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Biomedical subjects

N D Hall

Publications and source records attributed to N D Hall.

At least 19 recordsLinked to original sources
PubMed2000

MHC class II associations with autoantibody and T cell immune responses to the scleroderma autoantigen topoisomerase I.

Topoisomerase I (topo I) is a major autoantigen recognized by autoantibodies in about 30% of sera from patients with systemic sclerosis (SSc). Certain HLA-DRB1 and HLA-DQB1 alleles have been reported to be associated with autoantibody and T-cell responses to topo I suggesting a T-cell dependent process. We have examined the MHC class II allele associations with anti-topo I antibodies in 16 patients with SSc compared to 250 healthy controls. Furthermore, we have studied the T cell responses to a recombinant full-length topo I molecule purified from a baculovirus expression system in eight patients with SSc and eight controls (five healthy and three with autoimmune disease). HLA-DR5 was significantly increased in patients with anti-topo I antibodies (P< 0.02). Proliferative peripheral blood mononuclear cell (PBMC) responses to soluble topo I were present in nine of 16 individuals (four of eight with SSc and five of eight controls), including the three SSc patients with anti-topo I antibodies. Homozygosity for HLA DQB1:30:Y alleles was present in five of nine responders (P< 0.03) compared to none of the non-responders. Our findings support the notion that the MHC class II background influences the ability to generate an autoimmune response to intracellular autoantigens to which the immune system may not have been tolerized. Additional factors associated with the generation of autoantibodies appear to be more intimately associated with the development of SSc.

Alleles↗
PubMed2000

Class II MHC antigens in early rheumatoid arthritis in Bath (UK) and Madrid (Spain).

OBJECTIVE: A number of studies have indicated that rheumatoid arthritis (RA) is a less severe disease in Mediterranean countries than in Northern Europe. We investigated whether differences in the frequency of class II MHC antigens might contribute to this variation in disease severity. METHODS: Typing at HLA-DR and -DQ loci was carried out at low and high resolutions by polymerase chain reaction amplification in patients with early RA of less than 6 months' duration (68 patients in Madrid and 68 in Bath) and in control subjects (929 in Madrid and 226 in Bath). Only ethnic Spanish and British individuals were included as patients and controls. RESULTS: Shared epitope (SE) alleles represented 19.8 and 28.9% of the total number of class II MHC alleles in controls from Madrid and Bath respectively (P: = 0.00001), this difference being largely due to increased numbers of DRB1*0401 individuals in the British subjects (P: = 0.0000001). Analysis of the patients showed the expected increase in SE alleles when compared with their respective control groups (Madrid, 31.6 vs 19.8%; Bath, 42.6 vs 28. 9%). In Bath the SE was mainly encoded by HLA-DR4 alleles (74.1%), while in Madrid it was encoded almost equally by DR4 (51.1%) and DR1 (44.7%) alleles. The risk of developing RA in carriers of SE alleles was similar in the two cities (Bath, odds ratio 1.83, 95% confidence interval 1.23-2.78; Madrid, odds ratio 1.87, 95% confidence interval 1.25-2.77), and was largely accounted for by HLA-DRB1*0401 alleles. CONCLUSION: We conclude that rheumatoid patients in Bath differ from their Spanish counterparts in class II antigen expression and allele frequency. This may be explained partly by genetic differences between the control populations in the two centres, and may help to explain the greater incidence of more severe rheumatoid disease expression seen in RA patients in the UK.

Alleles↗
PubMed1999

Lack of activation induced cell death in human T blasts despite CD95L up-regulation: protection from apoptosis by MEK signalling.

The generation of effective immunity requires that antigen-specific T cells are activated, clonally expanded and ultimately eliminated by apoptosis. The involvement of CD95-mediated apoptosis in T-cell elimination is well established, but the conditions which regulate the death pathway under normal circumstances are still emerging. Using superantigen-activated human T cells, we found that whilst T-cell receptor (TCR) signalling triggered up-regulation of CD95 ligand (CD95L), the majority of T cells were resistant to apoptosis induction, despite co-expressing high levels of CD95. Resistance was maintained following direct antibody-mediated cross-linking of CD95 and was not confined to early time periods following activation. Our data implicate TCR-derived signals in protection from apoptosis and reveal a role for the mitogen-activated protein (MAP) kinase pathway by use of a MAP kinase kinase (MEK) inhibitor. Collectively these data demonstrate that resistance to activation-induced cell death in human T cells is prolonged rather than transient, is not attributable to a lack of CD95L up-regulation and is due, at least in part, to signalling via the MEK pathway.

