Multicomponent intermetallic nanoparticles and superb mechanical behaviors of complex alloys

Alloy design based on single–principal-element systems has approached its limit for performance enhancements. A substantial increase in strength up to gigapascal levels typically causes the premature failure of materials with reduced ductility. Here, we report a strategy to break this trade-off by controllably introducing high-density ductile multicomponent intermetallic nanoparticles (MCINPs) in complex alloy systems. Distinct from the intermetallic-induced embrittlement under conventional wisdom, such MCINP-strengthened alloys exhibit superior strengths of 1.5 gigapascals and ductility as high as 50% in tension at ambient temperature. The plastic instability, a major concern for high-strength materials, can be completely eliminated by generating a distinctive multistage work-hardening behavior, resulting from pronounced dislocation activities and deformation-induced microbands. This MCINP strategy offers a paradigm to develop next-generation materials for structural applications.

The biosynthetic gene cluster for the microtubule-stabilizing agents epothilones A and B from Sorangium cellulosum So ce90

BACKGROUND

Epothilones are produced by the myxobacterium Sorangium cellulosum So ce90, and, like paclitaxel (Taxol((R))), they inhibit microtubule depolymerisation and arrest the cell cycle at the G2-M phase. They are effective against P-glycoprotein-expressing multiple-drug-resistant tumor cell lines and are more water soluble than paclitaxel. The total synthesis of epothilones has been achieved, but has not provided an economically viable alternative to fermentation. We set out to clone, sequence and analyze the gene cluster responsible for the biosynthesis of the epothilones in S. cellulosum So ce90.

RESULTS

A cluster of 22 open reading frames spanning 68,750 base pairs of the S. cellulosum So ce90 genome has been sequenced and found to encode nine modules of a polyketide synthase (PKS), one module of a nonribosomal peptide synthetase (NRPS), a cytochrome P450, and two putative antibiotic transport proteins. Disruptions in the genes encoding the PKS abolished epothilone production. The first PKS module and the NRPS module are proposed to co-operate in forming the thiazole heterocycle of epothilone from an acetate and a cysteine by condensation, cyclodehydration and subsequent dehydrogenation. The remaining eight PKS modules are responsible for the elaboration of the rest of the epothilone carbon skeleton.

CONCLUSIONS

The overall architecture of the gene cluster responsible for epothilone biosynthesis has been determined. The availability of the cluster should facilitate the generation of designer epothilones by combinatorial biosynthesis approaches, and the heterologous expression of epothilones in surrogate microbial hosts.

Isotopic (18O) shift in 31P nuclear magnetic resonance applied to a study of enzyme-catalyzed phosphate--phosphate exchange and phosphate (oxygen)--water exchange reactions

An isotopic shift of the (31)P nuclear magnetic resonance due to (18)O bonded to phosphorus of 0.0206 ppm has been observed in inorganic orthophosphate and adenine nucleotides. Thus, the separation between the resonances of (31)P(18)O(4) and (31)P(16)O(4) at 145.7 MHz is 12 Hz and, in a randomized sample containing approximately 50% (18)O, all five (16)O-(18)O species are resolved and separated from each other by 3 Hz. Not only does this yield the (18)O/(16)O ratio of the phosphate but, more important, the (18)O-labeled phosphate in effect can serve as a double label in following phosphate reactions, for oxygen in all cases and for phosphorus, provided the oxygen does not exchange with solvent water. Thus, it becomes possible to follow labeled phosphorus or labeled oxygen continuously as reactions proceed. Rate studies involving (i) phosphorus and (ii) oxygen are illustrated by continuous monitoring of the exchange reactions between (i) the beta phosphate of ADP and inorganic phosphate catalyzed by polynucleotide phosphorylase and (ii) inorganic orthophosphate and water catalyzed by yeast inorganic pyrophosphatase. In the ADP-P(i) exchange, the P(i) ((18)O(4)) yielded an alpha P((16)O(3) (18)O) and a beta P((18)O(4)), proving that bond cleavage occurs between the alpha P and the alpha-beta bridge oxygen. Among the many additional potential uses of this labeling technique and its spectroscopic observation are: (i) different labeling of each phosphate group of ATP, (ii) to follow rate of transfer of (18)O from a nonphosphate compound such as a carboxylic acid to a phosphate compound, and (iii) to follow the rate of scrambling (for example, of the beta-gamma bridge oxygen of ATP to nonbridge beta P positions) and simultaneously the rate of exchange of the gamma P nonbridge oxygens with solvent water in various ATPase reactions.

