A review of one year of British Armed Forces mental health hospital admissions

OBJECTIVES

The paper provides a review of one year of military Mental Health (MH) hospital admissions. This includes an exploration into demographic trends, differences in clinical opinion and how information gained is used to improve the service and ensure appropriate, cost effective care in the optimum environment.

METHODS

The sample group is entitled military MH hospital admissions from 1 April 2005 to 31 March 2006. Data was collected on questionnaires with SPSS used for the management and analysis of the quantitative data, with the information exposed to descriptive and inferential statistical analysis.

RESULTS

There were 344 admissions. The paper contains a detailed review of a number of variables. Depression was the most common diagnosis resulting in 112 (33%) hospital admissions and Post Traumatic Stress Disorder accounted for 23 (7%). There were statistically significant differences that may be attributable to gender with more women admitted with depression and more men with alcohol related disorders. The average length of stay was 21 days, with 48% of patients discharged within 3 weeks. 45% of all returns included significant events reporting that highlighted written evidence of good and poor practice.

CONCLUSION

This study is part of an extensive monitoring programme of military MH hospital admissions. Depression is the most common MH problem leading to hospital admission. The results indicate that Service-personnel have access to a highly responsive service that provides brief assessment and treatment within a safe therapeutic environment. 45% of returns included significant event information that resulted in policy changes, leading to improved patient care and a better interface with the NHS. Bench-marking, both internally between military Departments of Community Mental Health and externally have improved visibility and self awareness leading to better GP induction programmes, PHC educational seminars and the establishment of MH web-pages. The Armed Forces need an effective MH service that is accessible, readily available, non-stigmatised and which positively advocates a duty of care. The results highlight the importance of further studies regarding depression to ensure that the Armed Forces are in a better position to maximise the use of MH resources.

Disease-associated qualitative and quantitative trait loci in proteoglycan-induced arthritis and collagen-induced arthritis

Two autoimmune murine models--proteoglycan (aggrecan)-induced arthritis (PGIA) and collagen-induced arthritis (CIA)--were developed in parent strains, F1 and F2 hybrids of major histocompatibility complex (MHC)-matched (H-2) BALB/c x DBA/2 and MHC-unmatched (H-2/H-2) BALB/c x DBA/1 intercrosses. The major goal of this comparative study was to identify disease (model)-specific (PGIA or CIA) and shared clinical and immunologic loci in 2 types of genetic intercrosses. Qualitative (binary/susceptibility) and quantitative (severity and onset) clinical trait loci were separated and analyzed independently or together with various pathophysiologic/immunologic traits, such as antigen-specific T- and B-cell responses and cytokine production. The major quantitative trait locus (QTL) was the MHC on chromosome 17, which was especially dominant in CIA. In addition, chromosomes 3, 5, 10, and X contained shared clinical loci in both models, and a total of 8 QTLs (clinical traits together with immunologic traits) were colocalized in PGIA and CIA.

Impaired Fas signaling pathway is involved in defective T cell apoptosis in autoimmune murine arthritis

Proteoglycan (PG)-induced arthritis (PGIA) is a novel autoimmune murine model for rheumatoid arthritis induced by immunization with cartilage PG in susceptible BALB/c mice. In this model, hyperproliferation of peripheral CD4(+) T cells has been observed in vitro with Ag stimulation, suggesting the breakdown of peripheral tolerance. Activation-induced cell death (AICD) is a major mechanism for peripheral T cell tolerance. A defect in AICD may result in autoimmunity. We report in this study that although CD4(+) T cells from both BALB/c and B6 mice, identically immunized with human cartilage PG or OVA, express equally high levels of Fas at the cell surface, CD4(+) T cells from human cartilage PG-immunized BALB/c mice, which develop arthritis, fail to undergo AICD. This defect in AICD in PGIA may lead to the accumulation of autoreactive Th1 cells in the periphery. The impaired AICD in PGIA might be ascribed to an aberrant expression of Fas-like IL-1beta-converting enzyme-inhibitory protein, which precludes caspase-8 activation at the death-inducing signaling complex, and subsequently suppresses the caspase cascade initiated by Fas-Fas ligand interaction. Moreover, this aberrant expression of Fas-like IL-1beta-converting enzyme-inhibitory protein may also mediate TCR-induced hyperproliferation of CD4(+) T cells from arthritic BALB/c mice. Our data provide the first insight into the molecular mechanism(s) of defective AICD in autoimmune arthritis.

