The Salmonella SPI2 Effector SseI Mediates Long-Term Systemic Infection by Modulating Host Cell Migration

Host-adapted strains of Salmonella enterica cause systemic infections and have the ability to persist systemically for long periods of time despite the presence of a robust immune response. Chronically infected hosts are asymptomatic and transmit disease to naïve hosts via fecal shedding of bacteria, thereby serving as a critical reservoir for disease. We show that the bacterial effector protein SseI (also called SrfH), which is translocated into host cells by the Salmonella Pathogenicity Island 2 (SPI2) type III secretion system (T3SS), is required for Salmonella typhimurium to maintain a long-term chronic systemic infection in mice. SseI inhibits normal cell migration of primary macrophages and dendritic cells (DC) in vitro, and such inhibition requires the host factor IQ motif containing GTPase activating protein 1 (IQGAP1), an important regulator of cell migration. SseI binds directly to IQGAP1 and co-localizes with this factor at the cell periphery. The C-terminal domain of SseI is similar to PMT/ToxA, a bacterial toxin that contains a cysteine residue (C1165) that is critical for activity. Mutation of the corresponding residue in SseI (C178A) eliminates SseI function in vitro and in vivo, but not binding to IQGAP1. In addition, infection with wild-type (WT) S. typhimurium suppressed DC migration to the spleen in vivo in an SseI-dependent manner. Correspondingly, examination of spleens from mice infected with WT S. typhimurium revealed fewer DC and CD4+ T lymphocytes compared to mice infected with ΔsseI S. typhimurium. Taken together, our results demonstrate that SseI inhibits normal host cell migration, which ultimately counteracts the ability of the host to clear systemic bacteria

Cervicovaginal Microbiota: Simple Is Better

Vaginal microbiota differs within individuals and between human populations. Anahtar et al. (2015) identify a specific vaginal cervicotype commonly found in healthy South African women that causes localized inflammation including activation of antigen-presenting cells and vaginal recruitment of HIV target cells

Attenuation of oxidative stress induced mitochondrial dysfunction and cytotoxicity in fibroblast cells by sulfated polysaccharide from Padina gymnospora

In this present study, isolation, characterization and protective effect of sulfated polysaccharide (SP) isolated from the brown algae Padina gymnospora was investigated. SP was isolated and characterized through FT-IR, 1H NMR, TGA, GC–MS and CHN analysis. The molecular weight of SP was found to be 16 kDa. The isolated SP contains 29.4 ± 0.35% of sulfate, 27 ± 0.11% of fucose, 0.05 ± 0.12% of protein, respectively. Furthermore, SP exhibits its excellent radical scavenging effects were evaluated by DPPH, ABTS radical scavenging and reducing power assays. Moreover, pretreatment with SP significantly mitigates H2O2 induced cytotoxicity in L-929 cells in a dose dependent manner. Furthermore, SP pretreatment ameliorates oxidative stress induced apoptosis and DNA damage, alleviates the generation of intracellular reactive oxygen species (ROS) and restores mitochondrial membrane potential (MMP) in L-929 cells through its antioxidant potential. Together, these results suggest that SP can be exploited as a natural antioxidant in the food and pharmaceutical industries

The Systemic Immune State of Super-shedder Mice Is Characterized by a Unique Neutrophil-dependent Blunting of T_H1 Responses

<div><p>Host-to-host transmission of a pathogen ensures its successful propagation and maintenance within a host population. A striking feature of disease transmission is the heterogeneity in host infectiousness. It has been proposed that within a host population, 20% of the infected hosts, termed super-shedders, are responsible for 80% of disease transmission. However, very little is known about the immune state of these super-shedders. In this study, we used the model organism <i>Salmonella enterica</i> serovar Typhimurium, an important cause of disease in humans and animal hosts, to study the immune state of super-shedders. Compared to moderate shedders, super-shedder mice had an active inflammatory response in both the gastrointestinal tract and the spleen but a dampened T_H1 response specific to the secondary lymphoid organs. Spleens from super-shedder mice had higher numbers of neutrophils, and a dampened T cell response, characterized by higher levels of regulatory T cells (T_regs), fewer T-bet⁺ (T_H1) T cells as well as blunted cytokine responsiveness. Administration of the cytokine granulocyte colony stimulating factor (G-CSF) and subsequent neutrophilia was sufficient to induce the super-shedder immune phenotype in moderate-shedder mice. Similar to super-shedders, these G-CSF-treated moderate-shedders had a dampened T_H1 response with fewer T-bet⁺ T cells and a loss of cytokine responsiveness. Additionally, G-CSF treatment inhibited IL-2-mediated T_H1 expansion. Finally, depletion of neutrophils led to an increase in the number of T-bet⁺ T_H1 cells and restored their ability to respond to IL-2. Taken together, we demonstrate a novel role for neutrophils in blunting IL-2-mediated proliferation of the T_H1 immune response in the spleens of mice that are colonized by high levels of <i>S.</i> Typhimurium in the gastrointestinal tract.</p></div

