Role of the immune response induced by superantigens in the pathogenesis of microbial infections.

Superantigens (SAgs) are microbial proteins which have potent effects on the immune system. They are presented by major histocompatibility complex (MHC) class II molecules and interact with a large number of T cells expressing specific T cell receptor V beta domains. Encounter of a SAg leads initially to the stimulation and subsequently to the clonal deletion of reactive T cells. SAgs are expressed by a wide variety of microorganisms which use them to exploit the immune system to their own advantage. Bacterial SAgs are exotoxins which are linked to several diseases in humans and animals. A classical example is the toxic shock syndrome in which the massive release of cytokines by SAg-reactive cells is thought to play a major pathogenic role. The best characterized viral SAg is encoded by mouse mammary tumour virus (MMTV) and has proved to have a major influence on the viral life cycle by dramatically increasing the efficiency of viral infection. In this paper, we review the general properties of SAgs and discuss the different types of microorganisms which produce these molecules, with a particular emphasis on the role played by the SAg-induced immune response in the course of microbial infections.

Renal responses to three types of renin-angiotensin system blockers in patients with diabetes mellitus on a high-salt diet: a need for higher doses in diabetic patients?

Objective Activation of the renal renin-angiotensin system in patients with diabetes mellitus appears to contribute to the risk of nephropathy. Recently, it has been recognized than an elevation of prorenin in plasma also provides a strong indication of risk of nephropathy. This study was designed to examine renin-angiotensin system control mechanisms in the patient with diabetes mellitus.Methods We enrolled 43 individuals with type 2 diabetes mellitus. All individuals were on a high-salt diet to minimize the contribution of the systemic renin-angiotensin system. After an acute exposure to captopril (25 mg), they were randomized to treatment with either irbesartan (300 mg) or aliskiren (300 mg) for 2 weeks.Results All agents acutely lowered blood pressure and plasma aldosterone, and increased renal plasma flow and glomerular filtration rate. Yet, only captopril and aliskiren acutely increased plasma renin and decreased plasma angiotensin II, whereas irbesartan acutely affected neither renin nor angiotensin II. Plasma renin and angiotensin II subsequently did increase upon chronic irbesartan treatment. When given on day 14, irbesartan and aliskiren again induced the above hemodynamic, renal and adrenal effects, yet without significantly changing plasma renin. Irbesartan at that time did not affect plasma angiotensin II, whereas aliskiren lowered it to almost zero.Conclusion The relative resistance of the renal renin response to acute (irbesartan) and chronic (irbesartan and aliskiren) renin-angiotensin system blockade supports the concept of an activated renal renin-angiotensin system in diabetes, particularly at the level of the juxtaglomerular cell, and implies that diabetic patients might require higher doses of renin-angiotensin system blockers to fully suppress the renal renin-angiotensin system. J Hypertens 29: 2454-2461 (C) 2011 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.

RasGAP-derived fragment N increases the resistance of beta cells towards apoptosis in NOD mice and delays the progression from mild to overt diabetes.

The caspase-3-generated RasGAP N-terminal fragment (fragment N) inhibits apoptosis in a Ras-PI3K-Akt-dependent manner. Fragment N protects various cell types, including insulin-secreting cells, against different types of stresses. Whether fragment N exerts a protective role during the development of type 1 diabetes is however not known. Non-obese diabetic (NOD) mice represent a well-known model for spontaneous development of type 1 diabetes that shares similarities with the diseases encountered in humans. To assess the role of fragment N in type 1 diabetes development, a transgene encoding fragment N under the control of the rat insulin promoter (RIP) was back-crossed into the NOD background creating the NOD-RIPN strain. Despite a mosaic expression of fragment N in the beta cell population of NOD-RIPN mice, islets isolated from these mice were more resistant to apoptosis than control NOD islets. Islet lymphocytic infiltration and occurrence of a mild increase in glycemia developed with the same kinetics in both strains. However, the period of time separating the mild increase in glycemia and overt diabetes was significantly longer in NOD-RIPN mice compared to the control NOD mice. There was also a significant decrease in the number of apoptotic beta cells in situ at 16 weeks of age in the NOD-RIPN mice. Fragment N exerts therefore a protective effect on beta cells within the pro-diabetogenic NOD background and this prevents a fast progression from mild to overt diabetes.

