Initial characterization of CST1, a Toxoplasma gondii cyst wall glycoprotein

Toxoplasma gondii is an important protozoan pathogen of humans that can cause encephalitis in immunocompromised individuals such as those with AIDS. This encephalitis is due to reactivation of latent infection in T. gondii-seropositive patients. Latent organisms survive within tissue cysts, which are specialized parasitophorous vacuoles containing bradyzoites. The cyst wall of this structure is produced by modification of the parasitophorous vacuole by the parasite and is important in cyst survival. The components of the cyst wall have been poorly characterized. By using immunofluorescence and immunoelectron microscopy, we have identified a monoclonal antibody (MAb 93.18) that reacts with the cyst wall. This antibody recognizes a 116-kDa glycoprotein, which we have termed CST1, containing sugar residues that bind Dolichos biflorans lectin (DBA). CST1 is distinct from T. gondii antigen labeled with succinyl Triticum vulgare lectin (S-WGA) and represents the major DBA-binding component in T. gondii. The carbohydrate components of the tissue cyst, such as CST1, are probably important in both providing stability and facilitating persistence in its host. As is seen in the carbohydrate capsules of fungi, glycoproteins in the T. gondii cyst wall may protect cysts from the immune response of the host. Further characterization of the formation of the cyst wall and its components should lead to insights into the mechanism of tissue cyst persistence and may suggest novel therapeutic approaches to eliminate tissue cysts of this organism.

Trypanosoma cruzi infection (Chagas' disease) of mice causes activation of the mitogen-activated protein kinase cascade and expression of endothelin-1 in the myocardium

Chagas' disease, caused by the parasite Trypanosoma cruzi, is an important cause of heart disease. Previous studies from this laboratory revealed that microvascular spasm and myocardial ischemia were observed in infected mice. Infection of endothelial cells with this parasite increased the synthesis of biologically active endothelin-1 (ET-1). Therefore. in the myocardium of T. cruzi-infected mice, we examined ET-1 expression and the p42/44-mitogen activated protein kinase (MAPK)-AP-1 pathway that regulates the expression of ET-1. There was parasitism and myonecrosis in the myocardium of infected C57BL/6 mice. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed elevated mRNA expression of transcription factor AP-1 (c-jun and c-fos) and increased AP-1 DNA binding activity as determined by electrophoretic mobility shift assay (EMSA). Western blot analysis demonstrated an increase in the phosphorylated forms of extracellular signal-regulated kinase (ERK1/2). ET-1 mRNA was upregulated in the myocardium of infected mice. Immunohistochemical and immunoelectron microscopy using anti-ET-1 antibody detected increased expression in cardiac myocytes and endothelium of these mice. These data suggest that ET-1 contributes to chagasic cardiomyopathy and that the mechanism of the increased expression of ET-1 is a result of the activation of the MAPK pathway by T. cruzi infection.

A Ba(2+)-insensitive K+ conductance in the basolateral membrane of rabbit cortical thick ascending limb cells

The nature of the K+ exit across the basolateral membrane of microperfused rabbit cortical thick ascending limbs (cTALs) was investigated using the transepithelial and transmembrane potential difference (PDte, PDbl) and conductance measurements. An increase in bath K+ concentration from 4 to 10, 25, 50 mmol/l depolarized the basolateral membrane in a concentration-dependent manner, accompanied by a decrease in the fractional resistance of the basolateral membrane (FRbl). The Cl- channel blocker, 5-nitro-2-(3-phenylpropyl-amino)-benzoic acid (NPPB), did not prevent these effects. The effect of Ba2+ on PDbl was bimodally distributed: paradoxically, in the tubules in which Ba2+ largely depolarized, the effects on PDbl of the bath K+ concentration increases were not inhibited by extracellular Ba2+, in tubules in which Ba2+ moderately depolarized, Ba2+ partially inhibited the K+ concentration increase-induced depolarization of the basolateral membrane. However, the parallel decrease in FRbl was Ba2+ insensitive, indicating that the K+ channel of the basolateral membrane was not modified by extracellular Ba2+. The Ba(2+)-induced depolarizations were prevented by furosemide suggesting that Ba2+ acts by inhibiting basolateral KCl extrusion. Finally, the K+ concentration increase-induced depolarizations were insensitive to tetraethylammonium, charybdotoxin, apamin and verapamil. In conclusion, the present study provides evidence that, in addition to a Ba(2+)-sensitive KCl cotransport system, the basolateral membrane of rabbit cTAL cells possesses a K+ conductance which is insensitive to extracellular Ba2+.