Variations in susceptibility to proteoglycan-induced arthritis and spondylitis among C3H substrains of mice: evidence of genetically acquired resistance to autoimmune disease

OBJECTIVE

To identify and screen the level of arthritis susceptibility in C3H murine strains known to be resistant to proteoglycan (aggrecan)-induced arthritis, and to measure and correlate various immunologic and inflammatory parameters with susceptibility to either arthritis or spondylitis in various C3H substrains.

METHODS

Mice of 10 C3H substrains (subcolonies) were immunized with cartilage proteoglycan (aggrecan) for induction of arthritis. Animals were assessed for clinical symptoms, and the peripheral joints and spine were studied by histologic methods. Proteoglycan-specific T cell responses (T cell proliferation and production of interleukin-2 [IL-2], interferon-y, and IL-4) and the B cell response to lipopolysaccharide (LPS) were measured in spleen cell cultures. Serum levels of heteroantibodies and autoantibodies as well as various cytokines (IL-6, IL-10, IL-12, and tumor necrosis factor alpha) and soluble CD44 were determined by enzyme-linked immunosorbent assay.

RESULTS

Immunization with cartilage proteoglycan induced severe arthritis in the C3H/HeJCr substrain (95-100% incidence), whereas the original parent mice of the C3H/HeJ colony were resistant to proteoglycan (aggrecan)-induced arthritis. Furthermore, the progressive polyarthritis that is characteristic in susceptible C3H/HeJCr mice was accompanied by progressive inflammation around the spine. In subsequent experiments, 10 different C3H colonies with largely identical genetic backgrounds (all originating from the National Institutes of Health or Jackson Laboratory) exhibited extreme differences in susceptibility. Although none of the laboratory findings, including LPS hyporesponsiveness, immunologic parameters, and inflammatory markers, showed a correlation with susceptibility or resistance in the C3H/HeJCr and C3H/HeJ substrains, respectively, significant differences were found when all arthritic C3H mice were compared with all nonarthritic animals, regardless of their substrain origin.

CONCLUSION

Because many of the C3H substrains lost arthritis susceptibility or acquired resistance, our results suggest that a preferred site for a mutation(s) in a gene(s) in a relatively upstream position of the inflammatory cascade is present. This is the first autoimmune model that exhibits extreme differences in arthritis susceptibility in the same murine strain, and is therefore a valuable tool for identification of arthritis-susceptible (or arthritis-suppressive) genes.

A genome scan using a novel genetic cross identifies new susceptibility loci and traits in a mouse model of rheumatoid arthritis

Proteoglycan-induced arthritis (PGIA) is a murine model for rheumatoid arthritis (RA) both in terms of its pathology and its genetics. PGIA can only be induced in susceptible mouse strains and their F(2) progeny. Using the F(2) hybrids resulting from an F(1) intercross of a newly identified susceptible (C3H/HeJCr) and an established resistant (C57BL/6) strain of mouse, our goals were to: 1) identify the strain-specific loci that confer PGIA susceptibility, 2) determine whether any pathophysiological parameters could be used as markers that distinguish between nonarthritic and arthritic mice, and 3) analyze the effect of the MHC haplotype on quantitative trait loci (QTL) detection. To identify QTLs, we performed a genome scan on the F(2) hybrids. For pathophysiological analyses, we measured pro- and antiinflammatory cytokines such as IL-1, IL-6, IFN-gamma, IL-4, IL-10, IL-12, Ag-specific T cell proliferation and IL-2 production, serum IgG1 and IgG2 levels of both auto- and heteroantibodies, and soluble CD44. We have identified four new PGIA-linked QTLs (Pgia13 through Pgia16) and confirmed two (Pgia5, Pgia10) from our previous study. All new MHC-independent QTLs were associated with either disease onset or severity. Comprehensive statistical analysis demonstrated that while soluble CD44, IL-6, and IgG1 vs. IgG2 heteroantibody levels differed significantly between the arthritic and nonarthritic groups, only Ab-related parameters colocalized with the QTLs. Importantly, the mixed haplotype (H-2(b) and H-2(k)) of the C3H x C57BL/6 F(2) intercross reduced the detection of several previously identified QTLs to suggestive levels, indicating a masking effect of unmatched MHCs.

