Search PubMed⌕ Search

Biomedical subjects

R Martin

Publications and source records attributed to R Martin.

At least 37 records · Page 2Linked to original sources
PubMed2000

Contribution of individual amino acids within MHC molecule or antigenic peptide to TCR ligand potency.

The TCR recognition of peptides bound to MHC class II molecules is highly flexible in some T cells. Although progress has been made in understanding the interactions within the trimolecular complex, to what extent the individual components and their amino acid composition contribute to ligand recognition by individual T cells is not completely understood. We investigated how single amino acid residues influence Ag recognition of T cells by combining several experimental approaches. We defined TCR motifs for CD4+ T cells using peptide synthetic combinatorial libraries in the positional scanning format (PS-SCL) and single amino acid-modified peptide analogues. The similarity of the TCR motifs defined by both methods and the identification of stimulatory antigenic peptides by the PS-SCL approach argue for a contribution of each amino acid residue to the overall potency of the antigenic peptide ligand. In some instances, however, motifs are formed by adjacent amino acids, and their combined influence is superimposed on the overall contribution of each amino acid within the peptide epitope. In contrast to the flexibility of the TCR to interact with different peptides, recognition was very sensitive toward modifications of the MHC-restriction element. Exchanges of just one amino acid of the MHC molecule drastically reduced the number of peptides recognized. The results indicate that a specific MHC molecule not only selects certain peptides, but also is crucial for setting an affinity threshold for TCR recognition, which determines the flexibility in peptide recognition for a given TCR.

Amino Acids↗
PubMed2000

Decrypting the spectrum of antigen-specific T-cell responses: the avidity repertoire of MBP-specific T-cells.

Myelin basic protein (MBP) is a well-characterized autoantigen potentially involved in the pathogenesis of the most common human demyelinating disease of the central nervous system (CNS), multiple sclerosis (MS). It is known that MBP-specific T-cell responses differ widely among different individuals and also within a single donor in terms of fine specificity and functional characteristics including the avidity in antigen recognition. In this report, we demonstrate that the in vitro selection of MBP-reactive T-cell repertoire is strictly dependent upon the antigen dose used in the primary cultures. MBP-specific T-cell lines (TCLs) were generated from MS patients and healthy donors using different antigen concentration in cultures (0.1 to 50 microg/ml). In both MS patients and controls, the number of obtained T-cell lines was affected by the antigen concentration. In addition, low and high antigen concentrations selected in vitro different T-cell populations in terms of peptide specificity patterns and different functional avidities in antigen recognition. Low concentrations of MBP in the primary cultures yielded a small number of TCLs recognizing the specific antigen with higher avidity whereas high antigen concentrations allowed the in vitro expansion of a higher numbers of T-cells recognizing MBP with lower avidity. The use of different antigen concentrations in the primary cultures can be applied as a simple experimental system to investigate the overall avidity repertoire of antigen-specific T-cell response in humans.

Antibody Affinity↗
PubMed2000

Dipeptidyl peptidase IV in inflammatory CNS disease.

Current pathogenic concepts of inflammatory demyelinating disorders such as multiple sclerosis (MS) are based on the hypothesis that a T cell-mediated autoimmune response is involved in the disease process. One of the primary goals in the in the development of immunotherapies for autoimmune diseases has been to achieve inactivation of disease-inducing lymphocytes either by direct inhibition or suppression through regulatory cells and/or cytokines. The CD26 antigen is identical with the cell surface ectopeptidase dipeptidyl peptidase IV (DP IV, EC 3.4.14.5) which is involved in regulating T cell activation and growth. Activated T cells, including those specific for myelin antigens, express high levels of CD26/DP IV. In vitro, reversible DP IV inhibitors suppress T cell proliferation and pro-inflammatory cytokine production in response to myelin antigens. Further studies will evaluate the role of DP IV inhibition in T cell-mediated inflammatory disease of the central nervous system.

Animals↗
PubMed2000

Dipeptidyl peptidase IV (CD26): role in T cell activation and autoimmune disease.

