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R S Stephens

Publications and source records attributed to R S Stephens.

At least 55 records · Page 3Linked to original sources
PubMed1994

Treating adult marijuana dependence: a test of the relapse prevention model.

Men (n = 161) and women (n = 51) seeking treatment for marijuana use were randomly assigned to either a relapse prevention (RP; G.A. Marlatt & J.R. Gordon, 1985) or a social support (SSP) group discussion intervention. Data collected for 12 months posttreatment revealed substantial reductions in frequency of marijuana use and associated problems. There were no significant differences between the cognitive-behavioral RP intervention and the SSP group discussion conditions on measures of days of marijuana use, related problems, or abstinence rates. Men in the RP condition were more likely than men in the SSP condition to report reduced use without problems at 3-month follow-up. Posttreatment increases in problems associated with alcohol did not appear to relate to reduced marijuana use. Results are discussed in terms of the need for further research with marijuana-dependent adults and the efficacy of RP.

Adaptation, Psychological↗
PubMed1994

Trachoma and LGV biovars of Chlamydia trachomatis share the same glycosaminoglycan-dependent mechanism for infection of eukaryotic cells.

A sulphated glycosaminoglycan-dependent mechanism of microbial infection for mammalian cells was characterized for the Chlamydia trachomatis trachoma and lymphogranuloma venereum (LGV) biovars. We demonstrated that the trachoma and LGV biovars compete for the same receptor(s) on host cells and that their infectivity was inhibited by heparin or heparan sulphate. Using a specific heparan sulphate lyase (heparitinase) to treat organisms, the infectivity of both biovars was abolished. Furthermore, exogenous heparan sulphate rescued chlamydial infectivity following treatment with heparitinase and the restored infectivity was neutralized by an anti-heparan sulphate monoclonal antibody. These data suggest that heparan sulphate-like-mediated interactions between C. trachomatis and eukaryotic cells are essential for infectivity.

Animals↗
PubMed1994

Identification of individual genotypes of Chlamydia trachomatis from experimentally mixed serovars and mixed infections among trachoma patients.

Genetic polymorphisms in the major outer membrane protein gene (omp-1) of Chlamydia trachomatis B and Ba serovars have been demonstrated in Tunisian isolates. A total of 15 of 27 unique sequence signatures or omp-1 genotypes were identified. However, differentiation of unique signatures from sequences that reflect those of strains involved in a mixed infection is necessary to define the molecular epidemiology of chlamydial ocular infections. We devised a strategy for identifying mixed infections by characterizing their effects on omp-1 genotyping. Various ratios of elementary bodies from organisms of serovars A, B, Ba, and C that cause trachoma were amplified by PCR and were subjected to automated and manual sequencing. Serovar-specific primers were also designed so that each serovar could be individually amplified and its omp-1 genotype unequivocally determined. One of 27 Tunisian samples showed a mixed infection with sequences comparable to those of serovars B and D. The omp-1 genotypes of organisms involved in mixed infections can be accurately identified by automated sequencing and will be useful for molecular epidemiologic studies of populations worldwide who live where trachoma is endemic.

Bacterial Outer Membrane Proteins↗
PubMed1993

An intermolecular mechanism of T cell help for the production of antibodies to the bacterial pathogen, Chlamydia trachomatis.

Antibodies that neutralize infectivity are directed at the antigenically variant major outer membrane protein (MOMP) of Chlamydia trachomatis. A vaccine for chlamydia will need to include T cell determinants that elicit T helper (Th) cells which provide help to MOMP-specific B cells. A limited number of determinants on MOMP are able to elicit Th cells and sequence diversity in the MOMP molecule may alter T cell recognition of these determinants. We investigated whether two sequence invariant proteins of C. trachomatis that are both abundant and immunogenic could elicit T cell help for the production of antibody to MOMP. We found that outer membrane protein 2 (OMP2) but not outer membrane protein 3 (OMP3) was able to prime BALB/c mice for an anamnestic anti-MOMP response following boost with the intact organism. This demonstration of an intermolecular mechanism of T cell help in a bacterial system has important implications for the development of a chlamydial vaccine as well as the design of vaccines for other antigenically variant non-viral pathogens.

Animals↗
PubMed1993

Predictors of marijuana treatment outcomes: the role of self-efficacy.