Neutrophils control the dampened systemic T_H1 response of super-shedders.

<p>In super-shedders, high levels of <i>Salmonella</i> in the gastrointestinal tract induce systemic neutrophilia with extensive granulopoiesis occurring in the bone marrow, resulting in elevated neutrophil counts in the blood, GI tract and spleen. This is accompanied by dampened IL-2 and IL-6 cytokine responsiveness in splenic CD4 T cells, fewer T_H1 cells and more T_regs. In moderate shedders, low levels of gastrointestinal <i>Salmonella</i> induce very few neutrophils systemically, leading to an active IL-2 and IL-6 response with increased T_H1 cells and fewer T_regs. Induction of granulopoiesis in moderate-shedders results in the super-shedder immune phenotype with the exception of T_regs, which remain unchanged.</p

High fecal bacterial load is associated with systemic neutrophilia.

<p>All infections were conducted for 30 days unless otherwise indicated. A: Bacterial burden of indicated organs was quantified. B: Gr1⁺ cells are represented as a percentage of total cells of a single cell suspension of indicated organs. Data from at least three and a maximum of four mice per condition are shown. All differences between super-shedders, moderate-shedders and uninfected mice are significant with p<0.05 calculated using the Mann-Whitney U test, two-tailed. C: Cytospins were prepared from splenocytes of a representative super-shedder mouse infected for 30 days. A 1000 count differential was performed to identify the myeloid cell composition of the super-shedder spleen. These data are averaged across 4 mice and are representative of experiments including a total of 15 mice.</p

Streptomycin treatment induces the super-shedder phenotype in the gastrointestinal tract and the spleen.

<p>Mice were identified as moderate (<10⁶ cfu/gm) or super-shedder (>10⁸ cfu/gm) between day 15 and day 30 post infection. At 30 days post infection, they were treated with a single dose of 5 mg streptomycin via oral gavage and sacrificed three days after treatment. Data shown is representative of 2 independent experiments with a total of 8–10 mice in each condition. Significance was determined using a two-tailed Mann-Whitney U test with one asterisk representing p<0.05 and two representing a p<0.01. A: Bacterial burden was quantified in the spleen (red) and feces (black). B: Gr1⁺ cells are presented as the percentage of total cells in the spleen and the colon. C. Tbet⁺ T_H1 cells were quantified as percentage of total CD4⁺T cells. D. Splenocytes were stimulated with IL-6 for 15 minutes ex vivo, fixed and permeabilized and phosphoSTAT1 expression of total CD4 T cells quantified. E. Serum IL-6 levels measured by ELISA.</p

Distinct systemic immune profiles associated with fecal shedding states.

<p>Summary of the results in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003408#ppat-1003408-g001" target="_blank">Figures 1</a>,<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003408#ppat-1003408-g002" target="_blank">2</a> presenting a super-shedder immune state that is distinct from the moderate-shedder immune state in the parameters mentioned. It should be noted that the plus signs indicate greater frequency of the cell type or better cytokine responsiveness with respect to uninfected mice. Thus while moderate-shedders have high levels of splenic neutrophils (+) compared to uninfected mice, they have fewer neutrophils compared to super-shedder mice (+++). Similarly, the frequency of T_regs decreases during infection compared to uninfected. Thus, moderate shedders have fewer T_regs (−−−) compared to super-shedders (−).</p