Myocardial expression of endothelin-1 in murine Trypanosoma cruzi infection

Chagas' disease, caused by Trypanosoma cruzi, is an important cause of myocarditis and chronic cardiomyopathy and is accompanied by microvascular spasm and myocardial ischemia. We reported previously that infection of cultured endothelial cells with T. cruzi increased the synthesis of biologically active endothlein-1 (ET-1). In the present study, we examined the role of ET-1 in the cardiovascular system of CD1 mice infected with the Brazil strain of T. cruzi and C57BL/6 mice infected with the Tulahuen strain during acute infection. In the myocardium of infected mice myonecrosis and multiple pseudocysts were observed. There was also an intense vasculitis of the aorta, coronary artery, smaller myocardial vessels and the endocardial endothelium. Immunohistochemistry studies employing anti-ET-1 antibody revealed increased expression of ET-1 that was most intense in the endocardial and vascular endothelium. Elevated levels of mRNA for preproET-1, endothelin converting enzyme and ET-1 were observed in the same myocardial samples. Plasma ET-1 levels were significantly elevated in infected CD1 mice 10-15 days post infection. These observations suggest that increased levels of ET-1 are a consequence of the initial invasion of the cardiovascular system and provide a mechanism for infection-associated myocardial dysfunction.

Calcium-sensing receptor: regulation of electrolyte transport in the thick ascending limb of Henle's loop

A calcium-sensing receptor (CaR) has functionally been described in the cortical thick ascending limb of Henle's loop (CTAL) of rat and mouse. This G protein-coupled receptor activates phospholipase C and increases the intracellular Ca2+ concentration. We observed that in the mouse CTAL cAMP formation, induced by 10(-8) mol/l AVP, was inhibited by more than 90% when the extracellular Ca2+ concentration ([Ca2+]e) was increased from 0.5 to 3 mmol/l. Measurements of transepithelial potential difference (PDte) in rat and mouse CTAL and medullary thick ascending limb (mTAL) segments and of transepithelial ion net fluxes in the mouse CTAL (isotonic perfusion conditions: 150 mmol/l NaCl in the lumen and bath) showed that an increase in the [Ca2+]e had no effect on basal and arginine vasopressin (AVP, 10(-10) mol/l)-stimulated transepithelial PDte, NaCl and Mg2+ transport. However, Ca2+ reabsorption was strongly inhibited by increased [Ca2+]e. Addition of AVP reversed this inhibitory effect of increased [Ca2+]e. Under hypotonic perfusion conditions (lumen 50 mmol/l NaCl; bath 150 mmol/l NaCl), a high [Ca2+]e induced a 50% decrease in Mg2+ reabsorption which was restored by AVP. Under these conditions, the effects on Ca2+ transport described above were still observed. In conclusion, activation of the CaR in the mouse TAL has no effect on basal and AVP-stimulated transepithelial NaCl reabsorption despite its large inhibitory effect on cAMP synthesis. The CaR, however, could play a role in the regulation of transepithelial Ca2+ and Mg2+ reabsorption.

Cellular adaptation of the mouse cortical thick ascending limb of Henle's loop (CTAL) to dietary magnesium restriction: enhanced transepithelial Mg2+ and Ca2+ transport

Mice aged 4 or 8 weeks were fed with a low-Mg2+ diet for 1, 2, 3 or 4 days. After 1 day of diet, the urinary excretion of Mg2+ and Ca2+ was strongly reduced in both animal groups (4 and 8 weeks), accompanied by a significant fall in plasma Mg2+ concentration and an increase in urinary volume. This profile persisted after 2, 3 or 4 days of dietary Mg2+ restriction. After 1 day of diet, transepithelial ion net fluxes of Na+, Cl-, Ca2+ and Mg2+ (JNa' JCI, JCl, JMg) measured in vitro from isolated perfused cortical thick ascending limbs (CTALs) of these animals remained unchanged. After 2 days of diet, measurements of J(Ca) and J(Mg) in isolated perfused CTALs showed that transepithelial Mg2+ and Ca2+ reabsorption were enhanced in CTALs from Mg(2+)-depleted, 8-week-old animals, whereas transepithelial Mg2+ and Ca2+ transport were not altered in 4-week-old mice. JNa and JCl and the transepithelial potential (PDte) were not modified in CTALs from either animal group. Our results suggest that a low-Mg2+ diet leads to urinary retention of Mg2+ and Ca2+ which is most likely due to increased Mg2+ and Ca2+ transport in the CTAL. Furthermore, in response to dietary Mg2+ restriction, the reabsorption of divalent cations in the CTAL of adult, but not of young, mice undergoes cellular adaptation.

