Autophagy Pathways in the Genesis of Plasmodium-Derived Microvesicles: A Double-Edged Sword?

Malaria, caused by Plasmodium species (spp.), is a deadly parasitic disease that results in approximately 400,000 deaths per year globally. Autophagy pathways play a fundamental role in the developmental stages of the parasite within the mammalian host. They are also involved in the production of Plasmodium-derived extracellular vesicles (EVs), which play an important role in the infection process, either by providing nutrients for parasite growth or by contributing to the immunopathophysiology of the disease. For example, during the hepatic stage, Plasmodium-derived EVs contribute to parasite virulence by modulating the host immune response. EVs help in evading the different autophagy mechanisms deployed by the host for parasite clearance. During cerebral malaria, on the other hand, parasite-derived EVs promote an astrocyte-mediated inflammatory response, through the induction of a non-conventional host autophagy pathway. In this review, we will discuss the cross-talk between Plasmodium-derived microvesicles and autophagy, and how it influences the outcome of infection.

Plasmodium yoelii Uses a TLR3-Dependent Pathway to Achieve Mammalian Host Parasitism.

Malaria is associated with complicated immunopathogenesis. In this study, we provide evidence for an unexpected role of TLR3 in promoting the establishment of Plasmodium yoelii infection through delayed clearance of parasitemia in wild type C57BL/6jRj (B6) compared with TLR3 knockout mice. In this study, we confirmed an increased expression of Tlr3, Trif, Tbk1, and Irf7/Irf3 in the liver 42 h postinfection and the initiation of an early burst of proinflammatory response such as Ifng, NF-kB, and Tnfa in B6 mice that may promote parasite fitness. Interestingly, in the absence of TLR3, we showed the involvement of high IFN-γ and lower type I IFN response in the early clearance of parasitemia. In parallel, we observed an increase in splenic NK and NKT cells expressing TLR3 in infected B6 mice, suggesting a role for TLR sensing in the innate immune response. Finally, we find evidence that the increase in the frequency of CD19+TLR3+ B cells along with reduced levels of total IgG in B6 mice possibly suggests the initiation of TLR3-dependent pathway early during P. yoelii infection. Our results thus reveal a new mechanism in which a parasite-activated TLR3 pathway promotes blood stage infection along with quantitative and qualitative differences in Ab responses.

Expression of CD300lf by microglia contributes to resistance to cerebral malaria by impeding the neuroinflammation.

Genetic mapping and genome-wide studies provide evidence for the association of several genetic polymorphisms with malaria, a complex pathological disease with multiple severity degrees. We have previously described Berr1and Berr2 as candidate genes identified in the WLA/Pas inbreed mouse strain predisposing to resistance to cerebral malaria (CM) induced by P. berghei ANKA. We report in this study the phenotypic and functional characteristics of a congenic strain we have derived for Berr2WLA allele on the C57BL/6JR (B6) background. B6.WLA-Berr2 was found highly resistant to CM compared to C57BL/6JR susceptible mice. The mechanisms associated with CM resistance were analyzed by combining genotype, transcriptomic and immune response studies. We found that B6.WLA-Berr2 mice showed a reduced parasite sequestration and blood-brain barrier disruption with low CXCR3+ T cell infiltration in the brain along with altered glial cell response upon P. berghei ANKA infection compared to B6. In addition, we have identified the CD300f, belonging to a family of Ig-like encoding genes, as a potential candidate associated with CM resistance. Microglia cells isolated from the brain of infected B6.WLA-Berr2 mice significantly expressed higher level of CD300f compared to CMS mice and were associated with inhibition of inflammatory response.

Heme dampens T-cell sequestration by modulating glial cell responses during rodent cerebral malaria.

Cerebral malaria is the deadliest complication of Plasmodium falciparum infection. Its pathophysiology is associated with a strong pro-inflammatory reaction and the activation of glial cells. Among modulators released during the infection, heme seems to play a controversial role in the pathophysiology of malaria. Herein, we first investigated the phenotype of glial cells during cerebral malaria in C57BL/6 mice infected with P. berghei ANKA. Given the fact that high levels of heme were associated with cerebral malaria, we then investigated its impact on microglial, astrocyte, and T cell responses to further clarify its contribution in the neuropathophysiology. Surprisingly, we found that administration of heme twice a day from day three of infection induced the expression of the Heme oxygenase-1 (Hmox1) gene and prevented brain damages. More specifically, heme inhibited the M1 phenotype of microglia, hampered the activation of astrocytes, and decreased the cerebral expression of Ifng, Tnfa and Ip10. Heme might that way alter the migration of pathogenic CD4 and CD8 T lymphocytes within the brain observed during cerebral malaria. Taking into account that cerebral malaria results from a complex interplay between host- and parasite-derived factors, it is possible that genetic polymorphisms of Hmox1, which could be associated with the control of systemic levels of heme during P. falciparum infection, might explain its dual role and its contribution to the resistance to cerebral malaria.

