Cellular immune response of humans to the circumsporozoite protein of Plasmodium vivax

The cellular immune response to the circumsporozoite (CS) protein of plasmodium vivax of individuals from malaria-endemic areas of Brazil was studied. We examined the in vitro proliferative response of the peripheral blood mononuclear cells (PBMC) of 22 individuals when stimulated with a CS recombinant protein (rPvCS-2) and two other synthetic peptides based on the sequenceof the P. vivax CS protein. Seven of the individuals from malaria-endemic area displayed an antigen specific in vitro proliferative responseto the recombinant protein PvCS-2 and one out of 6, proliferative response to the peptide 308-320. In contrast, none of the individuals displayed a proliferative reponse when stimulated with the D/A peptide which represent some of the repeated units present in this CS protein. Our study, therefore, provides evidence for the presence, withinthe major surface antigen of P. vivax sporozoites, of epitopes capble to induce proliferation of human PBMC.

Experimental heteroxenous cycle of Lagochilascaris minor Leiper, 1909 (Nematoda: Ascarididae) in white mice and in cats

Reports of natural infections of sylvatic carnivores by adult worms of species similar to Lagochilascaris minor in the Neotropical region led to attempts to estabilish experimental cycles in laboratory mice and in cats. Also, larval development was seen in the skeletal muscle of an agouti (Dasyprocta leporina) infected per os with incubated eggs of the parasite obtained from a human case. In cats, adult worms develop and fertile eggs are expelled in the feces: in mice, larval stages of the parasite develop, and are encapsulate in the skeletal muscle, and in the adipose and subcutaneous connective tissue. From our observations, we conclude that the larva infective for the mouse is the early 3rd stage, while for the final host the infective form is the later 3rd stage. A single moult was seen in the mouse, giving rise to a small population of 4th stage larvae, long after the initial infection.

The dynamics of yeast telomeres and silencing proteins through the cell cycle.

Genes integrated near the telomeres of budding yeast have a variegated pattern of gene repression that is mediated by the silent information regulatory proteins Sir2p, Sir3p, and Sir4p. Immunolocalization and fluorescence in situ hybridization (FISH) reveal 6-10 perinuclear foci in which silencing proteins and subtelomeric sequences colocalize, suggesting that these are sites of Sir-mediated repression. Telomeres lacking subtelomeric repeat elements and the silent mating locus, HML, also localize to the periphery of the nucleus. Conditions that disrupt telomere proximal repression disrupt the focal staining pattern of Sir proteins, but not necessarily the localization of telomeric DNA. To monitor the telomere-associated pools of heterochromatin-binding proteins (Sir and Rap1 proteins) during mitotic cell division, we have performed immunofluorescence and telomeric FISH on populations of yeast cells synchronously traversing the cell cycle. We observe a partial release of Rap1p from telomeres in late G2/M, although telomeres appear to stay clustered during G2-phase and throughout mitosis. A partial release of Sir3p and Sir4p during mitosis also occurs. This is not observed upon HU arrest, although other types of DNA damage cause a dramatic relocalization of Sir and Rap1 proteins. The observed cell cycle dynamics were confirmed by direct epifluorescence of a GFP-Rap1p fusion. Using live GFP fluorescence we show that the diffuse mitotic distribution of GFP-Rap1p is restored to the interphase pattern of foci in early G1-phase.

Preliminary investigations on transmission and life cycle of the ear mites of the genus Raillietia trouessart (Acari: Gamasida) parasites of cattle

The life cycle of ear mites of the genus Raillietia Trouessart consists of egg, larva, proto-and deutonymph and adult. The proto-and deutonymph are free living, non feeding instars. The teneral adult is the transfer stage. The minimum period required for completion of the life cycle is approximately eight days.

Molecular and cellular basis of hepatic fibrogenesis in experimental schistosomiasis mansoni infection

Morbidity in schistosomiasis mansoni occurs primaryly as a result of the complications of hepatic fibrosis. Yet, the pathogenesis of schistosomal hepatic fibrosis is poorly understood. The fact that hepatic egg granuloma is the hallmark of this infection suggests a potential role for granulomatous inflamation in hepatic fibrogenesis. Our studies in a murine schistosomiasis model indicate that hepatic granuloma cells secrete a variety of fibrogenic cytokines that may initiate the scarring process. Among these cytokines, we identified a novel protein that we designated fibroplast stimulating factor-1 (FsF-1). FsF-1 is a lymphokine that can stimulate fibroplast growth and matrix synthesis. A notable feature of hepatic fibrosis in this model is that production of FsF-1 and other granuloma-derived fibrogenic cytokines is down-regulated in chronic infection, an event that may be under immunological control. The spontaneous reduction of FsF-1 secretion presumably accounts for reduced scar formation late in infection of mice. In the context of relevant clinical studies, our findings engender the hypothesis that Symmer's fibrosis may develop in a small suppopulation of individuals as a result of immunogenetically-determined dysregulation of fibrogenic cytokine production.

