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D Mathis

Publications and source records attributed to D Mathis.

At least 91 records · Page 5Linked to original sources
PubMed1995

Mice lacking terminal deoxynucleotidyl transferase: adult mice with a fetal antigen receptor repertoire.

TdT knock-out mice have established the role of this enzyme in vivo: TdT mediates the transition from the relatively limited fetal to the highly diverse adult antigen receptor repertoire by adding template independent "N" nucleotides and disrupting homology-directed recombination. Lacking this source of diversity, TdT degree mice harbor essentially fetal antigen receptor repertoires. In alpha beta TCRs, the TdT null mutation affects the length and diversity of the CDR3 loops thought to be important in "directing" MHC/peptide recognition. N- CDR3 loops appear to wield less influence than do their N+ counterparts--positive selection is more efficient in the TdT degree animals and the peripheral repertiore is more polyreactive and less peptide-oriented than is the N+ repertoire. However, this loss of specificity does not markedly diminish the response to specific peptides. Overall, mice harboring essentially fetal repertoires are robust and effectively respond to a wide variety of challenges to the immune system.

Animals↗
PubMed1995

Comparative studies on differential inhibition of the renin - angiotensin system in the anesthetized guinea pig.

The present study compares the hemodynamic effects and mechanisms of action of angiotensin II (AngII) antagonists, angiotensin converting enzyme (ACE) inhibitors, and renin inhibitors in the guinea pig, an animal with high similarity to primates in terms of in vitro and in vivo responses to several human renin inhibitors. Animals were anesthetized with urethane and ketamine. The carotid artery was catheterized for monitoring blood pressure and heart rate. After 30 min stabilization, drug (or vehicle) effects were monitored for 1 h following each increasing dose (i.v. bolus injection). Drugs tested include losartan, an AngII receptor antagonist; two renin inhibitors, BILA 2157 BS and PD-134672; and captopril, an ACE inhibitor. All drugs dose dependently decreased blood pressure. Diastolic blood pressure was reduced more than systolic blood pressure, suggestive of vasodilation. The maximum decrease (32 +/- 6%, p < 0.05 vs. vehicle) in mean arterial blood pressure (MABP) by losartan was achieved with a dose of 1 mg/kg. A similar decrease in MABP was observed with renin inhibitors at a dose of 3 mg/kg, without affecting heart rate. A further increase in the dose of renin inhibitors (6 mg/kg) decreased not only blood pressure but also heart rate. Captopril decreased MABP with a maximum of 48 +/- 3% (p < 0.05 vs. vehicle, losartan, and PD-134672). In the presence of HOE-140, a bradykinin antagonist, the MABP decrease by captopril was only 35 +/- 4%, (p < 0.05 vs. captopril alone). Bilateral nephrectomy reduced the peak MABP effect of PD-134672 by 67%, while the effects of captopril on MABP were affected to a lesser degree (57%). Therefore, captopril remains more effective in reducing MABP (p < 0.05 vs. that of PD-134672). These results suggest that renin inhibitors and AngII antagonists act more specifically on the renin - angiotensin system cascade, while captopril acts partially by a bradykinin-dependent mechanism. The small animal model described provides a novel tool for the comparative pharmacologic assessment of different renin - angiotensin system inhibitors.

Alanine↗
PubMed1995

Office laboratory diagnosis of vaginitis. Clinician-performed tests compared with a rapid nucleic acid hybridization test.

