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The relationship between invaders and the pathogens encountered in their new environment can have a large effect on invasion success. Invaders can become free from their natural pathogens and reallocate costly immune resources to growth and reproduction, thereby increasing invasion success. Release from enemies and relaxation of selective pressures could render newly founded populations more variable at immune-related genes, such as the major histocompatibility complex (MHC), particularly when they have different origins. Using rainbow and brown trout, two of the world's most successful fish invaders, we tested the general hypothesis that invaders should display high intrapopulation immunogenetic diversity and interpopulation divergence, due to the interplay between genetic drift and successive waves of genetically divergent introductions. We analysed genetic diversity and signatures of selection at the MHC class II ß immune-related locus. In both species, MHC diversity (allelic richness and heterozygosity) for southern hemisphere populations was similar to values reported for populations at their native range. However, MHC functional diversity was limited, and population immunogenetic structuring weaker than that observed using neutral markers. Depleted MHC functional diversity could reflect a decrease in immune response, immune-related assortative mating or selection for resistance to newly encountered parasites. Given that the role of MHC diversity in the survival of these populations remains unclear, depleted functional diversity of invasive salmonids could compromise their long-term persistence. A better understanding of the eco-immunology of invaders may help in managing and preventing the impact of biological invasions, a major cause of loss of biodiversity worldwide.

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A rare disease is a disease that occurs infrequently or rarely in the general population. In order to be considered as rare, each specific disease cannot affect more than a limited number of people out of the whole population, defined in Chile as 0.18 in 10,000 citizens (Minister of Health draft of the law on rare diseases). This figure can also be expressed as 18 patients with rare diseases out of 1 million citizens. While 0.18 out of 10,000 seems very few, in a total population of 17 million citizens this could mean as many as 306 individuals for each rare disease. It is important to underline that the number of patients with rare disease varies considerably from disease to disease, and that most people represented by the statistics in this field suffer from even rarer diseases, affecting only one in 100,000 people or less. Some rare diseases do only affect a couple of dozens patients. These very rare diseases make patients and their families particularly isolated and vulnerable.

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Niño de 11 años de edad con historia de dolor torácico intermitente de 6 meses de evolución y soplo cardíaco. El ecocardiograma mostró una masa tumoral en la válvula mitral con insuficiencia valvular moderada. Se intervino quirúrgicamente con resección extensa del tumor de la válvula mitral y de los músculos papilares al cual estaba adherido, se colocó una válvula mitral protésica. El diagnóstico patológico fue de mixoma de la válvula mitral. Este tumor es raro en la infancia, con una localización pocas veces descrita, de carácter benigno, pero potencialmente fatal.

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Niño con 26 días de edad al ingreso, presentó cianosis y dificultad respiratoria progresiva desde el nacimiento, se diagnosticó por ecocardiografía un tumor intracardíaco de la pared libre ventricular izquierda con derrame pericárdico leve. Durante la cirugía se encontró un tumor no resecable. El examen histológico lo clasificó como un fibroma. La mortalidad por fibromas cardíacos grandes es alta un disgnóstico temprano y una extirpación del tumor es mandatoria para aliviar la sintomatología y las consecuencias fatales, existen múltiples abordajes quirúrgicos para niños con fibromas cardíacos que van desde tomar la biopsia y esperar, hasta la resección parcial, total o incluso el trasplante cardíaco. Palabras clave: tumor cardíaco, fibroma, cirugía.

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The in vitro cytopathic effect of four strains of Trichomonas vaginalis on cultured epithelial monolayers was analyzed through electrophysiology and electron microscopy. Interaction of trichomonads of two virulent strains (GT-10 and GT-13) with cultured MDCK cell monolayers mounted in Ussing chambers produced a rapid decrease in transepithelial resistance to less than 30% of control values after only 15 min. By 30 min the electrical resistance was practically abolished by the virulent parasites. In contrast, of two attenuated strains of trichomonads (GT-3 and GT-7) analyzed under similar conditions, GT-3 trophozoites required 180 min to reduce transepithelial resistance to 9% of control values, while monolayers in contact with GT-7 parasites still showed 28% of control values at this time of incubation. Sequential scanning electron microscopy confirmed the much faster and widespread cytopathic effect of virulent parasites. In contrast, the slow lytic process produced by attenuated trophozoites was reduced to focal areas of direct contact with epithelial cells. Another difference was found by measurement of the surface charge of the four strains of T. vaginalis by means of cell microelectrophoresis. While the two virulent strains showed a negative surface charge, the two attenuated strains had no detectable surface charge at neutral pH. When parasites were incubated with cationized ferritin and studied with transmission electron microscopy the surface of virulent trichomonads appeared heavily labeled, whereas the surface of attenuated parasites had only sparse and irregular ferritin binding.

