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Biomedical subjects

H Field

Publications and source records attributed to H Field.

At least 37 records · Page 2Linked to original sources
PubMed1996

Intimin from enteropathogenic Escherichia coli restores murine virulence to a Citrobacter rodentium eaeA mutant: induction of an immunoglobulin A response to intimin and EspB.

The formation of attaching and effacing (A/E) lesions is central to the pathogenesis of enteropathogenic Escherichia coli (EPEC)-mediated disease in humans and Citrobacter rodentium (formerly C. freundii biotype 4280)-mediated transmissible colonic hyperplasia in mice. Closely related outer membrane proteins, known as intimins, are required for formation of the A/E lesion by both EPEC (Int(EPEC)) and C. rodentium (Int(CR)). A secreted protein, EspB (formally EaeB), is also necessary for A/E-lesion formation. Here we report that expression of a cloned Int(EPEC), encoded by plasmid pCVD438, restores murine virulence to an intimin-deficient mutant of C. rodentium DBS255. Replacement of Cys937 with Ala abolished the ability of the cloned EPEC intimin to complement the deletion mutation in DBS255. Ultrastructural examination of tissues from wild-type C. rodentium and DBS255(pCVD438)-infected mice revealed multiple A/E lesion on infected cells and loss of contact between enterocytes and basement membrane. Histological investigation showed that although both wild-type C. rodentium and DBS255(pCVD438) colonized the descending colon and induced colonic hyperplasia in orally infected 21-day-old mice, the latter strain adhered to epithelial cells located deeper within crypts. Nonetheless, infection with the wild-type strain was consistently more virulent, as indicated by a higher mortality rate. All the surviving mice, challenged with either wild-type C. rodentium or DBS255(pCVD438), developed a mucosal immunoglobulin A response to intimin and EspB. These results show that C. rodentium infection provides a relevant, simple, and economic model to investigate the role of EPEC proteins in the formation of A/E lesions in vivo and in intestinal disease.

Adhesins, Bacterial↗
PubMed1992

Cloning, sequencing, and demonstration of polymorphism in trypanothione reductase from Crithidia fasciculata.

Trypanothione reductase (TR) is a target for drug design since it is unique to trypanosomatids, substituting for the otherwise ubiquitous enzyme, glutathione reductase. We report the cloning and sequencing of several cDNAs and genes encoding Crithidia fasciculata TR, the structure of which has recently been solved by crystallography. Single base polymorphisms are detected in cDNAs (containing 80% of the coding sequence) and two different genomic clones, including a glutamine to glutamate change in the C-terminal region of the TR coding region; other nucleotide changes are silent. Homology (from genomic clones, both of which contained signals appropriate for expression) to the Trypanosoma congolense gene was 63% at the nucleic acid level, with 68% amino acid identity; the significance of homologies to human and Escherichia coli glutathione reductase sequences is discussed. Polymorphic sites in the genomic clones included sites found in the cDNAs, indicating that differences existing in the genomic sequence are real, and propagated to RNA.

Amino Acid Sequence↗
PubMed1991

X-ray structure of trypanothione reductase from Crithidia fasciculata at 2.4-A resolution.

Trypanosomes and related protozoan parasites lack glutathione reductase and possess instead a closely related enzyme that serves as the reductant of a bis(glutathione)-spermidine conjugate, trypanothione. The human and parasite enzymes have mutually exclusive substrate specificities, providing a route for the design of therapeutic agents by specific inhibition of the parasite enzyme. We report here the three-dimensional structure of trypanothione reductase from Crithidia fasciculata and show that it closely resembles the structure of human glutathione reductase. In particular, the core structure surrounding the catalytic machinery is almost identical in the two enzymes. However, significant differences are found at the substrate binding sites. A cluster of basic residues in glutathione reductase is replaced by neutral, hydrophobic, or acidic residues in trypanothione reductase, consistent with the nature of the spermidine linkage and the change in overall charge of the substrate from -2 to +1, respectively. The binding site is more open in trypanothione reductase due to rotations of about 4 degrees in the domains that form the site, with relative shifts of as much as 2-3 A in residue positions. These results provide a detailed view of the residues that can interact with potential inhibitors and complement previous modeling and mutagenesis studies on the two enzymes.