Identification of novel serine/threonine protein phosphatases in Trypanosoma cruzi: a potential role in control of cytokinesis and morphology

We cloned two novel Trypanosoma cruzi proteins by using degenerate oligonucleotide primers prepared against conserved domains in mammalian serine/threonine protein phosphatases 1, 2A, and 2B. The isolated genes encoded proteins of 323 and 330 amino acids, respectively, that were more homologous to the catalytic subunit of human protein phosphatase 1 than to those of human protein phosphatase 2A or 2B. The proteins encoded by these genes have been tentatively designated TcPP1alpha and TcPP1beta. Northern blot analysis revealed the presence of a major 2.3-kb mRNA transcript hybridizing to each gene in both the epimastigote and metacyclic trypomastigote developmental stages. Southern blot analysis suggests that each protein phosphatase 1 gene is present as a single copy in the T. cruzi genome. The complete coding region for TcPP1beta was expressed in Escherichia coli by using a vector, pTACTAC, with the trp-lac hybrid promoter. The recombinant protein from the TcPP1beta construct displayed phosphatase activity toward phosphorylase a, and this activity was preferentially inhibited by calyculin A (50% inhibitory concentration [IC(50)], approximately 2 nM) over okadaic acid (IC(50), approximately 100 nM). Calyculin A, but not okadaic acid, had profound effects on the in vitro replication and morphology of T. cruzi epimastigotes. Low concentrations of calyculin A (1 to 10 nM) caused growth arrest. Electron microscopic studies of the calyculin A-treated epimastigotes revealed that the organisms underwent duplication of organelles, including the flagellum, kinetoplast, and nucleus, but were incapable of completing cell division. At concentrations higher than 10 nM, or upon prolonged incubation at lower concentrations, the epimastigotes lost their characteristic elongated spindle shape and had a more rounded morphology. Okadaic acid at concentrations up to 1 microM did not result in growth arrest or morphological alterations to T. cruzi epimastigotes. Calyculin A, but not okadaic acid, was also a potent inhibitor of the dephosphorylation of (32)P-labeled phosphorylase a by T. cruzi epimastigotes and metacyclic trypomastigote extracts. These inhibitor studies suggest that in T. cruzi, type 1 protein phosphatases are important for the completion of cell division and for the maintenance of cell shape.

Infection of endothelial cells with Trypanosoma cruzi activates NF-kappaB and induces vascular adhesion molecule expression

Transcriptional activation of vascular adhesion molecule expression, a major component of an inflammatory response, is regulated, in part, by the nuclear factor-kappaB/Rel (NF-kappaB) family of transcription factors. We therefore determined whether Trypanosoma cruzi infection of endothelial cells resulted in the activation of NF-kappaB and the induction or increased expression of adhesion molecules. Human umbilical vein endothelial cells (HUVEC) were infected with trypomastigotes of the Tulahuen strain of T. cruzi. Electrophoretic mobility shift assays with an NF-kappaB-specific oligonucleotide and nuclear extracts from T. cruzi-infected HUVEC (6 to 48 h postinfection) detected two major shifted complexes. Pretreatment with 50x cold NF-kappaB consensus sequence abolished both gel-shifted complexes while excess SP-1 consensus sequence had no effect. These data indicate that nuclear extracts from T. cruzi-infected HUVEC specifically bound to the NF-kappaB consensus DNA sequence. Supershift analysis revealed that the gel-shifted complexes were comprised of p65 (RelA) and p50 (NF-kappaB1). Northern blot analyses demonstrated both the induction of vascular cell adhesion molecule 1 and E-selectin and the upregulation of intercellular adhesion molecule 1 mRNA in HUVEC infected with T. cruzi. Immunocytochemical staining confirmed adhesion molecule expression in response to T. cruzi infection. These findings are consistent with the hypothesis that the activation of the NF-kappaB pathway in endothelial cells associated with T. cruzi infection may be an important factor in the inflammatory response and subsequent vascular injury and endothelial dysfunction that lead to chronic cardiomyopathy.