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Leishmania differentiates from the promastigote to the amastigote stage during its digenetic life cycle. Characterization of the developmentally regulated genes during that process would help to elucidate the mechanisms of gene regulation. In this study, specific fragments of mRNAs from the amastigote stage of L. mexicana mexicana were discriminated from those of the promastigote and metacyclic stages by differential display. This technique combined with spliced-leader polymerase chain reaction allowed isolation of the complete gene VG7A5. The sequence of this gene did not align with any published L. mexicana sequence. More than one copy of this gene was identified in the genome by Southern-blot analysis and was transcribed exclusively in the amastigote stage. At 20 bp upstream from the splice AG site it has a trans-splicing polypyrimidine tract. The gene encodes the subcellular localization motifs 5'-GGACT and AAGCT-3' in the 3' untranslated region of the mRNA. The open reading frame of the gene VG7A5 predicts a polypeptide of 587 amino acid residues that has a KGRR amidation motif near its carboxyl terminus, suggesting that in the mammalian host this protein may be involved in the process of acute inflammation.

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The cytological features of Entamoeba dispar, recently recognized by biochemical and molecular biology criteria as a distinct species, were compared to those of Entamoeba histolytica When cultured under axenic conditions, living trophozoites of E. dispar strain SAW 76ORR clone A were more elongated in form, had a single frontal pseudopodium, and showed a noticeable uroid. In sections of E. dispar trophozoites stained with Toluidine blue, characteristic areas of cytoplasmic metachromasia were seen due to the presence of large deposits of glycogen, seldom found in E. histolytica strain HM1:IMSS. Under the light microscope the periphery of the nucleus in E. dispar was, lined by finer, more regularly distributed dense granules. With transmission electron microscopy the surface coat of E. dispar was noticeable thinner. In addition. E. dispar had a lower sensitivity to agglutinate with concanavalin A and a higher negative surface charge, measured by cellular microelectrophoresis. The cytopathic effect of E. dispar was much slower, analyzed by the gradual loss of transmural electrical resistance of MDCK epithelial cell monolayers mounted in Ussing chambers. Whereas in E. histolytica phagocytosis of epithelial cells plays an important role in its cytopathic effect. E. dispar trophozoites placed in contact with MDCK cells showed only rare evidence of phagocytosis. The results demonstrate that the morphology of E. dispar is different to that of E. histolytica, both at the light microscopical and the ultrastructural levels. In addition they show that E. dispar in axenic culture has a moderate cytopathic effect on epithelia] cell monoLayers. However, when compared to E. histolytica, the in vitro lytic capacity of E. dispar is much slower and less intense.

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During atrial septation, the septum primum fuses with the atrioventricular endocardial cushions and myocardial-mesenchymal interactions occur. In order to evaluate the cellular events that take place during this particular interaction a structural, ultrastructural and histochemical study was performed. Our findings indicate that from the fourth day of development, the distal myocardium of the interatrial septum, which interacts with mesenchymal tissue, loses its appearance of an epithelial sheet and becomes a loosely organized tissue. The distal myocytes of the interatrial septum which get progressively separated show features of migratory cells, the final localization of which is the mesenchymal tissue of the adjacent endocardial cushions. These tissue changes involve basal membrane disruption, reduction in the number of desmosomes and intercalated discs with the subsequent appearance of large intercellular spaces between myocytes, myofibrillar disarrangement and acquisition by myocytes of a secretory phenotype characterized by numerous cytoplasmic vesicles. These events occur in a similar way in the atrioventricular canal, where a myocardial-mesenchymal interaction also occurs. In both regions the mesenchymal endocardial cushions and its associated extracellular matrix seem to direct the dissociation of the myocardial tissue and the subsequent migratory cellular behaviour of the interacting myocytes. This is an interesting, and little known, example of a cellular phenotypic transformation during cardiac development.

