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Biomedical subjects

E H Yap

Publications and source records attributed to E H Yap.

At least 19 recordsLinked to original sources
PubMed2004

Delaying acute graft-versus-host disease in mouse bone marrow transplantation by treating donor cells with antibodies directed at l-selectin and alpha4-integrin prior to infusion.

Acute graft-versus-host disease (GVHD) is still a major hurdle for successful bone marrow transplantation (BMT). Although many immunosuppressive drugs are available, none of them alone or in combination are able to completely abolish acute GVHD. The lifelong immunosuppression profoundly reduces the quality of life of BMT recipients. Therefore, new therapeutic approaches are needed. We previously reported that, in an acute GVHD model using SCID mice as recipient, incubating donor spleen cells with antibodies directed at CD49d and CD62L could significantly delay the occurrence of acute GVHD. To test the potential usefulness of this treatment in BMT, we examined this therapeutic protocol in a mouse BMT model. The present mouse BMT study confirmed our previous results that incubation of donor cells with antibodies directed at CD49d and CD62L prior to infusion into the recipient can effectively delay acute GVHD, allowing the recipients to recover from the side effects of total body irradiation. This one-time treatment is easy and simple and may be modified for clinical usage.

Animals↗
PubMed2002

T cell infiltration and chemokine expression: relevance to the disease localization in murine graft-versus-host disease.

Acute graft-versus-host disease (GVHD) involves mainly skin, liver and intestines. Other organs such as heart, muscle and central nervous system are seldom affected, although their parenchymal cells also express alloantigens, such as MHC class I antigens. The mechanism of this selective involvement of distinct organs in acute GVHD is not well understood. We postulated that it might be related to the selective migration of activated alloreactive T cells. Indeed, T cell infiltration, revealed by examination of serial samples using flow cytometry and immunohistology, occurred early and continuously in the target organs such as the liver, but not in a non-target organ, the heart, in a murine acute GVHD model. Since T cell migration is largely controlled by the expression of chemokine and chemokine receptors, we investigated the chemokine spectrum in target/non-target organs of mice with acute GVHD. We found that in the spleen and liver MIP-1alpha, MIP-2 and Mig were the predominant chemokines expressed. In another target organ, the skin, MIP-1alpha, MIP-2, MCP-1 and MCP-3 were all highly expressed. In a non-target organ of acute GVHD, the heart, the predominant chemokines expressed were MCP-1 and MCP-3. This distinct pattern of chemokine expression in these organs may contribute to the preferential recruitment of inflammatory cells into the liver and skin, but not into the heart, in acute GVHD.

Acute Disease↗
PubMed2001

Do Blastocystis hominis colony forms undergo programmed cell death?

Ultrastructural observations were made on colony forms of the protozoan parasite, Blastocystis hominis. Cross-sections of entire colonies were observed by TEM. Cells within a colony were heterogeneous in morphology, consisting of vacuolar, amoeboid, multivacuolar and unusual forms. Dying cells appeared to be in the process of fragmenting into numerous membranebound vesicles, giving rise to empty spaces within the colony. Interestingly, older colonies appeared to show cell fragmentation which resulted in larger, membranebound structures. Numerous cytoplasmic inclusions were present in the central vacuole of some cells, with many containing mitochondria. Amoeboid forms were observed to harbour small membrane-bound vesicles in endosome-like compartments. Other unusual features included margination of chromatin material and distinct blebbing of nuclei. These ultrastructural features suggest that B. hominis colony forms perhaps undergo a form of programmed cell death.

Animals↗
PubMed2001

Exposure of Blastocystis species to a cytotoxic monoclonal antibody.

A recently described cytotoxic monoclonal antibody (mAb 1D5) raised against Blastocystis hominis isolate B, was tested for reactivity with 13 different isolates of Blastocystis. The isolates used were previously isolated from humans, rats and reptiles and were maintained as axenised cultures throughout the course of this study. Five B. hominis isolates (B, C, E, G and H) were found to react with mAb 1D5 in immunoblotting studies and the indirect fluorescence antibody test. The pattern of fluorescence observed for all five isolates was diffuse and patchy. Immunoblotting studies revealed that mAb 1D5 reacted with a 29-30-kDa protein found in all five isolates. Results of a cytotoxic assay showed that the mAb exhibited a complement-independent cytotoxic effect on all the exposed isolates. Microscopic observations showed differences in morphology between the Blastocystis cells exposed and unexposed to mAb. Acridine orange staining performed on both exposed and unexposed cells showed similar internal structures when viewed under fluorescence microscopy.

