The large diverse gene family var encodes proteins involved in cytoadherence and antigenic variation of Plasmodium falciparum-infected erythrocytes

The human malaria parasite Plasmodium falciparum evades host immunity by varying the antigenic and adhesive character of infected erythrocytes. We describe a large and extremely diverse family of P. falciparum genes (var) that encode 200-350 kDa proteins having the expected properties of antigenically variant adhesion molecules. Predicted amino acid sequences of var genes show a variable extracellular segment with domains having receptor-binding features, a transmembrane sequence, and a terminal segment that is a probable submembrane anchor. There are 50-150 var genes on multiple parasite chromosomes, and some are in clustered arrangements. var probes detect two classes of transcripts in steady-state RNA: 7-9 kb var transcripts, and an unusual family of 1.8-2.4 kb transcripts that may be involved in expression or rearrangements of var genes.

Switches in expression of Plasmodium falciparum var genes correlate with changes in antigenic and cytoadherent phenotypes of infected erythrocytes

Plasmodium falciparum expresses on the host erythrocyte surface clonally variant antigens and ligands that mediate adherence to endothelial receptors. Both are central to pathogenesis, since they allow chronicity of infection and lead to concentration of infected erythrocytes in cerebral vessels. Here we show that expression of variant antigenic determinants is correlated with expression of individual members of a large, multigene family named var. Each var gene contains copies of a motif that has been previously shown to bind diverse host receptors; expression of a specific var gene correlated with binding to ICAM-1. Thus, our findings are consistent with the involvement of var genes in antigenic variation and binding to endothelium.

"U" curve association of blood pressure and mortality in hemodialysis patients. Medical Directors of Dialysis Clinic, Inc

BACKGROUND

Hypertension may play an important role in the pathogenesis of the excess cardiovascular and cerebrovascular (CV) morbidity observed in hemodialysis patients (HD). However, the optimal blood pressure (BP) range for HD patients has not been defined. We postulated that there is a "U" curve relationship between BP and CV mortality. To explore this hypothesis we studied 5,433 HD patients in Dialysis Clinic Inc., a large not-for-profit chain, over a five year period.

METHODS

Cox regression, with fixed and time-varying covariates, was used to assess the effect of systolic blood pressure (SBP) and diastolic blood pressure (DBP), pre- and post-dialysis, on CV mortality, while adjusting for age, gender, ethnicity, primary cause of end-stage renal disease, Kt/V, serum albumin, and antihypertensive medications.

RESULTS

The overall impact of BP on CV mortality was modest. Pre-dialysis, neither systolic nor diastolic hypertension were associated with an increase in CV mortality. Post-dialysis, SBP > or = 180 mm Hg (RR = 1.96, P < 0.015) and DBP > or = 90 mm Hg (RR = 1.73, P < 0.05) were associated with increased CV mortality. Low SBP (SBP < 110 mm Hg) was associated with increased CV mortality, pre- and post-dialysis.

CONCLUSIONS

The results suggest the presence of a "U" curve relationship between SBP post-dialysis and CV mortality in HD patients.

Evidence that a point mutation in dihydrofolate reductase-thymidylate synthase confers resistance to pyrimethamine in falciparum malaria

Analysis of a genetic cross of Plasmodium falciparum and of independent parasite isolates from Southeast Asia, Africa, and South America indicates that resistance to pyrimethamine, an antifolate used in the treatment of malaria, results from point mutations in the gene encoding dihydrofolate reductase-thymidylate synthase (EC 1.5.1.3 and EC 2.1.1.45, respectively). Parasites having a mutation from Thr-108/Ser-108 to Asn-108 in DHFR-TS are resistant to the drug. The Asn-108 mutation occurs in a region analogous to the C alpha-helix bordering the active site cavity of bacterial, avian, and mammalian enzymes. Additional point mutations (Asn-51 to Ile-51 and Cys-59 to Arg-59) are associated with increased pyrimethamine resistance and also occur at sites expected to border the active site cavity. Analogies with known inhibitor/enzyme structures from other organisms suggest that the point mutations occur where pyrimethamine contacts the enzyme and may act by inhibiting binding of the drug.

