Marcus D. Säemann

Suppression of T cell signaling by polyunsaturated fatty acids: Selectivity in inhibition of mitogen-activated protein kinase and nuclear factor activation

Polyunsaturated fatty acids (PUFAs) are known to suppress inflammatory and autoimmune responses and, therefore, clinical applications of PUFAs as immunomodulatory substances are extensively studied. PUFAs are known to inhibit T cell responses, but with respect to TCR/CD3-mediated signal transduction only a block in CD3-induced phospholipase Cγ1/calcium signaling has been shown so far. In this study, we investigated PUFA-mediated changes in downstream T cell signal transduction. We show that among the mitogen-activated protein kinase families activation of c-Jun NH2-terminal kinase, but not phosphorylation of extracellular signal-regulated kinase-1/-2 or p38 is inhibited. CD3/CD28-induced activity of NF-AT was markedly reduced by PUFA treatment, while activation of other nuclear receptors (AP-1 and NF-κB) remained unaltered. Furthermore, IL-2 promoter activity, IL-2 and IL-13 mRNA levels, IL-2 secretion, and IL-2R α-chain expression were significantly diminished by PUFA treatment, whereas the expression of IFN-γ, IL-4, IL-10, and CD69 remained essentially unaffected by PUFAs. In conclusion, PUFA treatment of T cells inhibits selectively c-Jun NH2-terminal kinase and NF-AT activation, resulting in diminished production of IL-2 and IL-13.

Selective Inhibition of T Cell Activation Via CD147 Through Novel Modulation of Lipid Rafts

The plasma membrane is compartmentalized into microdomains and the association/dissociation of receptors and signaling molecules with/from these membrane domains is a major principle for regulation of signal transduction. By following the reorganization of microdomains on living cells and performing biochemical studies, we show that Ab targeting of the T cell activation-associated Ag CD147 prevents TCR stimulation-dependent reorganization and clustering of microdomains. Triggering CD147 induces a displacement of the GPI-anchored coreceptors CD48 and CD59 from microdomains in human T lymphocytes. This perturbation of microdomains is accompanied by a selective inhibition of TCR-mediated T cell proliferation. The CD147-inhibited cells secret normal levels of IL-2 but acquire reduced amounts of the IL-2 receptor α-chain CD25. These results indicate that negative regulating signals can modulate microdomains and suggest a general mechanism for inhibition of receptor signaling.

Induction of Hyporesponsiveness and Impaired T Lymphocyte Activation by the CD31 Receptor:Ligand Pathway in T Cells

CD31 is a member of the Ig superfamily expressed on various cell types of the vasculature, including a certain subpopulation of T lymphocytes. Previous reports suggest that interaction of CD31 with its heterophilic ligand on T cells (T cell CD31 ligand) plays a regulatory role in T lymphocyte activation. Here we demonstrate that a soluble rCD31-receptorglobulin (CD31Rg) specifically down-regulated the proliferation of human peripheral blood CD31− T lymphocytes stimulated via CD3 and CD28 mAbs. Notably, engagement of the T cell CD31 ligand by CD31Rg during primary stimulation also induced a prolonged unresponsive state in T cells. Retroviral transduction of CD31 into CD31− Th clones resulted in a significant inhibition of their proliferative capacity. When cocultured with purified CD31− T lymphocytes, irradiated CD31-transduced Th clones counterregulated the CD3/CD28-mediated activation of these cells. Furthermore, primary stimulation in the presence of CD31-transduced Th clones induced a comparable state of hyporesponsiveness in the T cell responders as the soluble CD31Rg. Thus, by counterregulating the activation of cognate T lymphocytes, CD31-expressing T cells might contribute to the establishment and maintenance of peripheral tolerance.