Isoenzyme profiles of Trypanosoma cruzi stocks from different areas of Paraguay

Twenty one Trypanosoma cruzi stocks from humans, domiciliary triatomines and one sylvatic animal of different areas of Paraguay were subjected to isoenzyme analysis. Thirteen enzyme systems (15 loci in total) were studied. MN cl2 (clonets 39) and SO34 cl4 (clonets 20) were used as references. Relationships between stocks were depicted by an UPGMA dendrogram constructed using the Jaccard´s distances matrix. Among the Paraguayan stocks 14 zymodemes were identified (Par1 to Par14), Par 5 being the most frequent. Polymorphism rate and clonal diversity were 0.73 and 0.93, respectively. Average number of alleles per polymorphic locus was 2.5 (range 2-4). These measurements show a high diversity, which is confirmed by the dendrogram topology. All stocks belong to the same lineage, as MN cl2 reference strain (T. cruzi II). Moreover three distinct subgroups were identified and two of them correspond to Brazilian and Bolivian zymodemes, respectively. The third subgroup, the most common in Paraguay, is related to Tulahuen stock. The large geographical distribution of some zymodemes agrees with the hypothesis of clonality for T. cruzi populations. However sample size was not adequate to detect genetic recombination in any single locality.

Different epitopes of the LACK protein are recognized by V beta 4 V alpha 8 CD4+ T cells in H-2b and H-2d mice susceptible to Leishmania major.

After inoculation of Leishmania major, a rapid production of IL-4 by LACK-specific CD4+ T cells has been shown to drive Th2 cell development in susceptible mice i.e. BALB/c and C57BL/6 mice rendered susceptible by neutralization of IFN-gamma at the onset of infection. Here, we showed that peptide AA 156-173 induced an early IL-4 mRNA expression not only in BALB/c mice but also in resistant B10.D2 mice when IFN-gamma is neutralized. Epitope mapping of LACK protein demonstrated that peptide containing AA 293-305 induced early IL-4 mRNA transcripts in susceptible H-2b mice i.e. BALB/b and resistant C57BL/6 mice when IFN-gamma is neutralized. Stringently, the early IL-4 response to the H-2d (AA 156-173) or the H-2b (AA 293-305) epitopes occurred in V beta 4 V alpha 8 CD4+ T cells from either H-2d or H-2b susceptible mice, respectively.

Dynamics of evolution and resistance to starvation of Triatoma vitticeps (Stal 1859) (Reduviidae: Triatominae), submitted to two different regimens of food deprivation

The resistance to starvation of Triatoma vitticeps has been analyzed comparatively, according to different regimens of food deprivation under laboratory conditions. One cohort, composed of 100 specimens of each evolutionary nymphal stage, was submitted to continuous fasting until death; the second group, arranged in the same way, was fed once on chicken. Through this work, it was possible not only to compare the results obtained from the first group with other authors' results but, also, to analyze the dynamics of evolution, molting, longevity and the increase in insect longevity, in the second group. The average values recorded for survival time revealed statistical differences between the two groups. Among the important results detected, there is one that deserves to be emphasized: the incredible increase in longevity among insects that received only one feed - an average increase in survival time that reached 2.95 to 3.30 times in nymphs of 3rd and 4th stages, respectively. One 5th stage nymph survived for up to 350 days and the females may triplicate their survival rate, what represents an important epidemiological factor. The knowledge about this type of biological characteristic of T. vitticeps may contribute to prevent the domiciliation of this species, what seems to be incipient in some municipal districts, in Brazil.

Quantification of in vivo short echo-time proton magnetic resonance spectra at 14.1 T using two different approaches of modelling the macromolecule spectrum

Reliable quantification of the macromolecule signals in short echo-time H-1 MRS spectra is particularly important at high magnetic fields for an accurate quantification of metabolite concentrations (the neurochemical profile) due to effectively increased spectral resolution of the macromolecule components. The purpose of the present study was to assess two approaches of quantification, which take the contribution of macromolecules into account in the quantification step. H-1 spectra were acquired on a 14.1 T/26 cm horizontal scanner on five rats using the ultra-short echo-time SPECIAL (spin echo full intensity acquired localization) spectroscopy sequence. Metabolite concentrations were estimated using LCModel, combined with a simulated basis set of metabolites using published spectral parameters and either the spectrum of macromolecules measured in vivo, using an inversion recovery technique, or baseline simulated by the built-in spline function. The fitted spline function resulted in a smooth approximation of the in vivo macromolecules, but in accordance with previous studies using Subtract-QUEST could not reproduce completely all features of the in vivo spectrum of macromolecules at 14.1 T. As a consequence, the measured macromolecular 'baseline' led to a more accurate and reliable quantification at higher field strengths.

Detection of telomerase activity in Plasmodium falciparum using a nonradioactive method

A simple, quick and sensitive method was used to detect telomerase activity in Plasmodium falciparum. The telomeric repeat amplification protocol (TRAP assay) was modified using electrophoresis and staining with SYBR-green I to detect telomerase activity in a range of 10² to 10(7) parasites. This might be a useful way to ascertain telomerase activity in different types of nontumor cells.