Spontaneous thymocyte apoptosis is regulated by a mitochondrion-mediated signaling pathway

Most thymocytes that have not successfully rearranged their TCR genes or that express a receptor with subthreshold avidity for self-Ag/MHC enter a default apoptosis pathway, death by neglect. Spontaneous thymocyte apoptosis (STA), at least in part, may mimic this process in vitro. However, the molecular mechanism(s) by which thymocytes undergo this spontaneous apoptosis remains unknown. Here, we report that caspsase-1 and caspase-3 are activated during STA, but these caspases are dispensable for this apoptotic process. The inhibition of STA by a pan-caspase inhibitor, zVAD, suggests that multiple caspase pathways exist. Importantly, the early release of cytochrome c from mitochondria closely correlates with the degradation of Bcl-2 and Bcl-xL and a decrease in the ratios of Bcl-2 and Bcl-xL to Bax during STA. These findings suggest that the degradation of Bcl-2 and Bcl-xL may favor Bax to induce cytochrome c release from mitochondria, which subsequently activates downstream caspases in STA. Our data provide the first biochemical insight into the molecular mechanism of STA.

Complex pattern of Th1 and Th2 activation with a preferential increase of autoreactive Th1 cells in BALB/c mice with proteoglycan (aggrecan)-induced arthritis

The central role of CD4+ T cells and the balance between T helper (Th) subpopulations in the pathogenesis of autoimmune diseases have been extensively studied. Proteoglycan (aggrecan)-induced arthritis (PGIA) is a murine model for rheumatoid arthritis (RA), which is characterized by a Th1 dominance at the onset of the disease. In addition to CD4+ T cells, antigen-presenting B cells and autoantibodies seem to play an important role in the development and regulation of PGIA. To identify proteoglycan-specific CD4+ T cell subsets and Th1- and Th2-supported antibody isotypes during the progression of PGIA, spleen cells of proteoglycan-immunized BALB/c mice were harvested at different times of immunization, and at different stages of the disease, and their cytokine production and antigen-specific antibody isotype profiles were determined by enzyme-linked immunospot (ELISPOT) assays. Both Th1 and Th2 cytokine-producing cells, with the predominance of IL-4/IL-5-secreting cells, were detected during the prearthritic stage, and a shift toward a Th1 dominance was observed at the time of onset of arthritis. Tissue homogenates of acutely inflamed joints contained significantly higher levels of interferon-gamma than IL-4. The prearthritic period and both the acute and chronic phases of joint inflammation were characterized by IgG1 dominance in the sera and this correlated with the number of IgG1-secreting B cells in the spleen. However, the ratio of autoreactive IgG1/IgG2a-secreting cells decreased in arthritic animals. These results indicate the activation and possible regulatory roles of both Th1 and Th2 subsets in the autoimmune process, with the necessity of a relative increase of autoreactive Th1 cells for the induction of joint inflammation.