Human cytomegalovirus mutant with sequence-dependent resistance to the phosphorothioate oligonucleotide fomivirsen (ISIS 2922)

A human cytomegalovirus mutant that was isolated for resistance (10-fold) to the antisense oligonucleotide fomivirsen (ISIS 2922) exhibited cross-resistance to a modified derivative of fomivirsen with an identical base sequence but little or no resistance to an oligonucleotide with an unrelated sequence. No changes in the mutant's DNA corresponding to the fomivirsen target sequence were found.

Cephalometric and occlusal changes following maxillary expansion and protraction

A prospective clinical trial was conducted to determine the cephalometric and occlusal changes following maxillary expansion and protraction. Twenty Southern Chinese patients (eight males and 12 females with a mean age of 8.4 +/- 1.8 years) with skeletal Class III malocclusions were treated consecutively with maxillary expansion and a protraction facemask. Growth adaptation of these patients was followed for 2 years after removal of the appliances and compared with a control group of subjects with no treatment. Lateral cephalometric radiographs were used to quantify the skeletal and dental changes before treatment (T1), immediately after treatment (T2) and 2 years after removal of appliances (T3). With 8 months of treatment (T2-T1), overjet was overcorrected from a -2.0 to 3.5 mm. The maxilla moved forwards by an average of 2.1 mm and the molar relationship was improved to a Class I dental arch relationship. The palatal and occlusal planes were tilted upward 1.0 and 2.0 degrees, respectively. Two years following removal of the appliances (T3-T2), a positive overjet was maintained in 18 out of 20 patients. The maxilla continued to move forwards in the treated subjects similar to the controls. The mandible outgrew the maxilia. In most instances, dental compensation with proclination of the maxillary incisors was observed. The palatal plane returned to pre-treatment value. The occlusal plane continued to tilt upward due to eruption of the molars and proclination of the incisors. Analysis of dental casts showed a significant increase in maxillary intercanine (2.2 mm) and intermolar widths (2.3 mm) with 7 days of rapid palatal expansion followed by maxillary protraction. The percentage relapse in maxillary intermolar widths was 30-45 per cent after 1 year, in most cases with minimal retention. In the mandibular arch, the concurrent increase in intermolar width (2.3 mm) was primarily due to buccal uprighting of the posterior molars when the maxilla was protracted into a Class I skeletal relationship and was stable after 1 year. The results of this study indicate stability of orthopaedic treatment of Class III malocclusions directed at the maxilla. Despite some relapse, a net improvement in maxillomandibular relationship and a positive overjet was maintained in 18 out of 20 patients at the end of the follow-up period.

Combination Therapy Does Not Improve Rate of Clinical or Endoscopic Remission in Patients with Inflammatory Bowel Diseases Treated With Vedolizumab or Ustekinumab

BACKGROUND & AIMS

Patients with Crohn's disease (CD) or ulcerative colitis (UC) often receive combination therapy with an immunomodulator and tumor necrosis factor antagonists, especially infliximab. However, the benefits of combination therapy with vedolizumab and ustekinumab are unclear.

METHODS

We performed a retrospective study of patients with CD or UC initiating vedolizumab or ustekinumab therapy at Massachusetts General Hospital (USA), Alberta Health Sciences (Canada), or Nancy University Hospital (France) with at least 1 year of follow up. The primary outcome was clinical remission or response at week 14, based on the Harvey Bradshaw index for CD or simple clinical colitis index or partial Mayo score for UC. We separately examined week 30 and week 54 clinical outcomes, endoscopic response, and durability of therapy using multivariable regression models and adjusting for relevant confounders.