Antibodies, Monoclonal↗
PubMed1998

Down-regulation of CD28 via Fas (CD95): influence of CD28 on T-cell apoptosis.

Following antigen engagement of the T-cell receptor (TCR), T-cell survival is largely dictated by the provision of additional signals, such as those from costimulatory receptors and cytokine receptors. Whilst CD28-mediated signalling is increasingly associated with survival, ligation of alternative T-cell antigens, such as Fas (CD95), can trigger apoptosis. The T-cell response following antigen engagement may therefore be influenced by the relative expression levels of these coreceptors as well as by the availability of their ligands (CD80/86 and Fas-L). In this study we demonstrate functional interplay between the death receptor Fas and the costimulatory receptor CD28 in human T cells. In Jurkat T cells, we show that Fas signalling leads to rapid and selective CD28 down-regulation, and that this is associated with a specific decrease in mRNA for CD28, indicating that mechanisms exist which target CD28 at a transcriptional level. Moreover, cells that down-regulate CD28 also undergo apoptosis. Studies on activated human peripheral blood T cells demonstrate that cells expressing high levels of CD28 are resistant to Fas-mediated apoptosis whereas cells expressing low levels are more susceptible, implicating CD28 in the provision of anti-apoptotic signals. Consistent with this hypothesis, direct ligation of CD28 using B7 transfectants concomitant with anti-Fas challenge protects from apoptosis. Since antigen-presenting cells may express Fas-L under certain circumstances, the maintenance of T-cell CD28 expression may be crucial for the prevention of Fas-mediated apoptosis during the course of antigen engagement.

Apoptosis↗
PubMed1997

Modulation of cytokine production by human mononuclear cells following impairment of Na, K-ATPase activity.

Cytokines, including TNF alpha and IL-l beta, are central to the chronic inflammatory process and tissue damage that characterises diseases such as rheumatoid arthritis. The mechanisms responsible for long-term generation of these molecules are poorly understood. We have previously demonstrated impaired activity of Na, K-ATPase, a key enzyme regulating intracellular cation levels, on rheumatoid mononuclear cells. Mimicking this 'defect' on normal mononuclear cells with ouabain has been shown to induce TNF alpha and, in particular, IL-l beta production, whereas IL-6 synthesis was suppressed. A similar pattern of cytokine generation was noted when mononuclear cells were treated with the sodium ionophore, monensin. Induction of cytokine production was related to up-regulation of the appropriate mRNA, although enhanced secretion of processed IL-l beta was also observed. The mechanism underlying these cellular responses appears to involve sodium/calcium exchange across the cell membrane. Impaired Na,K-ATPase activity might promote pro-inflammatory cytokine secretion in patients with rheumatoid arthritis.

Calcimycin↗
PubMed1997

Expression of the cutaneous lymphocyte antigen and its counter-receptor E-selectin in the skin and joints of patients with psoriatic arthritis.

We have investigated whether the skin-homing T lymphocytes identified by the cutaneous lymphocyte antigen (CLA) are increased in the synovial membrane of patients with psoriatic arthritis. Twenty-six synovial samples (13 psoriatic arthritis, seven rheumatoid arthritis, six osteoarthritis) were obtained from involved knees. Lesional skin biopsies were taken from nine of the patients with psoriatic arthritis and six patients with psoriasis alone. All samples were single- and dual-stained for CLA and CD3 (to identify T lymphocytes) using HECA-452 (anti-CLA) and anti-CD3 monoclonal antibodies. E-selectin expression was also determined. The percentage of dual-stained lymphocytes was significantly greater in psoriatic skin than in synovium (P < 0.001) and similar between psoriatic and rheumatoid synovium. There was no significant difference in the percentages of CLA-positive cells in psoriatic skin in patients with psoriatic arthritis compared with psoriasis alone. The intensity of endothelial E-selectin expression was significantly greater in skin psoriasis than in synovium (P < 2 x 10(-5)), and rheumatoid synovium had significantly greater expression than psoriatic synovium (P < 0.05). However, there was no significant correlation between E-selectin expression and the percentages of CLA-positive lymphocytes. This study provides further evidence that the CLA antigen is enriched on skin-homing lymphocytes. Conversely, the link between skin and joint inflammation in psoriatic arthritis does not seem to be explained by increased trafficking of CLA T cells to psoriatic synovium.