BACKGROUND: The traditional diagnosis of vaginitis incorporates patient symptoms, clinical findings observed during vaginal examination, and laboratory analysis of vaginal fluid. The purpose of this study was to evaluate routine clinician-performed office laboratory diagnostic techniques for women with abnormal vaginal symptoms, and to compare these results with those obtained by a DNA hybridization test for Trichomonas vaginalis, Gardnerella vaginalis, and Candida species. METHODS: The study included 501 symptomatic women who were between the ages of 14 and 67 years. Three vaginal specimens were obtained for saline wet mount, potassium hydroxide (KOH) prep, amine "sniff", pH, and nucleic acid hybridization (T vaginalis, G vaginalis, and Candida sp) tests. Clinicians and medical technicians independently evaluated the wet mount, KOH prep, amine, and pH tests. A medical technician processed the DNA tests according to manufacturer's protocol. RESULTS: Of 499 subjects for whom complete data were available, vulvovaginal candidiasis was diagnosed in 20.0%, vaginal trichomoniasis in 7.4%, and bacterial vaginosis in 52.1%. Fourteen percent of subjects had multiple vaginal infections. The sensitivity and specificity of clinician microscopically diagnosed vulvovaginal candidiasis, vaginal trichomoniasis, and bacterial vaginosis were 39.6% and 90.4%, 75.0% and 96.6%, and 76.5% and 70.8%, respectively. The sensitivity and specificity of the DNA probe diagnosis of the same types of vaginitis were 75.0% and 95.7%, 86.5% and 98.5%, and 95.4% and 60.7%, respectively. When only women with multiple vaginal infections were considered, the percentages of correct clinician diagnoses for vulvovaginal candidiasis, vaginal trichomoniasis, and bacterial vaginosis were 49.3%, 83.6%, and 59.7%, respectively. For the DNA probe test, the percentages of correct diagnoses were 72.9%, 92.9%, and 90.0%, respectively. CONCLUSIONS: Primary care clinicians demonstrated a high specificity but low sensitivity when identifying vaginal trichomoniasis and vulvovaginal candidiasis by microscopic techniques. Correct microscopic diagnosis of bacterial vaginosis was even more difficult for clinicians, as was the diagnosis of multiple vaginal infections. Clinicians were not as accurate as the DNA probe test in diagnosing vaginal infections. Clinicians need more education in the laboratory diagnosis of vaginitis. Clinicians should carefully scrutinize each microscopic slide, systematically examine the slide for each type of vaginitis, and consider specimen pH and the presence of leukocytes, Lactobacillus organisms, or amine odor as additional clues to infection.

Adolescent↗
PubMed1995

Treatment of bacterial vaginosis: a comparison of oral metronidazole, metronidazole vaginal gel, and clindamycin vaginal cream.

BACKGROUND: Treatment options for bacterial vaginosis are numerous. The purpose of this study was to compare the efficacy of oral metronidazole, metronidazole vaginal gel, and clindamycin vaginal cream for the treatment of bacterial vaginosis using traditional clinical and laboratory methods, as well as a new DNA probe test. We also determined the percentage of patients receiving each treatment who developed posttreatment vaginal candidiasis, a potential complication of treating bacterial vaginosis. METHODS: One hundred one women in whom bacterial vaginosis was diagnosed by standard criteria were randomly assigned to receive: oral metronidazole 500 mg twice daily for 1 week, 0.75% metronidazole vaginal gel 5 g twice daily for 5 days, or 2% clindamycin vaginal cream 5 g once daily for 7 days. Women with coexisting vulvovaginal candidiasis or vaginal trichomoniasis were excluded. Tests of cure by vaginal saline wet prep and potassium hydroxide microscopic examinations, Gram's stain, pH and DNA probe tests for Gardnerella vaginalis and Candida species were scheduled 7 to 14 days following treatment. RESULTS: There were no statistically significant differences in cure rates for oral metronidazole (84.2%), metronidazole vaginal gel (75.0%), or clindamycin vaginal cream (86.2%) (chi 2 = 1.204, df = 2, P = .548) using traditional clinical and laboratory criteria. Cure rates were lower based on DNA testing, indicating that Gardnerella vaginalis may remain after a clinical cure. This would explain cases of recurrent disease. Posttreatment vulvovaginal candidiasis was experienced by 12.5% of subjects treated with oral metronidazole, 14.8% of subjects treated with clindamycin vaginal cream, and 30.4% of subjects treated with metronidazole vaginal gel (chi 2 = 2.607, df = 2, P = .272). CONCLUSIONS: Oral metronidazole, metronidazole vaginal gel, and clindamycin vaginal cream achieved nearly equivalent cure rates for the treatment of bacterial vaginosis. Patients treated with these agents experienced similar rates of posttreatment vulvovaginal candidiasis, but those using the intravaginal products reported being more satisfied with the treatment.

Administration, Intravaginal↗
PubMed1994

Evidence for a single-niche model of positive selection.

