Biomedical subjects

M R Clark

Publications and source records attributed to M R Clark.

At least 19 recordsLinked to original sources

PubMed2005

The pre-B cell receptor in B cell development: recent advances, persistent questions and conserved mechanisms.

B cell development is a process tightly regulated by the orchestrated signaling of cytokine receptors, the pre-B cell receptor (BCR) and the B cell receptor (BCR). It commences with common lymphoid progenitors (CLP) up-regulating the expression of B cell-related genes and committing to the B cell lineage. Cytokine signaling (IL-7, stem cell factor, FLT3-L) is essential at this stage of development as it suppresses cell death, sustains proliferation and facilitates heavy chain rearrangements. As a result of heavy chain recombination, the pre-BCR is expressed, which then becomes the primary determiner of survival, cell cycle entry and allelic exclusion. In this review, we discuss the mechanisms of B cell lineage commitment and describe the signaling pathways that are initiated by the pre-BCR. Finally, we compare pre-BCR and pre-TCR structure, signal transduction and function, drawing parallels between early pre-B and pre-T cell development.

Animals↗

PubMed2005

Activation of the coagulation system in cancerogenesis and metastasation.

The activation of the coagulation system in cancer patients is a well-known phenomenon responsible for recurrent clinical problems. A number of fascinating molecular mechanisms have been recognized showing that the tumor not only activates the coagulation system, but vice versa, activated coagulation proteins are able to induce molecular effects in tumor cells. The molecular basis is the expression of defined membrane receptors by tumor cells that are activated, for example, by thrombin. As the liberation of thrombin from prothrombin is one of the key events in coagulation, it's impact upon biological processes, such as cancerogenesis and metastasation, seems to be a regular pathophysiological consequence. These perceptions are not only interesting for the comprehension of cancerogenesis, metastasation, and clinical phenomena, but they also have a high impact upon modern strategies of tumor therapy. Especially, the development of clinically useful coagulation inhibitors, such as modern low molecular weight heparins or melagatran, created the possibility of therapies that combine cell biological approaches with apoptosis-inducing principals such as chemotherapy. Several clinical studies that demonstrate the implication of these strategies have already been published recently. In this article the cell biological basics for these approaches are reviewed.

Anticoagulants↗

PubMed2004

Depressive disorder as a long-term antecedent risk factor for incident back pain: a 13-year follow-up study from the Baltimore Epidemiological Catchment Area sample.

BACKGROUND: The co-occurrence of affective distress and back pain is well documented but the relationship between them is less certain. This study examines the relationship between lifetime occurrence of depressive disorder and incident back pain reported over a 13-year period. METHOD: The Baltimore Epidemiologic Catchment Area Study is a prospective study of a household-residing cohort, selected probabilistically from East Baltimore in 1981. Between 1982-3 (wave 2) and again between 1993-6 (wave 3), a follow-up study of the original cohort was conducted. Questions on depressive disorder and back pain were drawn from the Diagnostic Interview Schedule. Logistic regression analyses were used to evaluate whether depressive disorder acts as a risk factor for incident back pain. RESULTS: In cross-sectional analyses, lifetime occurrence of depressive disorder was a significant correlate of lifetime prevalence of back pain at wave 1 (OR = 1.6, P = 0.01). During the 13-year follow-up, across three data collection points, there was an increase in the risk for incident back pain when depressive disorder was present at baseline (OR = 1.9, 95% CI 1.03, 3.4). However, during the short-term follow-up period of 1 year, between baseline and wave 2, depressive disorder at baseline was unrelated to first-ever reports of back pain. Lifetime depressive disorder in both waves 1 (baseline) and 2 (1 year later) was associated with a more than three times greater risk for a first-ever report of back pain during the 12 to 13 year follow-up period, in comparison to those who did not have depressive disorder at waves 1 or 2 (OR = 3.4, 95% CI 1.4, 7.8). Back pain at wave 1 was not significantly associated with an increased risk for depression in the longitudinal analysis (OR = 0.8, 95% CI 0.5, 1.4). CONCLUSIONS: Depressive disorder appears to be a risk factor for incident back pain independent of other characteristics often associated with back pain. Back pain is not a short-term consequence of depressive disorder but emerges over periods longer than 1 year. Moreover, in this study the alternative pathway of back pain as a risk factor for depressive disorder could not be supported.

