-feeding does not stimulate Peyer's patch B cells in situ to humoral antibody synthesis, antigen-feeding can markedly alter the reactivity of the antigen-sensitive cell population in Peyer's patches. We previously demonstrated that T cells in Peyer's patches could be specifically carrier primed for helper function by SRBC feeding. We have now demonstrated that antigen-feeding reduced significantly the frequency of B cells in Peyer's patches capable of responding to the fed antigen. Peyer's patches appear to serve an important function as a sampling site for intestinal antigens.     

Pattern of macrophage activation in yersinia-resistant and yersinia-susceptible strains of mice

Th1 cells, in cooperation with activated macrophages, are required to overcome Yersinia enterocolitica infection in mice. The pathway macrophages utilize to metabolize arginine can alter the outcome of inflammation in different ways. The objective of this study was to verify the pattern of macrophages activation in Y. enterocolitica infection of BALB/c (Yersinia-susceptible) and C57BL/6 (Yersinia-resistant) mice. Both strains of mice were infected with Y. enterocolitica O:8 WA 2707. Peritoneal macrophages and spleen cells were obtained on the 1st, 3rd and 5th day post-infection. The iNOS and the arginase activities were assayed in supernatants of macrophage cultures, by measuring their NO/citrulline and ornithine products, respectively. TGFbeta-1 production was also assayed. The Th1 and Th2 responses were evaluated in supernatants of lymphocyte cultures, by IFN-gamma and IL-4 production. Our results showed that in the early phase of Y. enterocolitica infection (1st and 3rd day), the macrophages from C57BL/6 mice produced higher levels of NO/citrulline and lower levels of ornithine than macrophages from BALB/c mice. The infection with Y. enterocolitica leads to an increase in the TGF-beta1 and IL-4 production by BALB/c mice and to an increase in the IFN-gamma levels produced by C57BL/6 mice. These results suggest that Y. enterocolitica infection leads to the modulation of M1 macrophages in C57Bl/6 mice, and M2 macrophages in BALB/c mice. The predominant macrophage population (M1 or M2) at the 1st and 3rd day of infection thus seems to be important in determining Y. enterocolitica susceptibility or resistance.     

Mechanisms of acquired resistance to plague in mice infected byYersinia enterocolitica O3

Yersinia enterocolitica, serogroup O3, injected either intravenously or intragastrically to mice, induced acquired resistance toYersinia pestis. The digestive infection byY. enterocolitica O3 was mostly located into the Peyer’s patches and the ileum wall; the blood, the mesenteric lymph node, and the spleen were not invaded. Serum fromY. enterocolitica O3 convalescing mice failed to protect passively againstY. pestis. In contrast, lymphoid cells from the stimulated Peyer’s patches permitted transfer of efficient bactericidal activity againstY. pestis.     

Liver abscess due to Yersinia bacteremia in a well-controlled type I diabetic patient

Yersiniae enterocolitica, a gram negative rod-like organism, causes terminal ileitis and mesenteric adenitis in adolescents and adults. Some forms present with liver and spleen abscesses and have worse prognosis. We report a type 1 diabetic patient with a liver abscess mimicking metastatic liver disease who was successfully treated with percutaneous drainage and antibiotic administration; culture from blood was positive for Yersinia enterocolitica, but drainage material from the liver abscess did not yield a positive result for Yersinia enterocolitica. Although the prognosis is not good in such cases, with high mortality rates, our patient recovered from the disease with appropriate treatment.     

Studies on the pathogenicity of Yersinia enterocolitica. III. Comparative studies between Y. enterocolitica and Y. pseudotuberculosis

Comparative studies on pathogenicity between Yersinia enterocolitica and Yersinia pseudotuberculosis were performed using experimental infection systems in vivo and in vitro. All of thestra ins of both species successfully produced experimental enterocolitis in rabbits although the severity varied with the strains challenged. The changes were characterized by granulomatous lesions with necrobiotic centers in reticuloendothelial tissues of the intestine, mesenteric lymph nodes, liver and spleen. These strains uniformly had the ability to penetrate HeLa cells and to survive or multiply within cultured rabbit peritoneal macrophages. In addition, in infections with strain TP-2 or PST-III of Y. pseudotuberculosis, catarrhal inflammation all over the small intestine and/or focal necrosis and parenchymatous degeneration in the liver were observed, along with the granulomatous lesions. These strains, at the same time, exhibited cytotoxic effects on the cultured cells. The pathogenic factors of Y. enterocolitica are discussed in comparison with those of Y. pseudotuberculosis.     