Regulation of intercellular adhesion molecule-1 (CD54) gene expression

Intercellular adhesion molecule-1 (ICAM-1, CD54) is an inducible cell adhesion glycoprotein of the immunoglobulin supergene family expressed on the surface of a wide variety of cell types. ICAM-1 interactions with the beta2 integrins CD11a/CD18 (LFA-1) and CD11b/CD18 (MAC-1) on the surface of leukocytes are important for their transendothelial migration to sites of inflammation and their function as costimulatory molecules for T cell activation. ICAM-1 is constitutively expressed on the cell surface and is up-regulated in response to a variety of inflammatory mediators, including proinflammatory cytokines, hormones, cellular stresses, and virus infection. These stimuli increase ICAM-1 expression primarily through activation of ICAM-1 gene transcription. During the past decade much has been learned about the cell type- and stimulus-specific transcription of ICAM-1. The architecture of the ICAM-1 promoter is complex, containing a large number of binding sites for inducible transcription factors, the most important of which is nuclear factor-kappa B (NF-kappaB). NF-kappaB acts in concert with other transcription factors and co-activators via specific protein-protein interactions, which facilitate the assembly of distinct stereospecific transcription complexes on the ICAM-1 promoter. These transcription complexes presumably mediate the induction of ICAM-1 expression in different cell types and in response to different stimuli. In this review, we summarize our current understanding of ICAM-1 gene regulation with a particular emphasis on the transcription factors and signal transduction pathways critical for the cell type- and stimulus-specific activation of ICAM-1 gene transcription.

A mental health service after major trauma

Although 75-80% of people involved in a major trauma do not have any long-term psychological problems, many will experience significant psychological distress during the first four weeks. Most individuals will make a full recovery if provided with local, immediate and appropriate support. People who have experienced a major trauma should have access to support as soon as possible after the event until symptoms are resolved.

Proteoglycan (aggrecan)-induced arthritis in BALB/c mice is a Th1-type disease regulated by Th2 cytokines

In animal models of arthritis induced with Ags or infectious agents, disease severity correlates with a dominant Th1-type response characterized by a higher ratio of IFN-gamma to IL-4. Analysis of BALB/c mice revealed a genetic predisposition toward developing CD4+ Th2-type responses. The bias toward an IL-4-dominant response in BALB/c mice protects mice from severe Lyme-induced arthritis and spontaneous autoimmune disease. Since BALB/c mice immunized with proteoglycan develop severe arthritis, we were interested in testing whether arthritis is associated with a Th2-type response and thus is different from other arthritic models. BALB/c mice immunized with proteoglycan generated a higher ratio of IFN-gamma to IL-4 that peaks at the onset of arthritis. We investigated whether when Th1 cells were dominant, disease outcome could be modified with pharmacological amounts of Th2 cytokines. Treatment with IL-4 prevented disease and induced a switch from a Th1-type to a Th2-type response. Proinflammatory cytokine mRNA transcripts were reduced in joints of cytokine-treated mice. Th2 cytokine therapy at the time of maximum joint inflammation also suppressed symptoms of disease. Despite the predisposition of BALB/c mice to a Th2-type response, proteoglycan-induced arthritis is a Th1-type disease. The effectiveness of IL-4 treatment was particularly striking because in other models of arthritis, treatment in a similar manner with IL-4 was not sufficient to inhibit arthritis. The effective control of arthritis and the switch from a Th1 to Th2 response suggest that levels of endogenous IL-4 in BALB/c mice may increase their responsiveness to Th2 cytokine therapy.

Interleukin-10 enhances tumor necrosis factor-alpha activation of HIV-1 transcription in latently infected T cells

