Impact of Epstein-Barr virus co-infection on natural acquired Plasmodium vivax antibody response

BackgroundThe simultaneous infection of Plasmodium falciparum and Epstein-Barr virus (EBV) could promote the development of the aggressive endemic Burkitt’s Lymphoma (eBL) in children living in P. falciparum holoendemic areas. While it is well-established that eBL is not related to other human malaria parasites, the impact of EBV infection on the generation of human malaria immunity remains largely unexplored. Considering that this highly prevalent herpesvirus establishes a lifelong persistent infection on B-cells with possible influence on malaria immunity, we hypothesized that EBV co-infection could have impact on the naturally acquired antibody responses to P. vivax, the most widespread human malaria parasite.Methodology/Principal findingsThe study design involved three cross-sectional surveys at six-month intervals (baseline, 6 and 12 months) among long-term P. vivax exposed individuals living in the Amazon rainforest. The approach focused on a group of malaria-exposed individuals whose EBV-DNA (amplification of balf-5 gene) was persistently detected in the peripheral blood (PersV_DNA, n = 27), and an age-matched malaria-exposed group whose EBV-DNA could never be detected during the follow-up (NegV_DNA, n = 29). During the follow-up period, the serological detection of EBV antibodies to lytic/ latent viral antigens showed that IgG antibodies to viral capsid antigen (VCA-p18) were significantly different between groups (PersV_DNA > NegV_DNA). A panel of blood-stage P. vivax antigens covering a wide range of immunogenicity confirmed that in general PersV_DNA group showed low levels of antibodies as compared with NegV_DNA. Interestingly, more significant differences were observed to a novel DBPII immunogen, named DEKnull-2, which has been associated with long-term neutralizing antibody response. Differences between groups were less pronounced with blood-stage antigens (such as MSP1-19) whose levels can fluctuate according to malaria transmission.Conclusions/SignificanceIn a proof-of-concept study we provide evidence that a persistent detection of EBV-DNA in peripheral blood of adults in a P. vivax semi-immune population may impact the long-term immune response to major malaria vaccine candidates.     

Inherited non-autosomal effects on body fat in F2 mice derived from an AKR/J × SWR/J cross

In this study we describe the contribution of matrilineal and patrilineal effects on the adiposity, body weight, and on the weights of individual fat pads in F₂ male mice derived from an SWR/J × AKR/J cross. AKR/J mice become obese after 12 weeks on a high-fat diet, whereas SWR/J mice remain relatively lean. Here we report that mice with AKR maternal and AKR paternal grandmothers have significantly larger epidydimal and retroperitoneal fat pads than those with SWR maternal and paternal grandmothers. However, grandparental strain had no effect on the overall adiposity (AI) or the weights of the inguinal, subcutaneous or mesenteric fat pads. The strain of the paternal grandparents had a small but significant effect on body weight. These effects can be attributed to in utero effects, imprinting effects, cytoplasmic and/or Y chromosome transmission of factors controlling body fat. We also describe the presence of a quantitative trait locus (QTL) on Chromosome X, close to DXMit174, which is linked to adiposity, body weight, and to the weights of the individual fat depots. However, this QTL is not responsible for the grandparental strain effects described above. Received: 3 March 1997 / Accepted: 5 May 1997     

Role of the stable signal peptide and cytoplasmic domain of G2 in regulating intracellular transport of the Junín virus envelope glycoprotein complex

Enveloped viruses utilize the membranous compartments of the host cell for the assembly and budding of new virion particles. In this report, we have investigated the biogenesis and trafficking of the envelope glycoprotein (GP-C) of the Junín arenavirus. The mature GP-C complex is unusual in that it retains a stable signal peptide (SSP) as an essential component in association with the typical receptor-binding (G1) and transmembrane fusion (G2) subunits. We demonstrate that, in the absence of SSP, the G1-G2 precursor is restricted to the endoplasmic reticulum (ER). This constraint is relieved by coexpression of SSP in trans, allowing transit of the assembled GP-C complex through the Golgi and to the cell surface, the site of arenavirus budding. Transport of a chimeric CD4 glycoprotein bearing the transmembrane and cytoplasmic domains of G2 is similarly regulated by SSP association. Truncations to the cytoplasmic domain of G2 abrogate SSP association yet now permit transport of the G1-G2 precursor to the cell surface. Thus, the cytoplasmic domain of G2 is an important determinant for both ER localization and its control through SSP binding. Alanine mutations to either of two dibasic amino acid motifs in the G2 cytoplasmic domain can also mobilize the G1-G2 precursor for transit through the Golgi. Taken together, our results suggest that SSP binding masks endogenous ER localization signals in the cytoplasmic domain of G2 to ensure that only the fully assembled, tripartite GP-C complex is transported for virion assembly. This quality control process points to an important role of SSP in the structure and function of the arenavirus envelope glycoprotein.     