The ectoenzyme dipeptidyl peptidase IV (DP IV; EC 3.4.14.5; CD26) has been shown to play a crucial role in T cell activation. In the present study, we show by flow cytometry and by enzymatic DP IV assay that myelin basic protein (MBP)-specific, CD4+ T cell clones (TCC) derived from patients with multiple sclerosis (MS) express high levels of DP IV/CD26. The enzymatic activity of resting TCC was found to be three to fourfold higher than on resting peripheral blood T cells and close to that of T cells 48 hours after PHA stimulation. The DP IV inhibitors Lys[Z(NO2)]-thiazolidide and Lys[Z(NO2)]-pyrrolidide suppress in a dose-dependent manner DNA synthesis and IFN-gamma, IL-4, and TNF-alpha production of the antigen-stimulated TCC. These data suggest that CD26 plays a role in regulating activation of autoreactive TCC. Further in vivo investigations will clarify, whether the inhibition of the enzymatic activity of DP IV could be a useful tool for therapeutic interventions in MS and/or other autoimmune diseases.

Autoimmune Diseases↗
PubMed2000

Onset of spinal block is more rapid with isobaric than hyperbaric bupivacaine.

PURPOSE: To compare isobaric with hyperbaric 9.75 mg bupivacaine injected intrathecally, and to evaluate the effects of subsequent injection of lidocaine 2% into the epidural space. METHODS: Patients in group 1 (n = 30) received isobaric 9.75 mg bupivacaine and in group 2 (n = 30) hyperbaric 9.75 mg bupivacaine injected into the subarachnoid space in a combined spinal-epidural technique. They were undergoing urological, gynecological, orthopedic, gastro-intestinal or vascular surgery. Using a double blind technique, the followings parameters were measured: cutaneous analgesia to pinprick, motor blockade, time for two segment regression, time for complete regression of the motor block, quality of anesthesia. In 12 patients the effect of epidural injections of 3 ml lidocaine 2% was observed. RESULTS: Motor and sensory block developed more rapidly (five minutes) in the isobaric group (P<0.05). Maximum upper level (T7+/-2), two-segment regression (52 min in both groups), motor recovery (160 vs. 157 min), and quality of anesthesia did not differ between the two groups. Thirty nine epidural injections of 3 ml lidocaine 2% were given in 12 patients 10 min after spinal injection, 28 were in the hyperbaric group (P<0.05). Twenty six of the epidural injections produced an increase in sensory block of 0 or 1 dermatome, and 13, of 2 or more. CONCLUSION: The block developed more rapidly in the isobaric group, but both isobaric and hyperbaric 9.75 mg bupivacaine produced adequate upper levels of analgesia for surgery. The effect of epidural injections of 3 ml lidocaine 2% was usually minimal.

Adult↗
PubMed2000

Incidence of mosaic cell lines in vivo and malsegregation of chromosome 21 in lymphocytes in vitro of trisomy 21 patients: detection by fluorescence in situ hybridization on binucleated lymphocytes.

In order to detect aneuploidy in interphase human lymphocytes, both in vivo and in vitro, fluorescence in situ hybridization (FISH) was carried out on binucleated cells cytokinesis-blocked by cytochalasin B at the first mitosis after phytohemagglutinin stimulation. A pericentric chromosome-21-specific DNA probe prepared from yeast artificial chromosome clone 881D2 by the polymerase chain reaction was employed. One thousand binucleated cells per individual were scored from cultures from twelve trisomy 21 patients aged 0.01-8.9 years (mean 4.3 years) and 20 normal children of similar age. Of trisomy 21 patients, increased frequencies of disomic cells in vivo (1.690+/-1.070%) and cells containing six signals with nondisjunction (0.822+/-0.554%) were found, compared with those of monosomic 21 cells in vivo (0.265+/-0.130%) and cells containing four signals with nondisjunction in normal children (0.369+/-0.250%; P=0.000 and P=0.000, respectively). These results show that malsegregation of chromosome 21 occurs more often in trisomic 21 cells than in disomic cells from normal children. The frequency of nondisjunction was significantly higher than the loss of chromosome 21 in both cultured trisomic (0.822+/-0.554% vs 0.043+/-0.049%, P=0.000) and disomic (0.369+/-0.250% vs 0.010+/-0.30%, P=0.000) cells. Comparisons of in vivo and in vitro data on aneuploidy indicate that a cell selection mechanism may exist in vivo. All these results show that FISH, with a chromosome-specific probe, on binucleated lymphocytes is a powerful tool for simultaneously detecting mosaic cell lines in vivo and malsegregation (loss and nondisjunction) of a corresponding chromosome in vitro in the same cell population.

