Origins and evolution of antigenic diversity in malaria parasites

Each year, malaria parasites cause more than 500 million infections and 0.5-3 million deaths worldwide, mostly among children under five living in sub-Saharan Africa. In contrast with several viral and bacterial pathogens, which elicit long-lived immunity after a primary infection, these parasites require several years of continuous exposure to confer partial, usually non-sterilizing immune protection. One of the main obstacles to the acquisition of antimalarial immunity is the high degree of antigenic diversity in potential target antigens, which enables parasites to evade immune responses elicited by past exposure to variant forms of the same antigen. Allelic polymorphism, the existence of genetically stable alternative forms of antigen-coding genes, originates from nucleotide replacement mutations and intragenic recombination. In addition, malaria parasites display antigenic variation, whereby a clonal lineage of parasites expresses successively alternate forms of an antigen without changes in genotype. This review focuses on molecular and evolutionary processes that promote allelic polymorphism and antigenic variation in natural malaria parasite populations and their implications for naturally acquired immunity and vaccine development.     

Putative role of heparan sulfate proteoglycan expression and shedding on the proliferation and survival of cells after photodynamic therapy

INTRODUCTION: Photodynamic therapy is based on the selective retention of a photosensitizer by highly proliferating cells and its activation with light at the appropriate wavelength. This combination generates reactive oxygen species that ultimately kill the cells. Some cells, however, may survive photodynamic therapy and the interaction of these cells with the extracellular matrix has profound effect in tumor biology. The knowledge of photodynamic therapy action on the extracellular matrix has not been fully explored. It has been focused mainly on integrins, matrix metalloproteinases and on growth factors and immunological mediators. Other important molecules involved in the regulation of many cell processes are the glycosaminoglycans, polymers of disaccharide units, present on the cell surface and in the extracellular matrix. In most cases, the glycosaminoglycans occur as proteoglycans. AIMS: The purpose of the present investigation is to evaluate heparan sulfate proteoglycan expression and shedding, and its relation to the survival of the remaining cells, after a liposomal-AlClPc based photodynamic treatment. MATERIALS: A wild-type endothelial cell derived from rabbit aorta and its counterpart transfected with EJ-ras oncogene were used. RESULTS: Both cell lines presented augmented heparan sulfate proteoglycan syndecan-4 mRNA expression, augmented synthesis of heparan sulfate chains and increased shedding. Also, the formation of stress fibers on the border of the cells and the arrest in G(1) phase of the cell cycle was observed. CONCLUSIONS: These results show that surviving cells after photodynamic therapy exhibit changes in their morphology and cell processes that differ from that of non-treated cells, and these changes are probably hindering the cells from resuming normal proliferation.     

A preliminary investigation of pre-dispersal seed predation by Acanthoscelides schrankiae Horn (Coleoptera: Bruchidae) in Mimosa bimucronata (DC.) Kuntze trees

This is the first record of Acanthoscelides schrankiae Horn. feeding in seeds of Mimosa bimucronata (DC.) Kuntze. We investigated the pattern of oviposition and seed exploitation by A. schrankiae, and the distribution of mature fruits and seed predation in the inflorescences. We also compared the percentage of predated seeds, the total dry weight of fruits and non-predated seeds, the percentage of aborted seeds, and the percentage of non-emergent insects, among different quadrants of the M. bimucronata canopy. To determine the occurring species, the emergence of bruchids and parasitoids was observed in the laboratory, resulting altogether, only in individuals of A. schrankiae and Horismenus sp. (Hymenoptera: Eulophidae) species, respectively. Mean number of fruits produced in the median region of inflorescence was significantly higher than in the inferior and superior regions, and the frequencies (observed and expected) of predated and non-predated seeds differed among the different regions of inflorescence. Females of A. schrankiae laid their eggs on fruits, and larvae, after emergence, perforated the exocarp to reach the seeds. Most fruits presented one to three eggs and only one bruchid larva was observed in each seed. The highest value of the rate "number of eggs/fruit" and the highest percentage of predated seeds were recorded in April. Dry weight of fruits (total) and seeds (non-predated), proportions of predated seeds, seed abortions, and non-emergent seed predators, were evenly distributed in the canopy.     

Evaluation of the sticky MosquiTRAP for detecting Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) during the dry season in Belo Horizonte, Minas Gerais, Brazil

MosquiTRAP is a sticky trap specifically designed to capture gravid females of Aedes aegypti (L.) and allows the identification of the mosquito in the field during the inspection of the trap. This study aims to compare this sticky trap to larval and ovitrap surveys for field monitoring of A. aegypti during the dry season. The study was conducted from March to June of 2003 in 20 blocks of the district of Itapo?, Belo Horizonte, MG. The traps were monitored every week while the larval survey was conducted on a monthly basis. The larval index: Premise Index (PI) and Breteau Index (BI) had equal values throughout the experiment (1.72 in the first two months and zero in the last two). The container index (CI) during the first two months was 0.09 and 0.1%, respectively and zero in the last two. The Ovitrap Positive Index (OPI) ranged from 16.7 to 76.9%, and the MosquiTRAP Positive Index (MPI) ranged from 0 to 31.5%. The Egg Density Index (EDI) ranged from 26.6 to 82.8, while the Adult Density Index ranged from 0 to 1.6 throughout the experiment. Temperature and rainfall did not affect the Positive and Density Indices, although these environmental variables seemed to have affected the larvae indices. Although the MosquiTRAP caught a low number of Aedes mosquitoes during the study, it was more sensitive than the larval survey to detect the presence of Aedes mosquitoes.     