High levels of immunoglobulin E autoantibody to 14-3-3 epsilon protein correlate with protection against severe Plasmodium falciparum malaria.

Plasmodium falciparum infection generally induces elevated total plasma levels of immunoglobulins, some of which recognize self- or parasite-specific antigens. To our knowledge, we are the first to report high levels of functional immunoglobulin E (IgE) autoantibodies recognizing brain 14-3-3 protein ε in asymptomatic P. falciparum malaria. 14-3-3 ε protein belongs to a family of proteins that binds to CD81, a member of the tetraspanin superfamily elicited in hepatocyte invasion by sporozoites. Levels of expression of 14-3-3 ε protein were found to be increased in vivo and in vitro during Plasmodium yoelii and P. falciparum intrahepatic development. Collectively, these results indicate that self-reactive IgE is produced during malaria. In addition, the negative correlation between levels of self-reactive IgE to 14-3-3 ε protein and parasitemia in asymptomatic malaria due to P. falciparum supports a role for these IgE molecules in defense mechanisms, probably by interfering with development of liver-stage parasites through the CD81 pathway.

An early burst of IFN-gamma induced by the pre-erythrocytic stage favours Plasmodium yoelii parasitaemia in B6 mice.

BACKGROUND: In murine models of malaria, an early proinflammatory response has been associated with the resolution of blood-stage infection. To dissect the protective immune mechanism that allow the control of parasitaemia, the early immune response of C57BL/6 mice induced during a non-lethal plasmodial infection was analysed. METHODS: Mice were infected with Plasmodium yoelii 265BY sporozoites, the natural invasive form of the parasite, in order to complete its full life cycle. The concentrations of three proinflammatory cytokines in the sera of mice were determined by ELISA at different time points of infection. The contribution of the liver and the spleen to this cytokinic response was evaluated and the cytokine-producing lymphocytes were identified by flow cytometry. The physiological relevance of these results was tested by monitoring parasitaemia in genetically deficient C57BL/6 mice or wild-type mice treated with anti-cytokine neutralizing antibody. Finally, the cytokinic response in sera of mice infected with parasitized-RBCs was analysed. RESULTS: The early immune response of C57BL/6 mice to sporozoite-induced malaria is characterized by a peak of IFN-gamma in the serum at day 5 of infection and splenic CD4 T lymphocytes are the major producer of this cytokine at this time point. Somewhat unexpected, the parasitaemia is significantly lower in P. yoelii-infected mice in the absence of IFN-gamma. More precisely, at early time points of infection, IFN-gamma favours parasitaemia, whereas helping to clear efficiently the blood-stage parasites at later time points. Interestingly, the early IFN-gamma burst is induced by the pre-erythrocytic stage. CONCLUSION: These results challenge the current view regarding the role of IFN-gamma on the control of parasite growth since they show that IFN-gamma is not an essential mediator of protection in P. yoelii-infected C57BL/6 mice. Moreover, the mice parasitaemia is more efficiently controlled in the absence of an early IFN-gamma production, suggesting that this cytokine promotes parasite's growth. Finally, this early burst of IFN-gamma is induced by the pre-erythrocytic stage, showing the impact of this stage on the immune response taking place during the subsequent erythrocytic stage.

Primary infection of C57BL/6 mice with Plasmodium yoelii induces a heterogeneous response of NKT cells.

NKT cells are a population of innate-like lymphocytes that display effector functions and immunoregulatory properties. We characterized the NKT cell response induced in C57BL/6 mice during a primary infection with Plasmodium yoelii sporozoites. We observed a heterogeneous NKT cell response that differed between liver and spleen. Hepatic NKT cells found in infected livers consisted mainly of CD1d-dependent CD4+ and double-negative (DN) NKT cells, whereas CD1d-independent NKT cells exhibiting a TCR(high) CD4(high) phenotype were prominent among splenic NKT cells during the infection. Hepatic and splenic NKT cells isolated from infected mice were activated and secreted mainly gamma interferon and tumor necrosis factor alpha in response to stimulation. Finally, P. yoelii-activated hepatic DN NKT cells inhibited the parasite's liver stage in a CD1d-dependent manner in vitro. However, experiments using B6.CD1d-deficient mice showed that CD1d and CD1d-restricted NKT cells are not necessary to control the parasite's development in vivo during neither the preerythrocytic stage nor the erythrocytic stage. Thus, our results show that a primary P. yoelii infection induces a heterogeneous and organ-specific response of NKT cells and that CD1d-dependent NKT cells play a minor role in the control of the development of Plasmodium in vivo in our model.