This study tested the ability of sets of demographic, socioeconomic, marijuana use/abuse, psychological distress, and self-efficacy variables to predict posttreatment indices of marijuana intake and problems related to use. Subjects were 167 adults who participated in one of two outpatient treatments for marijuana dependence and completed the 3-, 6-, and 12-month posttreatment follow-ups. Only pretreatment marijuana quantity-frequency of intake and self-efficacy variables made significant and consistent contributions to the regression equations predicting posttreatment frequency of use. In contrast, socioeconomic and severity of abuse indicators predicted posttreatment marijuana-related problems. Contrary to social cognitive theory (Bandura, 1986), there was no evidence that self-efficacy mediated the effects of other predictors. Results are discussed in terms of the specificity of predictor-outcome relationships and the need for improvements in self-efficacy measurement.

Adult↗
PubMed1993

Adult marijuana users seeking treatment.

In an effort to study the efficacy of attracting and intervening with adult marijuana users, 290 men and 92 women were screened for participation in a treatment-outcome study focused on marijuana cessation. The well-educated, self-referred sample reported using marijuana on 79 of the past 90 days before testing. Indices of the severity of marijuana abuse and general psychopathology were in the clinical range for a majority of Ss. Ss who did not report evidence of alcohol or other drug abuse (n = 144) reported less severe consequences of marijuana use and experienced less general psychological distress than Ss who also reported lifetime (n = 165) or current abuse (n = 73) of other substances in addition to marijuana. The findings indicate the need for clinical research targeting adults who are dependent on marijuana.

Adult↗
PubMed1993

Workshop on in vitro neutralization of Chlamydia trachomatis: summary of proceedings.

A task force evaluated an in vitro antibody-mediated chlamydial neutralization assay for its utility as a method to assess functional correlates of antibody responses to Chlamydia trachomatis. Two monoclonal antibodies that recognize different major outer membrane protein (MOMP) epitopes for a C. trachomatis serovar B strain exhibit good in vitro neutralizing activity, with a maximum of 90% neutralization. Calculations based on the 50% neutralization point indicated that 100% neutralization could theoretically be achieved when only 10% of the MOMP molecules bound antibody. Monoclonal antibodies that recognized either a heterologous MOMP or the genus-specific chlamydial lipopolysaccharide did not produce neutralizing activity. The standardized assay will be useful to establish if in vitro neutralizing antibody responses are predictive of protective immunity and will aid in defining chlamydial antigens and epitopes that may be attractive vaccine candidates.

Animals↗
PubMed1993

Lack of allelic polymorphism for the major outer membrane protein gene of the agent of guinea pig inclusion conjunctivitis (Chlamydia psittaci).

The major outer membrane protein gene (omp1) was sequenced for each of six Chlamydia psittaci (guinea pig inclusion conjunctivitis [GPIC]) strains isolated from guinea pigs. Five of the isolates were obtained in the United States during the 1960s and 1970s, including the prototype strain isolated by Murray in 1962. The other isolate was obtained from a guinea pig in England. The nucleotide sequence of the omp1 gene for each strain was identical. The lack of omp1 allelic polymorphism among GPIC isolates suggests that, unlike C. trachomatis, the GPIC agent lacks antigenic variation in the major outer membrane protein.

Alleles↗
PubMed1992

Mechanism of C. trachomatis attachment to eukaryotic host cells.

A novel trimolecular mechanism of microbial attachment to mammalian host cells was characterized for the obligate intracellular pathogen Chlamydia trachomatis. Using purified glycosaminoglycans (GAGs) and specific GAG lyases, we demonstrated that a heparan sulfate-like GAG present on the surface of chlamydia organisms is required for attachment to host cells. These observations were supported by inhibition of attachment following binding of heparan sulfate receptor analogs to chlamydiae and by demonstrating that chlamydiae synthesize a unique heparan sulfate-like GAG. Furthermore, exogenous heparan sulfate, as an adhesin analog, restored attachment and infectivity to organisms that had lost these attributes following treatment with heparan sulfate lyase. These data suggest that a GAG adhesin ligand mediates attachment by bridging mutual GAG receptors on the host cell surface and on the chlamydial outer membrane surface.