Case-Control Studies↗
PubMed2000

Multiple sclerosis associated amino acids of polymorphic regions relevant for the HLA antigen binding are confined to HLA-DR2.

Among the candidate genes for multiple sclerosis (MS), the strongest influence is conferred by human leucocyte antigen (HLA) class II genes, in particular the DR2, DQ6, Dw2 haplotype (DRB1*1501, DQA1*0102, DQB1*0602). Similar to other autoimmune diseases, it is not clear yet how the presence of a specific HLA-DR or -DQ molecule translates into an increased disease susceptibility. Previous observations by us and others imply a HLA-DR2 dependent propensity of antigen-specific T-cell lines to produce increased amounts of TNF-alpha/beta as one mechanism how DR2 could contribute to susceptibility. In this article, we investigated the distribution of polymorphic stretches of the DRB1, DQA1, and DQB1 chains known to be relevant for antigen binding, in 66 unrelated patients with relapsing remitting MS and 210 unrelated controls. We found a significant association with disease for the appearance of proline at position 11, arginine at position 13, and alanine at position 71 of HLA-DRbeta1. Surprisingly, we identified only residues preferentially expressed in the MS group that were related to HLA-DR2. Thus, the contribution of HLA class II to the pathogenesis of MS is not mediated by allele-overlapping antigen binding sites, but is confined to the disease associated HLA allele.

Alleles↗
PubMed2000

The influence of hypoxia on the myocardium of experimentally diabetic rats with and without protection by Ginkgo biloba extract. I. Ultrastructural and biochemical investigations on cardiomyocytes.

The influence of acute respiratoric hypoxia in streptozotocin-diabetic rats and protective effects of Ginkgo biloba extract (EGb 761)-pretreatment were investigated by the means of ultrastructural morphometry, biochemical parameters of oxidative stress and iNOS transcription and expression. Ultrastructural parameters revealed that acute hypoxia deteriorated the morphologic condition of the diabetic cardiomyocytes: volume fractions of sarcoplasm, t-tubules, mitochondria, cytoplasmic vacuoles, and degenerative intramitochondrial areas increased after hypoxia, those of myofibrils and mitochondrial cristae decreased. Since these alterations are more striking than after hypoxia of non-diabetic animals as demonstrated in preceding studies, we regard them as indicative for reduced hypoxia tolerance of the diabetic myocardium. EGb-treatment of the diabetic animals could improve the above mentioned parameters thus indicating a gradual improvement of the hypoxia tolerance. The biochemical parameters of oxidative stress (malondialdehyde, superoxide dismutase) were decreased after hypoxia in the diabetic myocardium but increased after EGb-pretreatment. The ultrastructural damage by hypoxia and its prevention by EGb should be regarded rather as a consequence of ATP--and energy deficiency and breakdown of membrane functions and--structure resp. as membrane stabilizing and enzyme-regulating effects of EGb than as radical-related events. The hypoxia-induced deprivation of creatine kinase activity of the diabetic myocardium was not prevented by EGb-treatment. Immunohistochemical demonstration of iNOS expression was strongest in the unprotected diabetic myocardium, absent after additional hypoxia and in the controls, and very weak in the protected hypoxic specimens. Transcription of iNOS as demonstrated by RT-PCR was present in few diabetic, some of the hypoxic diabetic, in most of the EGb-treated hypoxic diabetic, and in all control animals. EGb-treatment seems to improve the hypoxia tolerance of diabetic myocardium concerning ultratructural parameters. The partly conflicting immunohistochemical and biochemical results require further investigations.

Animals↗
PubMed2000

Long-term effect of vital labelling on mixed Schwann cell cultures.

