How a haemosporidian parasite of bats gets around: the genetic structure of a parasite, vector and host compared.

Parasite population structure is often thought to be largely shaped by that of its host. In the case of a parasite with a complex life cycle, two host species, each with their own patterns of demography and migration, spread the parasite. However, the population structure of the parasite is predicted to resemble only that of the most vagile host species. In this study, we tested this prediction in the context of a vector-transmitted parasite. We sampled the haemosporidian parasite Polychromophilus melanipherus across its European range, together with its bat fly vector Nycteribia schmidlii and its host, the bent-winged bat Miniopterus schreibersii. Based on microsatellite analyses, the wingless vector, and not the bat host, was identified as the least structured population and should therefore be considered the most vagile host. Genetic distance matrices were compared for all three species based on a mitochondrial DNA fragment. Both host and vector populations followed an isolation-by-distance pattern across the Mediterranean, but not the parasite. Mantel tests found no correlation between the parasite and either the host or vector populations. We therefore found no support for our hypothesis; the parasite population structure matched neither vector nor host. Instead, we propose a model where the parasite's gene flow is represented by the added effects of host and vector dispersal patterns.

A comparative study of the intercellular connections between parasite/host in two Gelidiocolax/Gelidium algal parasitic systems

Comparative ultrastructural study of the intercellular connections between parasite and host cells in two algal parasitic systems, Gelidiocolax christianae Feldmann and Feldmann/Ge/iV/ium spathulatum (Kutz.) Bornet and Gelidiocolax deformans Seoane Camba/Gelidium sesquipedale (Clem.) Thur, shows quantitative and structural differences. The number of free conjunctor cells (before fusión with the adjacent host cells) differs between the two parasitic systems and is inversely related to the number of complex pit connections. The fibrillar cell wall structure of the conjunctor cells and the lamellar structure of the complex pit plugs in the two systems are also different A hypothesis concerning the different activity of the conjuntor cell wall in the two parasitic systems, related with the different structural appearance, is proposed.

Measles virus infection – Interplay between virus and host cells

Measles, caused by measles virus (MV), is a highly contagious viral disease causing severe respiratory infection and a typical rash. Despite the availability of a protective vaccine, measles is still the leading vaccine-preventable cause of childhood mortality worldwide. The high mortality associated with the disease is mainly due to an increased susceptibility to secondary infections during the period of immunosuppression that continues for several weeks after recovery. The present study was undertaken to elucidate the role of cytoskeletal components in the regulation of MV infection. The most interesting finding was that MV replication was activated in unstimulated peripheral blood mononuclear cells (PBMC) when globular actin was converted into the filamentous form with jasplakinolide. This provides a new aspect in our understanding of MV infection in PBMC. In the second part of the thesis we investigated MV-induced structural changes of cellular nuclear matrix, which is a proteinaceous framework of the nucleus similar to the cytoskeleton in the cytoplasm. We showed that cleavage of nuclear markers was virusspecific and a general caspase inhibitor rescued MV-infected cells from cell death. Furthermore, we studied MV-induced innate immune mechanisms in lung epithelial and endothelial cells. Our results showed that MV infection resulted in activation of the double stranded RNA (dsRNA) binding molecules melanoma differentiation-associated gene 5 (mda-5), retinoic acid inducible gene I (RIG-I), and toll-like receptor 3 (TLR3) gene expression, followed by high expression of antiviral cytokine mRNA.

Apoptosis in parasites and parasite-induced apoptosis in the host immune system: a new approach to parasitic diseases

Apoptosis, a form of programmed cell death (PCD), has been described as essential for normal organogenesis and tissue development, as well as for the proper function of cell-renewal systems in adult organisms. Apoptosis is also pivotal in the pathogenesis of several different diseases. In this paper we discuss, from two different points of view, the role of apoptosis in parasitic diseases. The description of apoptotic death in three different species of heteroxenic trypanosomatids is reviewed, and considerations on the phylogenesis of apoptosis and on the eventual role of PCD on their mechanism of pathogenesis are made. From a different perspective, an increasing body of evidence is making clear that regulation of host cell apoptosis is an important factor on the definition of a host-pathogen interaction. As an example, the molecular mechanisms by which Trypanosoma cruzi is able to induce apoptosis in immunocompetent cells, in a murine model of Chagas' disease, and the consequences of this phenomenon on the outcome of the experimental disease are discussed.