Neprilysin carboxydipeptidase specificity studies and improvement in its detection with fluorescence energy transfer peptides

We examined the substrate specificity of the carboxydipeptidase activity of neprilysin (NEP) using fluorescence resonance energy transfer (FRET) peptides containing ortho-aminobenzoyl (Abz) and 2,4-dinitrophenyl (Dnp) as a donor/acceptor pair. Two peptide series with general sequences Abz-RXFK(Dnp)-OH and Abz-XRFK(Dnp)-OH (X denotes the position of the altered amino acid) were synthesized to study P1 (cleavage at the X-F bond) and P2 (cleavage at R-F bond) specificity, respectively. In these peptides a Phe residue was fixed in P1' to fulfill the well-known NEP S1' site requirement for a hydrophobic amino acid. In addition, we explored NEP capability to hydrolyze bradykinin (RPPGFSPFR) and its fluorescent derivative Abz-RPPGFSPFRQ-EDDnp (EDDnp=2,4-dinitrophenyl ethylenediamine). The enzyme acts upon bradykinin mainly as a carboxydipeptidase, preferentially cleaving Pro-Phe over the Gly-Phe bond in a 9:1 ratio, whereas Abz-RPPGFSPFRQ-EDDnp was hydrolyzed at the same bonds but at an inverted proportion of 1:9. The results show very efficient interaction of the substrates' C-terminal free carboxyl group with site S2' of NEP, confirming the enzyme's preference to act as carboxydipeptidase at substrates with a free carboxyl-terminus. Using data gathered from our study, we developed sensitive and selective NEP substrates that permit continuous measurement of the enzyme activity, even in crude tissue extracts.     

The structure of CMS2MS2, a mitogenic protein isolated from Carica candamarcensis

In a recent study we showed that two proteinases (CMS2MS2 and CMS2MS3) from Carica candamarcensis enhance mammalian cell proliferation. The aim of the present study is the determination of the primary structure of CMS2MS2 and prediction of its three-dimensional structure. The protein contains 214 residues, including the catalytic triad composed of Cys(25), His(159), and Asn(175). A phylogenetic tree analysis demonstrated that CMS2MS2 ranks closer to chymopapain than to papain. The overall predicted three-dimensional structure is similar to proteinases from the papain family. These results suggest that minor structural differences within CMS2MS2 must account for its proliferative action.     

Implications of dealing with airborne substances and reactive oxygen species: what mammalian lungs, animals, and plants have to say?

A gas-exchange structure interacts with the environment andis constantly challenged by contaminants that may elicit defenseresponses, thus compromising its primary function. It is alsoexposed to high concentrations of O₂ that can generate reactiveoxygen species (ROS). Revisiting the lung of mammals, an integrativepicture emerges, indicating that this bronchi-alveolar structuredeals with inflammation in a special way, which minimizes compromisingthe gas-exchange role. Depending on the challenge, pro-inflammatoryor antiinflammatory responses are elicited by conserved molecules,such as surfactant proteins A and D. An even broader picturepoints to the participation of airway sensors, responsive toinflammatory mediators, in a loop linking the immunologicaland nervous systems and expanding the role played by respiratoryorgans in functions other than gas-exchange. A byproduct ofexposure to high concentration of O₂ is the formation of superoxide(), hydrogen peroxide (H₂O₂),hydroxyl radical (HO^•), and other ROS, which are knownto be toxic to different types of cells, including the lungepithelium. A balance between antioxidants and oxidants exists;in pulmonary epithelial cells high intracellular and extracellularlevels of antioxidants are found. Antioxidant adaptations relatedto plant and animal life-styles involve a broad range of overlappingstrategies based on well-conserved molecules. Glutathione (GSH)is an abundant and ubiquitous thiol-tripeptide antioxidant,also present in lungs, whose role in providing information onthe intracellular redox state of animals and plants is wellestablished. In these organisms, GSH influences gene expressionassociated with stress, maximizing defense responses. Severalenzymatic antioxidants, such as glutathione peroxidase (GPx),glutathione reductase, glutathione S-transferase, and glucose6-phosphate dehydrogenase participate in the redox system; inanimals that are stress-tolerant GPx is a key element againstoxidative assaults. Most importantly, alternative roles of ROSas signaling molecules have been found in all plants and animals.For example, alveolar macrophages produce that act as second messengers, in addition tohaving a bactericidal role. The nonradical ROS H₂O₂ signalsinflammation in mammalian lungs, apoptosis in different animaltissues, and is also involved in stomatal closure, root development,gene expression, and defense responses of plants. Antioxidantadaptations in some water-breathing animals involve the excretionof H₂O₂ by diffusion through gas-exchange structures. The finebalance among a multitude of factors and cells makes the differencebetween damage and protection in animals and plants. Knowledgeabout the mechanisms and consequences of these molecular interactionsis now starting to be integrated.