Molecular basis of differential resistance to cycloguanil and pyrimethamine in Plasmodium falciparum malaria

Proguanil and pyrimethamine are antifolate drugs with distinct chemical structures that are used commonly in the prophylaxis and treatment of Plasmodium falciparum malaria. Clinical reports and field studies have suggested that some parasites refractory to proguanil can be treated with pyrimethamine, and vice versa. Analysis of the P. falciparum dihydrofolate reductase (DHFR) from different parasites reveals the structural basis for differential susceptibility to these antifolate drugs. Parasites harboring a pair of point mutations from Ala-16 to Val-16 and from Ser-108 to Thr-108 are resistant to cycloguanil (the active metabolite of proguanil) but not to pyrimethamine. A single Asn-108 mutation, on the other hand, confers resistance to pyrimethamine with only a moderate decrease in susceptibility to cycloguanil. Significant cross-resistance to both drugs occurs in parasites having mutations that include Ser-108----Asn-108 and Ile-164----Leu-164. These results reflect the distinct structures of pyrimethamine and cycloguanil and suggest fine differences in binding within the active site cavity of DHFR. Alternative inhibitors, used alone or in combination, may be effective against some strains of cycloguanil- or pyrimethamine-resistant malaria.

A redox-based O2 sensor in rat pulmonary vasculature

The effector mechanism of hypoxic pulmonary vasoconstriction (HPV) involves K+ channel inhibition with subsequent membrane depolarization. It remains uncertain how hypoxia modulates K+ channel activity. The similar effects of hypoxia and mitochondrial electron transport chain (ETC) inhibitors on metabolism and vascular tone suggest a common mechanism of action. ETC inhibitors and hypoxia may alter cell redox status by causing an accumulation of electron donors from the Krebs cycle and by decreasing the production of activated O2 species (AOS) by the ETC. We hypothesized that this shift toward a more reduced redox state elicits vasoconstriction by inhibition of K+ channels. Pulmonary artery pressure and AOS, measured simultaneously using enhanced chemiluminescence, were studied in isolated perfused rat lungs during exposure to hypoxia, proximal ETC inhibitors (rotenone and antimycin A), and a distal ETC inhibitor (cyanide). Patch-clamp measurements of whole-cell K+ currents were made on freshly isolated rat pulmonary vascular smooth muscle cells during exposure to hypoxia and ETC inhibitors. Hypoxia, rotenone, and antimycin A decreased lung chemiluminescence (-62 +/- 12, -46 +/- 7, and -148 +/- 36 counts/0.1 s, respectively) and subsequently increased pulmonary artery pressure (+14 +/- 2, +13 +/- 3, and +21 +/- 3 mm Hg, respectively). These agents reversibly inhibited an outward, ATP-independent, K+ current in pulmonary vascular smooth muscle cells. Antimycin A and rotenone abolished subsequent HPV. In contrast, cyanide increased AOS and did not alter K+ currents or inhibit HPV. The initial effect of rotenone, antimycin A, and hypoxia was a change in redox status (evident as a decrease in production of AOS). This was associated with the reversible inhibition of an ATP-independent K+ channel and vasoconstriction. These findings are consistent with the existence of a redox-based O2 sensor in the pulmonary vasculature.