Localization and activity of nitric oxide synthases in the gastrointestinal tract of Trypanosoma cruzi-infected mice

Chagas' disease, caused by the protozoan parasite, Trypanosoma cruzi, is associated with gastrointestinal abnormalities. Since nitric oxide (NO) has been shown to be a factor influencing intestinal function we evaluated the distributions and activities of the NO synthase (NOS) isoforms, in the gut of mice infected with T. cruzi. Ca2+-dependent (NOS1/NOS3) activity was decreased, whereas Ca2+-independent (NOS2) activity was increased in infected mice. NOS2-immunoreactivity was demonstrated in cells within the muscle layers and epithelium in infected mice and NOS1 immunoreactivity was seen in nerve structures. These data indicate that alterations in the NO-system may be important in the pathogenesis of the gastrointestinal manifestations in Chagas' disease.

Application of cardiac gated magnetic resonance imaging in murine Chagas' disease

To evaluate the role of gated cardiac magnetic imaging resonance (MRI) in Chagas' disease, we infected mice with Trypanosoma cruzi (Brazil strain). Two models were chosen for study, the CD1 and the inducible nitric oxide synthase knockout (NOS2-/-) mice. Infection of CD1 mice was associated with a significant increase in the right ventricular inner diameter (RVID) that was reversed in some mice by verapamil. Expression of cardiac NOS2 has been associated with myocardial dysfunction. Therefore, we evaluated chagasic cardiomyopathy in NOS2-/- and syngeneic wild type (WT) mice. Infected WT mice exhibited an increase in RVID in the acute phase (< 60 days postinfection) that was more marked during chronic infection (>100 days postinfection). Chronically infected NOS2-/- mice had an increase in RVID. The RVID in infected WT mice was greater than in NOS2-/- mice. These data demonstrate that MRI is a useful tool in the serial evaluation of the heart in murine Chagas' disease. In addition, it supports the notion that the NOS2-/-/NO pathway may contribute to the pathogenesis of murine chagasic cardiomyopathy.

The putative mechanistic basis for the modulatory role of endothelin-1 in the altered vascular tone induced by Trypanosoma cruzi

Chagas' disease, caused by Trypanosoma cruzi, is an important cause of heart disease in Latin America. T. cruzi-induced microvascular compromise, in turn, is thought to play a major role in chagasic heart disease. Previous in vitro studies have implicated endothelin-1 (ET-1) as a potentially important vasomodulator present in increased levels in the supernatant of T. cruzi infected cultured human umbilical vein endothelial cells (HUVEC). Thus, the goal of the present investigation was to further evaluate the potentially important contribution of ET-1 to T. cruzi-induced alterations in vascular tone in vitro. Bioassay studies once again documented that exposure of isolated rat aortic rings to infected HUVEC supernatants elicited contractile responses whose steady-state magnitude was significantly greater than contractile responses elicited by exposure of aortic rings to uninfected HUVEC supernatants. Furthermore, the increased aortic contractility was significantly attenuated by the presence of the ET(A) subtype selective antagonists BMS-182,874 or BQ-123. Additionally, incubation of HUVEC with either verapamil or phosphoramidon prior to infection was also associated with reduced aortic contractility, upon exposure to the supernatant. Phosphoramidon, but not verapamil, produced a significant decrease in the measured ET-1 levels in the HUVEC supernatant. Consistent with the bioassay results, preincubation of Fura-2-loaded cultured rat aortic vascular smooth muscle cells with verapamil resulted in a near complete ablation of ET-1-induced transmembrane Ca2+ flux. Taken together, these data are consistent with the hypothesis that ET-1-induced vasoconstriction may play an important modulatory role in the vascular compromise characteristic of T. cruzi infection.