Animals↗
PubMed1992

Comparison of the major outer membrane protein variant sequence regions of B/Ba isolates: a molecular epidemiologic approach to Chlamydia trachomatis infections.

The molecular evaluation of the chlamydial major outer membrane protein (MOMP) gene (omp1) can facilitate epidemiologic investigations of this pathogen. Genotyping of omp1 provides a more precise characterization of Chlamydia trachomatis than do current immunotyping techniques. Genetic omp1 variants of serovars that are responsible for ocular disease in Tunisia were identified. Archival conjunctival samples collected during 1972 and 1975 from trachoma patients in Douz were sequenced by automation along with additional B and Ba trachoma and genital isolates. Over 90% of the nucleotide changes resulted in an amino acid substitution. Different amino acid sequence changes in variable segments 1, 2, and 4 were found in the specimens collected in 1975 from those collected in 1972. Determination of omp1 genotypes responsible for trachoma will be useful for prospective, epidemiologic studies to identify chlamydial reservoirs within the host, evaluate transmission patterns, and determine the antigenic variation of MOMP for rational vaccine development.

Amino Acid Sequence↗
PubMed1992

Evaluation of the humoral immune response in trachoma to Chlamydia trachomatis major outer membrane proteins by sequence-defined immunoassay.

The Chlamydia trachomatis immunodominant major outer membrane protein (MOMP) is both a target of neutralizing antibodies and the serotyping antigen and thus has been a focus of diagnostic, seroepidemiologic, and experimental investigations. The microimmunofluorescence (MIF) test has been the principal tool in serologic investigations of chlamydial infections but is difficult and expensive for routine use; moreover, since it uses whole organisms as antigen, it is incapable of revealing the molecular specificity of the humoral response to infection. These limitations were resolved by using synthetic peptides corresponding to serovar-specific antigenic regions of MOMP in an ELISA-based format to analyze the serospecificity of sera from trachoma cases. The ELISA reaction to the surface-exposed MOMP sequence variable segment 1 was immunodominant and serovar-specific and was in concordance with serovar specificity according to paired MIF test determinations. Understanding the patterns of humoral responses to MOMP determinants in patient populations will advance our knowledge of their role in the immunobiology of naturally acquired infection.

Amino Acid Sequence↗
PubMed1992

Overexpression and surface localization of the Chlamydia trachomatis major outer membrane protein in Escherichia coli.

The Chlamydia trachomatis major outer membrane protein (MOMP) is the quantitatively predominant surface protein which has important functional, structural and antigenic properties. We have cloned and overexpressed the MOMP in Escherichia coli. The MOMP is surface exposed in C. trachomatis and capable of eliciting protective antibodies in infected hosts, and therefore has potential as a candidate vaccine to prevent infection with this significant human pathogen. The recombinant MOMP clone, L2rMOMP, contained the entire MOMP gene including the encoded leader sequence. Large quantities of chlamydial MOMP were expressed, some of which was processed and translocated to the E. coli surface. Surface localization of the MOMP was demonstrated by the binding of anti-MOMP monoclonal antibodies to the surface of the induced clone, and was visualized by fluorescence and electron microscopy. The induction of MOMP expression had a rapidly lethal effect on the L2rMOMP E. coli clone. Although no genetic system exists for Chlamydia, development of a stable, inducible E. coli clone which overexpresses the chlamydial MOMP permits a study of the biological properties of the MOMP, including the contribution of the MOMP variable segments to the topographical interactions which determine the antigenic structure responsible for human immune response.

Antibodies, Bacterial↗
PubMed1992

Identification of Chlamydia trachomatis antigens by use of murine T-cell lines.

Chlamydia-specific short-term T-cell lines were used in conjunction with immunoblot techniques to examine Chlamydia trachomatis proteins for T-cell-stimulatory activity. This study was undertaken because of the known role of T cells in the resolution and pathogenesis of chlamydial infections. Therefore, determination of which chlamydial proteins are T-cell antigens and whether they evoke protective immunity or contribute to immunopathology is crucial. Immune lymph node cells were stimulated with whole chlamydial organism (elementary body) to derive predominantly CD4+ T-cell lines. Proteins from the elementary body and the outer membrane and cloned proteins were examined for antigenicity with these T-cell lines in a proliferation assay. Although a majority of the elementary body protein fractions were positive in this assay, only four of the outer membrane fractions were stimulatory. The cloned major outer membrane protein and outer membrane protein 2 were stimulatory in the assay and may account for the reactivity in three of the four positive outer membrane fractions. The C. trachomatis heat shock protein 60, examined because of its putative role in causing delayed-type hypersensitivity, was found to stimulate the CD4+ T cells. This approach with short-term T-cell lines with polyclonal reactivity was sensitive and specific in identifying chlamydial proteins as T-cell antigens.