Interleukin-10 (IL-10) is elevated in HIV-1-infected individuals and has been implicated in disease progression. We previously reported that IL-10 cooperates with tumor necrosis factor-alpha (TNF-alpha) to activate HIV-1 expression synergistically in acutely infected monocyte-derived macrophages and the chronically infected U1 promonocytic cell line. To determine whether IL-10 also cooperates with TNF-alpha to activate latent HIV-I expression in lymphocytes, we examined the effects of IL-10 on proviral expression in the chronically infected T-cell line, ACH-2. Although IL-10 inhibited HIV-1 expression acting alone, in combination with suboptimal concentrations of TNF-alpha, IL-10 increased HIV-1 steady-state mRNA expression and p24 core antigen production in ACH-2 cells. Interestingly, IL-10 concentrations that synergistically induced virus also maximally stimulated endogenous TNF-alpha expression, suggesting that cell-derived TNF-alpha may contribute to cytokine synergy. Transfection studies in ACH-2 cells indicated that IL-10 combined with TNF-alpha to activate the HIV-1 long terminal repeat (LTR). IL-10 also cooperated with TNF-alpha to activate HIV-1 LTR in 1G5 cells, a Jurkat T-cell line stably transfected with an LTR-dependent luciferase reporter gene. Pyrrolidine dithiocarbamate, a potent transcriptional inhibitor of the viral LTR, abrogated the cytokine responses in both U1 and ACH-2 cells, suggesting a common TNF-alpha-mediated transcriptional mechanism in these cell types despite their different modes of provirus latency. Taken collectively, these data suggest that IL-10 enhances suboptimal TNF-alpha activation of HIV-1 transcription in chronically infected T-cells at least in part through induction of endogenous TNF-alpha expression.

Critical roles of glycosaminoglycan side chains of cartilage proteoglycan (aggrecan) in antigen recognition and presentation

Systemic immunization of BALB/c mice with proteoglycan (aggrecan) from fetal human cartilage induces progressive polyarthritis, an experimental disease similar to human rheumatoid arthritis. The development of the disease in this genetically susceptible murine strain is based on cross-reactive immune responses between the immunizing fetal human and mouse self-proteoglycans. One of the cross-reactive and arthritogenic T cell epitopes (92GR/QVRVNSA/IY) is localized in the G1 domain of human/murine proteoglycan. Susceptible BALB/c mice, however, develop arthritis only if both the chondroitin sulfate (CS) and keratan sulfate (KS) side chains of the arthritogenic human proteoglycans are removed. The function of these two glycosaminoglycan side chains is opposite. The presence of a KS side chain in adult proteoglycan inhibits the recognition of arthritogenic T cell epitopes, prevents the development of T cell response, and protects animals from autoimmune arthritis. In contrast, the depletion of the CS side chain generates clusters of CS stubs and provokes a strong B cell response. These carbohydrate-specific B cells are the most important proteoglycan APC. Taken together, proteoglycan-induced progressive polyarthritis is dictated by three major components: genetic background of the BALB/c strain, highly specific T cell response to epitope(s) masked by a KS chain in aging tissue, and the presence of proteoglycan (CS stub)-specific B cells required for sufficient Ag presentation.

Inhibition of JAK3 and STAT6 tyrosine phosphorylation by the immunosuppressive drug leflunomide leads to a block in IgG1 production

Leflunomide is an immunosuppressive drug capable of inhibiting T and B cell responses in vivo. A number of studies demonstrate that leflunomide functions both as a pyrimidine synthesis inhibitor and as a tyrosine kinase inhibitor. We previously reported that leflunomide inhibits LPS-stimulated B cell proliferation, cell cycle progression, and IgM secretion. This inhibition can be reversed by the addition of exogenous uridine, suggesting that leflunomide functions as a pyrimidine synthesis inhibitor in B cells. We report here that while the addition of uridine restored proliferation and IgM secretion to leflunomide-treated LPS-stimulated B cells, as determined by metabolic labeling and immunoprecipitation, it did not completely restore secretion of IgG Ab. We hypothesized that leflunomide inhibits LPS-induced IgG secretion by inhibiting tyrosine kinase activity required for isotype switch. We tested this hypothesis in a well-defined model of isotype switch, LPS plus IL-4 induction of IgG1. Leflunomide inhibited IgG1 secretion in this model in a dose-dependent manner. The signal transduction pathway utilized by IL-4 to induce IgG1 involves tyrosine phosphorylation of the IL-4 receptor, JAK1, JAK3, and STAT6 proteins induced by IL-4 binding to the IL-4R. Leflunomide diminished the tyrosine phosphorylation of JAK3 and STAT6 in the absence or presence of uridine. In gel mobility shift studies, STAT6 binding to the STAT6 DNA binding site in the IgG1 promoter decreased in the presence of leflunomide or leflunomide plus uridine. Taken together, these data suggest that leflunomide acts as a tyrosine kinase inhibitor to block IgG1 production.