Isolation of Aeromonas hydrophila from a metropolitan water supply: seasonal correlation with clinical isolates

The occurrence of Aeromonas spp. in the metropolitan water supply of Perth, Western Australia, Australia, was monitored at several sampling points during a period of 1 year. Water within the distribution system conformed to international standards for drinking water but contained Aeromonas spp. in numbers comparable to those in raw surface water, although this water was free of Escherichia coli. Coliforms and E. coli were found in raw surface waters, and Aeromonas spp. were found in raw water from surface and underground sources. Chemical treatment, followed by chlorination at service reservoirs, resulted in water free of E. coli and a decrease in the number of Aeromonas spp. Aeromonas spp. were found in the greatest numbers in summer. Multiple regression analysis showed that growth of Aeromonas spp. in chlorinated water was related to water temperature, residual chlorine, and interaction between these variables. The incidence of Aeromonas-associated gastroenteritis, determined from isolates referred to us for enterotoxin testing, paralleled the pattern of isolation of Aeromonas spp. in water within the distribution systems. We suggest that the presence of Aeromonas spp. in drinking water needs public health appraisal and that further work should be undertaken to permit reevaluation of standards for the quality of drinking water.

Identification of a novel selD homolog from eukaryotes, bacteria, and archaea: is there an autoregulatory mechanism in selenocysteine metabolism?

Escherichia coli selenophosphate synthetase (SPS, the selD gene product) catalyzes the production of monoselenophosphate, the selenium donor compound required for synthesis of selenocysteine (Sec) and seleno-tRNAs. We report the molecular cloning of human and mouse homologs of the selD gene, designated Sps2, which contains an in-frame TGA codon at a site corresponding to the enzyme's putative active site. These sequences allow the identification of selD gene homologs in the genomes of the bacterium Haemophilus influenzae and the archaeon Methanococcus jannaschii, which had been previously misinterpreted due to their in-frame TGA codon. Sps2 mRNA levels are elevated in organs previously implicated in the synthesis of selenoproteins and in active sites of blood cell development. In addition, we show that Sps2 mRNA is up-regulated upon activation of T lymphocytes and have mapped the Sps2 gene to mouse chromosome 7. Using the mouse gene isolated from the hematopoietic cell line FDCPmixA4, we devised a construct for protein expression that results in the insertion of a FLAG tag sequence at the N terminus of the SPS2 protein. This strategy allowed us to document the readthrough of the in-frame TGA codon and the incorporation of 75Se into SPS2. These results suggest the existence of an autoregulatory mechanism involving the incorporation of Sec into SPS2 that might be relevant to blood cell biology. This mechanism is likely to have been present in ancient life forms and conserved in a variety of living organisms from all domains of life.

Low energy Helium-Neon laser in the prevention of oral mucositis in patients undergoing bone marrow transplant: results of a double blind randomized trial

PURPOSE

To evaluate the efficiency of Helium-Neon (He-Ne) laser in the prevention of oral mucositis induced by high dose chemoradiotherapy before autologous bone marrow transplantation (BMT).

METHODS AND MATERIALS

Between 1993 and 1995, 30 consecutive patients receiving an autologous peripheral stem-cell or bone marrow transplant (BMT) after high dose chemoradiotherapy were randomized to possibly receive prophylactic laser to the oral mucosa after giving informed consent. Chemotherapy consisted of cyclophosphamide, 60 mg/kg intravenously (I.V.) on day (d)-5 and d-4 in 27 cases, or melphalan 140 mg/kg I.V. on d-4 in three cases. Total body irradiation (TBI) consisted of 12 Gy midplane dose in six fractions (4 Gy/day for three days). He-Ne laser (632.8 nm wavelength, power 60 mW) applications were performed daily from d-5 to d-1 on five anatomic sites of the oral mucosa. Oral examination was performed daily from d0 to d + 20. Mucositis was scored according to an oral exam guide with a 16 item scale of which four were assessed by the patients themselves. Mean daily self assessment scores for oral pain, ability to swallow and oral dryness were measured. A daily mucositis index (DMI) and a cumulative oral mucositis score (COMS) were established. Requirement for narcotics and parenteral nutrition was recorded.