Shared and non-shared antigens from three different extracts of the metacestode of Echinococcus granulosus

Hydatid cyst fluid (HCF), somatic antigens (S-Ag) and excretory-secretory products (ES-Ag) of Echinococcus granulosus protoscoleces are used as the main antigenic sources for immunodiagnosis of human and dog echinococcosis. In order to determine their non-shared as well as their shared antigenic components, these extracts were studied by ELISA-inhibition and immunoblot-inhibition. Assays were carried out using homologous rabbit polyclonal antisera, human sera from individuals with surgically confirmed hydatidosis, and sera from dogs naturally infected with E. granulosus. High levels of cross-reactivity were observed for all antigenic extracts, but especially for ES-Ag and S-Ag. Canine antibodies evidenced lesser avidity for their specific antigens than antibodies from human origin. The major antigenic components shared by HCF, S-Ag, and ES-Ag have apparent molecular masses of 4-6, 20-24, 52, 80, and 100-104 kDa, including doublets of 41/45, 54/57, and 65/68 kDa. Non-shared polypeptides of each antigenic extract of E. granulosus were identified, having apparent masses of 108 and 78 kDa for HCF, of 124, 94, 83, and 75 kDa for S-Ag, and of 89, 66, 42, 39, 37, and 35 kDa for ES-Ag.

Localization of Brugia malayi (sub-periodic) adults in different organs of Mastomys coucha and its influence on microfilaraemia and host antibody response

Lymphatic filariasis caused by nematode parasites Wuchereria bancrofti or Brugia malayi is a spectral disease and produces wide range of immune responses and varying levels ofmicrofilaraemia in infected individuals. The relationship between the immune response of host and the developmental stage of the parasite as well as the microfilariae (mf) density and specific location of the adult worms is yet to be understood. As an experimental model, B. malayi adapted in the experimental animal Mastomys coucha has been used widely for various studies in filariasis. The present study was to assess microfilaraemia as well as the humoral immune response of M. coucha during various stages of B. malayi development and their localization in different organs. The result showed that the density of mf in the circulating blood of the experimental animal depended upon the number of female worms as well as the location and co-existence of male and female worms. The mf density in the blood increased with the increase in the number of females. The clearance of inoculated infective stage (L3) or single sex infection or segregation of male and female to different organs of infected host resulted in amicrofilaraemic condition. With respect to antibody response, those animals cleared L3 after inoculation and those with adult worm as well as mf showed low antibody levels. But those with developmental fourth stage and/or adult worms without mf showed significantly higher antibody levels.

The additive genetic variance after bottlenecks is affected by the number of loci involved in epistatic interactions.

We investigated the role of the number of loci coding for a neutral trait on the release of additive variance for this trait after population bottlenecks. Different bottleneck sizes and durations were tested for various matrices of genotypic values, with initial conditions covering the allele frequency space. We used three different types of matrices. First, we extended Cheverud and Routman's model by defining matrices of "pure" epistasis for three and four independent loci; second, we used genotypic values drawn randomly from uniform, normal, and exponential distributions; and third we used two models of simple metabolic pathways leading to physiological epistasis. For all these matrices of genotypic values except the dominant metabolic pathway, we find that, as the number of loci increases from two to three and four, an increase in the release of additive variance is occurring. The amount of additive variance released for a given set of genotypic values is a function of the inbreeding coefficient, independently of the size and duration of the bottleneck. The level of inbreeding necessary to achieve maximum release in additive variance increases with the number of loci. We find that additive-by-additive epistasis is the type of epistasis most easily converted into additive variance. For a wide range of models, our results show that epistasis, rather than dominance, plays a significant role in the increase of additive variance following bottlenecks.

Activity of Brazilian and Bulgarian propolis against different species of Leishmania

Extracts of propolis samples collected in Brazil and Bulgaria were assayed against four Leishmania species - Leishmania amazonensis, L. braziliensis, L. chagasi from the New World, and L. major from the Old World - associated to different clinical forms of leishmaniasis. The composition of the extracts has been previously characterized by high temperature high resolution gas chromatography coupled to mass spectrometry. Considering the chemical differences among the extracts and the behavior of the parasites, it was observed significant differences in the leishmanicidal activities with IC50/1 day values in the range of 2.8 to 229.3 µg/ml . An overall analysis showed that for all the species evaluated, Bulgarian extracts were more active than the ethanol Brazilian extract. As the assayed propolis extracts have their chemical composition determined it merits further investigation the effect of individual components or their combinations on each Leishmania species.