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During leishmania infection, parasites are inoculated to the human host through the bite of a sandfly vector into the dermis, where they first interact with tissue components, cells and extracellular matrix molecules. Since collagen is the most abundant component of the skin matrix, we investigated whether there is a specific interaction of Leishmania mexicana promastigotes with this host component. Promastigotes were able to attach to collagen fibrils and move through the matrix of mouse skin sections and to penetrate easily into a type I collagen gel. Denatured type I collagen coated beads (Cytodex 3) readily bound to the parasite surface. The interaction of promastigotes with type I collagen was dose dependent and saturable and was competitively and specifically inhibited with increasing concentrations of gelatin. Biotin-labeled parasite surface molecules were able to associate with both denatured collagen from microcarriers and native type I collagen from bovine kidney. It is suggested that the presence of parasite cell membrane receptors to collagen may confer a specific tropism for the skin, where collagen is the most abundant component of the matrix.

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Whole-cell voltage-clamp experiments were performed in vesicles derived from frog skeletal muscle plasma membranes. Capacitance measurements showed that these vesicles lack invaginations. In solutions containing K+, transient outward currents with reversal potentials close to EK were recorded with a maximum potassium conductance of 0.3 mS/cm2. These currents inactivated in a voltage-dependent manner with a time constant of decay that reached a limiting value of 26 ms at large depolarizations. The steady-state inactivation reached half-maximum values at -66 mV. Transient currents were completely blocked with 5 mM 4-aminopyridine. Single-channel recordings made in inside-out excised patches from the vesicles had ensemble averages with characteristics similar to those of the macroscopic currents, although with significantly faster inactivation time constants. The single-channel chord conductance was 21 pS when the pipette and bath solutions contained 2.5 mM and 120 mM KCl, respectively. It is concluded that these vesicles contain potassium channels that are very similar to A channels found in neurons and other cells.

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In vitro and in vivo ultrastructral studies reveal that the parasite entrance into the macrophage occurs by phagocytosis. The early stage of phagocytosis exhibited different ultrastructural characteristics in both forms of the parasite. Long and prominent projections from peritoneal exudate macrophages made focal contacts with the promastigote surface. The amastigotes, in turn, laid on cup-shaped extensions of the macrophage membrane. Later stages of the phagocytosis are characterized by progressive and complete engulfment of both promastigotes and amastigotes.

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Hereby, we present evidences of the presence of centromeric proteins in Leishmania mexicana. These proteins were partially purified and used to bind Leishmania DNA. The protein-DNA complex was immunoprecipitated and the DNA extracted, like in the human sample. Two major fragments of 1.2 and 2.2 Kbp, respectively, were resolved in agarose gel electrophoresis. A model of chromosomal structure and chromosomal segregation in Leishmania is presented.

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During the initial stages of host-parasite interaction between Entamoeba histolytica and its target cell, superficial molecules of both cells participate. The purpose of this study has been the study of the parasite's proteins which are involved in the process of adhesion, as well as localize the superficial sites of the host which bind with the amebic proteins. Antibodies directed against adhesin 112 kDa, and other amebic adhesins, specifically inhibited the destruction of the monolayers of the MDCK epithelial cell line. Soluble proteins of MDCK cells recognized was separated by electrophoresis and transferred to nitrocellulose paper, the amebic proteins of 112, 90 and 45 to 50 kDa. In a similar fashion, membrane proteins of MDCK cells marked with 125[I] specifically recognized amebic proteins of 112, 90, 45 and 32 kDa, as well as others of higher molecular wight. The localization of the binding sites of the E. histolytica molecules on semi-confluent monolayers of MDCK cells, was brought about by immunofluorescence using antibodies against the parasite's total proteins or against adhesins. For electron microscopy antibodies labelled with peroxidase were used. The amebic proteins were mainly found on the periphery of free cells, land in the intercellular cell junctions of monolayers.