Back Pain↗

PubMed2002

Opioids versus antidepressants in postherpetic neuralgia: a randomized, placebo-controlled trial.

BACKGROUND: Tricyclic antidepressants (TCA) provide less than satisfactory pain relief for postherpetic neuralgia (PHN), and the role of opioids is controversial. OBJECTIVE: To compare the analgesic and cognitive effects of opioids with those of TCA and placebo in the treatment of PHN. METHODS: Seventy-six patients with PHN were randomized in a double-blind, placebo-controlled, crossover trial. Each subject was scheduled to undergo three treatment periods (opioid, TCA, and placebo), approximately 8 weeks' duration each. Doses were titrated to maximal relief or intolerable side effects. The primary outcome measures were pain intensity (0 to 10 scale), pain relief (0 to 100%), and cognitive function. Analyses included patients who provided any pain ratings after having received at least a single dose of a study medication. RESULTS: Fifty patients completed two periods, and 44 patients completed all three. Mean daily maintenance doses were morphine 91 mg or methadone 15 mg and nortriptyline 89 mg or desipramine 63 mg. Opioids and TCA reduced pain (1.9 and 1.4) more than placebo (0.2; p < 0.001), with no appreciable effect on any cognitive measure. The trend favoring opioids over TCA fell short of significance (p = 0.06), and reduction in pain with opioids did not correlate with that following TCA. Treatment with opioids and TCA resulted in greater pain relief (38 and 32%) compared with placebo (11%; p < 0.001). More patients completing all three treatments preferred opioids (54%) than TCA (30%; p = 0.02). CONCLUSIONS: Opioids effectively treat PHN without impairing cognition. Opioids and TCA act via independent mechanisms and with varied individual effect.

Adult↗

PubMed2002

The contrasting IgG-binding interactions of human and herpes simplex virus Fc receptors.

A virally encoded, high-affinity Fc receptor (FcR) is found on herpes simplex virus type 1 (HSV-1) particles and infected cells where its binding of non-immune IgG protects cells from host-mediated lysis. Whilst mutation or aglycosylation of the IgG CH2 domain reduced binding to human FcR, the interaction with HSV-1 FcR was not affected. However, the HSV-1 FcR, unlike human FcR, discriminates between human IgG1 allotypes, being sensitive to changes at positions 214 (CH1) and 356/358 (CH3), away from its proposed binding site at the CH2-CH3 interface. The biological consequences are not known but this is the first evidence of a major functional difference between IgG1 allotypes.

Antibody-Dependent Cell Cytotoxicity↗

PubMed2002

The production and characterisation of a chimaeric human IgE antibody, recognising the major mite allergen Der p 1, and its chimaeric human IgG1 anti-idiotype.

BACKGROUND: Two mouse monoclonal antibodies have been described, namely: mAb 2C7 (IgG2bkappa), which is directed against the major house dust mite allergen Der p 1, and mAb 2G10 (IgG1kappa), which is an anti-idiotypic antibody raised against mAb 2C7. Given its broad IgE specificity, anti-idiotype mAb 2G10 could potentially have immunomodulatory applications. For example, a chimaeric human IgG version of mAb 2G10 could prove to be a useful molecule for binding to mast cell and basophil FcepsilonRI bound IgE, and in doing so co-ligating FcepsilonRI with FcgammaRIIB, which has been reported to have downregulatory effects. AIMS: To produce a chimaeric human IgE version of mAb 2C7 (mAb 2C7huE) and a chimaeric human IgG1 version of its anti-idiotype mAb 2G10 (mAb 2G10huG1). METHODS: The Vkappa and VH regions of mAb 2C7 and its anti-idiotype mAb 2G10 were engineered into human constant regions of the IgE and IgG1 isotypes, respectively. RESULTS: The production of chimaeric mAb 2C7huE and its anti-idiotype mAb 2G10huG1 confirmed that the respective mouse antibody V regions were successfully engineered into human constant regions and still retained the specificity of the original murine V regions. CONCLUSION: The newly constructed chimaeric antibodies will be useful to investigate the downregulation of IgE mediated hypersensitivity by the crosslinking of FcepsilonRI with FcgammaRIIB.