Animals↗
PubMed2001

Blastocystis hominis: evidence for caspase-3-like activity in cells undergoing programmed cell death.

We have shown previously that the human intestinal protozoan, Blastocystis hominis, undergoes apoptosis-like programmed cell death (PCD) when exposed to a cytotoxic monoclonal antibody (mAb), 1D5. In the present study, ELISA and immunoblot assays employing chicken anti-CPP32 antibody suggest that caspase-3-like antigens exist in B. hominis. Using colorimetric and flow cytometric assays for caspase-3 activity, we also observed an increase in activity between 1 h and 6 h after exposure to mAb 1D5, with greatest activity at 6 h. These findings suggest that caspase-3-like proteases play an important role in B. hominis undergoing PCD, similar to the phenomenon in higher eukaryotic organisms.

Animals↗
PubMed2001

Programmed cell death in a human intestinal parasite, Blastocystis hominis.

Although programmed cell death (PCD) has been associated with multicellular organisms, there have been more reports of its presence in some protozoans. Our study shows the existence of PCD in an intestinal protozoan, Blastocystis hominis. Light and electron microscopy, biochemical and flow cytometry studies showed apoptosis-like death in B. hominis cells exposed to a cytotoxic monoclonal antibody (MAb 1D5). B. hominis cells displayed key morphological and biochemical features of apoptosis, namely, nuclear condensation and in situ fragmentation, reduced cytoplasmic volume, some externalization of phosphatidylserine and maintenance of plasma membrane integrity. No oligonucleosomal DNA laddering was observed in gel electrophoresis. This study supports earlier observations that the cellular machinery that is required to carry out PCD may have existed before the advent of multicellularity. Our study also ascribes a novel function for the B. hominis central vacuole in apoptosis; it acts as a repository where apoptotic bodies are stored before being released into the extracellular space.

Animals↗
PubMed2001

Blocking L-selectin and alpha4-integrin changes donor cell homing pattern and ameliorates murine acute graft versus host disease.

L-selectin, LFA-1 and alpha(4) integrins play important roles in the homing of naïve T cells into peripheral lymphoid tissues. L-selectin- or LFA-1-deficient lymphocytes cannot effectively home to lymph nodes (LN), and antibody blockade of alpha(4) integrins also hinders lymphocytes homing. The present study was initiated to explore whether it is feasible to ameliorate acute graft-versus-host disease (aGVHD) by modulating the homing process of donor cells in the recipient in a mouse model. Using a fluorescence labeling method, we found that two monoclonal antibodies directed at L-selectin and alpha(4) integrins, respectively, when used in combination, could delay half of the donor C57BL/6J mouse spleen cells homing into the LN of recipient BALB/c mouse 15 h after injection. Spleen cells (1 x 10(7)) derived from C57BL/6J (H-2(b)) mice were injected into each C.B-17 SCID recipient mouse (H-2(d)) with or without prior incubation with 10 microg each of the two antibodies. T cell repopulation in the blood was observed in both groups of mice at a comparable level 14 days after injection of the donor cells. Eight control mice started to show aGVHD signs 7 - 14 days after the injection, and all died by day 31. However, among the ten mice that received the antibody-treated donor cells, two died before day 29, four survived between 36 and 78 days, and the remaining four survived more than 150 days, with two of them aGVHD free. It is apparent that the temporarily reduced lymphocyte homing into LN reduced the alloreactivity of the donor T cells, thus providing a simple way of modifying aGVHD. This novel approach may shed light on the prevention of aGVHD associated with clinical bone marrow transplantation.

Acute Disease↗
PubMed2000

Expression of angiotensin II AT2 receptor in the acute phase of stroke in rats.