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The surface charge of Giardia lamblia trophozoites from axenic cultures of strains recently isolated in Mexico from human cases of symptomatic and asymptomatic giardiasis was studied by means of cellular microelectrophoresis and ultrastructural cytochemistry. It is concluded that ionogenic surface groups confer a negative surface charge on trophozoites of G. lamblia and that no significant differences exist between the surface charge of trophozoites of symptomatic and asymptomatic origin.

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There is growing evidence suggesting that hepatic fat-storing cells (FSC) or Ito cells have an important function in vitamin A storage and metabolism and in the synthesis of connective tissue components in normal liver and during fibrogenesis. The purified FSC acquire a fibroblastic morphology and their vitamin A content decreases in culture. We cultivated cells under in vitro conditions that allowed the expression of FSC morphological and functional characteristics for 3-4 weeks of primary culture. Cells were isolated from rat liver by the collagenase-perfusion method without further purification and cultured with 3T3-conditioned medium, which seemed to stimulate the selective proliferation of the FSC. After 8-10 days, round and stellate cells grew actively from a few precursor cells in the primary culture and were not subcultivated; the stellate cells had the ability to become round and vice versa and were highly motile. The cells had intracytoplasmic lipid droplets, a well developed rough endoplasmic reticulum, Golgi complex, numerous vesicles filled with electron-dense material, and extracellular matrix (ECM) components on their surface. Both stellate and round cells showed the presence of desmin by immunofluorescence and vitamin A autofluorescence, but lacked peroxidase activity. The culture conditions we describe allowed the selective proliferation of cells with morphological and functional characteristics of the FSC in the normal liver, raising the possibility of studying FSC proliferation and differentiation.

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Levamisol (fenilimidotiazol), considerado um potente imunoestimulante, quando administrado a camundongos suíços näo causou aumento significante nos pesos do timo, figado ou baço, apesar de a droga ter sido usada em diferentes tempos antes da remoçäo desses órgäos. Doses elevadas da droga usadas no esquema profilático de 4 dias näo tiveram efeito anti-malárico. Entretanto quando dada a camundongos com malária, 24 horas antes, ao mesmo tempo ou 24 horas após inoculaçäo de uma cepa de Plasmodium berghei cloroquina-sensível ou uma cepa cloroquina-resistente o levamisol reduziu, ainda que discretamente, a parasitemia nos grupos tratados, sendo a dose de 1 mg/kg o melhor esquema. Foi observado também atraso na mortalidade por malária nos grupos tratados com o levamisol. No entanto, todos os animais morreram. Os dados sugerem que o levamisol tem efeito imunoestimulante, ainda que discreto, na resposta imune de animais, deprimida pela malária

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A comparative study of cell surface characteristics of pathogenic and nonpathogenic promastigotes of Leishmania braziliensis, NR and LBY strains, respectively, was carried out by means of concanavalin A agglutination and labeling with concanavalin A-fluorescein isothiocyanate, concanavalin A-ferritin, and cationized ferritin. Cytochemical examination showed cell surface differences in lectin receptors and negative charge moieties in the two strains of L. braziliensis. The pathogenic NR strain agglutinated with low concentrations of concanavalin A and presented abundant lectin-binding and cationized ferritin-binding surface labeling. The nonpathogenic LBY strain neither agglutinated when incubated with concanavalin A, bound lectins, or cationized ferritin at the cell surface.

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Streptolysin "O", an exotoxin of the beta-hemolytic streptococcus, has been shown to have very marked cardiotoxic effects. The data found in the literature suggest that ventricular conducting tissues are severely damaged by this toxin. The purpose of this paper is to study the effects that several concentration of the toxin have on the transmembrane potentials, input resistance and ultrastructure of canine isolate Purkinje fibers. When the preparations were exposed to the toxin, they showed important changes in most of the parameters of the transmembrane potentials. The most important were: a depolarization, a reduction of the amplitude of the action potentials and their upstroke velocities, and a marked shortening of their duration. Input resistance was also markedly decreased. These actions were progressive, until unexcitability was reached. All of the changes observed were irreversible. The ultrastructure of the cells also showed important alterations, mainly at the sarcolemma and mitochondriae. From the results described in this paper, both in terms of the electrophysiological and the morphological effects of streptolysin "O", we can conclude that the cardiotoxic effects of the toxin are due to an effect on the ventricular conducting tissues.

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