Adult↗
PubMed1996

Induction of activator protein (AP)-1 and nuclear factor-kappaB by CD28 stimulation involves both phosphatidylinositol 3-kinase and acidic sphingomyelinase signals.

A major obstacle in understanding the signaling events that follow CD28 receptor ligation arises from the fact that CD28 acts as a costimulus to TCR engagement, making it difficult to assess the relative contribution of CD28 signals as distinct from those of the TCR. To overcome this problem, we have exploited the observation that activated human T cell blasts can be stimulated via the CD28 surface molecule in the absence of antigenic challenge; thus, we have been able to observe the response of normal T cells to CD28 activation in isolation. Using this system, we observed that CD28 stimulation by B7-transfected CHO cells induced a proliferative response in T cells that was not accompanied by measurable IL-2 production. However, subsequent analysis of transcription factor generation revealed that B7 stimulation induced both activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB) complexes, but not NF-AT. In contrast, engagement of the TCR by class II MHC/superantigen, either with or without CD28 ligation, resulted in the induction of NF-AT, AP-1, and NF-kappaB as well as IL-2 production. Using selective inhibitors, we investigated the signaling pathways involved in the CD28-mediated induction of AP-1 and NF-kappaB. This revealed that NF-kappaB generation was sensitive to chloroquine, an inhibitor of acidic sphingomyelinase, but not to the phosphatidylinositol 3-kinase inhibitor, wortmannin. In contrast, AP-1 generation was inhibited by wortmannin and was also variably sensitive to chloroquine. These data suggest that in activated normal T cells, CD28-derived signals can stimulate proliferation at least in part via NF-kappaB and AP-1 generation, and that this response uses both acidic sphingomyelinase and phosphatidylinositol 3-kinase-linked pathways.

Animals↗
PubMed1996

Differential expression of the costimulatory molecules B7.1 (CD80) and B7.2 (CD86) in rheumatoid synovial tissue.

CD4+ T-lymphocytes require two signals to become activated--antigen receptor (TcR) occupancy and an antigen-presenting cell (APC)-derived costimulus. The latter may be provided by B7.1 (CD80) or B7.2 (CD86) on APC interacting with CD28 on T-cells. We have studied the expression of these costimulatory molecules in rheumatoid and osteoarthritic synovial membrane. Very few B7.1-positive cells were seen in synovial tissue from either established or early rheumatoid disease, or in rheumatoid arthritis (RA) or osteoarthritis (OA) synovia at arthroplasty. In contrast, B7.2 was readily detected in rheumatoid synovia, predominantly in the lining layer, in a pattern of expression that corresponded to the presence of CD68-positive macrophages. Only occasional B7.2-positive cells were seen in OA synovia. The presence of B7.2 but the relative lack of expression of B7.1 may be partly responsible for the observations of 'frustrated' T-cell activation or T-cell hyporesponsiveness in the rheumatoid synovium.

Antigens, CD↗
PubMed1996

Quantitation of IL-2Rp75 (CD122) expression on mononuclear cells in rheumatic disease.

OBJECTIVE: To compare expression of the p75 chain of the interleukin-2 receptor (IL-2Rp75, CD122) on peripheral and synovial mononuclear cells in rheumatoid and non-rheumatoid inflammatory arthritis. METHODS: Peripheral blood (PBMC) and synovial (SFMC) mononuclear cells were isolated from subjects with rheumatoid arthritis (n = 16) and non-rheumatoid inflammatory arthritis (n = 12). PBMC were isolated from six healthy controls. Expression of CD122 was examined using indirect immunofluorescence and quantitative flow cytometry. RESULTS: There was no difference in IL-2Rp75 expression on PBMC from rheumatoid arthritis patients, non-rheumatoid arthritis patients, and controls. In subjects with rheumatoid arthritis there was no difference in IL-2Rp75 expression on PBMC and SFMC. However, in the non-rheumatoid arthritis group there was an increase in IL-2Rp75 expression on SFMC compared with PBMC (P = 0.0032). On SFMC there was a greater expression of IL-2Rp75 in non-rheumatoid arthritis than in rheumatoid arthritis (P = 0.0007). Expression was greater on CD8 positive cells and in subjects with shorter duration of disease. CONCLUSIONS: The p75 chain of the IL-2 receptor, an important T cell activation antigen, is not upregulated in synovial fluid. This appears to be a disease specific defect and provides further support for the concept of "frustrated" or incomplete T cell activation in this disease.