A male Wistar rat model of stroke (middle cerebral artery occlusion; MCAO) was used to study the angiotensin II (Ang II) receptor subtype 2 (AT2) gene expression by reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemical staining. After permanent occlusion of the middle cerebral artery (MCA), AT2 receptor gene expression was found to increase in the infarct cortex by 2.7-fold (1 day) and 1.7-fold (3 days), respectively. Positive AT2 immunostaining was also observed in the infarct area of the cerebral cortex. Apoptotic markers were detected in the necrotic area of the stroke cerebral cortex 1 day after MCAO. This demonstrated up-regulation of AT2 receptor may be involved in the apoptosis of tissue repair after stroke.

Acute Disease↗
PubMed2000

Blastocystis hominis: A simplified, high-efficiency method for clonal growth on solid agar.

Colony growth of protozoan parasites in agar can be useful for axenization, cloning, and viability studies. This is usually achieved with the pour plate method, for which the parasite colonies are situated within the agar. This technique has been described for Giardia intestinalis, Trichomonas vaginalis, and Entamoeba and Blastocystis species. Extracting such colonies can be laborious. It would be especially useful if parasites could be grown on agar as colonies. These colonies, being exposed on the agar surface, could be conveniently isolated for further investigation. In this study, we report the successful culture of B. hominis cells as colonies on solid agar. Colonies were enumerated and the efficiency of plating was determined. It was observed that B. hominis could be easily cultured on agar as clones. The colonies were dome-shaped and mucoid and could grow to 3 mm in diameter. Flow cytometric analyses revealed that parasite colonies remained viable for up to 2 weeks. Viable colonies were conveniently expanded in liquid or solid media. Scanning electron microscopy revealed that each colony consists of two regions; a dome-shaped, central core region and a flattened, peripheral region. Older colonies possessed numerous strand-like surface coat projections. This study provides the first report of clonal growth of B. hominis on agar and a simple, effective method for cloning and expansion of B. hominis cells.

Agar↗
PubMed2000

Blastocystis elongation factor-1alpha: genomic organization, taxonomy and phylogenetic relationships.

The elongation factor-1 alpha (EF-1alpha) is a highly conserved ubiquitous protein that is involved in translation and is desirable for use in phylogenetic studies on Blastocystis, an enigmatic intestinal parasite with a contentious taxonomic position. In the present study, a PCR product (BEalpha) that codes for a major part of the coding region of the EF-lalpha protein was amplified. Genome walking experiments together with cloning were implemented to elucidate the 5' and 3' ends of the EF-1alpha gene of the human isolate, Blastocystis hominis C. The genomic organization and the potential transcription factor binding sites of the 5' end of B. hominis C EF-1alpha were identified. A comparative study on the deduced amino acid sequences of BEalpha of 13 Blastocystis isolates from various hosts was done to evaluate the phylogenetic relationship among the species. A phylogenetic reconstruction analysis with other eukaryotic EF-1alpha sequences was carried out to trace the phylogenetic position of Blastocystis among eukaryotic organisms.

Amino Acid Sequence↗
PubMed1999

Development of Blastocystis hominis cysts into vacuolar forms in vitro.

The development of cysts of Blastocystis hominis isolated from human feces by the Ficoll-Paque concentration method and cultured in Jones' medium containing 10% horse serum is described. The morphological changes were studied by light and transmission electron microscopy at different intervals for up to 48 h. The cysts developed into a large number of vacuolar forms within 24 h, and binary fission was the only mode of reproduction observed.

Animals↗
PubMed1999

Characterization of protein profiles and cross-reactivity of Blastocystis antigens by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis.

The protein profiles of Blastocystis hominis, B. lapemi, and B. ratti were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and species could be differentiated by this means as well as by Western-blot analysis with polyclonal antibodies. No intraspecies difference could be distinguished between the two B. hominis isolates or the three B. ratti isolates. Western-blot analysis showed extensive cross-reactivity of B. lapemi and B. hominis antigens with anti-B. ratti serum. Some of the cross-reactive antigens were glycoproteins as determined on the basis of their sensitivity to periodate treatment.