[The new doctor-patient relationship: the advent of "self-diagnosis"]. / La nouvelle relation médecin-patient et l'avènement de l'autodiagnostic.

The doctor-patient relationship has evolved enormously over the years. A series of health crises ("tainted blood", asbestos, etc.) have led patients to distrust their doctors. Associations have been created to defend patients' interests and to enable them to get the information they need. The internet has invaded most French homes, bringing direct information on health problems. New medical legislation has enhanced patients' rights. All these changes have reduced patients' dependency on their doctors, particularly when it come to information, and have led to the advent of "self-diagnosis" and "self-prescription".

NK cell responses to Plasmodium infection and control of intrahepatic parasite development.

Various components of innate and adaptive immunity contribute to host defenses against Plasmodium infection. We investigated the contribution of NK cells to the immune response to primary infection with Plasmodium yoelii sporozoites in C57BL/6 mice. We found that hepatic and splenic NK cells were activated during infection and displayed different phenotypic and functional properties. The number of hepatic NK cells increased whereas the number of splenic NK cells decreased. Expression of the Ly49 repertoire was modified in the spleen but not in the liver. Splenic and hepatic NK cells have a different inflammatory cytokines profile production. In addition, liver NK cells were cytotoxic to YAC-1 cells and P. yoelii liver stages in vitro but not to erythrocytic stages. No such activity was observed with splenic NK cells from infected mice. These in vitro results were confirmed by the in vivo observation that Rag2(-/-) mice were more resistant to sporozoite infection than Rag2(-/-) gamma c(-/-) mice, whereas survival rates were similar for the two strains following blood-stage infection. Thus, NK cells are involved in early immune mechanisms controlling Plasmodium infection, mostly at the pre-erythrocytic stage.

Current multiplanar imaging of the stapes.

PURPOSE: CT analysis of the stapes is difficult in the axial plane (AP), because of its oblique orientation. Oblique axial reformations could provide a more precise analysis of the stapes in normal and pathologic conditions. MATERIALS AND METHODS: CT of the temporal bone was performed in 31 patients. Only the normal side was examined in the AP and oblique axial plane (OAP), in the plane of the stapes superstructure. Conspicuousness of each stapes component was evaluated in both planes by 2 independent readers. Reproducibility between the 2 readers (R1 and R2) and comparison of conspicuousness between the AP and the OAP in the analysis of the stapes crura were evaluated. The normal position of the stapes arch in relationship to the footplate was determined in the OAP by using biometric landmarks. RESULTS: Conspicuousness of the stapes crura was increased by using OAP. The conspicuousness of the anterior crus was enhanced in 38% with the OAP according to R1 (P < .05) and 32% according to R2 (P < .05). The conspicuousness of the posterior crus was enhanced in 35% with the OAP according to R1 (P < .05), but not significantly enhanced in 22% with the OAP according to R2 (P = .095). Analysis of conspicuousness of the stapes crura was reproducible according to the kappa test. A perpendicular line to the footplate intersecting its midportion crosses the stapes head and the long process of the incus in the OAP in normal patients. CONCLUSION: OAP could enhance the CT analysis of the stapes and provide useful biometric landmarks in pathologic conditions.

Dynamic maneuvers in local staging of head and neck malignancies with current imaging techniques: principles and clinical applications.

Imaging has been widely demonstrated to be important in local staging of head and neck malignancies as a complement to clinical examination, including endoscopy. Recent developments in multidetector row computed tomography (CT) provide better anatomic resolution within a shorter acquisition time and wider anatomic coverage. However, in many cases lesions still remain undefined. In such cases, performance of dynamic maneuvers could provide useful information about the local extent of a tumor. The usefulness of dynamic maneuvers has increased with the improvement in temporal and spatial resolution that resulted from the most recent techniques of multidetector row CT. The puffed cheek technique and the modified Valsalva maneuver allow evaluation of a lesion that was poorly demonstrated owing to apposition of mucosal surfaces. In some cases, phonation improves demonstration of small lesions of the vocal cords and allows more precise anatomic localization. The open mouth technique allows demonstration of a lesion that was previously overlooked due to dental amalgam artifacts.