C. Demonceau

Molecular and pigment studies of the picophytoplankton in a region of the Southern Ocean (42–54°S, 141–144°E) in March 1998

Seven filtered seawater samples (depths between 30 and 55 m) collected during the SAZ project of the Austral summer of 1997–1998 were used for a simultaneous study of the picophytoplankton pigments based on high-performance liquid chromatography (HPLC) analyses and flow cytometry, and of the molecular diversity of the picophytoplankton based on their rDNA sequences. The sampling sites could be divided into three temperature zones, distinguished by their proximity to the Sub-Antarctic and Polar Fronts. HPLC analysis of total chlorophylls and carotenoids showed fairly low phytoplankton concentrations (77–262 ng chl a l � 1 ), with minimal values of the pigments in the two samples of the Polar Front Zone around 541S (water temperature of 41C at time of collection). In this zone, a similar decrease of particles, identified as cyanobacteria on the basis of their fluorescence, was observed by flow cytometry. Sequences very similar to the 16S rDNA sequence of Synechococcus WH8103 were present in all samples. This Synechococcus genotype is thus found in the Southern Ocean in addition to the Atlantic and Pacific locations where it has been previously observed. The yield of PCR products was lower in the two samples taken in the Polar Front Zone, showing a good agreement between molecular and pigment data. 16S rDNA sequences of plastids of eukaryotic algae also were retrieved, mostly related to those of an environmental clone called OM164, which has not been cultivated but has phylogenetic affinities to the Raphidophyceae. r 2002 Elsevier Science Ltd. All rights reserved.

Interaction between dendritic cells and nerve fibres in lymphoid organs after oral scrapie exposure

In transmissible spongiform encephalopathies (TSEs), the infectious agent, called PrPsc, an abnormal isoform of the cellular prion protein, accumulates and replicates in lymphoid organs before affecting the nervous system. To clarify the cellular requirements for the neuroinvasion of the scrapie agent from the lymphoid organs to the central nervous system, we have studied, by confocal microscopy, the innervations within Peyer’s patches, mesenteric lymph nodes and the spleen of mice in physiological conditions and after oral exposure to prion. Contacts between nerve fibres and PrPsc-associated cells, dendritic cells (DCs) and follicular dendritic cells (FDCs), were evaluated in preclinical prion-infected mice. Using a double immunolabelling strategy, we demonstrated the lack of innervation of PrPsc-accumulating cells (FDCs). Contacts between nerve fibers and PrPsc-propagating cells (DCs) were detected in T-cell zones and cell-trafficking areas. This supports, for the first time, the possible implication of dendritic cells in the prion neuroinvasion process.

Oral scrapie infection modifies the homeostasis of Peyer’s patches’ dendritic cells

In transmitted prion diseases the immune system supports the replication and the propagation of the pathogenic agent (PrPSc). DCs, which are mobile cells present in large numbers within lymph organs, are suspected to carry prions through the lymphoid system and to transfer them towards the peripheral nervous system. In this study, C57Bl/6 mice were orally inoculated with PrPSc (scrapie strain 139A) and sacrificed at the preclinical stages of the disease. Immunolabelled cryosections of Peyer’s patches were analysed by confocal microscopy. Membrane prion protein expression was studied by flow cytometry. In Peyer’s patches (PP), dissected at day one and day 105 after oral exposure to scrapie, we observed an increased population of DCs localised in the follicular-associated epithelium. On day 105, PrPSc was found in the follicles inside the PP of prion-infected mice. A subset of Peyer’s patches DCs, which did not express cellular prion protein on their surface in non-infected mice conditions, was prion-positive in scrapie conditions. Within Peyer’s patches oral scrapie exposure thus induced modifications of the homeostasis of DCs at the preclinical stages of the disease. These results give new arguments in favour of the implication of DCs in prion diseases.

Close interactions between sympathetic neural fibres and follicular dendritic cells network are not altered in Peyer’s patches and spleen of C57BL/6 mice during the preclinical stage of 139A scrapie infection

During preclinical stage of prion diseases, secondary lymphoid organs seem to play an important role in prion amplification prior the invasion of the associated peripheral nervous system. In mice, it was shown that the relative positioning of follicular dendritic cells (FDC) and sympathetic nervous system (SNS) affects the velocity of neuroinvasion following scrapie inoculation. In this study, we checked if scrapie infection, by oral or intraperitoneal route, could influence this neuroimmune interface between FDC and tyrosine hydroxylase (TH) positive neural fibres within Peyers patches (PP) and spleen of the C57BL/6 mouse strain. We concluded that, in vivo, scrapie 139A and ME7 strains do not modify FDC-SNS neuroimmune interface. However, age seems to alter this neuroimmune interface and thus could influence the neuroinvasion in prion pathogenesis.