Allergens↗

PubMed2001

The control and facilitation of MHC class II antigen processing by the BCR.

Antigens capable of cross-linking the BCR are preferentially captured, processed and presented to MHC-class-II-restricted T cells. Cross-linking antigens initiate tyrosine-kinase-dependent pathways that accelerate the delivery of antigen-receptor complexes to specialized late-endocytic processing compartments. Accelerated trafficking is mediated by the recruitment of signaling molecules required for transience through specific checkpoints along the endocytic pathway.

Animals↗

PubMed2001

PU.1/Spi-B regulation of c-rel is essential for mature B cell survival.

PU.1(+/-)Spi-B(-/-) mice exhibit reduced numbers of immature and mature B lymphocytes, which exhibit severe defects in response to BCR-mediated stimulation and poor survival. We found that expression of c-rel, a member of the Rel/NF-kappa B family, is dramatically reduced in PU.1(+/-)Spi-B(-/-) splenic B cells. Analysis of the murine c-rel promoter identified three PU.1/Spi-B binding sites critical for c-rel promoter activity. Furthermore, reintroduction of Rel protein restored wild-type B cell numbers to mice reconstituted with PU.1(+/-)Spi-B(-/-) bone marrow. These findings are the first to demonstrate that a member of the Rel/NF-kappa B family is directly regulated by Ets proteins and dissect the molecular basis for the function of two Ets factors, PU.1 and Spi-B, in promoting B lymphocyte survival.

Animals↗

PubMed2000

The herpes simplex virus type 1 Fc receptor discriminates between IgG1 allotypes.

Herpes simplex virus type 1 (HSV-1) expresses a complex of two virally encoded glycoproteins, gE and gl, which is capable of binding nonimmune human IgG. The gE-gl complex has thus become known as an Fc receptor (FcR), which reportedly binds human IgG subclasses in the order IgG4 > IgG1 > or = IgG2 and does not bind IgG3 from many individuals. There is, however, allelic variation in the genes encoding the human IgG1 heavy chain constant region and this gives rise to allotypes of IgG1. Using recombinant monoclonal IgG molecules of known isotype and mutants thereof we have unexpectedly discovered that the HSV-1 FcR discriminates between IgG1 allotypes. This is evidence of functional differences between IgG1 allotypes that may account for their distribution in populations. Furthermore, these findings suggest HSV-1 FcR binding sites on the IgG molecule some distance from the proposed binding site in the CH2-CH3 domain interface.

Animals↗

PubMed2000

In vivo detection of vascular adhesion protein-1 in experimental inflammation.

Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible endothelial glycoprotein which mediates leukocyte-endothelial cell interactions. To study the pathogenetic significance of VAP-1 in inflammatory disorders, an in vivo immunodetection method was used to detect the regulation of luminally expressed VAP-1 in experimental skin and joint inflammation in the pig and dog. Moreover, VAP-1 was studied as a potential target to localize inflammation by radioimmunoscintigraphy. Up-regulation of VAP-1 in experimental dermatitis and arthritis could be visualized by specifically targeted immunoscintigraphy. Moreover, the translocation of VAP-1 to the functional position on the endothelial surface was only seen in inflamed tissues. These results suggest that VAP-1 is both an optimal candidate for anti-adhesive therapy and a potential target molecule for imaging inflammation.

Amine Oxidase (Copper-Containing)↗

PubMed2000

Psychiatric symptoms and distress differ between patients with postherpetic neuralgia and peripheral vestibular disease.