Animals↗
PubMed1992

Immune specificity of murine T-cell lines to the major outer membrane protein of Chlamydia trachomatis.

The antigenically variant Chlamydia trachomatis major outer membrane protein (MOMP) is a target of antibody-mediated neutralization in vitro, and it is an important protein for designing a subunit vaccine. Knowledge of MOMP T-cell determinants will be essential to elicit rapid and strong immune responses following an encounter with infectious organisms. C. trachomatis-specific T-cell lines were derived from MOMP-immunized BALB/c mice and selected with intact organisms. We used these short-term T-cell lines to identify determinants of MOMP that could be recognized by T cells following processing of the intact organism. T-cell line proliferation in response to overlapping MOMP peptides showed that only a peptide encompassing the third variable segment (VS3) elicited a strong proliferative response. We further mapped determinants within the VS3 peptide and found that a sequence-conserved portion of the VS3 peptide elicited T-cell proliferation of T-cell lines from BALB/c mice. Thus, unlike the response to several MOMP peptides with unselected T cells, development of short-term T-cell lines with intact organisms restricted the repertoire of antigens capable of being recognized by MOMP-specific T cells.

Amino Acid Sequence↗
PubMed1992

Construction of physical and genetic maps of Chlamydia trachomatis serovar L2 by pulsed-field gel electrophoresis.

We constructed the physical map of Chlamydia trachomatis serovar L2 by using three restriction endonucleases, NotI (GC[GGCCGC), SgrAI (C(A/G)[CCGG(T/G)G), and Sse8387I (CCTGCA[GG), and we analyzed the fragments by pulsed-field gel electrophoresis. A total of 25 restriction endonuclease sites and 13 genes and/or operons were located on the map. The genome size was determined to be 1,045 kb. Neither highly transcribed chlamydia genes nor developmental cycle-specific genes were clustered on the genome.

Base Sequence↗
PubMed1992

Challenge of Chlamydia research.

Chlamydia is an obligate intracellular bacterial pathogen that severely challenges the patience and creativity of all its investigators--even to the point that some investigators have forsaken this field for more productive and fertile areas of research. The two principal difficulties that touch every aspect of chlamydial research are (a) that chlamydiae only grow within eukaryotic host cells and (b) there are limited genetic approaches available. Despite these technical difficulties, the fundamental underlying problem has been the expectation that chlamydiae are similar to other bacteria (or, historically, viruses) and amenable to study from this perspective. However, this has often turned out not to be the case. Chlamydiae have shown themselves to be unique at many levels and thus represent a formidable, yet enticing, research challenge.

Animals↗
PubMed1991

A single peptide from the major outer membrane protein of Chlamydia trachomatis elicits T cell help for the production of antibodies to protective determinants.

The protective immune response to infection with Chlamydia trachomatis is associated with antibody reactivity to serovar-specific determinants on the major outer membrane protein (MOMP). Because this immunity is T cell dependent, it is essential to define those Th cell determinants that promote natural boosting of the protective antibody response. The gene for MOMP of serovar B was separated into nine overlapping fragments that represent the five C and four V regions. These fragments were expressed as fusion peptides with GST and used to identify the regions of the MOMP that contain T cell determinants recognized in BALB/c mice. We identified peptides that elicit a T cell response to Chlamydia by immunizing mice with the fusion peptides and testing the proliferative response of T cells in vitro to intact organism. For analysis of determinants seen after infection, animals were inoculated with live organism and the T cell proliferative response to each fusion peptide was measured in vitro. In contrast to proliferative analysis in which several regions of the MOMP elicited T cell responses, functional analysis demonstrated that a single fusion peptide, containing V segment three, elicited T cell help in vivo for the production of high titered antisera, specific for protective determinants on the MOMP.

Animals↗