Secretion of Hepatitis C Virus Envelope Glycoproteins Depends on Assembly of Apolipoprotein B Positive Lipoproteins

The density of circulating hepatitis C virus (HCV) particles in the blood of chronically infected patients is very heterogeneous. The very low density of some particles has been attributed to an association of the virus with apolipoprotein B (apoB) positive and triglyceride rich lipoproteins (TRL) likely resulting in hybrid lipoproteins known as lipo-viro-particles (LVP) containing the viral envelope glycoproteins E1 and E2, capsid and viral RNA. The specific infectivity of these particles has been shown to be higher than the infectivity of particles of higher density. The nature of the association of HCV particles with lipoproteins remains elusive and the role of apolipoproteins in the synthesis and assembly of the viral particles is unknown. The human intestinal Caco-2 cell line differentiates in vitro into polarized and apoB secreting cells during asymmetric culture on porous filters. By using this cell culture system, cells stably expressing E1 and E2 secreted the glycoproteins into the basal culture medium after one week of differentiation concomitantly with TRL secretion. Secreted glycoproteins were only detected in apoB containing density fractions. The E1–E2 and apoB containing particles were unique complexes bearing the envelope glycoproteins at their surface since apoB could be co-immunoprecipitated with E2-specific antibodies. Envelope protein secretion was reduced by inhibiting the lipidation of apoB with an inhibitor of the microsomal triglyceride transfer protein. HCV glycoproteins were similarly secreted in association with TRL from the human liver cell line HepG2 but not by Huh-7 and Huh-7.5 hepatoma cells that proved deficient for lipoprotein assembly. These data indicate that HCV envelope glycoproteins have the intrinsic capacity to utilize apoB synthesis and lipoprotein assembly machinery even in the absence of the other HCV proteins. A model for LVP assembly is proposed

Efficiency of boundary conditions on the computation of local fields in a Representative Volume Element

International audienceWithin the framework of numerical homogeneization approaches, we focus on the effect of boundary conditions (BCs) on local mechanical fields computed by the Finite Element method. The influence of classical BCs (affine displacements, periodic conditions) imposed on the Representative Volume Element (RVE) has been largely studied with respect to the effective macroscopic behaviour. When a periodic microstructure can be generated at the RVE scale (periodic or model materials typically), periodic conditions produce more accurate results. However, these conditions come with technical difficultieslinked to the generation of the periodic mesh and additional costs in terms of computation time.In a multiscale use of numerical homogenization, local fields are of great importance to detect phenomena arising at the local scale. Moreover these fields must be computed in reasonable calculation times to make these numerical coupling approaches efficient. Very few studies focus on the effects of the BCs on the local behaviour. Affine displacement conditions, which are the computationnally most efficient technique, are subject to local boundary effects, located on cut inclusions in case of matrix-inclusion composites . Different ways are followed in order to improve the ratio precision over cost of such approaches : truncation or filtering, homogenization-based Dirichlet values, RVE without cut inclusions

Efficiency of boundary conditions on the computation of local fields in a Representative Volume Element

International audienceWithin the framework of numerical homogeneization approaches, we focus on the effect of boundary conditions (BCs) on local mechanical fields computed by the Finite Element method. The influence of classical BCs (affine displacements, periodic conditions) imposed on the Representative Volume Element (RVE) has been largely studied with respect to the effective macroscopic behaviour. When a periodic microstructure can be generated at the RVE scale (periodic or model materials typically), periodic conditions produce more accurate results. However, these conditions come with technical difficultieslinked to the generation of the periodic mesh and additional costs in terms of computation time.In a multiscale use of numerical homogenization, local fields are of great importance to detect phenomena arising at the local scale. Moreover these fields must be computed in reasonable calculation times to make these numerical coupling approaches efficient. Very few studies focus on the effects of the BCs on the local behaviour. Affine displacement conditions, which are the computationnally most efficient technique, are subject to local boundary effects, located on cut inclusions in case of matrix-inclusion composites . Different ways are followed in order to improve the ratio precision over cost of such approaches : truncation or filtering, homogenization-based Dirichlet values, RVE without cut inclusions