RESULTS

The COMS was significantly reduced among laser treated (L+) patients (p = 0.04). The improvement of DMI in L+ patients was also statistically significant (p < 0.05) from d + 2 to d + 7. Occurrence and duration of grade III oral mucositis were reduced in L+ patients (p = 0.01). Laser applications reduced oral pain as assessed by patients (p = 0.05) and L+ patients required less morphine (p = 0.05). Xerostomia and ability to swallow were improved among the L+ patients (p = 0.005 and p = 0.01, respectively). Requirement for parenteral nutrition was not reduced (p = NS).

CONCLUSION

Helium-Neon laser treatment was well tolerated, feasible in all cases, and reduced high dose chemoradiotherapy-induced oral mucositis. Optimal laser treatment schedules still needs to be defined.

A novel technique for laminoplasty augmentation of spinal canal area using titanium miniplate stabilization. A computerized morphometric analysis

STUDY DESIGN

Titanium miniplates are used to secure the posterior elements in the open position after expansive open-door laminoplasty. Preoperative and postoperative spinal canal dimensions are measured to assess the effectiveness of this technique.

OBJECTIVES

To develop a simple yet effective technique to stabilize the posterior elements after laminoplasty and to compare preoperative and postoperative spinal canal dimensions to accepted normal values.

SUMMARY OF BACKGROUND DATA

Expansive open-door laminoplasty has been offered as a simple alternative to laminectomy, which has been associated with postoperative kyphosis. Although the technique of laminoplasty is effective, a simple and reliable method of holding the posterior elements open has not been described.

METHODS

Ten myelopathic patients with multilevel cervical canal stenosis secondary to spondylosis or ossification of the posterior longitudinal ligament were treated with an expansive open-door laminoplasty. The posterior elements were stabilized in the open position with titanium miniplates. Computer-assisted morphometric analysis was performed on preoperative and postoperative computed tomography scans to obtain spinal canal dimensions. Plain radiographs were used to monitor construct integrity.

RESULTS

The preoperative sagittal canal diameter was 8.2 +/- 0.96 mm, and the canal area was 180.6 +/- 33.7 mm2. These dimensions increased after surgery to 16.6 +/- 1.5 mm and 321.9 +/- 29.7 mm2, respectively. The titanium miniplate constructs did not fail during the follow-up period (mean, 26.4 months), and the decompression was maintained. The single significant complication was transient C5 radiculopathy.

CONCLUSIONS

Normal canal dimensions can be reestablished with open-door laminoplasty. Achieving and maintaining an increased sagittal canal diameter is probably the most important change in anatomic parameters to facilitate neurologic recovery. The use of titanium miniplates to stabilize the posterior elements after laminoplasty is a simple, durable, and effective technique to maintain the increased sagittal diameter of the spinal canal.

A recombinant Salmonella typhimurium vaccine induces local immunity by four different routes of immunization

Immunization of mice with an attenuated Salmonella typhimurium strain (Phopc) carrying a plasmid encoding a hybrid form of the hepatitis B virus core antigen (HBc) induced specific antibody responses against the bacterial lipopolysaccharide (LPS) and HBc. Different mucosal routes of immunization, i.e., oral, nasal, rectal, and vaginal, were compared for their ability to induce a systemic as well as a mucosal response at sites proximal or distant to the site of immunization. Anti-LPS and anti-HBc immunoglobulin A (IgA) antibodies were measured in saliva, in feces, and in genital, bronchial, and intestinal secretions. Specific antibodies in serum and secretions were observed after immunization via all routes; however, the response to LPS was independent of that against HBc. In serum, saliva, and genital and bronchial secretions, high amounts of anti-HBc IgA were obtained by the nasal route of immunization. Vaginal immunization resulted in two different responses in mice: high and low. We observed a correlation between the level of specific immune response and the estrous status of these mice at the time of immunization. Rectal immunization induced high amounts of IgA against HBc and LPS in colonorectal secretions and feces but not at distant sites. These data suggest that S. typhimurium is able to invade different mucosal tissues and induce long-lasting local IgA responses against itself and a carried antigen after a single immunization.

