Pan-genomic analyses of 47 complete genomes of the Rickettsia genus and prediction of new vaccine targets and virulence factors of the species

The genus Rickettsia belongs to the Proteobacteria phylum and these bacteria infect animals and humans causing a range of diseases worldwide. The genus is divided into 4 groups and despite the public health threat and the knowledge accumulated so far, the mandatory intracellular bacteria behaviour and limitation for in vitro culture makes it difficult to create new vaccines and drug targets to these bacteria. In an attempt to overcome these limitations, pan-genomic approaches has used 47 genomes of the genus Rickettsia, in order to describe species similarities and genomics islands. Moreover, we conducted reverse vaccinology and docking analysis aiming the identification of proteins that have great potential to become vaccine and drug targets. We found out that the bacteria of the four Rickettsia groups have a high similarity with each other, with about 90 to 100% of identity. A pathogenicity island and a resistance island were predicted. In addition, 8 proteins were also predicted as strong candidates for vaccine and 9 as candidates for drug targets. The prediction of the proteins leads us to believe in a possibility of prospecting potential drugs or creating a polyvalent vaccine, which could reach most strains of this large group of bacteria.Communicated by Ramaswamy H. Sarma.

TNF-α blockade impairs in vitro tuberculous granuloma formation and down modulate Th1, Th17 and Treg cytokines

Tuberculosis (TB) is a granulomatous disease that has affected humanity for thousands of years. The production of cytokines, such as IFN-γ and TNF-α, is fundamental in the formation and maintenance of granulomas and in the control of the disease. Recently, the introduction of TNF-α-blocking monoclonal antibodies, such as Infliximab, has brought improvements in the treatment of patients with chronic inflammatory diseases, but this treatment also increases the risk of reactivation of latent tuberculosis. Our objective was to analyze, in an in vitro model, the influence of Infliximab on the granulomatous reactions and on the production of antigen-specific cytokines (TNF-α, IFN-γ, IL-12p40, IL-10 and IL-17) from beads sensitized with soluble Bacillus Calmette-Guérin (BCG) antigens cultured in the presence of peripheral blood mononuclear cells (PBMC) from TB patients. We evaluated 76 individuals, with tuberculosis active, treated and subjects with positive PPD. Granuloma formation was induced in the presence or absence of Infliximab for up to 10 days. The use of Infliximab in cultures significantly blocked TNF-α production (p <0.05), and led to significant changes in granuloma structure, in vitro, only in the treated TB group. On the other hand, there was a significant reduction in the levels of IFN-γ, IL-12p40, IL-10 and IL-17 after TNF-α blockade in the three experimental groups (p <0.05). Taken together, our results demonstrate that TNF-α blockade by Infliximab directly influenced the structure of granuloma only in the treated TB group, but negatively modulated the production of Th1, Th17 and regulatory T cytokines in the three groups analyzed.

Proteome of Rhipicephalus sanguineus tick saliva induced by the secretagogues pilocarpine and dopamine

One dimensional gel electrophoresis was used to separate proteins from the saliva of Rhipicephalus sanguineus female ticks fed on rabbits. Gel slices were subjected to tryptic digestion and analyzed by reversed-phase HPLC followed by MS/MS analysis. The data were compared to a database of salivary proteins of the same tick and to the predicted proteins of the host. Saliva was obtained by either pilocarpine or dopamine stimulation of partially fed ticks. Electrophoretic separations of both yielded products that were identified by mass spectrometry, although the pilocarpine-derived sample was of much better quality. The majority of identified proteins were of rabbit origin, indicating the recycling of the host proteins in the tick saliva, including hemoglobin, albumin, haptoglobin, transferring, and a plasma serpin. The few proteins found that were previously associated with parasitism and blood feeding include 2 glycine-rich, cement-like proteins, 2 lipocalins, and a thyropin protease inhibitor. Among other of the 19 tick proteins identified, albeit with undefined roles, were SPARC and cyclophilin A. This catalog provides a resource that can be mined for secreted molecules that play a role in tick-host interactions.

Defibrotide interferes with several steps of the coagulation-inflammation cycle and exhibits therapeutic potential to treat severe malaria

OBJECTIVE

The coagulation-inflammation cycle has been implicated as a critical component in malaria pathogenesis. Defibrotide (DF), a mixture of DNA aptamers, displays anticoagulant, anti-inflammatory, and endothelial cell (EC)-protective activities and has been successfully used to treat comatose children with veno-occlusive disease. DF was investigated here as a drug to treat cerebral malaria.

METHODS AND RESULTS

DF blocks tissue factor expression by ECs incubated with parasitized red blood cells and attenuates prothrombinase activity, platelet aggregation, and complement activation. In contrast, it does not affect nitric oxide bioavailability. We also demonstrated that Plasmodium falciparum glycosylphosphatidylinositol (Pf-GPI) induces tissue factor expression in ECs and cytokine production by dendritic cells. Notably, dendritic cells, known to modulate coagulation and inflammation systemically, were identified as a novel target for DF. Accordingly, DF inhibits Toll-like receptor ligand-dependent dendritic cells activation by a mechanism that is blocked by adenosine receptor antagonist (8-p-sulfophenyltheophylline) but not reproduced by synthetic poly-A, -C, -T, and -G. These results imply that aptameric sequences and adenosine receptor mediate dendritic cells responses to the drug. DF also prevents rosetting formation, red blood cells invasion by P. falciparum and abolishes oocysts development in Anopheles gambiae. In a murine model of cerebral malaria, DF affected parasitemia, decreased IFN-γ levels, and ameliorated clinical score (day 5) with a trend for increased survival.

CONCLUSION

Therapeutic use of DF in malaria is proposed.