Variation in the intensity of inbreeding depression among successive life-cycle stages and generations in gynodioecious Silene vulgaris (Caryophyllaceae).

Inbreeding depression is one of the hypotheses explaining the maintenance of females within gynodioecious plant populations. However, the measurement of fitness components in selfed and outcrossed progeny depends on life-cycle stage and the history of inbreeding. Comparative data indicate that strong inbreeding depression is more likely to occur at later life-cycle stages. We used hermaphrodite individuals of Silene vulgaris originating from three populations located in different valleys in the Swiss Alps to investigate the effect of two generations of self- and cross-fertilization on fitness components among successive stages of the life cycle in a glasshouse experiment. We detected significant inbreeding depression for most life-cycle stages including: the number of viable and aborted seeds per fruit, probability of germination, above ground biomass, probability of flowering, number of flowers per plant, flower size and pollen viability. Overall, the intensity of inbreeding depression increased among successive stages of the life cycle and cumulative inbreeding depression was significantly stronger in the first generation (delta approximately 0.5) compared with the second generation (delta approximately 0.35). We found no evidence for synergistic epistasis in our experiment. Our finding of more intense inbreeding depression during later stages of the life cycle may help to explain the maintenance of females in gynodioecious populations of S. vulgaris because purging of genetic load is less likely to occur.

Life cycle of Misumenops pallida (Araneae, Thomisidae)

Postembryonic development of Misumenops pallida (Keyserling) (Araneae, Thomisidae), one of the most abundant predator species in soybean fields in Buenos Aires Province (Argentina) was studied. The life cycle was observed in the laboratory from egg sacs collected in the field, and from egg sacs spined in the laboratory by gravid females collected in the field. Results indicated that instar length and feeding rate increased throughout the life cycle being higher in females than in males. Greater mortality was observed to third and fourth instars decreasing thereafter. These results may contribute to deternmine the efficiency of this species as a natural enemy of insect pests of soybean.

Life cycle and influence of age and feeding on the first mating of Triatoma mazzottii (Hemiptera: Reduviidae)

A cohort of 100 eggs of Triatoma mazzottii Usinger was studied to obtain information on its life cycle. Egg incubation took 24 days; mean duration of 1st, 2nd, 3rd, 4th, and 5th instar nymphs was 27, 36, 39, 46 and 64 days respectively; mean time from egg to adult was 236 days. The total duration of the nymphal stages was 212 days. The total nymph mortality in cohort was 16.3% and the embryonic egg mortality was 14.0%. The grater mortality occured in the 2nd instar. The average number of eggs/female/week was 9.8 during 15 weeks of observation. Of the total eggs laid (2,514), only 58.7% hatched. The total of insects that achieved the adult stage (72), 38 were females (52.8%), and 34 were males (47.2%). The influence of age and feeding on the first mating of T. mazzottii were also studied. It was found that the first mating depended on the male's age and it was on the average 30 days after the last imaginal molt. The female could be mating since 2nd days after the imaginal life. The nutritional status did not play an important role in the capacity of the insect for the first mating.

Dynamical modeling and analysis of large cellular regulatory networks.

The dynamical analysis of large biological regulatory networks requires the development of scalable methods for mathematical modeling. Following the approach initially introduced by Thomas, we formalize the interactions between the components of a network in terms of discrete variables, functions, and parameters. Model simulations result in directed graphs, called state transition graphs. We are particularly interested in reachability properties and asymptotic behaviors, which correspond to terminal strongly connected components (or "attractors") in the state transition graph. A well-known problem is the exponential increase of the size of state transition graphs with the number of network components, in particular when using the biologically realistic asynchronous updating assumption. To address this problem, we have developed several complementary methods enabling the analysis of the behavior of large and complex logical models: (i) the definition of transition priority classes to simplify the dynamics; (ii) a model reduction method preserving essential dynamical properties, (iii) a novel algorithm to compact state transition graphs and directly generate compressed representations, emphasizing relevant transient and asymptotic dynamical properties. The power of an approach combining these different methods is demonstrated by applying them to a recent multilevel logical model for the network controlling CD4+ T helper cell response to antigen presentation and to a dozen cytokines. This model accounts for the differentiation of canonical Th1 and Th2 lymphocytes, as well as of inflammatory Th17 and regulatory T cells, along with many hybrid subtypes. All these methods have been implemented into the software GINsim, which enables the definition, the analysis, and the simulation of logical regulatory graphs.