In vitro and in vivo mechanisms of action of the antiproliferative and immunosuppressive agent, brequinar sodium

Intracellular pyrimidine nucleotides (PyN) can be synthesized de novo from glutamine, CO2, and ATP, or they can be salvaged from preformed pyrimidine nucleosides. The antiproliferative and immunosuppressive activities of brequinar sodium (BQR) are thought to be due to the inhibition of the activity of dihydroorotate dehydrogenase, which results in a suppression of de novo pyrimidine synthesis. Here we describe the effects of the pyrimidine nucleoSide, uridine, on the antiproliferative and immunosuppressive activities of BQR. In vitro reduction of PyN levels in Con A-stimulated T cells and inhibition of cell proliferation by low concentrations of BQR (< or =65 microM) are reversed by uridine. However, uridine is unable to reverse the effects of high concentrations of BQR (> or =65 microM). The ability of BQR to induce anemia in BALB/c mice is prevented by the coadministration of uridine. In contrast, the immunosuppressive activity of BQR is unaffected by similar doses of uridine. PyN levels in the bone marrow, but not in the spleen, are depressed in mice treated with BQR. These observations suggest that the induction of anemia by BQR is due to depletion of intracellular PyN in hemopoietic stem cells located in the bone marrow. They also suggest that the mechanism of immunosuppression by BQR may be only marginally dependent on depletion of intracellular PyN in lymphocytes located in the periphery. We report a novel activity of BQR: inhibition of tyrosine phosphorylation, and hypothesize that the immunosuppressive activity may be due, in part, to this unsuspected ability of BQR to inhibit tyrosine phosphorylation in lymphocytes.

In vivo mechanism by which leflunomide controls lymphoproliferative and autoimmune disease in MRL/MpJ-lpr/lpr mice

Two activities have been identified for the immunosuppressive metabolite of leflunomide, A77 1726: inhibition of dihydroorotate dehydrogenase (DHO-DHase), an enzyme involved in the biosynthesis of pyrimidine nucleotides (PyN); and inhibition of protein tyrosine kinases. The in vitro potency of A77 1726 as a DHO-DHase inhibitor is reported to be 10- to 500-fold greater than as a tyrosine kinase inhibitor. These observations suggested that the immunosuppressive efficacy of leflunomide in vivo is related to inhibition of DHO-DHase. However, observations that patients with disorders in the PyN synthetic pathway are not overtly immunodeficient militate against this hypothesis. We investigated the effects of leflunomide in vivo and report that amelioration of lymphoproliferative and autoimmune diseases in MRL/MpJ-lpr/lpr (lpr/lpr) mice by leflunomide is not accompanied by reduced PyN concentrations in lymph node cells. Our hypothesis that lymphocytes could salvage serum uridine to counter the effects of reduced PyN synthesis in vivo was supported by in vitro studies. Finally, we observed that amelioration of disease correlated with a reduction of tyrosine phosphorylated proteins in lymph node cells of lpr/lpr mice. These observations suggest that the primary mechanism by which leflunomide prevents autoimmune and lymphoproliferative diseases in lpr/lpr mice is not depletion of PyN, but correlates with reduced tyrosine phosphorylation concentrations in lymph node cells.