Efficiency of boundary conditions on the computation of local fields in a Representative Volume Element

International audienceWithin the framework of numerical homogeneization approaches, we focus on the effect of boundary conditions (BCs) on local mechanical fields computed by the Finite Element method. The influence of classical BCs (affine displacements, periodic conditions) imposed on the Representative Volume Element (RVE) has been largely studied with respect to the effective macroscopic behaviour. When a periodic microstructure can be generated at the RVE scale (periodic or model materials typically), periodic conditions produce more accurate results. However, these conditions come with technical difficultieslinked to the generation of the periodic mesh and additional costs in terms of computation time.In a multiscale use of numerical homogenization, local fields are of great importance to detect phenomena arising at the local scale. Moreover these fields must be computed in reasonable calculation times to make these numerical coupling approaches efficient. Very few studies focus on the effects of the BCs on the local behaviour. Affine displacement conditions, which are the computationnally most efficient technique, are subject to local boundary effects, located on cut inclusions in case of matrix-inclusion composites . Different ways are followed in order to improve the ratio precision over cost of such approaches : truncation or filtering, homogenization-based Dirichlet values, RVE without cut inclusions

Efficiency of boundary conditions on the computation of local fields in a Representative Volume Element

International audienceWithin the framework of numerical homogeneization approaches, we focus on the effect of boundary conditions (BCs) on local mechanical fields computed by the Finite Element method. The influence of classical BCs (affine displacements, periodic conditions) imposed on the Representative Volume Element (RVE) has been largely studied with respect to the effective macroscopic behaviour. When a periodic microstructure can be generated at the RVE scale (periodic or model materials typically), periodic conditions produce more accurate results. However, these conditions come with technical difficultieslinked to the generation of the periodic mesh and additional costs in terms of computation time.In a multiscale use of numerical homogenization, local fields are of great importance to detect phenomena arising at the local scale. Moreover these fields must be computed in reasonable calculation times to make these numerical coupling approaches efficient. Very few studies focus on the effects of the BCs on the local behaviour. Affine displacement conditions, which are the computationnally most efficient technique, are subject to local boundary effects, located on cut inclusions in case of matrix-inclusion composites . Different ways are followed in order to improve the ratio precision over cost of such approaches : truncation or filtering, homogenization-based Dirichlet values, RVE without cut inclusions

Evolution of the incidence of hepatitis B virus infection and immunization rates in a large French cohort born between 1960 and 1994

International audienceIn France, several successive changes in anti-hepatitis B virus (HBV) vaccination policies occurred since 1982. We estimated the incidence and prevalence of HBV infection according to years of birth 1960 to 1994 in a large sentinel cohort to evaluate the epidemiology of HBV during vaccination policy changes. A retrospective cohort study included data from all HIV, HBV and hepatitis C virus (HCV) screening facilities in Grand Lyon. From 2005 to 2010, all 57113 individuals with complete HBV serologic status were enrolled. Survival analyses modeled separately various ages in each birth cohort. The proportion of immunized individuals increased in birth cohorts 1978 to 1984 (up to 58.3% (95% confidence interval (CI), 43.3-68.2 at age 15). In post-1985 birth cohorts, this proportion decreased to 19.5% (95% CI, 15.5-24) in birth cohort 1987 at age 15. Probability of past or current HBV infection increased constantly in birth cohorts 1960 to 1967, up to 12% (95% CI, 10.4-14) at age 30, then decreased gradually in birth cohorts 1968 to 1991, down to 0.9% (95% CI, 0.7-1.2) at age 17.5. In post-1991 cohorts, the probability of HBV infection increased again, up to 2.5% (95% CI, 1.7-3.6) at age 17.5. HBV incidence fluctuated between 5 and 8 per 1000 person-years in pre-1986 birth cohorts, decreased to 2.1 (95% CI, 1.5-2.7) in birth cohorts 1986 to 1991 but rebounded to 5 (95% CI, 3.5-7.1) in post-1991 birth cohorts. HBV incidence was remarkably high in young adults with noticeable variations concomitantly to vaccination policy changes. A dramatic decline in immunization rate was temporally associated with a sharp rebound of infection after withdrawal of systematic adolescent vaccination in 1998