RESULTS

Our study included 549 patients (263 with UC, 286 with CD) receiving maintenance therapy with vedolizumab and 363 patients (4 with UC, 359 with CD) receiving maintenance therapy with ustekinumab with 1 year of follow up. The mean disease duration was 13-15 years. One-hundred thirty-one patients receiving vedolizumab (23.9%; 78 receiving thiopurine, 53 receiving methotrexate) and 120 patients receiving ustekinumab (33.1%, 57 receiving thiopurine, 63 receiving methotrexate) were receiving combination therapy. For vedolizumab, there was no difference in clinical response or remission with combination therapy vs monotherapy at week 14 (68.2% vs 74.1%; P = .22), week 30 (74.3% vs 75.6%; P = .78) or week 54 (78.3% vs 72.9%, P = .33). For ustekinumab, there was no difference in clinical response or remission with combination therapy vs monotherapy at week 14 (54.6% vs 65.8%; P = .08), week 30 (71.6% vs 77.4%; P = .33) or week 54 (62.1% vs 67.0%; P = .52). There were similar proportions of patients remaining on treatment or with endoscopic response at 1 year among patients receiving combination or monotherapy with vedolizumab or ustekinumab.

CONCLUSIONS

In patients with CD or UC initiating ustekinumab or vedolizumab therapy, combination therapy with immunomodulators did not increase rates of clinical remission or response, endoscopic remission, or persistence of therapy at 1 year.

Extracardiac lesions and chromosomal abnormalities associated with major fetal heart defects: comparison of intrauterine, postnatal and postmortem diagnoses

OBJECTIVES

The clinical outcome of prenatally diagnosed congenital heart defects (CHD) continues to be affected significantly by associated extracardiac and chromosomal abnormalities. We sought to: determine the frequency and type of major extracardiac abnormalities (with impact on quality of life) and chromosomal abnormalities associated with fetal CHD; and compare the extracardiac abnormalities detected prenatally to the postnatal and autopsy findings in affected fetuses, to find the incidence of extracardiac abnormalities missed on prenatal ultrasound.

METHODS

We reviewed the computerized database of the Division of Cardiology of the Hospital for Sick Children in Toronto to identify all cases of major CHD detected prenatally from 1990 to 2002. Medical records, fetal echocardiograms and ultrasound, cytogenetic and autopsy reports were reviewed. The types of CHD detected were grouped into categories and the frequencies of major extracardiac and chromosomal abnormalities in these categories were noted. Prenatal ultrasound findings were compared with those at autopsy or postnatal examination.

RESULTS

Of 491 fetuses with major structural CHD, complete data were obtained for 382. Of these, there were 141 (36.9%) with major extracardiac abnormalities at autopsy or postnatal exam, of which 46 had chromosomal abnormalities and 95 did not. In the absence of chromosomal abnormalities, the organ systems most affected were urogenital (12.2%) and gastrointestinal (11.6%). CHDs with the highest incidence of extracardiac abnormalities (>25%) included: heterotaxy, single left ventricle and tricuspid atresia, hypoplastic left heart syndrome and tetralogy of Fallot. Ninety-four of 334 (28.1%) fetuses tested had chromosomal abnormalities. The most common chromosomal abnormalities were trisomies 21 (43.6%), 18 (19.1%) and 13 (9.6%), monosomy X (7.4%) and 22q11.2 deletion (7.4%). Of 289 extracardiac abnormalities from the complete series, 134 (46.4%) were not identified prenatally. Of the missed extracardiac abnormalities, 65 were considered not detectable at prenatal ultrasound, so 23.9% (69/289) of detectable extracardiac abnormalities were missed prenatally.

CONCLUSIONS

Major extracardiac and chromosomal abnormalities are common in fetuses with major fetal CHD. Many important associated extracardiac abnormalities may be missed prenatally, which should be taken into consideration in the prenatal counseling for fetal CHD.