Schwann cell transplantation following neuronal injury could encourage regeneration of spinal cord as well as improving peripheral nerve gap repair. In order to gain a better understanding of the role of transplanted Schwann cells in vivo, it is essential to be able to follow their behaviour after transplantation. Our aim was to evaluate the suitability of two vital fluorescent labels on the proliferation rate and phenotypic stability of Schwann cells, in either pure culture or mixed co-culture. Primary cultures of Schwann cells were obtained from Dark Agouti and Lewis neonatal rats and labelled with H33342 and PKH26, respectively. In mixed cultures, a 50: 50 mixture of Dark Agouti and Lewis Schwann cells was present. Labelled cultured cells were examined at 1, 2 and 4 weeks for viability and phenotypic marker expression of S100, GFAP, p75, MHC I, MHC II and compared with corresponding unlabelled cells. The results showed that although there was no deleterious interaction in the mixed cultures, the viability was reduced by the labelling after 2 weeks. Labelled cells could be distinguished up to 4 weeks, but there was leakage of H33342 label after 2 weeks. Labelled Schwann cells showed reduced expression of phenotypic markers, especially p75 when labelled with H33342. In conclusion, H33342 and PKH26 can be used as fluorescent markers of Schwann cells for short-term studies, for a maximum of 2 weeks, but different markers may be needed for longer experiments.

Animals↗
PubMed2000

Dissociative disorders in the Sultanate of Oman.

OBJECTIVE: To study the clinical manifestations and psychosocial aspects of dissociative (conversion) disorders (DD) in the Sultanate of Oman. METHOD: A retrospective analysis was made of data derived from case records of patients admitted as in-patients to the Sultan Qaboos University Hospital, Oman, over a period of 8 years. RESULTS: A higher prevalence of DD was noted in Oman compared to western countries. The female preponderance was less marked in Oman. The most common presentations were dissociative convulsions, dissociative motor and dissociative trance disorders. Interpersonal difficulties with family and academic problems were the important identified precipitants. CONCLUSION: The study highlights the characteristic clinical and psychosocial features of the dissociative phenomena in Oman.

Adult↗
PubMed2000

Encephalitogenic potential of the myelin basic protein peptide (amino acids 83-99) in multiple sclerosis: results of a phase II clinical trial with an altered peptide ligand.

Myelin-specific T lymphocytes are considered essential in the pathogenesis of multiple sclerosis. The myelin basic protein peptide (a.a. 83-99) represents one candidate antigen; therefore, it was chosen to design an altered peptide ligand, CGP77116, for specific immunotherapy of multiple sclerosis. A magnetic resonance imaging-controlled phase II clinical trial with this altered peptide ligand documented that it was poorly tolerated at the dose tested, and the trial had therefore to be halted. Improvement or worsening of clinical or magnetic resonance imaging parameters could not be demonstrated in this small group of individuals because of the short treatment duration. Three patients developed exacerbations of multiple sclerosis, and in two this could be linked to altered peptide ligand treatment by immunological studies demonstrating the encephalitogenic potential of the myelin basic protein peptide (a.a. 83-99) in a subgroup of patients. These data raise important considerations for the use of specific immunotherapies in general.

Adolescent↗
PubMed2000

The relationship between anxiety levels and outcome of cocaine abuse treatment.

Although a number of studies have examined the comorbidity of anxiety disorders and substance use disorders, much less is known about the impact of anxiety symptoms on substance use and on substance abuse treatment outcome. In the current study, we examined how self-reported anxiety levels, as measured by the Spielberger State-Trait Anxiety Inventory, were related to cocaine use variables and patterns following substance abuse treatment. There were 108 patients in substance abuse treatment who met DSM-III-R diagnostic criteria for cocaine abuse or dependence who completed an assessment battery at pretreatment, posttreatment, and 3-month follow-up. State anxiety scores significantly declined from pre- to posttreatment and remained stable into the 3-month follow-up period regardless of relapse status. Trait anxiety was correlated positively with negative consequences due to cocaine use and negatively correlated with days in treatment. State and trait anxiety both were correlated positively with the Alcohol Composite Index of the Addiction Severity Index (ASI). These findings suggest that elevated anxiety scores at pretreatment subside with time, do not require clinical management of associated anxiety symptoms, and may be a temporary by-product of experiencing negative consequences due to recent cocaine use.

Adolescent↗
PubMed2000

Minimal peptide length requirements for CD4(+) T cell clones--implications for molecular mimicry and T cell survival.