Pharmacological characterization of alpha1- and beta-adrenergic synergism of 5'DII activity in rat brown adipocytes

The role of adrenoceptor subtypes was studied in rat brown adipose tissue (BAT). The type II 5'-deiodinase (5'DII) was activated in response to simultaneous stimulation by beta3- and alpha1-adrenergic agonists, BRL 37344 or CGP 12177, and cirazoline, in brown adipocytes. Inhibition of the alpha1- and beta-adrenergic phenylephrine-stimulated 5'DII activity was obtained by the alpha1-adrenergic antagonists in the order of prazosin >/= wb 4101 > 5-methylurapidil. In comparison, the binding of [3H]prazosin to rat BAT plasma membranes was inhibited by alpha1-adrenergic antagonists in the order of prazosin > WB 4101 = benoxathian > 5-methylurapidil. Although the order of the alpha1-adrenergic competition seemed to be rather typical for the alpha1B-adrenergic receptors, a molecular analysis on adrenoceptor mRNAs should be made to confirm the exact alpha1-adrenergic subtypes at the level of brown adipocytes, since the possibility of a mixture of different receptor subtypes in brown fat cells and/or tissue may interact with the pharmacological characterization. Thus, specific alpha1- and beta-adrenoceptor subtypes participate in the regulation of 5'DII activity in the rat brown adipocytes, and therefore, an impaired alpha1- and beta-adrenergic co-work may be involved in a defective BAT function, e.g., in obese Zucker rats, too. An interesting possibility is that the decreased number of alpha1-adrenoceptors in the BAT of obese Zucker rats is due to the decrease in the alpha1B-adrenoceptor subtype which would further be involved especially in the regulation of BAT 5'DII activity.     

Spatial variation in molluscan assemblages from coralline turfs of Argentinean Patagonia

Patterns of spatial variation of molluscan communities associatedwith coralline algal turfs were evaluated over 1,000 kmof the coast of Argentinean Patagonia. A hierarchically-nestedexperimental design was used to determine the relative importanceof molluscan assemblage variation at three different spatialscales (shores, sites and cores). Hypotheses were also testedabout the potential role of habitat variables (frond density,frond length, sediment and epiphytes) for determining molluscancommunity structure. In total, 38 molluscan species were foundcomprising 16, 18 and 4 species of bivalves, gastropods andpolyplacophorans, respectively. Densities of molluscs in corallineturfs reached ca 77,000 individuals per m² and were dominatedby mussels, especially Perumytilus purpuratus. Multivariateand univariate analyses of assemblage structure consistentlyshowed that variation at scales of metres and hundreds of kilometresdominated, with sites 20–50 m apart always contributingless than 24% of the total. Significant associations betweenmolluscan community structure and both frond density and frondlength demonstrated the potential importance of habitat structurein determining community structure at local scales. Variationin molluscan assemblages at the scale of shores, however, didnot appear to correlate with latitudinal, temperature or waveexposure gradients, indicating that other processes must beoperating. The compositions of molluscan assemblages in corallineturfs on the coast of Argentina were similar to those reportedfor central Chile. Comparisons of the richness of these SouthAmerican assemblages to other parts of the world revealed somestriking biogeographical patterns that warrant further investigation.Overall, this work highlights the general importance of small-scalevariation in molluscan assemblages on rocky shores and the consistentinfluence of habitat complexity in determining the structureof diverse molluscan communities associated with mat-like habitats. (Received 10 August 2006; accepted 20 January 2007)     

Trophic cul-de-sac, Pyrazus ebeninus, limits trophic transfer through an estuarine detritus-based food web