Thymocyte maturation depends on interactions with thymic stromal elements expressing major histocompatibility complex (MHC) molecules. Mutant mouse strains lacking MHC class I (beta 2-microglobulin-null) or class II (A beta-null) expression fail to generate normal CD8 or CD4 T-cell populations and provide model systems for reconstitution experiments. We have constructed in vitro chimeras between normal and MHC-deficient thymi to evaluate the efficiency of positive selection. Unexpectedly, the generation of mature single-positive thymocytes was proportional to the fraction of wild-type (i.e., MHC-expressing) stroma over a wide range of chimerism. Similar results were obtained for the development of T-cell receptor-transgenic thymocytes in graded chimeras expressing selecting and nonselecting MHC alleles. These findings are best explained by hypothesizing that positive selection involves a rate-limiting step at which each thymocyte can interact with only one stromal cell niche.

Animals↗
PubMed1994

Role of coreceptors in positive selection and lineage commitment.

Recent experiments have re-awakened interest in a stochastic/selective model of positive selection of T lymphocytes. A revised version of the model has been proposed whereby commitment of double-positive thymocytes to either the CD4 or CD8 lineage requires two engagements with MHC molecules: the first, initiating the differentiation program, signals down-regulation of one or the other coreceptor, regardless of the T cell receptor's specificity for MHC class I or II molecules; the second, leading to terminal differentiation, screens the choice of coreceptor by permitting only those cells with matched receptors and coreceptors to proceed. Here we explore the role of coreceptors in the two stages of positive selection by manipulating CD8 expression in MHC class II-deficient mice, crossing them with either CD8-negative animals or animals carrying combinations of CD8 alpha and CD8 beta transgenes. We find that coreceptors are required at both stages of positive selection and that artificial expression of the down-modulated CD8 molecule can quite efficiently rescue cells that have made a 'mistake' in their choice of coreceptor. We also establish that commitment to the CD4 pathway and to the helper phenotype can be linked.

Animals↗
PubMed1994

MHC control of the naive TCR alpha-chain repertoire.

The naive T cell repertoire is shaped by interactions between developing thymocytes and thymic stroma. Both positive and negative selection involve the clonotypic TCR and MHC molecules carrying self-peptides. Except for the MHC-dependent effects of superantigens on TCR V beta usage; there has been little evidence that the TCR structure of naive T cell varies with the selecting MHC products. To examine this point from another angle, in particular the TCR alpha-chain, we have analyzed alpha-chain usage in a system in which the vast majority of T cells express a transgene-encoded TCR beta-chain, compatible with efficient T cell development on a wide range of MHC haplotypes. Endogenous TCR alpha-chains are thus selected without interference from the forces known to act on TCR-beta, permitting us to observe MHC influences on alpha-chain selection. We have used V alpha-specific Abs to quantitate alpha-chain usage in MHC congenic, MHC recombinant, and MHC transgenic mice and provide evidence that the naive TCR alpha-chain repertoire is under MHC control. The data demonstrate a direct impact of known MHC class II products but also reflect more complex influences, apparently involving other gene products within the MHC. Sequence analysis of differentially selected TCR suggests that selection acts on the entire alpha-chain, including V alpha, J alpha, and the junctional region.

Amino Acid Sequence↗
PubMed1994

Dominant negative analogs of NF-YA.

NF-Y is a highly conserved heteromeric CCAAT-binding transcription factor involved in the function of several promoters. The NF-YA subunit contains a domain of high homology to yeast HAP2, which we show to be necessary and sufficient to mediate interactions with the NF-YB subunit and with DNA. Using protein affinity columns derivatized with amino acid substitution mutants, we further dissect this region into two functionally separable subdomains. The subunit association function resides in a 21-amino acid stretch, which is almost perfectly conserved among different species, while interaction with DNA resides in another short segment. We also show that DNA-binding mutants act as dominant repressors of NF-Y-DNA complex formation and of NF-Y-dependent transcription.

Amino Acid Sequence↗
PubMed1994

Diversity of endogenous epitopes bound to MHC class II molecules limited by invariant chain.