CD4(+) T lymphocytes usually recognize peptides of 12-16 amino acids in the context of HLA class II molecules. We have recently used synthetic peptide combinatorial libraries to dissect in detail antigen recognition by autoreactive CD4(+) T cell clones (TCC). The results of these studies demonstrated that antigen recognition by T cells is highly degenerate and that many cross-reactive ligands can be defined, some of which much more potent than the selecting autoantigen. Based on these observations, we examined the response of a myelin basic protein-specific HLA class II-restricted CD4(+) TCC to truncation variants of optimal ligands. Surprisingly, pentapeptides, tetrapeptides and even tripeptides derived from different segments of the optimal ligands were recognized by the TCC, and some were even more potent than the selecting autoantigen. In addition, these peptides enhanced the survival of the TCC at low concentration. The relevance of this finding was supported by the generation of pentapeptide-specific CD4(+) TCC from peripheral blood lymphocytes. These observations not only change existing views on the length requirements for activation of CD4(+) HLA class II-restricted T cells, but also extend our knowledge about the flexibility of TCR recognition and the potential for cross-reactivity in the immune system.

Antigen Presentation↗
PubMed2000

Compositional bias and mimicry toward the nonself proteome in immunodominant T cell epitopes of self and nonself antigens.

We investigated whether and how molecular mimicry affects the shaping of the helper T cell repertoire. We implemented an algorithm that measures the probability of mimicry between epitopes of known immunogenicity and self or nonself proteomes. This algorithm yields 'similarity profiles', which represent the probability of matching between all contiguous overlapping peptides of the antigen under examination and those in the proteome(s) considered. Similarity profiles between helper T cell epitopes (of self or microbial antigens and allergens) and human or microbial SWISSPROT collections were produced. For each antigen, both collections yielded largely overlapping profiles, demonstrating that self-nonself discrimination does not rely on qualitative features that distinguish human from microbial peptides. However, epitopes whose probability of mimicry with self or nonself prevails are, respectively, tolerated or immunodominant and coexist within the same (auto-)antigen regardless of its self/nonself nature. Epitopes (on self and nonself antigens) can cross-stimulate T cells at increasing potency as their similarity with nonself augments. Mimicry, rather than complicating self-nonself discrimination, assists in the shaping of the immune repertoire and helps define the defensive or autoreactive potential of a T cell. Being a predictor of epitope immunogenicity, it bears relevance to vaccine design.

Algorithms↗
PubMed2000

Treating sexually abused children with posttraumatic stress symptoms: a randomized clinical trial.

OBJECTIVE: To evaluate the efficacy of child and caregiver participation in the cognitive-behavioral treatment of sexually abused children with posttraumatic stress symptoms. METHOD: Thirty-six sexually abused children (aged 5-17 years) were randomly assigned to a child-alone cognitive-behavioral treatment condition, a family cognitive-behavioral treatment condition, or a waiting-list control condition. RESULTS: Compared with controls, children who received treatment exhibited significant improvements in posttraumatic stress disorder symptoms and self-reports of fear and anxiety. Significant improvements also occurred in relation to parent-completed measures and clinician ratings of global functioning. In general, parental involvement did not improve the efficacy of cognitive-behavioral therapy. Maintenance of improvement was evident at a 12-week follow-up assessment. CONCLUSIONS: Cognitive-behavioral treatment was useful, but further research is required on caregiver involvement.

Adolescent↗
PubMed2000

A three-factor model of trait anger: dimensions of affect, behavior, and cognition.

The structure of trait anger was tested in a study of 24 self-report scales. Exploratory factor analyses in an undergraduate sample (N = 457) yielded a two-factor model (comprising cynicism and aggression) and a three-factor model (representing angry emotions, aggressive behaviors, and cynicism). Subsequent evaluations, including confirmatory factor analyses, indicated that the three-factor model provided the best characterization of the trait anger domain. The three-factor solution was consistent with an "ABC" conceptualization of trait anger, consisting of the dimensions of affect, behavior, and cognition. The three factors showed strikingly different associations with the Big Five personality traits. Angry Affect was most strongly related to Neuroticism, whereas Behavioral Aggression was associated with low Agreeableness. Cynical Cognition represented a blend of neurotic and disagreeable characteristics. Modest mean-level differences were observed between the genders for each factor.

Adolescent↗