Human germinal center B cells differ from naive and memory B cells by their aggregated MHC class II‐rich compartments lacking HLA‐DO

To generate memory B cells bearing high‐affinity antibodies, naive B cells first encounter antigen in the T cell‐rich areas of secondary lymphoid organs. There, they are activated by antigen‐specific T cells and become germinal center (GC) founder B cells. GC founders enter the GC to become centroblasts that proliferate and mutate their BCR. Centroblasts differentiate into centrocytes that undergo selection, which requires both the recognition/capture of antigen on follicular dendritic cells and the presentation of processed antigen to GC T cells. Because at each stage of differentiation B cells act as antigen‐presenting cells, we analyzed their content of HLA‐DR+‐rich compartments (MIIC), as well as their expression of HLA‐DM, which catalyzes peptide loading of class II molecules, and HLA‐DO, which interacts with HLA‐DM and focuses MHC class II peptide loading on antigens internalized by the BCR. Naive and memory B cells concentrate HLA‐DR, ‐DM and ‐DO into compartments dispersed under the cell surface, which are identified by their expression of lysosome‐associated membrane protein (Lamp)‐1 as late endosomes/lysosomes. GC founders and GC B cells express larger Lamp‐1+DR+ compartments that are concentrated in the juxta‐nuclear region. These compartments express lower levels of HLA‐DM and virtually no HLA‐DO. Upon induction of a GC founder phenotype through the prolonged (days) co‐ligation of BCR and CD40, the naive B cell's peripheral DR+DM+Lamp‐1+ compartments aggregate in a polar fashion close to the nucleus. Furthermore, HLA‐DO expression virtually disappears, whereas low levels of HLA‐DM remain co‐localized with HLA‐DR. Anti‐κ/λ antibodies, used as surrogate antigens, are promptly (minutes) endocytosed in naive, memory and GC B cells. Then, naive and memory B cells target the surrogate antigen to their peripheral HLA‐DO+ MIIC, while GC B cells target it to their HLA‐DO- MIIC aggregates. Taken together, our results show that human GC B cells differ from naive and memory B cells by their aggregated MIIC that lack HLA‐D

Highly efficient transduction of human plasmacytoid dendritic cells without phenotypic and functional maturation

<p>Abstract</p> <p>Background</p> <p>Gene modified dendritic cells (DC) are able to modulate DC functions and induce therapeutic immunity or tolerance in an antigen-specific manner. Among the different DC subsets, plasmacytoid DC (pDC) are well known for their ability to recognize and respond to a variety of viruses by secreting high levels of type I interferon.</p> <p>Methods</p> <p>We analyzed here, the transduction efficiency of a pDC cell line, GEN2.2, and of pDC derived from CD34+ progenitors, using lentiviral vectors (LV) pseudotyped with different envelope glycoproteins such as the vesicular stomatitis virus envelope (VSVG), the gibbon ape leukaemia virus envelope (GaLV) or the feline endogenous virus envelope (RD114). At the same time, we evaluated transgene expression (E-GFP reporter gene) under the control of different promoters.</p> <p>Results</p> <p>We found that efficient gene transfer into pDC can be achieved with VSVG-pseudotyped lentiviral vectors (LV) under the control of phoshoglycerate kinase (PGK) and elongation factor-1 (EF1α) promoters (28% to 90% of E-GFP⁺cells, respectively) in the absence of phenotypic and functional maturation. Surprisingly, promoters (desmin or synthetic C5–12) described as muscle-specific and which drive gene expression in single strand AAV vectors in gene therapy protocols were very highly active in pDC using VSVG-LV.</p> <p>Conclusion</p> <p>Taken together, our results indicate that LV vectors can serve to design pDC-based vaccines in humans, and they are also useful <it>in vitro </it>to evaluate the immunogenicity of the vector preparations, and the specificity and safety of given promoters used in gene therapy protocols.</p

Toxoplasmosis and Chagas disease : report of severe cases of troops in French Guiana and review on foodborne mode of transmission in Amazonia

In contrast with the usual clinical feature of toxoplasmosis, a cosmopolitan disease, severe cases with visceral disorders have been reported in non-immunocompromised adult patients, particularly in French Guiana. Most of the cases seem to result from the consumption of undercooked game meat or ingestion of non-filtered surface water. In Amazonia, a sylvatic cycle of toxoplasmosis involves large felids as definitive hosts and numerous mammals and birds as intermediate hosts. Atypical strains of Toxoplasma gondii, characterized by increased virulence, are involved in these complex cycles. Although Chagas disease, caused by another protozoan parasite, Trypanosoma cruzi, has been known for a long time, a new foodborne mode of transmission to man seems to emerge. Several outbreaks have been reported, mainly in Brasil, resulting from the contamination of food items by infected Triatominae or their dejections. When food or water are taken from the natural environment, measures have to be implemented in order to prevent these serious diseases.Contrastant avec la toxoplasmose habituelle, maladie cosmopolite, des formes sévères avec atteinte viscérale sont apparues chez des patients adultes non immunodéprimés, notamment en Guyane française. La consommation de viande de gibier mal cuite ou l'ingestion d'eau de surface non filtrée semblent être à l'origine de la plupart des cas. En Amazonie, un cycle sylvestre de la toxoplasmose s'établit entre les grands félidés hôtes définitifs et de nombreux mammifères et oiseaux, hôtes intermédiaires. Dans ces cycles complexes, circulent des souches atypiques de Toxoplasma gondii, caractérisées par une virulence accrue. Bien que la maladie de Chagas, provoquée par un autre protozoaire, Trypanosoma cruzi, soit connue de longue date, le mode de transmission à l'homme par la voie alimentaire semble émerger. Plusieurs foyers sont rapportés, surtout au Brésil, résultant de la contamination de denrées par des Triatominae infectées ou leurs déjections. Lorsque des ressources en aliments ou en eau sont prélevées dans le milieu naturel, des mesures sont à appliquer pour prévenir l'apparition de ces maladies graves

West Nile Virus in Horses, sub-Saharan Africa

To evaluate the presence and extension of West Nile virus where French soldiers are stationed in Africa, specific antibody prevalence was determined by using ELISA and Western blot. Among 245 horses living in close proximity to the soldiers, seroprevalence was particularly high in Chad (97%) and Senegal (92%)

Foxp3+ Regulatory and Conventional CD4+ T Cells Display Similarly High Frequencies of Alloantigen-Reactive Cells

Foxp3+ regulatory T cells (Tregs) play a major role in acquired immune tolerance to allogenic transplants. Their suppressive activity is thought to require T cell receptor (TCR)-driven antigen recognition; little, however, is known about the fraction of Tregs able to recognize alloantigens within this T cell subset primarily educated against self-antigens. Performing transfer experiments of Tregs or conventional T cells (Tconv) into both lymphoreplete and lymphopenic mice, we observed a similarly high proportion of cells signaling through their TCR and proliferating in allogenic hosts. Furthermore, using an in vivo proliferation assay with limited T cell numbers infused into lymphopenic mice, we found that the overall frequency of alloreactive Tregs was similar if not higher to that of alloreactive Tconv. Overall our study highlights a noticeably high level of alloreactive Foxp3+ regulatory T cells accounting for their predominant role in transplantation tolerance