OB-BP1/Siglec-6. a leptin- and sialic acid-binding protein of the immunoglobulin superfamily

We report the expression cloning of a novel leptin-binding protein of the immunoglobulin superfamily (OB-BP1) and a cross-hybridizing clone (OB-BP2) that is identical to a recently described sialic acid-binding I-type lectin called Siglec-5. Comparisons to other known Siglec family members (CD22, CD33, myelin-associated glycoprotein, and sialoadhesin) show that OB-BP1, OB-BP2/Siglec-5, and CD33/Siglec-3 constitute a unique related subgroup with a high level of overall amino acid identity: OB-BP1 versus Siglec-5 (59%), OB-BP1 versus CD33 (63%), and OB-BP2/Siglec-5 versus CD33 (56%). The cytoplasmic domains are not as highly conserved, but display novel motifs which are putative sites of tyrosine phosphorylation, including an immunoreceptor tyrosine kinase inhibitory motif and a motif found in SLAM and SLAM-like proteins. Human tissues showed high levels of OB-BP1 mRNA in placenta and moderate expression in spleen, peripheral blood leukocytes, and small intestine. OB-BP2/Siglec-5 mRNA was detected in peripheral blood leukocytes, lung, spleen, and placenta. A monoclonal antibody specific for OB-BP1 confirmed high expression in the cyto- and syncytiotrophoblasts of the placenta. Using this antibody on peripheral blood leukocytes showed an almost exclusive expression pattern on B cells. Recombinant forms of the extracellular domains of OB-BP1, OB-BP2/Siglec-5, and CD33/Siglec-3 were assayed for specific binding of leptin. While OB-BP1 exhibited tight binding (K(d) 91 nM), the other two showed weak binding with K(d) values in the 1-2 microM range. Studies with sialylated ligands indicated that OB-BP1 selectively bound Neu5Acalpha2-6GalNAcalpha (sialyl-Tn) allowing its formal designation as Siglec-6. The identification of OB-BP1/Siglec-6 as a Siglec family member, coupled with its restricted expression pattern, suggests that it may mediate cell-cell recognition events by interacting with sialylated glycoprotein ligands expressed on specific cell populations. We also propose a role for OB-BP1 in leptin physiology, as a molecular sink to regulate leptin serum levels.

Soluble and membrane-bound forms of signaling lymphocytic activation molecule (SLAM) induce proliferation and Ig synthesis by activated human B lymphocytes

In this study it is shown that both membrane-bound and soluble forms of signaling lymphocytic activation molecule (SLAM) induce proliferation and Ig synthesis by activated human B cells. Activated B cells express the membrane-bound form of SLAM (mSLAM), the soluble (s) and the cytoplasmic (c) isoforms of SLAM, and the expression levels of mSLAM on B cells are rapidly upregulated after activation in vitro. Importantly, recombinant sSLAM and L cells transfected with mSLAM efficiently enhance B cell proliferation induced by anti-mu mAbs, anti-CD40 mAbs or Staphylococcus aureus Cowan I (SAC) in the presence or absence of IL-2, IL-4, IL-10, IL-12, or IL-15. sSLAM strongly enhances proliferation of both freshly isolated B cells and B cells derived from long-term in vitro cultures, indicating that SLAM acts not only during the initial phase of B cell activation but also during the expansion of preactivated B cells. In addition, sSLAM enhances production of IgM, IgG, and IgA by B cells activated by anti-CD40 mAbs. SLAM has recently been shown to be a high affinity self-ligand, and the present data suggest that signaling through homophilic SLAM-SLAM binding during B-B and B-T cell interactions enhances the expansion and differentiation of activated B cells.

Limited humoral immunity in hepatitis C virus infection

BACKGROUND & AIMS

The extremely high rate of chronicity to hepatitis C virus (HVC) infection suggests an inefficient immune response. The humoral immune response to HCV was evaluated in 60 patients with chronic HCV infection and in 12 patients acutely infected with HCV.

