OmpU porins are increasingly recognized as key determinants of pathogenic host Vibrio interactions. Although mechanisms remain incompletely understood, various species, including the human pathogen Vibrio cholera, require OmpU for host colonization and virulence. We have shown previously that OmpU is essential for virulence in the oyster pathogen Vibrio splendidus LGP32. Here, we showed that V. splendidus LGP32 invades the oyster immune cells, the hemocytes, through subversion of host-cell actin cytoskeleton. In this process, OmpU serves as an adhesin/invasin required for β-integrin recognition and host cell invasion. Furthermore, the major protein of oyster plasma, the extracellular superoxide dismutase CgEcSOD, is used as an opsonin mediating the OmpU-promoted phagocytosis through its RGD sequence. Finally, the endocytosed bacteria were found to survive intracellularly, evading the host defense by preventing acidic vacuole formation and limiting reactive oxygen species production. We conclude that (i) V. splendidus is a facultative intracellular pathogen that manipulates host defense mechanisms to enter and survive in host immune cells, and (ii) that OmpU is a major determinant of host cell invasion in Vibrio species, used by V. splendidus LGP32 to attach and invade oyster hemocytes through opsonisation by the oyster plasma Cg-EcSOD.T he oyster pathogen, Vibrio splendidus strain LGP32 was isolated from massive mortality events in the production of Crassostrea gigas oysters (1). However, up to now, little has been known about the route of infection and pathogenic processes of LGP32 (2, 3). A metalloprotease has been associated with toxicity (4, 5) and the outer membrane protein (OMP) OmpU was shown to be a major determinant of LGP32 virulence (6).As bacterial surface components, OMPs are both used by hosts for pathogen recognition and by pathogens for interaction with and invasion of host cells, serving as adhesion proteins (adhesins)

This study explored a novel system combining plant-based production and the elastin-like peptide (ELP) fusion strategy to produce vaccinal antigens against tuberculosis. Transgenic tobacco plants expressing the mycobacterial antigens Ag85B and ESAT-6 fused to ELP (TBAg-ELP) were generated. Purified TBAg-ELP was obtained by the highly efficient, cost-effective, inverse transition cycling (ICT) method and tested in mice. Furthermore, safety and immunogenicity of the crude tobacco leaf extracts were assessed in piglets. Antibodies recognizing mycobacterial antigens were produced in mice and piglets. A T-cell immune response able to recognize the native mycobacterial antigens was detected in mice. These findings showed that the native Ag85B and ESAT-6 mycobacterial B- and T-cell epitopes were conserved in the plant-expressed TBAg-ELP. This study presents the first results of an efficient plant-expression system, relying on the elastin-like peptide fusion strategy, to produce a safe and immunogenic mycobacterial Ag85B-ESAT-6 fusion protein as a potential vaccine candidate against tuberculosis.

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bTrypanosoma brucei gambiense, a parasitic protozoan belonging to kinetoplastids, is the main etiological agent of human African trypanosomiasis (HAT), or sleeping sickness. One major characteristic of this disease is the dysregulation of the host immune system. The present study demonstrates that the secretome (excreted-secreted proteins) of T. b. gambiense impairs the lipopolysaccharide (LPS)-induced maturation of murine dendritic cells (DCs). The upregulation of major histocompatibility complex class II, CD40, CD80, and CD86 molecules, as well as the secretion of cytokines such as tumor necrosis factor alpha, interleukin-10 (IL-10), and IL-6, which are normally released at high levels by LPS-stimulated DCs, is significantly reduced when these cells are cultured in the presence of the T. b. gambiense secretome. Moreover, the inhibition of DC maturation results in the loss of their allostimulatory capacity, leading to a dramatic decrease in Th1/Th2 cytokine production by cocultured lymphocytes. These results provide new insights into a novel efficient immunosuppressive mechanism directly involving the alteration of DC function which might be used by T. b. gambiense to interfere with the host immune responses in HAT and promote the infectious process.

We have analysed by multilocus enzyme electrophoresis (MLEE) at 21 genetic loci 10 Trypanosoma cruzi stocks isolated from chronic chagasic patients and 3 stocks isolated from Triatoma dimidiata collected in human habitats from the coastal part of Ecuador (all stocks isolated in August-December 1998). Isoenzyme profiles were compared to those of 4 laboratory-cloned stocks representing the major phylogenetic subdivisions of T. cruzi. This parasite's genetic variability in Ecuador proved to be considerable, even in this limited sample, since all main isoenzyme genotypes were recorded. Four stocks from patients were identical at all loci to the reference stock MNcl2 ('major clonet #39'; T. cruzi II) isolated in Chile. The 3 stocks isolated from T. dimidiata were closely related to the formerly described zymodeme I (T. cruzi I). Finally, 3 stocks from chronic chagasic patients (one with an asymptomatic form, 2 with a cardiac-digestive form) were closely related to the formerly described zymodeme III (presently not classified in either T. cruzi I or T. cruzi II). This is the first observation of this category of T. cruzi genotypes in chronic chagasic patients. In the past it was recorded only in acute patients, wild mammals and wild triatomine bugs. The epidemiological implications of these results are discussed.

Trypanosoma cruzi is highly heterogeneous in terms of genetics and biological properties. To explore the diversity of T. cruzi, we focused our study on the T. cruzi Tc52 protein playing a critical immunosuppressive role during infection. Sequence variability and expression levels of this virulence factor were analysed in various strains. Among the 40 amino acid substitutions detected in the Tc52 coding sequences, three substitutions may have an impact on protein activity or function, as two are localized in sites involved in the glutathione binding and the third is present in the region bearing immunomodulatory function. This sequence variability was consistent with the genetic subdivisions of T. cruzi. Moreover, we observed that the level of Tc52 transcripts and proteins varied between the different strains, but we did not find a significant correlation between Tc52 expression and the phylogeny of the parasite. Thus, both diversity in the sequences and differences in the expression levels of Tc52 protein may be involved in the biological variability of T. cruzi, especially in virulence and immunosuppression properties of T. cruzi strains.

Immunopathology of Chagas' disease in Balb/c mice infected with 2 Trypanosoma cruzi clones, belonging to the T. cruzi I lineage and presenting different in vitro virulence (P/209 cl1 > SO34 c14) was compared. In the acute phase, evading mechanisms such as parasite-induced lymphocyte polyclonal activation and T cell immunosuppression were higher in mice infected with the clone giving a higher parasitaemia (P/209 cl1). A similar increase of non-specific isotypes was observed in both infections with IgG2a prevalence. Interestingly, CD8+ cell hypercellularity and lymphocyte immunosuppression were observed during the chronic phase (245 days post-infection) in mice infected by the most virulent clone. In the same way, the parasite-specific antibody response was more intense in P/209 cl1-infected mice over the acute phase. During the chronic phase this response remarkably dropped down in SO34 cl4-infected mice exclusively. Finally, P/209 cl1-infected mice presented a more severe inflammation and tissue damage in heart and quadriceps than SO34 cl4-infected mice. This comparative study showed differences between the two clones: a higher virulence in vivo being clearly associated with a greater ability to induce evasion mechanisms and severe tissue damage.

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