The Ca2+-sensing receptor in the rabbit cortical thick ascending limb (CTAL) is functionally not coupled to phospholipase C

The recently cloned rabbit kidney Ca2+-sensing receptor (RabCaR) was functionally characterized in microperfused rabbit cortical thick ascending limb (CTAL) segments. Reverse transcriptase polymerase chain reaction (RT-PCR) confirmed that this nephron segment contains mRNAs coding for the RabCaR. Elevation of the extracellular Ca2+ concentration ([Ca2+]e) from 1 to 5 mmol l-1 induced an increase in the fluorescence emission ratio (R), thus reflecting an increase in intracellular Ca2+ activity ([Ca2+]i). This increase was inhibited by verapamil, nifedipine and SKF 96365, and potentiated by a previous application of Bay K 8644. Neither verapamil nor Bay K 8644 modified the resting [Ca2+]i. This suggests that the basolateral Ca2+ influx induced by a high [Ca2+]e occurs via verapamil- and dihydropyridine-sensitive Ca2+ channels, which are not open under resting conditions. In contrast to that evoked by antidiuretic hormone (ADH), the [Ca2+]i increase induced by a high [Ca2+]e did not result from an accumulation of inositol phosphates. Neomycin, Gd3+, Mg2+, commonly used agonists of the Ca2+-sensing receptor, did not increase the [Ca2+]i. In the presence of verapamil, ADH still produced a transient [Ca2+]i increase that was not observed in the presence of an increased [Ca2+]e. These results suggest that the RabCaR in rabbit CTAL cells is not functionally coupled to phospholipase C. In conclusion, the high [Ca2+]e-induced [Ca2+]i increase involves verapamil- and dihydropyridine-sensitive Ca2+ channels and is independent of phosphoinositide metabolism. Whether these channels are activated by the RabCaR remains to be elucidated.

A cluster of transfusion-associated babesiosis cases traced to a single asymptomatic donor

CONTEXT

The risk of acquiring babesiosis by blood transfusion is largely unknown since in areas where it is endemic it is often an asymptomatic infection.

OBJECTIVE

To investigate and treat a cluster of blood transfusion-associated babesiosis cases.

DESIGN

Case series and epidemiologic investigation.

SETTING

Urban inner-city hospital.

PATIENTS

Six persons who received Babesia microti-infected blood components from a donor.

MAIN OUTCOME MEASURE

Diagnosis and successful therapy of babesiosis following transfusion.

RESULTS

Six individuals (1 adult, 1 child, and 4 neonates) were exposed to products from a single blood donation by an asymptomatic Babesia-infected donor. Three of the 6 exposed patients became parasitemic. Polymerase chain reaction testing, animal inoculation studies, and indirect immunofluorescent antibody testing were used to confirm the presence of Babesia microti in the donor's blood and to establish the presence of infection in 3 of the 6 recipients. The 3 infected recipients and 1 additional recipient were treated without incident.

CONCLUSION

Physicians should consider babesiosis in the differential diagnosis of a febrile hemolytic disorder after blood transfusion. Prompt diagnosis is important since babesiosis is responsive to antibiotic therapy and, untreated, can be a fatal disease in certain risk groups.

Expression of cardiac cytokines and inducible form of nitric oxide synthase (NOS2) in Trypanosoma cruzi-infected mice

Expression of Cardiac Cytokines and Inducible Form of Nitric Oxide Synthase (NOS2) in Trypanosoma cruzi-infected Mice. Journal of Molecular and Cellular Cardiology (1999) 31, 75-88. Both cardiac cytokine and inducible nitric oxide synthase (NOS2) expression have been implicated in the cardiac dysfunction associated with myocarditis and cardiomyopathy. Chagas' disease, caused by Trypanosoma cruzi, is an important cause of cardiomyopathy. We examined the effect of T. cruzi (Brazil strain) infection with or without verapamil treatment on the expression of cytokines and NOS2 in the heart. Messenger RNA for NOS2, IL-1beta, and TNF-alpha was induced in the myocardium of infected mice, and Western blot analysis as well as immunohistochemistry demonstrated a significant increase in NOS2 protein. Verapamil treatment reduced the expression of cardiac NOS2 protein and the mRNAs for NOS2, TNF-alpha, and IL-1beta. Infection-associated increases in cardiac L-citrulline were also reduced by verapamil treatment. Verapamil-treated infected mice that survived for 80 days exhibited less inflammation and fibrosis compared to untreated mice. Gated MRI and echocardiography revealed an increased right ventricular inner diameter (RVID) in untreated but not in verapamil-treated infected CD1 mice. This suggests that the infection-associated expression of cytokines and NOS2 in the heart correlate with the severity of myocarditis and the effect of verapamil. The RVID was significantly increased in infected wild-type (WT) compared to infected syngeneic NOS2 knockout (NOS2-/-) mice. Fractional shortening was decreased and myocardial L-citrulline was increased in infected WT mice. These data suggest that NO generated from cardiac NOS2 may participate in the pathogenesis of murine chagasic heart disease.

