Pathogenesis of infection by entamoeba histolytica

Entamoeba histolytica, a protozoan parasite, is the etiologic agent of amoebiasis in humans. It exists in two forms-the trophozoite which is the active, dividing form, and the cyst which is dormant and can survive for prolonged periods outside the host. In most infected individuals the trophozoites exist as commensals. In a small percentage of infections, the trophozoites become invasive and penetrate the intestinal mucosa, causing ulcers. The trophozoites may reach other parts of the body-mainly liver, where they cause tissue necrosis, leading to lifethreatening abscesses. It is thought that pathogenesis of infection by Entamoeba histolytica is governed at several levels, chief among them are (i) adherence of trophozoite to the target cell, (ii) lysis of target cell, and (iii) phagocytosis of target cell. Several molecules which may be involved in these processes have been identified. A lectin inhibitable by galactose and N-acetyl-D-galactosamine is present on the trophozoite surface. This is implicated in adherence of trophozoite to the target cell. Various amoebic poreforming proteins are known, of which 5kDa protein (amoebapore) has been extensively studied. These can insert into the lipid bilayers of target cells, forming ion-channels. The phagocytic potential of trophozoites is directly linked to virulence as measured in animal models. Factors like association of bacteria with trophozoites also influence virulence. Thus, pathogenesis is determined by multiple factors and a unifying picture taking into account the relative contributions of each factor is sought. Recent technical advances, which includes the development of a transfection system to introduce genes into trophozoites, should help to understand the mechanism of pathogenesis in amoebiasis

Evidence-based national vaccine policy

India has over a century old tradition of development and production of vaccines. The Government rightly adopted self-sufficiency in vaccine production and self-reliance in vaccine technology as its policy objectives in 1986. However, in the absence of a full-fledged vaccine policy, there have been concerns related to demand and supply, manufacture vs. import, role of public and private sectors, choice of vaccines, new and combination vaccines, universal vs. selective vaccination, routine immunization vs. special drives, cost-benefit aspects, regulatory issues, logistics etc. The need for a comprehensive and evidence based vaccine policy that enables informed decisions on all these aspects from the public health point of view brought together doctors, scientists, policy analysts, lawyers and civil society representatives to formulate this policy paper for the consideration of the Government. This paper evolved out of the first ever ICMR-NISTADS national brainstorming workshop on vaccine policy held during 4-5 June, 2009 in New Delhi, and subsequent discussions over email for several weeks, before being adopted unanimously in the present form

A second short repeat sequence detected downstream of rRNA genes in the entamoeba histolytica rDNA episome

This article does not have an abstract

Pneumococal Surface Protein A (PspA) Regulates Programmed Death Ligand 1 Expression on Dendritic Cells in a Toll-Like Receptor 2 and Calcium Dependent Manner.

Pneumonia leads to high mortality in children under the age of five years worldwide, resulting in close to 20 percent of all deaths in this age group. Therefore, investigations into host-pathogen interactions during Streptococcus pneumoniae infection are key in devising strategies towards the development of better vaccines and drugs. To that end, in this study we investigated the role of S. pneumoniae and its surface antigen Pneumococcal surface protein A (PspA) in modulating the expression of co-stimulatory molecule Programmed Death Ligand 1 (PD-L1) expression on dendritic cells (DCs) and the subsequent effects of increased PD-L1 on key defence responses. Our data indicate that stimulation of DCs with PspA increases the surface expression of PD-L1 in a time and dose dependent manner. Characterization of mechanisms involved in PspA induced expression of PD-L1 indicate the involvement of Toll-Like Receptor 2 (TLR2) and calcium homeostasis. While calcium release from intracellular stores positively regulated PD-L1 expression, calcium influx from external milieu negatively regulated PD-L1 expression. Increase in PD-L1 expression, when costimulated with PspA and through TLR2 was higher than when stimulated with PspA or through TLR2. Further, knockdown of TLR2 and the intermediates in the TLR signaling machinery pointed towards the involvement of a MyD88 dependent pathway in PspA induced PD-L1 expression. Incubation of DCs with S. pneumoniae resulted in the up-regulation of PD-L1 expression, while infection with a strain lacking surface PspA failed to do so. Our data also suggests the role of PspA in ROS generation. These results suggest a novel and specific role for PspA in modulating immune responses against S. pneumoniae by regulating PD-L1 expression

Anti-SP0845^23–350 antibodies are functional as assessed by blood bactericidal assay.

<p>Pneumococcal cells (100–150 cfu) from strains TIGR4 (A), ATCC 6303 (B), ATCC 6314 (C) and D39 (D) were pretreated with either preimmune (PI, dark bar) or mouse anti-SP0845^23–350 hyperimmune (HI, grey bar) sera and incubated with peripheral blood from CBA/N mice at 37°C for 3 h with rotation. The surviving bacteria were enumerated by plating serial dilutions on TSA plates in duplicate. The data represents the mean ± SD values. The data was analyzed using Student's unpaired t test.</p

Route of calcium entry differentially regulates PspA induced PD-L1 expression.

<p>Mouse bone marrow derived DCs were incubated with bio-pharmacological inhibitors to indicated molecules for 1h followed by stimulation with 15 μg/ml PspA for 24h. PD-L1 levels were monitored by flow cytometry. Dotted lines represent unstimulated cells. Thin lines represent cells stimulated with PspA. Bold lines represent cells treated with inhibitors to indicated molecules followed by stimulation with PspA. One of three independent experiments is shown. PD-L1 expression is represented as bar graph indicating fold increase in Relative Mean Fluorescence Intensity (MFI) for various groups. Bars represent mean ± SD of three independent experiments. For Panel B, mouse bone marrow derived DCs were incubated in the presence or absence of TMB-8 or EGTA for 1h followed by stimulations with 15 μg/ml PspA for 24h. Cells were incubated with phycoerythrin conjugated anti-mouse PD-L1 antibody. Merged images with DAPI (blue) and PD-L1 (red) staining are depicted. For Panel C total RNA was isolated from cells stimulated as indicated and PD-L1 transcript levels were measured by semi-quantitative RT-PCR. One of three independent experiments is shown.</p

PspA induces PD-L1 expression in a MyD88 dependent pathway.

<p>Mouse bone marrow derived DCs were transfected with siRNAs against indicated molecules for 36h followed by stimulations with 1 μg/ml Pam₃Csk₄ and 15 μg/ml PspA for 24h. PD-L1 levels were monitored by flow cytometry. Dotted line represents unstimulated cells transfected with control siRNAs. Thin lines represent cells transfected with control siRNAs followed by stimulations with 1 μg/ml Pam₃Csk₄ and 15 μg/ml PspA. Bold lines represent cells transfected with specific siRNAs to indicated molecules followed by stimulations with 1 μg/ml Pam₃Csk₄ and 15 μg/ml PspA. Data from one of three independent experiments are shown. In Panel B, PD-L1 expression is represented as bars indicating fold increase in Relative Mean Fluorescence Intensity (MFI) for various groups. Bars represent mean ± S.D. of three independent experiments.</p