METHODS

A number of recombinant HCV antigens including the core, envelope 2 (E2), nonstructural (NS) 3, NS4, and NS5 proteins, and NS4a and E2-HVR-1 peptides were used in enzyme-linked immunoassays.

RESULTS

Immunoglobulin (Ig) G antibody responses to these viral antigens, except for the HCV core, were highly restricted to the IgG1 isotype. The prevalence of antibodies of the IgG1 isotype specific for the HCV core, E2, E2-HVR1, NS3 (helicase domain), NS4, and NS5 antigens was 97%, 98%, 28%, 88%, 33%, and 68%, respectively. Antibodies of the IgG3 isotype specific for E2, E2-HVR-1, NS3, NS4, and NS5 were detected in a minority of serum samples. The IgG2 and IgG4 isotypes were rarely if ever detected. Furthermore, antibody responses to HCV viral antigens were of relatively low titer and, with the exception of anti-HCV core, were delayed in appearance until the chronic phase of infection.

CONCLUSIONS

The IgG1 restriction, low titer, and delayed appearance of antibody responses elicited during HCV infection suggest that the immunogenicity of HCV proteins is limited in the context of natural infection. Inasmuch as recombinant HCV viral antigens perform as relatively normal immunogens in small animals, we suggest that the defective humoral immune responses during HCV infection may be attributable to an "immune avoidance" strategy.

Neural Control of Walking in People with Parkinsonism

People with Parkinson's disease exhibit debilitating gait impairments, including gait slowness, increased step variability, and poor postural control. A widespread supraspinal locomotor network including the cortex, cerebellum, basal ganglia, and brain stem contributes to the control of human locomotion, and altered activity of these structures underlies gait dysfunction due to Parkinson's disease.

A wheat HMW glutenin subunit gene reveals a highly repeated structure

A wheat genomic library was screened with two synthetic oligonucleotides (24 and 25 bases in length) complementary to a partial cDNA clone encoding a glutenin gene [Thompson et al. (1983) Theor. Appl. Genet. 67, 87-96]. Glutenins are large molecular weight aggregated proteins of grain endosperm, and major determinants of bread making quality of wheat. Of the two clones obtained one was fully characterized. It contained the sequence of the high molecular weight subunit of glutenin. The amino acid sequence derived from the gene sequence reveals a mature protein (817 amino acids) with a highly repeated structure of two different motifs corresponding to the high glutamine (35.7%), glycine (20.1%) and proline (13.1%) content. The gene does not contain an intron, and possesses a typical eukaryotic promoter; the RNA initiation site is 25-30 bases downstream.

Dietary tocotrienols reduce concentrations of plasma cholesterol, apolipoprotein B, thromboxane B2, and platelet factor 4 in pigs with inherited hyperlipidemias

Normolipemic and genetically hypercholesterolemic pigs of defined lipoprotein genotype were fed a standard diet supplemented with 50 micrograms/g tocotrienol-rich fraction (TRF) isolated from palm oil. Hypercholesterolemic pigs fed the TRF supplement showed a 44% decrease in total serum cholesterol, a 60% decrease in low-density-lipoprotein (LDL)-cholesterol, and significant decreases in levels of apolipoprotein B (26%), thromboxane-B2 (41%), and platelet factor 4 (PF4; 29%). The declines in thromboxane B2 and PF4 suggest that TRF has a marked protective effect on the endothelium and platelet aggregation. The effect of the lipid-lowering diet persisted only in the hypercholesterolemic swine after 8 wk feeding of the control diet. These results support observations from previous studies on lowering plasma cholesterol in animals by tocotrienols, which are naturally occurring compounds in grain and palm oils and may have some effect on lowering plasma cholesterol in humans.