A novel merozoite surface antigen of Plasmodium falciparum (MSP-3) identified by cellular-antibody cooperative mechanism antigenicity and biological activity of antibodies

We report the identification of a 48kDa antigen targeted by antibodies which inhibit Plasmodium falciparum in vitro growth by cooperation with blood monocytes in an ADCI assay correlated to the naturally acquired protection. This protein is located on the surface of the merozoite stage of P. falciparum, and is detectable in all isolates tested. Epidemiological studies demonstrated that peptides derived from the amino acid sequence of MSP-3 contain potent B and T-cell epitopes recognized by a majority of individuals living in endemic areas. Moreover human antibodies either purified on the recombinant protein, or on the synthetic peptide MSP-3b, as well as antibodies raised in mice, were all found to promote parasite killing mediated by monocytes.

Development of sporogonic cycle of Plasmodium vivax in experimentally infected Anopheles albimanus mosquitoes

The sporogonic cycle of Plasmodium vivax was established and maintained under laboratory conditions in two different strains of Anopheles albimanus mosquitoes using as a parasite source blood from human patients or from Aotus monkeys infected with the VCC-2 P.vivax colombian isolate. Both the Tecojate strain isolate from Guatemala and the Cartagena strain from the colombian Pacific coast were susceptible to infections with P.vivax. A higher percentage of Cartagena mosquitoes was infected per trial, however the Tecojate strain developed higher sporozoite loads. Intravenous inoculation of Aotus monkeys with sporozoites obtained from both anopheline strains resulted in successful blood infections. Animals infected with sporozoites from the Tecojate strain presented a patent period of 21-32 days whereas parasitemia appeared between days 19-53 in monkeys infected with sporozites from Cartagena strain.

Peroxisome proliferator-activated receptors: insight into multiple cellular functions.

Peroxisome proliferator-activated receptors, PPARs, (NR1C) are nuclear hormone receptors implicated in energy homeostasis. Upon activation, these ligand-inducible transcription factors stimulate gene expression by binding to the promoter of target genes. The different structural domains of PPARs are presented in terms of activation mechanisms, namely ligand binding, phosphorylation, and cofactor interaction. The specificity of ligands, such as fatty acids, eicosanoids, fibrates and thiazolidinediones (TZD), is described for each of the three PPAR isotypes, alpha (NR1C1), beta (NR1C2) and gamma (NR1C3), so as the differential tissue distribution of these isotypes. Finally, general and specific functions of the PPAR isotypes are discussed, namely their implication in the control of inflammatory responses, cell proliferation and differentiation, the roles of PPARalpha in fatty acid catabolism and of PPARgamma in adipogenesis.

In vivo detection of brain Krebs cycle intermediate by hyperpolarized magnetic resonance.

The Krebs (or tricarboxylic acid (TCA)) cycle has a central role in the regulation of brain energy regulation and metabolism, yet brain TCA cycle intermediates have never been directly detected in vivo. This study reports the first direct in vivo observation of a TCA cycle intermediate in intact brain, namely, 2-oxoglutarate, a key biomolecule connecting metabolism to neuronal activity. Our observation reveals important information about in vivo biochemical processes hitherto considered undetectable. In particular, it provides direct evidence that transport across the inner mitochondria membrane is rate limiting in the brain. The hyperpolarized magnetic resonance protocol designed for this study opens the way to direct and real-time studies of TCA cycle kinetics.

Utilització de plantes d'Arabidopsis thaliana mutants de CK2 per a l'establiment de línies cel·lulars i per a l'estudi de la implicació de la CK2 en l'estructuració de la cromatina

La proteïna CK2 és una Ser/Thr fosfotransferasa evolutivament conservada. Està formada per dues subunitats diferents, α (catalítica) i β (reguladora), que s’associen en un complex heterotetramèric (α2β2). L’activitat d’aquest enzim està regulada per varis mecanismes que la modulen diferencialment en funció del substrat, entre ells, la localització subcel·lular de les diferents subunitats. A partir de plantes transgèniques que contenen les subunitats de CK2 fusionades a una proteïna fluorescent (GFP o YFP) hem establert línies cel·lulars que permetran analitzar, en treballs futurs, els canvis de localització subcel·lular de les subunitats de CK2 provocats per diferents estímuls. La CK2 intervé en un gran nombre de processos cel·lulars, entre d’altres, metabolisme, transport a nucli, control del cicle cel·lular i reparació del DNA. Amb la finalitat d’estudiar el paper de la CK2 en el desenvolupament de les plantes, membres del grup van generar un mutant dominant negatiu per transformació estable de plantes d’Arabidopsis thaliana. Estudis previs mostraven que la pèrdua d’activitat CK2 en aquestes plantes provocava una alteració de l’activitat mitòtica i un bloqueig del cicle cel·lular. Els resultats obtinguts en aquest treball indiquen que aquests fenotips podrien ser conseqüència de la implicació de la CK2 en processos d’estructuració de la cromatina.