OBJECTIVE: No previous studies have investigated the psychiatric characteristics of patients with postherpetic neuralgia (PHN). Similarly, no studies have been performed on patients with different chronic somatic symptoms due to a defined medical disease to compare the characteristics of psychiatric morbidity associated with each etiology. METHODS: After completing the subscales of the Symptom Checklist 90-R, a psychiatrist administered the Diagnostic Interview Schedule to all subjects. The psychiatric comorbidity in 35 patients with pain due to PHN was compared with a control group of 34 patients with the nonpainful aversive symptom of vertigo due to a peripheral vestibular disorder that caused unilateral hypofunction. RESULTS: PHN patients had significantly more symptoms of major depression and somatization disorder. No significant differences were found between groups for psychiatric diagnoses. Patients with PHN reported significantly less acutely distressing somatic symptoms. CONCLUSION: These results suggest that the psychiatric symptoms of patients with PHN are distinct from nonspecific acute distress and may be related to the experience of suffering from chronic neuropathic pain. Patients with PHN may not meet criteria for a psychiatric diagnosis, but their psychiatric comorbidity places them at substantial risk for increased pain, suicidal ideation, sustained disability, and the numerous complications of excessive medical evaluation and treatment. Patients with PHN should be evaluated specifically for psychiatric symptoms to reduce potential negative consequences through appropriate treatment.

Adaptation, Psychological↗

PubMed2000

A rapid one-stage whole-blood HPA-1a phenotyping assay using a recombinant monoclonal IgG1 anti-HPA-1a.

Severe neonatal alloimmune thrombocytopenia and patients with HPA-1a-specific antibodies require transfusion of HPA-1a-negative platelets. Identifying HPA-1a-negative donors requires simple and reliable typing methods. Most existing techniques use polyclonal antibodies, are time consuming and involve platelet isolation. We have used a horseradish peroxidase (HRP)-conjugated recombinant IgG1 anti-HPA-1a (CAMTRAN007) to develop a rapid and reliable enzyme-linked immunosorbent assay (ELISA), which eliminates sample preparation and reduces the incubation and wash steps associated with traditional sandwich ELISAs. The assay uses simultaneous incubation of the monoclonal antibody RFGP56 to capture GPIIbIIIa from whole blood and the recombinant IgG1 antibody to detect captured HPA-1a antigen. It allows 96 samples to be typed in less than 1 h and can be used on stored samples. Initial testing of 85 samples of known HPA-1a genotype demonstrated that HPA-1a-negative samples had OD values of < 0.266, whereas HPA-1a-positive samples had OD values of > 0.6. Testing of 1862 random donor samples in two blood centres confirmed these OD cut-off values and identified 45 HPA-1a-negative samples (2.4%), all except one giving OD values of < 0.2. The remaining HPA-1a-negative sample had an OD value of 0.303. The HPA-1a status on all the negative samples and an equivalent number of randomly selected positive samples was confirmed by flow cytometry and polymerase chain reaction with sequence-specific primers (PCR- SSP).

Antigens, Human Platelet↗

PubMed2000

Heterogenous patterns of sensory dysfunction in postherpetic neuralgia suggest multiple pathophysiologic mechanisms.

BACKGROUND: Postherpetic neuralgia (PHN) is considered by some investigators to be predominantly a deafferentation-type central pain syndrome; others suggest that activity of remaining peripheral nociceptors plays a critical role. The authors investigated the sensory dysfunction in subjects with PHN of varying duration and at different sites to gain further insight into the mechanisms responsible for the clinical features of neuropathic pain. In addition, the relationships between ongoing pain and pain evoked by mechanical and thermal stimuli were compared in patients with trigeminal and truncal PHN, to determine if the pathophysiologic mechanisms differed among subjects. METHODS: In 63 subjects with PHN, quantitative sensory testing was performed in the region of maximum allodynia or ongoing pain and the corresponding contralateral site. The intensity of ongoing pain was recorded. Sensory thresholds for warmth, coolness, heat pain, and cold pain were determined. Pain induced by various mechanical stimuli (dynamic, static, punctate) was rated using a numerical rating scale of 0-10. RESULTS: The mean rating of ongoing PHN pain was 7.3 +/- 2.0 (mean +/- SD). Allodynia induced by one or more mechanical stimuli was observed in 78% of subjects. A smaller subset (40%) had hyperalgesia to heat or cold stimuli. In subjects with duration of PHN of < or = 1 yr duration, but not in those with duration of > 1 yr, the intensity of ongoing pain correlated with intensity of allodynia induced by dynamic stimuli. Deficits in thresholds for heat and cold pain were observed in the affected region of subjects with PHN in the thoracic dermatomes (P < 0.005), but not in the trigeminal distribution. No relationship was observed between the thermal deficits and ongoing pain or mechanical allodynia in the groups of subjects with either trigeminal or thoracic PHN. CONCLUSION: Despite a common cause, the patterns of sensory abnormalities differ between subjects. Particular differences were noted between groups with facial or truncal PHN and between groups with recent or more chronic PHN. The observations suggest that the relative contributions of peripheral and central mechanisms to the pathophysiology of pain differ among subjects and may vary over the course of PHN.