Variation in the frequency and type of sperm chromosomal abnormalities among normal men

The chromosomal constitution of 1582 human sperm from 30 normal men of proven fertility was investigated after sperm penetration of hamster eggs. A minimum of 30 sperm chromosome complements were analysed per donor so that the distribution and variation in the frequency and type of sperm chromosomal abnormalities could be assessed. The mean frequency of sperm chromosomal abnormalities in individual men was 10.4% (+/- 6.0%) with a range of 0-24.7%. For numerical abnormalities the mean was 4.7% (+/- 2.9%) with a range of 0-10% and for structural abnormalities the mean was 6.2% (+/- 6.0%) with a range of 0-23.1%. The 95% confidence intervals for the mean of an individual male were 0-10.5% for numerical abnormalities, 0-18.2% for structural abnormalities, and 0-22.4% for total abnormalities. There was a significant excess of hypohaploid complements compared with hyperhaploid complements. Since hypohaploid complements could be caused by technical artefact, a conservative estimate of aneuploidy was obtained by doubling the frequency of hyperhaploid sperm, yielding an estimate of 2.4% aneuploidy. The proportion of X-bearing (53%) and Y-bearing (47%) sperm did not differ significantly. These results were compared to the other two large studies of sperm chromosome complements from normal men.

Cloning of a major surface-antigen gene of Trypanosoma cruzi and identification of a nonapeptide repeat

The parasitic protozoan Trypanosoma cruzi can establish infection in humans and other vertebrate hosts through direct penetration of host cells by trypomastigotes transmitted by the insect vector. Although the molecular processes involved in trypomastigote interiorization of vertebrate cells are unknown, several studies suggest that surface glycoproteins are involved. It is likely that the proteins involved are specific to the trypomastigote stage of the parasite, since only trypomastigotes found in both the insect vector and the vertebrate host bloodstream are capable of invading vertebrate cells. In contrast, the epimastigote stage, found exclusively in the vector, and the amastigote stage, an intracellular stage in the vertebrate host, cannot penetrate the cell directly. We have therefore concentrated our efforts on trypomastigote surface proteins and, along with others, have identified two trypomastigote-specific surface glycoproteins of relative molecular mass (Mr) 90,000 (90K) and 85,000 (85K). Antibody neutralization experiments indicate that the 85K glycoprotein is necessary for efficient interiorization of trypomastigotes in mammalian cells. Here we describe the molecular cloning of a genomic DNA fragment that encodes antigenic determinants present in the 85K trypomastigote surface antigen. The polypeptide fragment encoded by the cloned DNA is recognized by serum from a T. cruzi-infected host and is inferred by DNA sequence analysis to contain a nonapeptide unit that is tandemly repeated five times. Also, the messenger complementary to the cloned DNA fragment is present only in the trypomastigote stage of the parasite.

Isolation of multiple sequences from the Plasmodium falciparum genome that encode conserved domains homologous to those in erythrocyte-binding proteins

Open reading frames in the Plasmodium falciparum genome encode domains homologous to the adhesive domains of the P. falciparum EBA-175 erythrocyte-binding protein (eba-175 gene product) and those of the Plasmodium vivax and Plasmodium knowlesi Duffy antigen-binding proteins. These domains are referred to as Duffy binding-like (DBL), after the receptor that determines P. vivax invasion of Duffy blood group-positive human erythrocytes. Using oligonucleotide primers derived from short regions of conserved sequence, we have developed a reverse transcription-PCR method that amplifies sequences encoding the DBL domains of expressed genes. Products of these reverse transcription-PCR amplifications include sequences of single-copy genes (including eba-175) and variably transcribed genes that cross-hybridize to multiple regions of the genome. Restriction patterns of the multicopy genes show a high degree of polymorphism among different parasite lines, whereas single-copy genes are generally conserved. Characterization of the single-copy genes has identified a gene (ebl-1) that is related to eba-175 and is likely to be involved in erythrocyte invasion.

