Dengue 2 genotypes in the state of Oaxaca, Mexico.

To genetically characterize dengue 2 (DEN-2) viruses in Oaxaca, Mexico, the C protein, and a portion of the prM protein genes of 8 isolates from the 2001 DEN epidemic were sequenced. The sequences were compared to those of prototype DEN-2 viruses from various parts of the world. Phylogenetic analysis suggested that the 2001 isolates of DEN-2 were of the American/Asian genotype and were most similar to the Jamaica and Venezuelan isolates MARA3, LARD1996 and LARD1910. Molecular analyses confirmed the origin of the isolates. This study indicates that DEN-2 strains of American/Asian genotype probably from Southeast Asian are circulating in Oaxaca.

Entamoeba histolytica trophozoites activated by collagen type I and Ca(2+) have a structured cytoskeleton during collagenase secretion.

A peculiar characteristic of Entamoeba histolytica trophozoites is their capacity to invade human tissues. One of the cellular determinants of invasion may include adhesion to extracellular matrix components such as collagen, induction, and secretion of electron-dense granules (EDG) and tissue digestion. The mechanism and receptors involved in this process are not well understood. Previous results suggested that cytoskeleton plays a very important role during EDG secretion. We present evidence suggesting that adhesion to collagen and activation of EDG secretion are integrin-dependent events, since beta1 subunits detected by antibodies are concentrated at membrane sites where collagen and actin were colocalized. Furthermore, the involvement of actin, vimentin, and tubulin in restructuring cytoskeleton during EDG secretion was evident, since cytoskeleton isolation was possible exclusively in activated cells. Studies of immunolocalization of tubulin, actin, and vimentin by immunofluorescence and transmission electron microscopy suggest a role for cytoskeleton in EDG secretion.

Expression of polymorphic msp1beta genes during acute anaplasma Marginale rickettsemia.

Immunization of cattle with native MSP1 induces protection against Anaplasma marginale. The native immunogen is composed of a single MSP1a protein and multiple, undefined MSP1b polypeptides. In addition to the originally sequenced gene, designated msp1beta(F1), we identified three complete msp1beta genes in the Florida strain: msp1beta(F2), msp1beta(F3), and msp1beta(F4). Each of these polymorphic genes encodes a structurally unique MSP1b protein, and unique transcripts can be identified during acute A. marginale rickettsemia. The structural polymorphism is clustered in discrete variable regions, and each MSP1b protein results from a unique mosaic of five variable regions. Although each of the MSP1b proteins in the Florida strain contains epitopes recognized by serum antibody induced by protective immunization with the native MSP1 complex, the variable regions also include epitopes expressed by some but not all of the MSP1b proteins. These data support testing recombinant vaccines composed of the multiple antigenically and structurally unique MSP1b proteins combined with MSP1a in order to mimic the efficacy of native MSP1 immunization.

Surface redistribution and release of antibody-induced caps in entamoebae.

Polyspecific antibodies bound to Entamoeba induced surface redistribution of membrane components toward the uroid region. Capping of surface antigens was obtained with a single layer of antibodies in E. histolytica and E. invadens. This surface segregation progressed to a large accumulation of folded plasma membrane that extruded as a defined vesicular cap. A spontaneous release of the cap at the end of the capping process took place. These released caps contained most of the antibodies that originally bound to the whole cell surface. Two-thirds of radiolabeled antibodies bound to the surface of E. histolytica were released into the medium in 2 h. Successive capping induced by repeated exposure of E. invadens to antibodies produced conglomerates of folded surface membrane, visualized as stacked caps, in proportion to the number of antibody exposures. These results indicate the remarkable ability of Entamoeba to rapidly regenerate substantial amounts of plasma membbrane. The properties of surface redistribution, liberation of caps, and plasma membrane regeneration, may contribute to the survival of the parasite in the host during infection.

[Characterization of surface molecules of Entamoeba invadens]. / Caracterización de moléculas superficiales de Entamoeba invadens.

In this paper we studied the externally disposed plasma membrane antigens in Entamoeba invadens using the enzymatic iodination technique. Sodiumdodecyl-sulfate-polyacrylamide gels of solubilized trophozoite proteins revealed six labeled peaks ranging from 14,000 to 67,000 daltons in gradient slab gels. Over 60 percent of the labeled was in the polypeptide of 67,000 daltons. Concanavalin A binding to these trophozites induced cell surface coat release consituted by three radioactive bands of 67,000, 60,000 and 24,000 daltons. Using an affinity chromatography method with Con A conjugated to Sepharose 4B, trophozoites in culture mixture with these beads during three hours at 22 degree C, released three components that were eluted from immobilized Con A, 67,000, 60,000 and 56,000 daltons revealed in gradient slab gels. In several determinations, the 67,000 daltons glycoprotein consistently was the major surface component, and the most immunogenic as analyzed from rabbits sera immunized with whole cell extracts as well with cell surface coat.