The importance to food‐webs of trophic cul‐de‐sacs, species that channel energy flow away from higher trophic levels, is seldom considered outside of the pelagic systems in which they were first identified. On intertidal mudflats, inputs of detritus from saltmarshes, macroalgae or microphytobenthos are generally regarded as a major structuring force underpinning food‐webs and there has been no consideration of trophic cul‐de‐sacs to date. A fully orthogonal three‐factor experiment manipulating the density of the abundant gastropod, Pyrazus ebeninus, detritus and macrobenthic predators on a Sydney mudflat revealed large deleterious effects of the gastropod, irrespective of detrital loading or the presence of predators. Two months after experimental manipulation, the standing‐stock of microphytobenthos in plots with high (44 per m²) densities of P. ebeninus was 20% less than in plots with low (4 per m²) densities. Increasing densities of P. ebeninus from low to high halved the abundance of macroinvertebrates and the average number of species. In contrast, the addition of detritus had differing effects on microphytobenthos (positively affected) and macroinvertebrates (negatively affected). Over the two‐months of our experiment, no predatory mortality of P. ebeninus was observed and high densities of P. ebeninus decreased impacts of predators on macroinvertebrate abundances. Given that the dynamics of southeast Australian mudflats are driven more by disturbance than seasonality in predators and their interactions with prey, it is likely that Pyrazus would be similarly resistant to predation and have negative effects on benthic assemblages at other times of the year, outside of our study period. Thus, in reducing microphytobenthos and the abundance and species richness of macrofauna, high abundances of the detritivore P. ebeninus may severely limit the flow of energy up the food chain to commercially‐important species. This study therefore suggests that trophic cul‐de‐sacs are not limited to the eutrophied pelagic systems in which they were first identified, but may exist in other systems as well.     

Inositol polyphosphate kinases: regulators of nuclear function

Recent work has uncovered roles for inositide signalling pathways downstream of phospholipase C activation and inositol 1,4,5-trisphosphate in the regulation of nuclear processes including gene expression, mRNA export and DNA metabolism. The identification of several IPKs (inositol polyphosphate kinases) has renewed interest in the cellular roles of inositol tetra-, penta-, hexa- and pyro-phosphates. Discoveries of inositide receptors and novel mechanisms of inositide action have provided important insights into how such messengers couple to nuclear machinery. In this chapter, we discuss the IPK family members and the nuclear processes that their inositide products regulate.     

Analysis of the role of bleomycin hydrolase in antigen presentation and the generation of CD8 T cell responses

Long oligopeptides (>10 residues) are generated during the catabolism of cellular proteins in the cytosol. To be presented to T cells, such peptides must be trimmed by aminopeptidases to the proper size (typically 8-10 residues) to stably bind to MHC class I molecules. Aminopeptidases also destroy epitopes by trimming them to even shorter lengths. Bleomycin hydrolase (BH) is a cytosolic aminopeptidase that has been suggested to play a key role in generating MHC class I-presented peptides. We show that BH-deficient cells from mice are unimpaired in their ability to present epitopes from N-extended precursors or whole Ags and express normal levels of MHC class I molecules. Similarly, BH-deficient mice develop normal CD8(+) T cell responses to eight epitopes from three different viruses in vivo. Therefore, BH by itself is not essential for the generation or destruction of MHC class I peptides. In contrast, when BH(-/-) mice are crossed to mice lacking another cytosolic aminopeptidase, leucine aminopeptidase, the resulting BH(-/-)leucine aminopeptidase(-/-) progeny show a selective increase in CD8(+) T cell responses to the gp276 epitope from lymphocytic choriomeningitis virus, whereas the ability to present and respond to several other epitopes is unchanged. Therefore, BH does influence presentation of some Ags, although its role is largely redundant with other aminopeptidases.     

Bitopic membrane topology of the stable signal peptide in the tripartite Junín virus GP-C envelope glycoprotein complex

The stable signal peptide (SSP) of the GP-C envelope glycoprotein of the Junín arenavirus plays a critical role in trafficking of the GP-C complex to the cell surface and in its membrane fusion activity. SSP therefore may function on both sides of the lipid membrane. In this study, we have investigated the membrane topology of SSP by confocal microscopy of cells treated with the detergent digitonin to selectively permeabilize the plasma membrane. By using an affinity tag to mark the termini of SSP in the properly assembled GP-C complex, we find that both the N and C termini reside in the cytosol. Thus, SSP adopts a bitopic topology in which the C terminus is translocated from the lumen of the endoplasmic reticulum to the cytoplasm. This model is supported by (i) the presence of two conserved hydrophobic regions in SSP (hphi1 and hphi2) and (ii) our previous demonstration that lysine-33 in the ectodomain loop is essential for pH-dependent membrane fusion. Moreover, we demonstrate that the introduction of a charged side chain or single amino acid deletion in the membrane-spanning hphi2 region significantly diminishes SSP association in the GP-C complex and abolishes membrane fusion activity. Taken together, our results suggest that bitopic membrane insertion of SSP is centrally important in the assembly and function of the tripartite GP-C complex.