Adult↗

PubMed2000

Characterisation of a mouse monoclonal anti-idiotype reactive with a V region sequence commonly used by human immunoglobulins.

BACKGROUND: A mouse monoclonal antibody (2C7/IgG2b kappa) has been described recently, which is directed against the major house dust mite allergen Der p 1, and whose epitope specificity is representative of a major component of the human IgE anti-Der p 1 response. AIMS: To characterise an anti-idiotypic antibody (2G10/IgG1 kappa) raised against monoclonal antibody 2C7 as surrogate human IgE anti-Der p 1. METHODS: The specificity of the anti-idiotype antibody 2G10 was determined by competitive inhibition experiments using human and mouse immunoglobulins of known VH gene families. The epitope recognised by monoclonal antibody 2G10 was located on the molecular model of the Fv (fragment variable) region of monoclonal antibody 2C7. RESULTS: The data suggest that monoclonal antibody 2G10 is directed against a crossreactive idiotype on human IgE that is shared by polyclonal IgG. Competitive inhibition studies against human immunoglobulins, representative of VH2, VH3, and VH4 gene families, showed that monoclonal antibody 2G10 is mostly likely to be directed against sequences encoded by either VH3 or VH4 genes. The fact that monoclonal antibody 2G10 binds to the humanized (complementarity determining region (CDR) grafted) CAMPATH-1H antibody, but not to the original rat CAMPATH-1 YTH34.5.6 antibody, indicates that it is directed against a framework region rather than the CDRs. Analysis of amino acids in the VH region for charge, hydrophobicity, and accessibility suggests that reactivity with monoclonal antibody 2G10 is defined by a hexapeptide spanning residues 74-79 within framework region 3. CONCLUSION: The anti-idiotype monoclonal antibody 2G10 could potentially be used as a probe for determining the contribution of the VH3 and VH4 gene segments to antigenic specificity.

Amino Acid Sequence↗

PubMed1999

CD45 negatively regulates lyn activity by dephosphorylating both positive and negative regulatory tyrosine residues in immature B cells.

Using CD45-deficient clones from the immature B cell line, WEHI-231, we previously demonstrated that CD45 selectively dephosphorylates the Src-family protein tyrosine kinase Lyn and inhibits its kinase activity. To further define the mechanisms of CD45 action on Lyn, we metabolically labeled Lyn from CD45-positive and -negative WEHI-231 cells and analyzed cyanogen bromide fragments by SDS-PAGE analysis. Phosphoamino acid analysis confirmed that Lyn is tyrosine phosphorylated with little serine or threonine phosphorylation. In CD45-negative cells, two bands at 8.2 and 4.1 kDa were phosphorylated in the absence of B cell Ag receptor (BCR) ligation. The 8.2-kDa band corresponded to a fragment containing the positive regulatory site (Tyr397), as assessed by its size and its phosphorylation in an in vitro kinase assay. The 4.1-kDa band was phosphorylated by COOH-terminal Src kinase, suggesting that it contains the COOH-terminal negative regulatory site (Tyr508). CD45 was also shown to dephosphorylate autophosphorylated Lyn in vitro. Thus, CD45 dephosphorylates not only the negative but also the positive regulatory tyrosine residues of Lyn. Furthermore, coimmunoprecipitations using anti-Igalpha Ab demonstrated that Lyn associated with the resting BCR was constitutively phosphorylated and activated in CD45-negative cells. In the parental cells, both regulatory sites were phosphorylated on BCR ligation. Taken collectively, these results suggest that CD45 keeps both BCR-associated and total cytoplasmic pools of Lyn in an inactive state, and a mechanism by which Lyn is activated by relative reduction of CD45 effect may be operative on BCR ligation.