Spectroscopic characterization of carbon chains in nanostructured tetrahedral carbon films synthesized by femtosecond pulsed laser deposition

A comparative study of carbon bonding states and Raman spectra is reported for amorphous diamondlike carbon films deposited using 120 fs and 30 ns pulsed laser ablation of graphite. The presence of sp(1) chains in femtosecond carbon films is confirmed by the appearance of a broad excitation band at 2000-2200 cm(-1) in UV-Raman spectra. Analysis of Raman spectra indicates that the concentrations of sp(1)-, sp(2)-, and sp(3)-bonded carbon are approximately 6%, approximately 43%, and approximately 51%, respectively, in carbon films prepared by femtosecond laser ablation. Using surface enhanced Raman spectroscopy, specific vibrational frequencies associated with polycumulene, polyyne, and trans-polyacetylene chains have been identified. The present study provides further insight into the composition and structure of tetrahedral carbon films containing both sp(2) clusters and sp(1) chains.

Review: The roles and functions of glutamine on intestinal health and performance of weaning pigs

The gut is composed of a single layer of intestinal epithelial cells and plays important roles in the digestion and absorption of nutrients, immune and barrier functions and amino acid metabolism. Weaning stress impairs piglet intestinal epithelium structural and functional integrities, which results in reduced feed intake, growth rates and increased morbidity and mortality. Several measures are needed to maintain swine gut development and growth performance after weaning stress. A large body of evidence indicates that, in weaning piglets, glutamine, a functional amino acid, may improve growth performance and intestinal morphology, reduce oxidative damage, stimulate enterocyte proliferation, modulate cell survival and death and enhance intestinal paracellular permeability. This review focuses on the effects of glutamine on intestinal health in piglets. The aim is to provide evidentiary support for using glutamine as a feed additive to alleviate weaning stress.

Activation of lecithin:cholesterol acyltransferase by a synthetic model lipid-associating peptide

We have synthesized a model lipid-associating peptide of 20 residues (LAP-20) and studied its association with the phospholipid dimyristoyl phosphatidylcholine (DMPC) and its activation of the plasma enzyme lecithin:cholesterol acyl-transferase (EC 2.3.1.43). The lipid-associating behavior of LAP-20 is similar to that of well-characterized native plasma apolipoproteins after which it was modeled. Upon forming an isolated complex with DMPC, LAP-20 exhibits a large blue-shift in its intrinsic fluorescence, converts from a random coil to an alpha -helix, and changes turbid multilamellar structures of DMPC into small complexes that are optically clear. Addition of 2 mol % cholesterol does not detectably alter the structure or properties of the complex. The cholesterol-containing complexes of LAP-20 and DMPC are substrates for LCAT, having an activity 65% of that of complexes composed of DMPC, cholesterol, and the natural activator, apolipoprotein A-I. These findings suggest that the LCAT-activating regions of apoA-I may be confined to relatively short sequences that contain a lipid-binding determinant.

Role of N-linked oligosaccharide chains in the processing and antigenicity of measles virus haemagglutinin protein

The effects of N-linked oligosaccharides on the haemagglutinin (H) protein of measles virus (MV) were assessed with respect to the processing and antigenicity of the molecule. The functional glycosylation sites on the H protein were determined by eliminating each of the five potential positions, Asn-168, Asn-187, Asn-200, Asn-215 and Asn-238, for N-linked glycosylation by oligonucleotide-directed mutagenesis on a cDNA clone. Expression of the mutant H proteins in BHK-21 cells by a recombinant vaccinia virus encoding T7 polymerase indicated that the first four sites were used in the H glycoprotein for the addition of N-linked oligosaccharide chains. Heterogeneity of oligosaccharide processing was demonstrated. One of the four glycosylation sites had a different carbohydrate structure from those of the other three glycosylation sites and this varied glycosylation was responsible for the appearance of two forms of the H protein. The functional glycosylation sites were systematically removed in various combinations from the H protein to form a panel of mutants in which the role of carbohydrate chains, singly or in different combinations, could be evaluated. Investigations of these glycosylation mutants indicated that (i) two of the four individual carbohydrate side-chains have a large influence on the antigenicity of the molecule; (ii) individual carbohydrate side-chains have little effect on the folding and oligomerization of the molecule, and are not sufficient or necessary alone to facilitate the transport of the molecule to the plasma membrane; (iii) at least two carbohydrate side-chains are required for the H protein to move along the exocytic pathway to the plasma membrane and various combinations of oligosaccharide side-chains, irrespective of the carbohydrate localizations, influence equally the processing of the molecule.