Animals↗
PubMed1999

In vitro encystation and excystation of Blastocystis ratti.

Cysts of Blastocystis ratti were produced in vitro by culturing the parasite in Iscove's modified Dulbecco's medium (IMDM) with increasing concentrations of horse serum. Yields up to 3 x 10(6) cysts/ml of culture medium were obtained after 72 h. Encystation efficiency was time, strain and inoculum size dependent. A viability of > 70% was determined by flow cytometry employing fluorescein diacetate and propidium iodide staining. The presence of chitin as a cyst wall component was demonstrated by Calcofluor White M2R staining with which cystic stages showed blue fluorescence. The changes in morphology during excystation were examined by transmission electron microscopy. The cyst enlarged in size and some vacuoles appeared within the condensed cytoplasm. The vacuoles were full of inclusions and small glycogen aggregates. Coalescence of the vacuoles led to central body formation. Glycogen deposits were prominent throughout the excystation process. Some cysts divided by binary fission before the completion of the excystation.

Animals↗
PubMed1999

Kinetics of interferon-gamma secretion and its regulatory factors in the early phase of acute graft-versus-host disease.

Increased serum levels of interferon-gamma (IFN-gamma) have been observed in acute graft-versus-host disease (GVHD). Recent in vitro studies have demonstrated that interleukin-12 (IL-12) and interleukin-18 (IL-18) synergistically up-regulate IFN-gamma secretion. In this communication, we investigated the factors relevant to IFN-gamma secretion in acute GVHD. A murine model of acute GVHD was established by injecting donor spleen cells into severe combined immunodeficiency (SCID) mice. A series of specimens, including sera, livers and spleens derived from the GVHD mice, were investigated with histological examination, enzyme-linked immunosorbent assay (ELISA), flow cytometry, and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). IFN-gamma secretion increased in serum 3 days after spleen cell transfer, peaked on day 7, and then gradually decreased close to the baseline level by day 35. A synchronized increase of activated T cells and mRNA expression of IL-12, IL-18 and their respective receptors was observed after spleen cell transfer. However, only the kinetic expression pattern of IL-12 receptor (IL-12R) beta2 chains was closely correlated with that of IFN-gamma, while IL-12 dropped to the baseline level earlier than IFN-gamma. Therefore, IFN-gamma expression in the early phase of acute GVHD is a mono-peak and self-restricted pattern. Its secretion is closely related with T-cell activation, the presence of IL-12, IL-18 and their respective receptors. However, the limiting factors for IFN-gamma secretion seem to be IL-12 and IL-12R beta2 chains.

Acute Disease↗
PubMed1998

Genomic polymorphism among Blastocystis hominis strains and development of subtype-specific diagnostic primers.

Genomic polymorphisms among nine strains of Blastocystis hominis were examined by random amplified polymorphic DNA (RAPD) using four different arbitrary polymerase chain reaction (PCR) primers. Based on the RAPD patterns, nine strains were classified into three groups. The specific primers designed from the unique bands yielded a single band from within each same group, but did not amplify between all the groups examined. Specificity of these diagnostic primers was tested against several common intestinal parasites and a yeast, and no amplification was confirmed. Since the current criteria indicates that Blastocystis organisms isolated from humans are designated as B. hominis, the authors propose to classify several subtypes among B. hominis groups based on the difference of genomic DNA using three diagnostic primers.

Animals↗
PubMed1998

Cytopathic effect of Blastocystis hominis after intramuscular inoculation into laboratory mice.

The present study investigated the pathogenesis of Blastocystis hominis by intramuscular injection of the organism into experimental mice. A total of 27 naïve BALB/c mice aged 6-8 weeks were injected in the leg muscle with axenic culture isolate B of B. hominis. Histological examination at different times revealed that B. hominis could produce a severe inflammatory reaction and myonecrosis. Most changes were observed at 6 h after injection and for up to 2-3 days. By 2 weeks the muscle had regained normal histology. There was infiltration of polymorphonuclear leukocytes (PML) into the injection site, indicating that B. hominis had a strong chemoattractant activity for PML.

Animals↗