The invariant chain (Ii) binds nascent major histocompatibility complex (MHC) class II molecules, blocking peptide binding until the complex dissociates in the endosomes. This may serve to differentiate the MHC class I and II antigen presentation pathways and enable class II molecules to efficiently bind peptides in the endosomes. This hypothesis was addressed by probing spleen cells from a combination of knock-out and transgenic mice with a large panel of T cell hybridomas. The Ii molecule blocked the presentation of a range of endogenously synthesized epitopes, but some epitopes actually required Ii. Thus, the influence of Ii on presentation does not follow simple rules. In addition, mice expressing Ii were not tolerant to epitopes unmasked in its absence, a finding with possible implications for autoimmunity.

Amino Acid Sequence↗
PubMed1994

A mechanism for divalent cation regulation of beta 3-integrins.

Integrins alpha IIb beta 3 and alpha V beta 3 mediate numerous cell-matrix and cell-cell contacts. Both integrins contain multiple divalent cation-binding motifs that regulate ligand binding. Here, we elucidate a major difference in the regulation of alpha IIb beta 3 and alpha V beta 3 by divalent ions. Fibrinogen binding to alpha IIb beta 3 in Ca(2+)-containing buffer is rapid, with an apparent association rate constant (k1app) of 8.2 x 10(5) M-1 s-1, but Ca2+ does not support association between fibrinogen and alpha V beta 3. Interestingly, Mn2+ supports fibrinogen binding to both integrins, albeit with a relatively slow association rate (k1app = 10(4) M-1 s-1). This influence of divalent ions on ligand association rates accounts for the opposite divalent ion requirements for platelet aggregation and tumor cell adhesion to fibrinogen. Furthermore, the regulation of fibrinogen binding to alpha V beta 3 is complex when both Ca2+ and Mn2+ are present. Physiological concentrations of Ca2+ completely ablated adhesion. Kinetic analysis demonstrated that Ca2+ is a mixed-type inhibitor of Mn(2+)-supported fibrinogen binding to alpha V beta 3. Consequently, the data presented here suggest a mechanism in which two separate cation-binding sites regulate ligand binding to beta 3-integrins.

Calcium↗
PubMed1994

In favor of the selective model of positive selection.

The mechanisms of thymocyte commitment towards the CD4+ and CD8+ lineage remain unresolved. Two models--one based on instruction, the other on selection--have previously been proposed. The instructional model has been popularly received based on results of earlier studies. However, our data from MHC class II, class I, and double-deficient mice suggest otherwise. There exists a significant population of CD4+ cells that is intermediate in maturity between CD4+ CD8+ and fully mature CD4+ CD8- thymocytes in class II-deficient animals; an analogous population of CD4-CD8+ cells exists in class I-negative mice. We suggest that a selective model in which two TCR-MHC molecule engagements are required: the first induces a random down-modulation of either CD4 or CD8 and some differentiation; the second, involving the participation of the appropriate coreceptor, permits end-stage differentiation.

Animals↗
PubMed1994

More efficient positive selection of thymocytes in mice lacking terminal deoxynucleotidyl transferase.

Mice with a drastic mutation in the terminal deoxynucleotidyl transferase (TdT) gene have recently been engineered. Igs and TCRs in these mice are essentially devoid of N-region diversity. Here we report that TdT0 mice contain elevated numbers of CD3hi single-positive (SP) thymocytes because more thymocytes make the transition from the immature double-positive to the mature SP stage. This suggests that the repertoire of TCRs encoded in the germline may be enriched for specificities capable of interacting with MHC molecules and that the loss of some of this affinity is the price paid for TdT-generated diversity.

Amino Acid Sequence↗
PubMed1994

Graft rejection across transgene-encoded MHC class II molecules.

To investigate the capacity of class II gene products of the major histocompatibility complex to serve as targets for allograft rejection, we have used lines of transgenic mice which express such genes on a common genetic background. These lines allow us to test the function of single class II molecules, or of single chains of the class II heterodimers, in graft rejection or tolerance induction. Our data show that some class II molecules (A alpha, A beta) can induce very efficient rejection, while others are relatively inert (E), and that tolerance induction requires matching for both chains of the target class II heterodimers.

Animals↗