Thioredoxin reduces post-ischemic myocardial apoptosis by reducing oxidative/nitrative stress

BACKGROUND AND PURPOSE

Thioredoxin (Trx) is an oxidoreductase that prevents free radical-induced cell death in cultured cells. Here we assessed the mechanism(s) underlying the cardioprotective effects of Trx in vivo.

EXPERIMENTAL APPROACH

The effects of myocardial ischemia (30 min) and reperfusion were measured in mice, with assays of myocardial apoptosis, superoxide production, NOx and nitrotyrosine content, and myocardial infarct size. Recombinant human Trx (rhTrx, 0.7-20 mg kg(-1), i.p.) was given 10 min before reperfusion.

KEY RESULTS

Treatment with 2 mg kg(-1) rhTrx significantly decreased myocardial apoptosis and reduced infarct size (P<0.01). Nitrotyrosine content of cardiomyocytes was markedly reduced in rhTrx-treated animals (P<0.01). To further identify the mechanisms by which rhTrx may exert its anti-nitrative effect, iNOS expression and production of NOx and superoxide were determined. Treatment with rhTrx had no significant effect on iNOS expression or NOx content in the ischemic/reperfused heart. However, it markedly upregulated mSOD and reduced tissue superoxide content. To further establish a causative link between the anti- peroxynitrite effect and the cardioprotective effect of rhTrx, cultured adult cardiomyocytes were incubated with SIN-1, a peroxynitrite donor, (50 microM for 3 h) resulting in a nitrotyrosine content comparable to that seen in the ischemic/reperfused heart and causing significant cardiomyocyte apoptosis (P<0.01). Treatment with rhTrx markedly decreased SIN-1 induced apoptosis (P<0.01).

CONCLUSIONS AND IMPLICATIONS

These results demonstrate that Trx is a novel anti-apoptotic and cardioprotective molecule that exerts its cardioprotective effects by reducing ischemia/reperfusion-induced oxidative/nitrative stress.

Neutrophils from human immunodeficiency virus (HIV)-seronegative donors induce HIV replication from HIV-infected patients' mononuclear cells and cell lines: an in vitro model of HIV transmission facilitated by Chlamydia trachomatis

Infection with a sexually transmitted disease (STD) increases the risk for human immunodeficiency virus (HIV) infection. Polymorphonuclear leukocytes (PMNs) are recruited into the genital tract by STD pathogens, such as Chlamydia trachomatis. Semen of HIV-infected men contains HIV associated with mononuclear cells. This study investigated the interaction among PMNs from HIV-uninfected persons, C. trachomatis, and HIV-infected cells and examined the mechanisms for enhanced HIV replication. We demonstrated that PMNs from HIV-seronegative donors induced HIV replication in mononuclear cells from 17 HIV-infected patients in medium without exogenous IL-2. HIV in the cell-free supernatants from cocultures of PMNs and patients' peripheral blood mononuclear cells (PBMCs) was replication competent, as indicated by their capacity to propagate HIV in a second round of culture using PBMCs from HIV-seronegative individuals and by the fact that proviral DNA was found in these cells. PMNs from HIV-seronegative donors increased HIV replication over 100-fold in chronically HIV-infected cell lines of the monocytic, T, and B cell lineages. Moreover, PMNs increased U1 cells' production of p24 antigen by as much as ninefold when compared with U1 cells cocultured with PBMCs. The addition of C. trachomatis to PMN and U1 coculture increased HIV replication by an additional ninefold at 24 h, whereas C. trachomatis alone had no effect on p24 antigen production by U1 cells. Thus, C. trachomatis serves not only to recruit PMNs, but also to interact with PMNs to increase HIV replication. HIV replication is triggered by contact of HIV-infected cells with PMNs, by the generation of reactive oxygen intermediates (ROIs), and by soluble factors such as TNF-alpha and IL-6. This is based on the findings that production of p24 antigen, IL-6, and TNF-alpha induced by PMNs is abrogated by disrupting or partitioning PMNs from HIV-infected cells; is inhibited by superoxide dismutase and catalase, enzymes that destroy ROIs; is enhanced by differentiated HL60 cells capable of producing ROIs; and is induced by PMNs tested negative for CMV. Furthermore, the production of ROIs is independent of HIV infection of mononuclear cells, since PMNs cocultured with HIV-uninfected parental monocytic and T cell lines generated ROIs. Therefore, the increased risk for acquiring HIV infection associated with chlamydia cervicitis may be related to the local recruitment of PMNs by C. trachomatis and the induction of infectious virus from mononuclear cells present in semen. These observations provide a rationale for strategies to reduce HIV transmission by control of STD.