In vivo mechanism by which leflunomide controls lymphoproliferative and autoimmune disease in MRL/MpJ-lpr/lpr mice

Two activities have been identified for the immunosuppressive metabolite of leflunomide, A77 1726: inhibition of dihydroorotate dehydrogenase (DHO-DHase), an enzyme involved in the biosynthesis of pyrimidine nucleotides (PyN); and inhibition of protein tyrosine kinases. The in vitro potency of A77 1726 as a DHO-DHase inhibitor is reported to be 10- to 500-fold greater than as a tyrosine kinase inhibitor. These observations suggested that the immunosuppressive efficacy of leflunomide in vivo is related to inhibition of DHO-DHase. However, observations that patients with disorders in the PyN synthetic pathway are not overtly immunodeficient militate against this hypothesis. We investigated the effects of leflunomide in vivo and report that amelioration of lymphoproliferative and autoimmune diseases in MRL/MpJ-lpr/lpr (lpr/lpr) mice by leflunomide is not accompanied by reduced PyN concentrations in lymph node cells. Our hypothesis that lymphocytes could salvage serum uridine to counter the effects of reduced PyN synthesis in vivo was supported by in vitro studies. Finally, we observed that amelioration of disease correlated with a reduction of tyrosine phosphorylated proteins in lymph node cells of lpr/lpr mice. These observations suggest that the primary mechanism by which leflunomide prevents autoimmune and lymphoproliferative diseases in lpr/lpr mice is not depletion of PyN, but correlates with reduced tyrosine phosphorylation concentrations in lymph node cells.

The immunosuppressive metabolite of leflunomide, A77 1726, affects murine T cells through two biochemical mechanisms

The immunosuppressive metabolite of leflunomide, A77 1726, inhibits the enzymatic activity of protein tyrosine kinases and of dihydro-orotic acid dehydrogenase, an enzyme involved in pyrimidine biosynthesis. Here murine CTLL cell lines were studied to determine which of the biochemical targets of A77 1726 was responsible for the observed inhibition of proliferation and cytotoxic activity. At low concentrations of A77 1726, pyrimidine biosynthesis is the target, since inhibition of proliferation correlates with a reduction in pyrimidine NTP levels and is reversed by uridine. At higher concentrations of A77 1726, uridine no longer reverses the inhibition of proliferation even though pyrimidine NTP levels are restored. This second mechanism for inhibiting proliferation is probably inhibition of protein tyrosine kinases, since these higher concentrations of A77 1726 inhibit IL-2-induced tyrosine phosphorylation of Jak1 and Jak3, the protein tyrosine kinases initiating signaling by the IL-2R. Tyrosine phosphorylation of the beta-chain of the IL-2R, which is required for IL-2-driven proliferation, is also inhibited by A77 1726. Cytotoxicity of a CTLL line that overexpresses the Lck protein tyrosine kinase is inhibited by A77 1726; this inhibition is not affected by uridine, but does correlate with inhibition of an Lck in vitro kinase reaction. These studies establish that inhibition of pyrimidine biosynthesis and that of protein tyrosine kinase both contribute to the effects of A77 1726 on CTLL cell lines.

The immunosuppressive metabolite of leflunomide, A77 1726, affects murine T cells through two biochemical mechanisms

The immunosuppressive metabolite of leflunomide, A77 1726, inhibits the enzymatic activity of protein tyrosine kinases and of dihydro-orotic acid dehydrogenase, an enzyme involved in pyrimidine biosynthesis. Here murine CTLL cell lines were studied to determine which of the biochemical targets of A77 1726 was responsible for the observed inhibition of proliferation and cytotoxic activity. At low concentrations of A77 1726, pyrimidine biosynthesis is the target, since inhibition of proliferation correlates with a reduction in pyrimidine NTP levels and is reversed by uridine. At higher concentrations of A77 1726, uridine no longer reverses the inhibition of proliferation even though pyrimidine NTP levels are restored. This second mechanism for inhibiting proliferation is probably inhibition of protein tyrosine kinases, since these higher concentrations of A77 1726 inhibit IL-2-induced tyrosine phosphorylation of Jak1 and Jak3, the protein tyrosine kinases initiating signaling by the IL-2R. Tyrosine phosphorylation of the beta-chain of the IL-2R, which is required for IL-2-driven proliferation, is also inhibited by A77 1726. Cytotoxicity of a CTLL line that overexpresses the Lck protein tyrosine kinase is inhibited by A77 1726; this inhibition is not affected by uridine, but does correlate with inhibition of an Lck in vitro kinase reaction. These studies establish that inhibition of pyrimidine biosynthesis and that of protein tyrosine kinase both contribute to the effects of A77 1726 on CTLL cell lines.