Polar tube proteins of microsporidia of the family encephalitozoonidae

Encephalitozoonidae are microsporidia associated with human infections including hepatitis, encephalitis, conjunctivitis, and disseminated disease. Microsporidia produce a small resistant spore containing a polar tube which serves as a unique vehicle of infection. Polar tube proteins (PTPs) from Encephalitozoon hellem. Encephalitozoon (Septata) intestinalis, and Encephalitozoon cuniculi were purified to homogeneity by HPLC. By SDS-PAGE, the Mr of E. hellem PTP was 55 kDa, while the Mr of E. intestinalis and E. cuniculi PTP was 45 kDa. Polyclonal rabbit antiserum to these purified PTPs localized to polar filaments by immunogold electron microscopy and immunofluorescence, and demonstrated cross-reactivity by both immunoblotting and immunogold electron microscopy. These PTPs have similar solubility properties, hydrophobicity, and proline content to a 43-kDa PTP we have previously purified from Glugea americanus, a fish microsporidium. As the polar tube is critical in the transmission of this organism, further study of PTPs may lead to the development of new therapeutic strategies and diagnostic tests.

Bradyzoite development in Toxoplasma gondii and the hsp70 stress response

Toxoplasma gondii is a well-described ubiquitous Apicomplexan protozoan parasite that is an important opportunistic pathogen. The factors affecting the transition of tachyzoites to the latent bradyzoite stage remain to be defined. The induction of bradyzoite development in vitro has been linked to temperature, pH, mitochondrial inhibitors, sodium arsenite, and many of the other stressors associated with heat shock protein (hsp) induction. There is evidence for other organisms that hsps are developmentally regulated. Therefore, we examined whether hsp induction is an early event in bradyzoite differentiation. Extracellular and intracellular T. gondii cells, after exposure to pH 8.1 or 7.1, were analyzed for the expression of inducible hsp70 by using monoclonal antibody C92F3A-5 (specific to hsp70). Western blotting demonstrated that a 72-kDa protein reactive with C92F3A-5 (hsp70), which we believe is part of the hsp70 family, is induced during bradyzoite development. By immunofluorescence and immunoelectron microscopy, we were able to demonstrate that hsp70 staining colocalized to T. gondii expressing bradyzoite-specific antigens and the presence of hsp70 in bradyzoites isolated from mouse brain. Quercetin, a bioflavonoid which inhibits the synthesis of hsp90, hsp70, and hsp27, suppresses the induction of bradyzoite development in vitro. Reverse transcription-PCR with conserved hsp70 primers demonstrated an increase in hsp70 in T. gondii on exposure to conditions which induce bradyzoite formation. A T. gondii hsp70 was subsequently cloned and sequenced by using this amplified fragment. We believe our evidence suggests that hsps are important in the process of bradyzoite differentiation.

The ethnic minority traveler

Although the ethnic minority traveler is exposed to the same risks as other travelers, there are special considerations that make them vulnerable to certain diseases. In addition, many ethnic minority travelers are traditionally underserved by the medical community and often travel without the benefit of adequate counseling and immunization. The specific disease entities covered in this article include parasitic diseases (e.g. malaria, trypanosomiasis, intestinal helminths), tuberculosis, and other respiratory diseases, dengue, and sexually transmitted diseases and HIV.

Brachiola vesicularum, n. g., n. sp., a new microsporidium associated with AIDS and myositis

Brachiola vesicularum, n. g., n. sp., is a new microsporidum associated with AIDS and myositis. Biopsied muscle tissue, examined by light and electron microscopy, revealed the presence of organisms developing in direct contact with muscle cell cytoplasm and fibers. No other tissue types were infected. All parasite stages contain diplokaryotic nuclei and all cell division is by binary fission. Sporogony is disporoblastic, producing 2.9 x 2 microns diplokaryotic spores containing 8-10 coils of the polar filament arranged in one to three rows, usually two. Additionally, this microsporidium produces electron-dense extracellular secretions and vesiculotubular appendages similar to Nosema algerae. However, the production of protoplasmic extensions which may branch and terminate in extensive vesiculotubular structures is unique to this parasite. Additionally, unlike Nosema algerae, its development occurred at warm blooded host temperature (37-38 degrees C) and unlike Nosema connori, which disseminates to all tissue types, B. vesicularum infected only muscle cells. Thus, a new genus and species is proposed. Because of the similarities with the genus Nosema, this new genus is placed in the family Nosematidae. Successful clearing of this infection (both clinically and histologically) resulted from treatment with albendazole and itraconozole.