New insights into the impact of Lactobacillus population on host-bacteria metabolic interplay

We aimed at evaluating the association between intestinal Lactobacillus sp. composition and their metabolic activity with the host metabolism in adult and elderly individuals. Faecal and plasma metabolites were measured and correlated to the Lactobacillus species distribution in healthy Estonian cohorts of adult (n=16; <48 y) and elderly (n=33; >65 y). Total cholesterol, LDL, C-reactive protein and glycated hemoglobin were statistically higher in elderly, while platelets, white blood cells and urinary creatinine were higher in adults. Aging was associated with the presence of L. paracasei and L. plantarum and the absence of L. salivarius and L. helveticus. High levels of intestinal Lactobacillus sp. were positively associated with increased concentrations of faecal short chain fatty acids, lactate and essential amino acids. In adults, high red blood cell distribution width was positively associated with presence of L. helveticus and absence of L. ruminis. L. helveticus was correlated to lactate and butyrate in faecal waters. This indicates a strong relationship between the composition of the gut Lactobacillus sp. and host metabolism. Our results confirm that aging is associated with modulations of blood biomarkers and intestinal Lactobacillus species composition. We identified specific Lactobacillus contributions to gut metabolic environment and related those to blood biomarkers. Such associations may prove useful to decipher the biological mechanisms underlying host-gut microbial metabolic interactions in an ageing population.

A Social Parasite Evolved Reproductive Isolation from Its Fungus-Growing Ant Host in Sympatry

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Role of cyclooxygenase-2 in Trypanosoma cruzi survival in the early stages of parasite host-cell interaction

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Trypanosoma cruzi invades host cells through the activation of endothelin and bradykinin receptors: a converging pathway leading to chagasic vasculopathy

BACKGROUND AND PURPOSE Independent studies in experimental models of Trypanosoma cruzi appointed different roles for endothelin-1 (ET-1) and bradykinin (BK) in the immunopathogenesis of Chagas disease. Here, we addressed the hypothesis that pathogenic outcome is influenced by functional interplay between endothelin receptors (ETAR and ETBR) and bradykinin B2 receptors (B2R). EXPERIMENTAL APPROACH Intravital microscopy was used to determine whether ETR/B2R drives the accumulation of rhodamine-labelled leucocytes in the hamster cheek pouch (HCP). Inflammatory oedema was measured in the infected BALB/c paw of mice. Parasite invasion was assessed in CHO over-expressing ETRs, mouse cardiomyocytes, endothelium (human umbilical vein endothelial cells) or smooth muscle cells (HSMCs), in the presence/absence of antagonists of B2R (HOE-140), ETAR (BQ-123) and ETBR (BQ-788), specific IgG antibodies to each GPCRs; cholesterol or calcium-depleting drugs. RNA interference (ETAR or ETBR genes) in parasite infectivity was investigated in HSMCs. KEY RESULTS BQ-123, BQ-788 and HOE-140 reduced leucocyte accumulation in HCP topically exposed to trypomastigotes and blocked inflammatory oedema in infected mice. Acting synergistically, ETAR and ETBR antagonists reduced parasite invasion of HSMCs to the same extent as HOE-140. Exogenous ET-1 potentiated T. cruzi uptake by HSMCs via ETRs/B2R, whereas RNA interference of ETAR and ETBR genes conversely reduced parasite internalization. ETRs/B2R-driven infection in HSMCs was reduced in HSMC pretreated with methyl-beta-cyclodextrin, a cholesterol-depleting drug, or in thapsigargin-or verapamil-treated target cells. CONCLUSIONS AND IMPLICATIONS Our findings suggest that plasma leakage, a neutrophil-driven inflammatory response evoked by trypomastigotes via the kinin/endothelin pathways, may offer a window of opportunity for enhanced parasite invasion of cardiovascular cells.