Arthritis↗
PubMed1995

Detection of anti-topoisomerase I antibodies using a full length human topoisomerase I recombinant protein purified from a baculovirus expression system.

Topoisomerase I (topo I) is a major systemic sclerosis (SSc)-associated autoantigen. A cDNA construct encoding full length human topo I in a recombinant baculovirus transfer vector was used to infect insect cells in culture from which recombinant protein was purified. An ELISA using recombinant protein was evaluated in 340 sera including sera from 134 patients with SSc, of whom 33 had anti-topo I antibodies detected by immunodiffusion. A high yield of pure topo I of expected molecular mass and catalytic activity was obtained. The recombinant topo I ELISA was 92% sensitive and 98% specific in detecting anti-topo I antibodies which were present almost exclusively in patients with SSc. Therefore, the potential advantages of expressing human autoantigens in eukaryotic systems for diagnostic purposes were confirmed.

Animals↗
PubMed1993

B7/BB1, the ligand for CD28, is expressed on repeatedly activated human T cells in vitro.

The activation of T cells is now thought to require at least two distinct signals. One signal is delivered through the interaction of the antigen-specific T cell receptor with major histocompatibility complex (MHC) molecules and peptide, while the other is received from interactions with less precisely defined accessory or costimulatory molecules. In the absence of this second costimulatory signal, some T cells subsequently become unresponsive to antigenic stimulation. One of the major candidates for providing such a second signal to T cells is the molecule B7 interacting with the T cell glycoprotein CD28. In the present study we have investigated whether B7 is expressed on human T cell lines and clones, since these cells have the capacity to present antigen to each other by expressing MHC class II molecules. Our results demonstrate that B7 can be detected on T cell clones and on repeatedly activated but not freshly isolated peripheral blood T cells. The expression of B7 is dependent on the state of activation of the cells, being maximally expressed shortly after restimulation and becoming undetectable as the cells quiesce. Together, these results suggest that B7 expression may be of importance to T cells, perhaps in the avoidance of anergy.

Antigens, CD↗
PubMed1993

Ligation of CD28 receptor by B7 induces formation of D-3 phosphoinositides in T lymphocytes independently of T cell receptor/CD3 activation.

The co-stimulatory role of B7/CD28 interactions is important in promoting T cell activation. Very little is known about the intracellular events that follow CD28 engagement although recent evidence has implicated coupling of CD28 to a protein tyrosine kinase signal transduction pathway. In this study we have investigated the putative role of D-3 phosphoinositides as mediators of CD28 receptor signaling, since phosphoinositide (PI) 3-kinase, the enzyme responsible for D-3 phosphoinositide formation, is a known substrate for protein tyrosine kinases associated with certain T cell surface receptors such as CD4 and interleukin-2 receptor. The lipid products of PI 3-kinase activity have been suggested to play a role in mitogenic signaling and growth regulation in other cells. Chinese hamster ovary cells (CHO) previously transfected with B7 cDNA, induced time-dependent elevation above basal levels of phosphatidylinositol(3,4)-bisphosphate (PtdIns(3,4)P2) and PtdIns(3,4,5)P3, while parental CHO cells that did not express B7 had no effect on these lipids. Moreover, the elevation of these same lipids by CD3 ligation was potentiated in an additive manner by CHO-B7+ but not by CHO-B7- cells. CHO-B7+ and CHO-B7- cells did not activate phospholipase C as evidenced by their inability to modulate basal or CD3-induced changes in the levels of phosphatidic acid or D-4 and D-5 phosphoinositides. These data imply that PI 3-kinase but not phospholipase C, may be an important signal transduction molecule with respect to CD28-mediated co-stimulation and T cell activation following ligation by B7.