Interleukin-10 inhibits interferon-gamma-induced intercellular adhesion molecule-1 gene transcription in human monocytes

Interleukin-10 (IL-10) is a potent monocyte regulatory cytokine that inhibits gene expression of proinflammatory mediators. In this study, we investigated the mechanism by which IL-10 downregulates expression of intercellular adhesion molecule-1 (ICAM-1) on the cell surface of normal human monocytes activated with interferon-gamma (IFN-gamma). IL-10 inhibition of IFN-gamma-induced ICAM-1 expression was apparent as early as 3 hours and was blocked by an anti-IL-10 antibody but not by an isotype-matched control antibody. Northern blot analysis showed that IL-10 reduced the accumulation of ICAM-1 mRNA in IFN-gamma-stimulated monocytes. IL-10 inhibition of ICAM-1 steady-state mRNA was detected at 3 hours and remained at 24 hours. Nuclear run-on transcription assays showed that IL-10 inhibited the rate of IFN-gamma-induced transcription of the ICAM-1 gene, and mRNA stability studies showed that IL-10 did not alter the half-life of IFN-gamma-induced ICAM-1 message. Thus, IL-10 inhibits IFN-gamma-induced ICAM-1 expression in monocytes primarily at the level of gene transcription. Activation of IFN-gamma-responsive genes requires tyrosine phosphorylation of the transcriptional factor STAT-1alpha (signal transducer and activator of transcription-1alpha). However, IL-10 did not affect IFN-gamma-induced tyrosine phosphorylation of STAT-1alpha or alter STAT-1alpha binding to the IFN-gamma response element (IRE) in the ICAM-1 promoter. Instead, IL-10 prevented IFN-gamma-induced binding activity at the NF-kappaB site of the tumor necrosis factor alpha (TNF-alpha)-responsive NF-kappaB/C-EBP composite element in the ICAM-1 promoter. These data indicate that IL-10 inhibits IFN-gamma-induced transcription of the ICAM-1 gene by a regulatory mechanism that may involve NF-kappaB.

The immunodominant region of Staphylococcal nuclease is represented by multiple peptide sequences

Several published reports have lead to the characterization of naturally processed peptides that are presented in association with either class I or class II MHC molecules. Most peptides isolated from class II molecules are heterogeneous in length and exhibit ragged amino and carboxy termini. An intriguing finding was that one region of a molecule was often represented by many distinct peptides, rather than by a single dominant peptide species. Each of the peptides representing this dominant region exhibited a common core of amino acids, suggesting that this core may play a significant role in the binding of the peptide to class II and the recognition by peptide-specific T cells. Work from our laboratory has focused on the mechanisms involved in the immunodominance of antigenic determinants using the bacterial antigen Staphylococcal nuclease (Nase) as a model. Using truncated synthetic peptides, we have identified the immunodominant determinant of Nase to be located within the region 81-100 with a minimal antigenic core of 91-100 as determined. Addition of five residues to the carboxy terminus of this peptide had a negative effect on T cell recognition of this region. The present studies were undertaken in an effort to determine the sequence of the naturally processed immunodominant Nase determinant(s) presented in association with I-Ek class II. Our results indicate that the dominant region of the Nase molecule is represented by at least four distinct peptide species that are predicted to lie between residues 86 and 106 with a common core sequence of 91-96. These results indicate that the negative effects of flanking regions are dependent upon length and amino acid composition, and thus the use of truncated peptides to study minimal antigenic determinants may be misleading.