Recurrent acyclovir-resistant herpes simplex in an immunocompromised patient: can strain differences compensate for loss of thymidine kinase in pathogenesis?

To investigate how acyclovir-resistant (ACVr) herpes simplex virus (HSV) evades drug therapy and causes disease, HSV-1 isolates from a bone marrow transplant (BMT) patient were studied. The patient developed ACVr disease after an initial BMT and, following a second BMT, reactivated ACVr HSV despite high-dose acyclovir prophylaxis. ACVr isolates from each episode contained the same point mutation in the viral thymidine kinase (tk) gene, documenting the emergence, latency, and reactivation of this mutant. The mutants were exceedingly impaired for TK activity in sensitive enzyme, plaque autoradiography, and drug-susceptibility assays. Nevertheless, these mutants and a tk deletion mutant constructed in the same genetic background reactivated from latency in mouse trigeminal ganglia, in contrast to similar mutants from laboratory strains. It is hypothesized that alleles in the clinical isolate compensate for the loss of TK in this animal model. Such genetic variability may be important for ACVr disease in humans.

Molecular characterization of epitopes on the measles virus hemagglutinin protein

The measles virus (MV) hemagglutinin (H) gene nucleotide sequences of the LEC-WI strain and 11 branched sequential neutralization escape variants of the strain derived by selection with five monoclonal antibodies (Mabs) were determined by direct analysis of amplified polymerase chain reaction products. The parental LEC-WI strain isolated from a patient with subacute sclerosing panencephalitis exhibited H gene sequence characteristics similar to other persistent virus strains derived from brain materials. Mostly single-point H gene mutations, coding for single amino acid substitutions in the H protein, were found to provide explanations for the resistance to the individual Mabs. Resistance to Mabs 16-CD11 and I-41 resulted from changes of Gly-491 to Asp (or Val) and Phe-552 to Val, respectively. One variant (B89) selected by Mab 16-CD11 had a mutation introduced by a single nucleotide deletion and subsequent nucleotide insertion, which caused a shift in the open reading frame. The epitope of Mab I-29 was assigned to Ser-313 or Gly-314, which were changed to Leu and Arg, respectively. The variants subjected to the Mab I-44 selection exhibited change of Ser-189 to Pro. Radioimmunoprecipitation assay and endoglycosidase H (Endo H) treatment revealed that this change destroyed a potential N-linked glycosylation site, indicating that the carbohydrate chain participates in formation of the epitope or indirectly influences its properties. Resistance to Mab 16-DE6 involved three specific amino acid changes in three different places, Gly-211 to Ser, Gly-388 to Asp, and Ser-532 to Phe or Arg-533 to Gly, reflecting the occurrence of a conformational epitope. In conclusion, this study identifies the precise positions of several critical sites on the MV H protein which react with neutralizing antibodies.