Animals↗
PubMed1993

Impaired activity of thiol-dependent ATPases in rheumatoid mononuclear cell membranes.

Ion-motive ATPase play an essential role in many aspects of cell biology, including mononuclear cell (MNC) functions relevant to chronic inflammation. For example, ouabain, a specific inhibitor of Na+, K+ ATPase, suppresses both T and B cell proliferation but induces synthesis of IL-1. Using a cytochemical assay quantified by microdensitometry, total and ouabain-sensitive ATPase activities have been compared in MNC from rheumatoid and control subjects. The sensitivity of these enzymes to inactivation by thiol-blocking reagents has been studied by preincubation with an impermeant SH blocker p-hydroxymercuriphenylsulphonate (pHMPSA). The results show that rheumatoid MNC have significantly impaired ATPase activity compared to healthy cells and that both total and ouabain-sensitive ATPase activities are readily inhibited by pHMPSA. The depressed ATPase activity in rheumatoid MNC could thus be due to blockade/oxidation of a reactive surface thiol, and could contribute to perpetuation of the chronic inflammatory process in these patients.

Adenosine Triphosphatases↗
PubMed1993

Suppressive effects of a novel antioxidant compound on human T cell functions in vitro.

The use of antioxidant compounds with differing modes of action has clearly demonstrated involvement of oxidative processes in the activation of T lymphocytes. In this paper, we show that a novel antioxidant (lazaroid U75412E, a free radical scavenger) suppressed mitogen-induced T cell proliferation in vitro. Similar results were obtained with diphenylene iodonium (DPI), a known inhibitor of NADPH oxidase. The lazaroid was further shown to inhibit IL 2 production but to be less potent in suppressing IL 2 receptor expression. Thus, scavenger-type antioxidants act on T cells primarily by blocking a signal necessary for the induction of IL 2 synthesis such as the activation of NF kappa B. Furthermore, the potent inhibition of lymphocyte responses caused by the specific enzyme inhibitor DPI provides direct proof of the source of the oxidants involved in these processes.

Antioxidants↗
PubMed1993

Rhythms in the immune system.

This report reviews the evidence that cells within the immune system are subject to rhythmic influences that affect numbers of circulating cells and their function both in vitro and in vivo. It is concluded that, although periodicity has clearly been demonstrated for numbers of immunocompetent cells in the circulation, significant functional changes have not been consistently observed. A number of neuroendocrine hormones, which modulate immune responsiveness in vitro and which are released in a rhythmic manner, are considered as mediators of the observed effects on the immune system and this is related to changes in expression and activity of immune-mediated diseases such as rheumatoid arthritis.

Animals↗
PubMed1993

B7/CD28 but not LFA-3/CD2 interactions can provide 'third-party' co-stimulation for human T-cell activation.

The requirement for co-stimulation in T-cell activation has become firmly established, whilst the precise identity of the molecules involved remains uncertain. Some of the major co-stimulatory molecules include ICAM-1, LFA-3 and B7. We have investigated the abilities of both LFA-3 and B7 to co-stimulate T-cell proliferation under a number of conditions using transfected Chinese hamster ovary cells. Using anti-CD3 antibodies we observed that B7 but not LFA-3 transfectants were capable of co-stimulating proliferation in purified peripheral blood T cells. In addition, both LFA-3 and B7 could induce proliferation in response to phytohaemagglutinin (PHA) and we obtained additive effects using both B7 and LFA-3 together. Using the superantigen staphylococcal enterotoxin B (SEB), we observed that presentation to purified T cells required the presence of class II-positive transfectants and that sensitivity to antigen was increased approximately 100-fold by the co-transfection of either B7 or LFA-3. However, when co-stimulatory molecules were provided by cells separate from those engaging the T-cell receptor (TcR), only B7 was capable of enhancing proliferation. Kinetic studies which investigated the time dependence for co-stimulation revealed that T cells responding to anti-CD3 antibodies required the B7 co-stimulation within the first few hours, for proliferation to be effective. Our data differentiate between the co-stimulatory abilities of B7 and LFA-3 and support the concept of a pivotal role for B7 in T-cell proliferation.

Antigens, CD↗