Expressed var genes are found in Plasmodium falciparum subtelomeric regions

The antigenic variation and cytoadherence of Plasmodium falciparum-infected erythrocytes are modulated by a family of variant surface proteins encoded by the var multigene family. The var genes occur on multiple chromosomes, often in clusters, and 50 to 150 genes are estimated to be present in the haploid parasite genome. Transcripts from var genes have been previously mapped to internal chromosome positions, but the generality of such assignments and the expression sites and mechanisms that control switches of var gene expression are still in early stages of investigation. Here we describe investigations of closely related var genes that occur in association with repetitive elements near the telomeres of P. falciparum chromosomes. DNA sequence analysis of one of these genes (FCR3-varT11-1) shows the characteristic two-exon structure encoding expected var features, including three variable Duffy binding-like (DBL) domains, a transmembrane sequence, and a carboxy-terminal segment thought to anchor the protein product in knobs at the surface of the parasitized erythrocyte. FCR3-varT11-1 cross-hybridizes with var genes located close to the telomeres of many other P. falciparum chromosomes, including a transcribed gene (FCR3-varT3-1) in chromosome 3 of the P. falciparum FCR3 line. The relatively high level transcription from this gene shows that the polymorphic chromosome ends of P. falciparum, which have been proposed to be transcriptionally silent, can be active expression sites for var genes. The pattern of the FCR3-varT11-1 and FCR3-varT3-1 genes are variable between different P. falciparum lines, presumably due to DNA rearrangements. Thus, recombination events in subtelomeric DNA may have a role in the expression of novel var forms.

Isolation of Aeromonas spp. from an unchlorinated domestic water supply

The recovery of Aeromonas spp. from the unchlorinated water supply for a Western Australian city of 21,000 people was monitored at several sampling points during a period of 1 year. Membrane filtration techniques were used to count colonies of Aeromonas spp., coliforms, and Escherichia coli in water sampled before entry to service reservoirs, during storage in service reservoirs, and in distribution systems. Aeromonas spp. were identified by subculture on blood agar with ampicillin, oxidase tests, and the use of Kaper medium and then were tested for production of enterotoxins and hemolysins. During the same period, two-thirds of all fecal specimens sent for microbiological examination were cultured on ampicillin-blood agar for Aeromonas spp. Recovery of Aeromonas spp. from water supplies at distribution points correlated with fecal isolations and continued during autumn and winter. Coliforms and E. coli were found most commonly in late summer to autumn. This pattern differs from the summer peak of Aeromonas isolations both from water and from patients with Aeromonas spp.-associated gastroenteritis in Perth, Western Australia, a city with a chlorinated domestic water supply. Of the Aeromonas strains from water, 61% were enterotoxigenic, and 64% produced hemolysins.

Genotoxicity of radiofrequency radiation. DNA/Genetox Expert Panel

During the past several years, concerns have been raised regarding the potential adverse effects of exposures to nonionizing radiation, particularly in the extremely low frequency (ELF) range (50 to 60 MHz) and radiofrequency radiation (RFR) with frequencies ranging from 30 KHz to 30,000 MHz. One focus of concern has been potential DNA interactions. Publications reviewing the genotoxicity of ELF radiation [McCann et al. (1993): Mutat Res 297(1):61-95; Murphy et al. (1993): Mutat Res 296:221-240; NAS (1997)], have been uniform in concluding that the weight of evidence does not indicate any genotoxic risk from exposure to this type of radiation. Concern that RFR may be associated with adverse biological effects [WHO, 1993], including recent allegations that they may be involved in the production of brain tumors in humans [Elmer-Dewit (1993): Time, February 8:42], has resulted in the production of a large number of publications describing the effects of RFR on the integrity of nucleic acids. Data from studies conducted in a frequency range from 800 to 3,000 MHz were reviewed and subjected to a weight-of-evidence evaluation. The evaluation focused on direct toxicological effects of RFR as well as on studies addressing basic biological responses to RFR at the cellular and molecular level. The data from over 100 studies suggest that RFR is not directly mutagenic and that adverse effects from exposure of organisms to high frequencies and high power intensities of RFR are predominantly the result of hyperthermia; however, there may be some subtle indirect effects on the replication and/or transcription of genes under relatively restricted exposure conditions.