Yersinia pseudotuberculosis disseminates directly from a replicating bacterial pool in the intestine

Dissemination of Yersinia pseudotuberculosis within mice after oral inoculation was analyzed. Y. pseudotuberculosis translocated to organs such as the liver and spleen shortly after oral inoculation, but was quickly cleared. In contrast, a second temporally distinct bacterial translocation event resulted in successful hepatosplenic replication of the bacteria. Replicating pools of bacteria could be established in these organs in mouse mutants that lacked Peyer's patches. These animals frequently had sterile mesenteric lymph nodes, a finding consistent with translocation taking place independently of regional lymph node colonization. In further contradiction to accepted models for dissemination of enteropathogens, clonal analysis revealed that bacteria causing disease in the spleen and liver of C57BL/6J mice were derived from populations located outside the intestinal lymph nodes. Replication of bacteria in the intestine before translocation appeared critical for dissemination, as transient selective suppression by streptomycin of bacterial growth in the intestine delayed dissemination of Y. pseudotuberculosis. These results collectively indicate that hepatosplenic colonization appears intimately connected with the ability of Y. pseudotuberculosis to successfully establish replication in the intestinal lumen and does not result from ordered spread leading from the intestine to regional lymph nodes before dissemination

CD8+ T Cells Restrict Yersinia pseudotuberculosis Infection: Bypass of Anti-Phagocytosis by Targeting Antigen-Presenting Cells

All Yersinia species target and bind to phagocytic cells, but uptake and destruction of bacteria are prevented by injection of anti-phagocytic Yop proteins into the host cell. Here we provide evidence that CD8+ T cells, which canonically eliminate intracellular pathogens, are important for restricting Yersinia, even though bacteria are primarily found in an extracellular locale during the course of disease. In a model of infection with attenuated Y. pseudotuberculosis, mice deficient for CD8+ T cells were more susceptible to infection than immunocompetent mice. Although exposure to attenuated Y. pseudotuberculosis generated TH1-type antibody responses and conferred protection against challenge with fully virulent bacteria, depletion of CD8+ T cells during challenge severely compromised protective immunity. Strikingly, mice lacking the T cell effector molecule perforin also succumbed to Y. pseudotuberculosis infection. Given that the function of perforin is to kill antigen-presenting cells, we reasoned that cell death marks bacteria-associated host cells for internalization by neighboring phagocytes, thus allowing ingestion and clearance of the attached bacteria. Supportive of this model, cytolytic T cell killing of Y. pseudotuberculosis–associated host cells results in engulfment by neighboring phagocytes of both bacteria and target cells, bypassing anti-phagocytosis. Our findings are consistent with a novel function for cell-mediated immune responses protecting against extracellular pathogens like Yersinia: perforin and CD8+ T cells are critical for hosts to overcome the anti-phagocytic action of Yops.Molecular and Cellular Biolog

Modelling the effects of glucagon during glucose tolerance testing.

From Europe PMC via Jisc Publications RouterHistory: ppub 2019-12-01, epub 2019-12-12Publication status: PublishedBACKGROUND:Glucose tolerance testing is a tool used to estimate glucose effectiveness and insulin sensitivity in diabetic patients. The importance of such tests has prompted the development and utilisation of mathematical models that describe glucose kinetics as a function of insulin activity. The hormone glucagon, also plays a fundamental role in systemic plasma glucose regulation and is secreted reciprocally to insulin, stimulating catabolic glucose utilisation. However, regulation of glucagon secretion by α-cells is impaired in type-1 and type-2 diabetes through pancreatic islet dysfunction. Despite this, inclusion of glucagon activity when modelling the glucose kinetics during glucose tolerance testing is often overlooked. This study presents two mathematical models of a glucose tolerance test that incorporate glucose-insulin-glucagon dynamics. The first model describes a non-linear relationship between glucagon and glucose, whereas the second model assumes a linear relationship. RESULTS:Both models are validated against insulin-modified and glucose infusion intravenous glucose tolerance test (IVGTT) data, as well as insulin infusion data, and are capable of estimating patient glucose effectiveness (sG) and insulin sensitivity (sI). Inclusion of glucagon dynamics proves to provide a more detailed representation of the metabolic portrait, enabling estimation of two new diagnostic parameters: glucagon effectiveness (sE) and glucagon sensitivity (δ). CONCLUSIONS:The models are used to investigate how different degrees of pax'tient glucagon sensitivity and effectiveness affect the concentration of blood glucose and plasma glucagon during IVGTT and insulin infusion tests, providing a platform from which the role of glucagon dynamics during a glucose tolerance test may be investigated and predicted

YopE specific CD8+ T cells provide protection against systemic and mucosal Yersinia pseudotuberculosis infection.