Characterization of phi8, a bacteriophage containing three double-stranded RNA genomic segments and distantly related to Phi6

The three double-stranded RNA genomic segments of bacteriophage Phi8 were copied as cDNA, and their nucleotide sequences were determined. Although the organization of the genome is similar to that of Phi6, there is no similarity in either the nucleotide sequences or the amino acid sequences, with the exception of the motifs characteristic of viral RNA polymerases that are found in the presumptive polymerase sequence. Several features of the viral proteins differ markedly from those of Phi6. Although both phages are covered by a lipid-containing membrane, the protein compositions are very different. The most striking difference is that protein P8, which constitutes a shell around the procapsid in Phi6, is part of the membrane in Phi8. The host attachment protein consists of two peptides rather than one and the phage attaches directly to the lipopolysaccharide of the host rather than to a type IV pilus. The host range of Phi8 includes rough strains of Salmonella typhimurium and of pseudomonads

Visual acuity in northern China in an urban and rural population: the Beijing Eye Study

AIM

To evaluate prevalence and demographic associations of visual impairment in an urban and rural population in northern China.

METHODS

In the Beijing Eye Study, a population based cohort study in northern China, visual acuity was assessed for 8876 eyes (4438 subjects) according to a response rate of 83.4%. The study was divided into a rural part (1972 subjects) and an urban part (n=2466). Mean age was 56.20 (SD 10.59) years (median 56 years; range 40-101 years).

RESULTS

Mean uncorrected visual acuity measured 0.72 (0.32) (median, 0.80), and mean best corrected visual acuity measured 0.91 (0.21) (median, 1.0). In a multiple regression analysis, best corrected visual acuity was significantly correlated with age (p<0.001), degree of nuclear cataract (p<0.001), amount of cortical cataract (p=0.014), amount of subcapsular cataract (p<0.001), educational background (p<0.001), and refractive error (p<0.001). Rural region versus urban region (p=0.34) and sex (p=0.053) were not statistically significantly associated with best corrected visual acuity.

CONCLUSIONS

In northern China, determinants of a low degree of best corrected visual acuity are age, cataract, low educational background, and myopia. Despite marked differences in educational background and family income, sex, and rural area versus urban area are not markedly associated with best corrected visual acuity.

Effect of age on the expressed B cell repertoire: role of B cell subsets

Aged humans and experimental animals are impaired in their responses to most foreign antigens although they produce greater amounts of autoantibodies. We have examined the effect of age on the production of antibodies to a prototypic foreign antigen, sheep erythrocytes (SRBC), and to a prototypic autoantigen, bromelain-treated mouse erythrocytes (BrMRBC), in young and old mice before and after immunization with SRBC. Old mice express more anti-BrMRBC plaque-forming cell (PFC) antibodies before and an even greater number after immunization with SRBC than young mice. Conversely, old mice produce far fewer anti-SRBC PFC than young mice following immunization with SRBC. We hypothesized that the differences in the responses of old mice to BrMRBC and SRBC reflects differences in the activity of CD5+ and CD5- B cells. To test this hypothesis we immunized young and old mice with foreign antigens reported (and confirmed in our studies) to stimulate CD5+ B cells [TNP-ficoll and phosphorylcholine-keyhole limpet hemocyanin (KLH)] or CD5- B cells (SRBC and TNP-KLH). We found that the PFC response of old mice to antigens mediated by CD5+ B cells was equal to or greater than that of young mice. In contrast the PFC response of old mice induced by antigens mediated by CD5- B cells was only 10% that of young mice. Thus it appears that the immune response of old mice is well maintained for antigens which elicit a CD5+ B cell response but not for those which elicit a CD5- B cell response.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective expression of a subset of measles virus receptor-competent CD46 isoforms in human brain

The human cell surface protein CD46 is the main measles virus (MV) receptor. We analyzed the CD46 isoforms expressed in the brain of three patients who died with persistent MV infections and in an unaffected brain. Complete CD46 cDNAs were produced and found to code exclusively for CD46 isoforms with cytoplasmic tail 2. Selective expression of tail 2 isoforms was shown in a second control brain by Western blots with antibodies specific for each of the cytoplasmic tails. Binding of purified MV particles and virus-dependent cell fusion were tested after transient expression of brain-derived CD46 proteins in mouse cells. All the brain-derived proteins mediated MV binding and virus-dependent fusion. Isoforms containing both serine/threonine/proline (STP)-rich domains were more active in virus binding, whereas isoforms with only one STP domain were more efficient in mediating fusion.