Animals↗

PubMed1999

Ig alpha and Ig beta are required for efficient trafficking to late endosomes and to enhance antigen presentation.

The B cell Ag receptor (BCR) is a multimeric complex, containing Ig alpha and Ig beta, capable of internalizing and delivering specific Ags to specialized late endosomes, where they are processed into peptides for loading onto MHC class II molecules. By this mechanism, the presentation of receptor-selected epitopes to T cells is enhanced by several orders of magnitude. Previously, it has been reported that, under some circumstances, either Ig alpha or Ig beta can facilitate the presentation of Ags. However, we now demonstrate that if these Ags are at low concentrations and temporally restricted, both Ig alpha and Ig beta are required. When compared with the BCR, chimeric complexes containing either chain alone were internalized but failed to access the MHC class II-enriched compartment (MIIC) or induce the aggregation and fusion of its constituent vesicles. Furthermore, Ig alpha/Ig beta complexes in which the immunoreceptor tyrosine-based activation motif tyrosines of Ig alpha were mutated were also incapable of accessing the MIIC or of facilitating the presentation of Ag. These data indicate that both Ig alpha and Ig beta contribute signaling, and possibly other functions, to the BCR that are necessary and sufficient to reconstitute the trafficking and Ag-processing enhancing capacities of the intact receptor complex.

Animals↗

PubMed1999

Recombinant human IgG molecules lacking Fcgamma receptor I binding and monocyte triggering activities.

Subclasses of human IgG have a range of activity levels with different effector systems but each triggers at least one mechanism of cell destruction. We are aiming to engineer non-destructive human IgG constant regions for therapeutic applications where depletion of cells bearing the target antigen is undesirable. The attributes required are a lack of killing via Fcgamma receptors (R) and complement but retention of neonatal FcR binding to maintain placental transport and the prolonged half-life of IgG. Eight variants of human IgG constant regions were made with anti-RhD and CD52 specificities. The mutations, in one or two key regions of the CH2 domain, were restricted to incorporation of motifs from other subclasses to minimize potential immunogenicity. IgG2 residues at positions 233 - 236, substituted into IgG1 and IgG4, reduced binding to FcgammaRI by 10(4)-fold and eliminated the human monocyte response to antibody-sensitized red blood cells, resulting in antibodies which blocked the functions of active antibodies. If glycine 236, which is deleted in IgG2, was restored to the IgG1 and IgG4 mutants, low levels of activity were observed. Introduction of the IgG4 residues at positions 327, 330 and 331 of IgG1 and IgG2 had no effect on FcgammaRI binding but caused a small decrease in monocyte triggering.

Amino Acid Sequence↗

PubMed1999

PU.1 and Spi-B are required for normal B cell receptor-mediated signal transduction.

PU.1 and Spi-B have previously been implicated in the regulation of genes encoding B cell receptor (BCR) signaling components. Spi-B-/- B lymphocytes respond poorly to BCR stimulation; PU.1-/- mice, however, lack B cells, precluding an analysis of BCR responses. We now show that PU.1+/- Spi-B-/- B cells exhibit more extensive defects than Spi-B-/- B cells, indicating that both PU.1 and Spi-B are required for normal BCR signaling. Strikingly, BCR cross-linking results in substantially reduced protein tyrosine phosphorylation in mutant B cells. Further analysis shows that Igalpha is phosphorylated and syk is recruited and becomes phosphorylated but that BLNK and PLCgamma phosphorylation are defective in mutant cells. Our data support the existence of a novel component coupling syk to downstream targets.

Animals↗