Prior studies indicated that CD8+ T cells responding to a surrogate single antigen expressed by Y. pseudotuberculosis, ovalbumin, were insufficient to protect against yersiniosis. Herein we tested the hypothesis that CD8+ T cells reactive to the natural Yersinia antigen YopE would be more effective at providing mucosal protection. We first confirmed that immunization with the attenuated ksgA- strain of Y. pseudotuberculosis generated YopE-specific CD8+ T cells. These T cells were protective against challenge with virulent Listeria monocytogenes expressing secreted YopE. Mice immunized with an attenuated L. monocytogenes YopE+ strain generated large numbers of functional YopE-specific CD8+ T cells, and initially controlled a systemic challenge with virulent Y. pseudotuberculosis, yet eventually succumbed to yersiniosis. Mice vaccinated with a YopE peptide and cholera toxin vaccine generated robust T cell responses, providing protection to 60% of the mice challenged mucosally but failed to show complete protection against systemic infection with virulent Y. pseudotuberculosis. These studies demonstrate that vaccination with recombinant YopE vaccines can generate YopE-specific CD8+ T cells, that can provide significant mucosal protection but these cells are insufficient to provide sterilizing immunity against systemic Y. pseudotuberculosis infection. Our studies have implications for Yersinia vaccine development studies

YopE specific CD8⁺ T cells provide protection against systemic and mucosal <i>Yersinia pseudotuberculosis</i> infection - Table 1

YopE specific CD8⁺ T cells provide protection against systemic and mucosal <i>Yersinia pseudotuberculosis</i> infection - Table

CD4(+) T Cells and Toll-Like Receptors Recognize Salmonella Antigens Expressed in Bacterial Surface Organelles

A better understanding of immunity to infection is revealed from the characteristics of microbial ligands recognized by host immune responses. Murine infection with the intracellular bacterium Salmonella generates CD4(+) T cells that specifically recognize Salmonella proteins expressed in bacterial surface organelles such as flagella and membrane vesicles. These natural Salmonella antigens are also ligands for Toll-like receptors (TLRs) or avidly associated with TLR ligands such as lipopolysaccharide (LPS). PhoP/PhoQ, a regulon controlling Salmonella virulence and remodeling of LPS to resist innate immunity, coordinately represses production of surface-exposed antigens recognized by CD4(+) T cells and TLRs. These data suggest that genetically coordinated surface modifications may provide a growth advantage for Salmonella in host tissues by limiting both innate and adaptive immune recognition

Generation of YopE_69-77-specific CD8⁺ T cells in C57BL/6 mice exposed to attenuated <i>Y</i>. <i>pseudotuberculosis</i> strains.

<p>C57BL/6 mice were intravenously inoculated with <i>ksgA</i>^<i>-</i> (10² CFU) or Δ<i>yopK</i> (10³ CFU) bacteria, then sacrificed on day 8 and splenic cells analyzed by flow cytometry. (<b>A-C</b>) YopE_69-77-specific CD8⁺ T cells were detected by Kb/YopE_69-77 tetramer staining, as shown in representative FACS plots after gating for CD3⁺, CD4^- and CD8⁺ cells. The percent of Kb/YopE_69-77 tetramer⁺ cells in the CD8⁺ T cell population (<b>E</b>) is shown, with bars indicating mean values + S.E.M. The data are representative of two independent experiments (n = 4–5 mice). For multiple group comparisons Dunn’s multiple-comparison post-test was used: *, P ≤ 0.05, **, P ≤ 0.01, ***, P ≤ 0.001, ****, P ≤ 0.0001.</p

<i>ksgA</i>^<i>-</i> immunization protects against recombinant <i>L</i>. <i>monocytogenes</i> expressing YopE.

<p>60 days after intravenous immunization with 200 CFU <i>ksgA</i>^<i>-</i> <i>Y</i>. <i>pseudotuberculosis</i> (<i>Yptb</i>), 200 CFU <i>ksgA</i>^<i>-</i> <i>yopE</i>^<i>-</i> <i>Yptb</i>, or 5.0 x 10⁷ CFU Δ<i>actA</i> Δ<i>plcB L</i>. <i>monocytogenes</i> (<i>Lm</i>) or nothing (naïve), C57BL/6 mice were intravenously challenged with either 5.0 x 10⁵ CFU Lm 1043s <b>(A)</b> 5.0 x 10⁵ CFU (<b>C, E</b>) or 2.0 x 10⁶ CFU (<b>B, D, F</b>) of virulent <i>L</i>. <i>monocytogenes</i> expressing ActAYopE_1-219OVA and followed for mortality (% survival <b>(A, B, E, F</b>) or morbidity (% weight change, <b>C, D</b>) over a four to six week time course. The data are representative of two independent experiments (n = 4–6 mice/experiment <b>C, D, E</b>, and <b>F</b>) or a single experiment (n = 8 mice/group <b>A, B</b>). For multiple group comparisons Dunn’s multiple-comparison post-test was used for weight change differences at selected time points: *, P ≤ 0.05, **, P ≤ 0.01, ***, P ≤ 0.001, ****, P ≤ 0.0001. Log rank Mantel-Cox test was used for survival curves.</p