Gap junction disappearance in astrocytes and leptomeningeal cells as a consequence of protozoan infection

Trypanosoma cruzi and Toxoplasma gondii are protozoan parasites capable of causing infections of the nervous system. In order to determine effects of infection by these organisms on intercellular communication in the brain, dye coupling and connexin abundance and distribution were examined in leptomeningeal cells and astrocytes infected with T. cruzi or T. gondii. For both cell types infected with either type of protozoan parasite, intercellular diffusion of intracellularly injected Lucifer Yellow was dramatically reduced. Immunocytochemistry with antibodies specific for connexin43 (in astrocytes) or both connexin43 and connexin26 (for leptomeningeal cells) demonstrated that punctate gap junctional staining was much reduced in infected cells, although uninfected neighbors could display normal connexin abundance and distribution. Western blot analyses revealed that connexin43 abundance in both cell types infected with either parasite was similar to that in uninfected cells. Phosphorylation state of connexin43 (inferred from electrophoretic mobility of connexin43 isoforms) was not significantly affected by the infection process. Immunocytochemistry of whole brains from animals acutely infected with either parasite also showed a marked reduction in connexin43 expression. We conclude that infection of both types of brain cells with either protozoan parasite results in a loss of intercellular communication and organized gap junction plaques without affecting expression levels or posttranslational processing of gap junction proteins. Presumably, these changes in gap junction distribution result from altered targeting of the junctional protein to the plasma membrane, and/or from changes in assembly of subunits into functional channels.

TNP-470 is an effective antimicrosporidial agent

Therapy for microsporidia, which cause diarrhea and a wasting syndrome in persons with AIDS, has had limited success. Fumagillin, a naturally secreted water-insoluble antibiotic, has in vitro activity against microsporidia and has been used successfully in the treatment of superficial keratitis in patients with AIDS, but systemic therapy has been limited by toxicity of the currently available fumagillin salt. TNP-470, a semisynthetic analogue of fumagillin, was studied in vitro and in the athymic nude mouse model of microsporidiosis. RK13 cells were infected with microsporidia of the family Encephalitozoonidae and treated at day 3 with TNP-470. This agent was highly effective, with an ID50 (50% inhibitory dose compared with control) of 0.001 microg/mL. TNP-470 also demonstrated in vivo activity against Encephalitozoon cuniculi, with prolonged survival and the prevention of the development of ascites in infected athymic mice. These data suggest that the fumagillin derivative TNP-470 is a promising agent for the treatment of microsporidiosis.

Intracellular Ca2+ homeostasis in trypomastigotes of Trypanosoma cruzi

Trypomastigotes of Trypanosoma cruzi maintain an intracellular Ca2+ concentration ([Ca2+]i) of 64 +/- 30 nM. Equilibration of trypomastigotes in an extracellular buffer containing 0.5 mM [Ca2+]o (preloaded cells) increased [Ca2+]i < 20 nM whereas total cell Ca2+ increased by 1.5 to 2.0 pmole/cell. This amount of Ca2+ would be expected to increase [Ca2+]i to > 10 microM suggesting active sequestration of Ca2+. We tested the hypothesis that maintenance of [Ca2+]i involved both the sequestration into intracellular storage sites and extrusion into the extracellular space. Pharmacological probes known to influence [Ca2+]i through well characterized pathways in higher eukaryotic cells were employed. [Ca2+]i responses in the presence or absence of [Ca2+]o were measured to asses the relative contribution of sequestration or extrusion processes in [Ca2+]i homeostasis. In the presence of 0.5 mM [Ca2+]o, the ability of several agents to increase [Ca2+]i was magnified in the order ionomycin >>> nigericin > thapsigargin > monensin > valinomycin. In contrast, preloading markedly enhanced the increase in [Ca2+]i observed only in response to monensin. Manoalide, an inhibitor of phospholipase A2, enhanced the accumulation of [Ca2+]i due to all agents tested, particularly ionomycin and thapsigargin. Our results suggest that sequestration of [Ca2+]i involved storage sites sensitive to monensin and ionomycin whereas extrusion of Ca2+ may involve phospholipase A2 activity. A Na+/Ca2+ exchange mechanism did not appear to contribute to Ca2+ homeostasis.