Influence of N-linked oligosaccharide chains on the processing, cell surface expression and function of the measles virus fusion protein

The fusion (F) glycoprotein of measles virus, a structural component of the virion envelope, contains four potential sites for attachment of N-linked oligosaccharides. Three are located in the F2 subunit of the protein and one in the signal peptide. Four mutants were constructed by oligonucleotide-directed mutagenesis, in each case changing one N-linked glycosylation site from Asn-X-Ser/Thr to Ser-X-Ser/Thr. The wild-type and altered forms of the F protein were expressed in BHK-21 and HeLa T4 cells by use of the recombinant vaccinia virus-encoding T7 polymerase system. Analysis of these proteins revealed that three (residues 29, 61 and 67) potential sites for addition of N-linked glycans in the F2 subunit are actually utilized. The functional glycosylation sites were systematically removed in all possible combinations from the F protein to form a panel of mutants from which the role of carbohydrates, singly or in various combinations, could be evaluated. One single-site mutant protein lacking the glycosylation site of Asn-67 was processed, transported to the cell surface and could induce cell fusion. However, the other two single-site mutant proteins with deletions of glycosylation sites Asn-29 or Asn-61 exhibited a defect in processing, were not transported to cell surface and thus induced no cell fusion. The absence of any two of the three or of all three glycosylation sites resulted in protein retention in the endoplasmic reticulum. Therefore, it appears that glycosylation of sites Asn-29 and Asn-61 has important roles in maintaining the native structure of the F protein.

Construction of a 750-kb bacterial clone contig and restriction map in the region of human chromosome 21 containing the progressive myoclonus epilepsy gene

The gene responsible for progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1) is located on human chromosome 21q22.3 in a region defined by recombination breakpoints and linkage disequilibrium. As part of an effort to clone the EPM1 gene on the basis of its chromosomal location, we have constructed a 753-kb bacterial clone contig that encompasses the region containing the gene. Because DNA markers from the region did not identify intact yeast artificial chromosome (YAC) clones after screening several libraries, we built the contig from cosmid clones and used bacterial artificial chromosome (BAC) and bacteriophage P1 clones to fill gaps. In addition to constructing the clone contig, we determined the locations of the EcoRI, SacII, EagI, and NotI restriction sites in the clones, resulting in a high-resolution restriction map of the region. Most of the contig is represented by a level of redundancy that allows the orders of most restriction sites to be determined, provides multiple data points supporting the clone orders and orientations, and allows a set of clones with a minimum degree of overlap to be chosen for efficient additional analysis. The clone and restriction maps are in excellent agreement with maps generated of the region by other methods. These ordered bacterial clones and the mapping information obtained from them provide valuable reagents for isolating candidate genes for EPM1, as well as for determining the nucleotide sequence of a 750 kb region of the human genome.

Sequence analysis of the genes encoding the nucleocapsid protein and phosphoprotein (P) of phocid distemper virus, and editing of the P gene transcript

The nucleotide and deduced amino acid sequences of two genes of phocid distemper virus (PDV) were determined by cDNA cloning and sequencing. The long open reading frame of the gene encoding the nucleocapsid (N) protein is presented. As with other morbilliviruses, the phosphoprotein (P) gene of PDV was found to be located after the 5' end of the N gene and before the 3' end of the matrix protein gene. The P gene was shown to have the capacity to encode three distinct proteins, P, V and C, in analogy to other morbilliviruses. The results presented provide evidence for editing of the PDV P mRNA transcript by insertion of G residues. When the nucleotide and deduced amino acid sequences of the N, P, V and C genes were aligned with corresponding sequences of other established members of the morbillivirus genus, compelling homology was found between PDV and canine distemper virus (CDV), whereas there was markedly less similarity between PDV and measles virus or rinderpest virus. On the basis of the alignments presented, the estimated amino acid sequence similarity between the N and P genes of PDV and CDV was 84% and 76%, respectively. These differences at the genomic level indicate that the viruses are two separate entities.