Amino Acid Sequence↗
PubMed1990

Expression of mouse immunoglobulin light and heavy chain variable regions in Escherichia coli and reconstitution of antigen-binding activity.

The expression of immunoglobulin heavy and light chain variable regions in the cytoplasm of Escherichia coli and formation of a functional heterodimer has been demonstrated. Variable domain sequences were taken from the heavy and light chain cDNAs of the monoclonal antibody Gloop 2 and engineered for expression in a dual origin expression vector. The engineered genes vhg2 and vlg2 were separately subcloned into the vector, creating two expression plasmids. Expression of the heavy and light chain variable region genes (encoding 116 and 109 amino acids respectively) was investigated in eight E. coli strains; the polypeptides were rapidly degraded in a host strain optimized for expression and in E. coli strains deficient in the major protease La (lon-). Accumulation was permitted in severely protease-deficient E. coli having a defective heat-shock response. A lon- mutation in this genetic background permitted even higher accumulation. Expression levels were 7 and 1% of total bacterial protein for light and heavy chain variable regions respectively. Expression of the heavy chain variable region gene was increased by including a longer Shine-Dalgarno sequence. Similar constructions in the light chain vector had no effect on expression levels. The insoluble variable region polypeptides were reconstituted into a heterodimer possessing the full antigen binding characteristics of both the parent monoclonal antibody and its Fab fragment.

Animals↗
PubMed1982

Suppressor cell activity, splenic function and HLA B8 status in man.

The enhanced proliferative response of peripheral blood lymphocytes (P.B.L.) to Concanavalin A (Con A) occurring after a 24 hr period of incubation was used as the basis of a suppressor cell assay and the results expressed as a suppressor index (S.I.) which if low implies impaired suppressor cell activity. S.I. was measured on P.B.L. from 26 patients with coeliac disease and defined splenic function, 8 patients with splenic atrophy not associated with coeliac disease, 30 patients after surgical splenectomy, and 52 controls. S.I. was lower than control in the splenectomy group (P less than 0.01) and in the coeliac group, but coeliacs with splenic atrophy were no different from coeliacs with apparently normal splenic function, nor were the non-coeliac splenic atrophy group different from control. Coeliacs with the HLA B8 gene had lower S.I. than those without, as did controls. Suspensions of cells from spleens removed at laparotomy demonstrated suppressor activity but this was no more marked than in P.B.L. It is concluded that the intact spleen is required for normal activation of suppressor cells in man, but this function is retained in splenic atrophy, and that the HLA B8 gene is associated with low suppressor cell activity in coeliac disease and in health.

Celiac Disease↗
PubMed1981

The sensitivity of acyclovir-resistant mutants of herpes simplex virus to other antiviral drugs.

Three acyclovir (ACV)-resistant mutants derived from a strain of herpes simplex virus (HSV) type 1 were studied to determine the range of their resistance to nine drugs active against HSV. Two of the mutants were thymidine kinase-deficient (TK-) and were resistant to drugs that are usually phosphorylated by HSV TK. The other mutant induced normal levels of TK; it was of special interest since TK+ viruses appear more likely to multiply well in vivo. This mutant was inhibited by "TK-mediated" drugs: idoxuridine, which is already in use, and two drugs with promising clinical potential, 1-beta-arabinofuranosylthymine and E-5-(2-bromovinyl)-2'-deoxyuridine. All of the mutants were sensitive to trifluorothymidine and 9-beta-D-arabinofuranosyladenine. These results suggest that the study of cross-resistance of HSV strains in vitro will aid in the investigation of alternative drugs for use in effective chemotherapy.

Acyclovir↗
PubMed1978

Phenylethylamine overproduction in aggressive psychopaths.

Plasma concentrations of free and conjugated phenylacetic acid, the major metabolite of phenylethylamine, were higher in ten prisoners serving long terms of imprisonment for violent crimes than in pair-matched non-violent control prisoners. Since amphetamine, a compound closely related to phenylethylamine, can reduce aggressiveness in some violent subjects, the increase in phenylethylamine production may be an attempt to compensate for the unknown derangement of function responsible for increased aggression.

Adult↗