Hostile takeover by Plasmodium: reorganization of parasite and host cell membranes during liver stage egress

The protozoan parasite Plasmodium is transmitted by female Anopheles mosquitoes and undergoes obligatory development within a parasitophorous vacuole in hepatocytes before it is released into the bloodstream. The transition to the blood stage was previously shown to involve the packaging of exoerythrocytic merozoites into membrane-surrounded vesicles, called merosomes, which are delivered directly into liver sinusoids. However, it was unclear whether the membrane of these merosomes was derived from the parasite membrane, the parasitophorous vacuole membrane or the host cell membrane. This knowledge is required to determine how phagocytes will be directed against merosomes. Here, we fluorescently label the candidate membranes and use live cell imaging to show that the merosome membrane derives from the host cell membrane. We also demonstrate that proteins in the host cell membrane are lost during merozoite liberation from the parasitophorous vacuole. Immediately after the breakdown of the parasitophorous vacuole membrane, the host cell mitochondria begin to degenerate and protein biosynthesis arrests. The intact host cell plasma membrane surrounding merosomes allows Plasmodium to mask itself from the host immune system and bypass the numerous Kupffer cells on its way into the bloodstream. This represents an effective strategy for evading host defenses before establishing a blood stage infection.

The transforming parasite Theileria co-opts host cell mitotic and central spindles to persist in continuously dividing cells

The protozoan parasite Theileria inhabits the host cell cytoplasm and possesses the unique capacity to transform the cells it infects, inducing continuous proliferation and protection against apoptosis. The transforming schizont is a multinucleated syncytium that resides free in the host cell cytoplasm and is strictly intracellular. To maintain transformation, it is crucial that this syncytium is divided over the two daughter cells at each host cell cytokinesis. This process was dissected using different cell cycle synchronization methods in combination with the targeted application of specific inhibitors. We found that Theileria schizonts associate with newly formed host cell microtubules that emanate from the spindle poles, positioning the parasite at the equatorial region of the mitotic cell where host cell chromosomes assemble during metaphase. During anaphase, the schizont interacts closely with host cell central spindle. As part of this process, the schizont recruits a host cell mitotic kinase, Polo-like kinase 1, and we established that parasite association with host cell central spindles requires Polo-like kinase 1 catalytic activity. Blocking the interaction between the schizont and astral as well as central spindle microtubules prevented parasite segregation between the daughter cells during cytokinesis. Our findings provide a striking example of how an intracellular eukaryotic pathogen that evolved ways to induce the uncontrolled proliferation of the cells it infects usurps the host cell mitotic machinery, including Polo-like kinase 1, one of the pivotal mitotic kinases, to ensure its own persistence and survival.

The strategies of the Theileria parasite: a new twist in host-pathogen interactions

Theileria parasites infect and transform cells of the ruminant immune system. Continuous proliferation and survival of Theileria-transformed cells involves the well-orchestrated activation of several host-cell signalling pathways. Constitutive NF-kappa B (nuclear factor kappa B) activation is accomplished by recruiting the IKK (I kappa B kinase) complex, a central regulator of NF-kappa B pathways, to the surface of the transforming schizont, where it becomes permanently activated. Constitutive activation of the PI-3K-PKB [phosphoinositide 3-kinase-(Akt) protein kinase B] pathway is likely to be indirect and is essential for continuous proliferation. Theileria-transformed T cells express a range of anti-apoptotic proteins that can be expected to provide protection against apoptosis induced by death receptors, as well as cellular control mechanisms that are mobilised to eliminate cells that entered a cycle of uncontrolled proliferation.

Hijacking of host cell IKK signalosomes by the transforming parasite Theileria

Parasites have evolved a plethora of mechanisms to ensure their propagation and evade antagonistic host responses. The intracellular protozoan parasite Theileria is the only eukaryote known to induce uncontrolled host cell proliferation. Survival of Theileria-transformed leukocytes depends strictly on constitutive nuclear factor kappa B (NF-kappaB) activity. We found that this was mediated by recruitment of the multisubunit IkappaB kinase (IKK) into large, activated foci on the parasite surface. IKK signalosome assembly was specific for the transforming schizont stage of the parasite and was down-regulated upon differentiation into the nontransforming merozoite stage. Our findings provide insights into IKK activation and how pathogens subvert host-cell signaling pathways.

Genome of the host-cell transforming parasite Theileria annulata compared with T. parva

Theileria annulata and T. parva are closely related protozoan parasites that cause lymphoproliferative diseases of cattle. We sequenced the genome of T. annulata and compared it with that of T. parva to understand the mechanisms underlying transformation and tropism. Despite high conservation of gene sequences and synteny, the analysis reveals unequally expanded gene families and species-specific genes. We also identify divergent families of putative secreted polypeptides that may reduce immune recognition, candidate regulators of host-cell transformation, and a Theileria-specific protein domain [frequently associated in Theileria (FAINT)] present in a large number of secreted proteins.