A recombinant Salmonella typhimurium vaccine strain is taken up and survives within murine Peyer's patch dendritic cells

The attenuated Salmonella typhimurium PhoP^c strain is avirulent but immunogenic via the oral route in mice and is attenuated in survival in macrophage cell lines. In this study, the fate of PhoP^c bacteria expressing green fluorescent protein was investigated in murine Peyer's patches. The survival of PhoP^c was monitored after orogastric inoculation of BALB/c mice. Bacteria persisted for several weeks in the Peyer's patches and were also recovered from the mesenteric lymph nodes and spleen. Confocal microscopy analysis identified dendritic cells as the Peyer's patch cell type that internalized PhoP^c expressing green fluorescent protein at early time points. In addition, live PhoP^c were found in Peyer's patch dendritic cells and not in B cells 3 days after orogastric inoculation. Taken together, these results provide strong evidence that PhoP^c is internalized and survives within Peyer's patch dendritic cells. As these cells are potent antigen-presenting cells, these data could explain the immunogenicity of S. typhimurium vaccine strains in vivo .     

Role of immunoglobulin A in protection against reovirus entry into Murine Peyer's patches

Reovirus type 1 Lang (T1L) infects the mouse intestinal mucosa by adhering specifically to epithelial M cells and exploiting M-cell transport to enter the Peyer's patches. Oral inoculation of adult mice has been shown to elicit cellular and humoral immune responses that clear the infection within 10 days. This study was designed to determine whether adult mice that have cleared a primary infection are protected against viral entry upon oral rechallenge and, if so, whether antireovirus secretory immunoglobulin A (S-IgA) is a necessary component of protection. Adult BALB/c mice that were orally inoculated on day 0 with reovirus T1L produced antiviral S-IgA in feces and IgG in serum directed primarily against the reovirus sigma1 attachment protein. Eight hours after oral reovirus challenge on day 21, the Peyer's patches of previously exposed mice contained no detectable virus whereas Peyer's patches of naive controls contained up to 2,300 PFU of reovirus/mg of tissue. Orally inoculated IgA knockout (IgA(-/-)) mice cleared the initial infection as effectively as wild-type mice and produced higher levels of reovirus-specific serum IgG and secretory IgM than C57BL/6 wild-type mice. When IgA(-/-) mice were rechallenged on day 21, however, their Peyer's patches became infected. These results indicate that intestinal S-IgA is an essential component of immune protection against reovirus entry into Peyer's patch mucosa.     

Yersiniosis in a breeding unit of Macaca fascicularis (cynomolgus monkeys)

2 outbreaks of acute fatal enteric disease involving 20 animals in a breeding unit of approximately 200 cynomolgus monkeys were diagnosed as yersiniosis; Yersinia pseudotuberculosis was isolated from 50% of the clinically affected animals. Post-mortem findings included enlarged mesenteric lymph nodes with some enterocolitis and necrotic foci in liver and spleen. Approximately 7% of clinically healthy monkeys were found to be excreting Y. pseudotuberculosis and a further 5% Y. enterocolitica. Rectal swabs, though less convenient, were better than faecal samples for the detection of Yersinia spp. in 'healthy' monkeys. Efficiency of the cold saline technique and direct plating for isolating Yersinia spp. were compared. It is thought likely that the infection was introduced into the unit by asymptomatic infected monkeys.     

Immunomodulatory effect of (--)-matairesinol in vivo and ex vivo

Matairesinol is one of the lignan compounds found in a variety of plant foodstuffs. We investigated the immunomodulatory effects of (-)-matairesinol in vivo and ex vivo by using mice. Although we found no significant differences in the IgG, IgA and IgM levels in the serum, the IgE level was strongly suppressed by the uptake of (-)-matairesinol in both intact and ovalbumin-immunized mice. The immunoglobulin produced by lymphocytes from the spleen was not activated by the intake of (-)-matairesinol. However, lymphocytes in such gut-associated lymphatic tissues as Peyer's patches and mesenteric lymph nodes were activated by the administration of (-)-matairesinol.     

MAdCAM-1 expressing sacral lymph node in the lymphotoxin beta-deficient mouse provides a site for immune generation following vaginal herpes simplex virus-2 infection

The members of the lymphotoxin (LT) family of molecules play a critical role in lymphoid organogenesis. Whereas LT alpha-deficient mice lack all lymph nodes and Peyer's patches, mice deficient in LT beta retain mesenteric lymph nodes and cervical lymph nodes, suggesting that an LT beta-independent pathway exists for the generation of mucosal lymph nodes. In this study, we describe the presence of a lymph node in LT beta-deficient mice responsible for draining the genital mucosa. In the majority of LT beta-deficient mice, a lymph node was found near the iliac artery, slightly misplaced from the site of the sacral lymph node in wild-type mice. The sacral lymph node of the LT beta-deficient mice, as well as that of the wild-type mice, expressed the mucosal addressin cell adhesion molecule-1 similar to the mesenteric lymph node. Following intravaginal infection with HSV type 2, activated dendritic cells capable of stimulating a Th1 response were found in this sacral lymph node. Furthermore, normal HSV-2-specific IgG responses were generated in the LT beta-deficient mice following intravaginal HSV-2 infection even in the absence of the spleen. Therefore, an LT beta-independent pathway exists for the development of a lymph node associated with the genital mucosa, and such a lymph node serves to generate potent immune responses against viral challenge.