C4d deposits in renal allografts are associated with inferior graft outcome

HERE IS INCREASING evidence for a pathogenetic role of humoral immunity in acute kidney allograft rejection. The complement split product C4d represents an attractive marker for antibody-mediated graft injury. Capillary C4d deposits in kidney allograft biopsies were found to be associated with the appearance of posttransplant anti-donor antibodies 1 and with poor graft outcome. 2 The objective of this retrospective study was to analyze the incidence and clinical relevance of C4d deposition in biopsies not selected for a specific type of allograft dysfunction with special emphasis on correlations between C4d staining patterns and histopathologic features of acute rejection.

Hyporesponsiveness in alloreactive T-cells by NF-kappaB inhibitor-treated dendritic cells: resistance to calcineurin inhibition.

Dendritic cells (DC) are the most potent antigen‐presenting cells (APC) initiating primary T‐cell responses. Beyond this immunostimulatory function, certain DC subsets have been shown to induce T‐cell tolerance in vitro and in vivo. In this study, immature monocyte‐derived DC were activated in the presence of the NF‐κB inhibitor pyrrolidine dithiocarbamate (PDTC) and characterized with regard to phenotype, cytokine production and allostimulatory potential. Furthermore, the functional consequences of calcineurin inhibition were studied in T cells exposed to PDTC‐modulated DC. We demonstrate that PDTC treatment of DC leads to an arrest in maturation as reflected by down‐regulated major histocompatibility complex (MHC) antigens and costimulatory molecules, suppressed immunostimulatory cytokines and an impaired capability to support allogeneic T‐cell activation. Allogeneic T cells challenged with PDTC‐treated DC are refractory upon restimulation with alloantigens but not to polyclonal stimuli. Interestingly, the successful establishment of alloantigenic hyporesponsiveness is not prevented by concomitant calcineurin inhibition in vitro as well as in T cells from patients under cyclosporine A (CsA)‐based immunosuppression ex vivo. These data may have important implications for the design of clinical regimens for the establishment of antidonor hyporeactivity in organ transplantation using in vitro‐modulated DC.

Stable prodrugs of n-butyric acid: suppression of T cell alloresponses in vitro and prolongation of heart allograft survival in a fully allogeneic rat strain combination.

Abstract n-Butyric acid has previously been shown in vitro to suppress T cell alloresponses and beyond that to induce a state of alloantigen-specific hyporesponsiveness suggesting a potential relevance for suppressing alloresponses also in vivo. The clinical use of butyrate salt derivatives, however, is limited by an extremely short half-life due to rapid metabolism. This prompted us to investigate the effect of butyric acid derivatives with prolonged residence time in vivo on T cell alloresponses in vitro and further to explore the immuno-suppressive capacity of esterified n-butyric acid in vivo. First, the effect of three butyric acid esters, i.e. glucose pentabutyrate, diacetone glucose butyrate and tributyrin on T cell proliferation in a human mixed lymphocyte culture (MLC) was evaluated. All three derivatives were found to inhibit T cell alloresponses in a concentration-dependent manner. Based on the ED50 values, glucose pentabutyrate was found to be most effective in inhibiting T cell alloreactivity in vitro (11 μM), followed by diacetone glucose butyrate (122 μM), tributyrin (146 μM) and sodium butyrate (539 μM). Because of its favourable in vitro properties, glucose pentabutyrate was chosen for in vivo experiments. To test the effect of this compound on allograft survival in vivo, in the second part of this study, heterotopic heart transplants were performed in a high responder fully allogeneic rat strain combination (Brown Norway to Lewis strain rats). We found that intraperitoneal (i.p.) injection of glucose pentabutyrate at 500 mg/kg/day (day 0 and daily up to 12 days post-transplant) induced a significant prolongation of allograft survival as compared to animals treated with vehicle (glycerol formal, i.p.) alone (14.1 ± 6.3 versus 9.6 ± 3.2 days, p = 0.036), whereby at lower dosage (100 mg/kg/day) no such effect was observed (10.2 ± 2.1 days, p = 0.21). Our findings suggest that stable prodrugs of n-butyric acid might have potential clinical relevance for inhibiting alloresponses in vivo.

Thiazolidinediones in the treatment of patients with Post-Transplant-Hyperglycemia or new-onset diabetes mellitus after renal transplantation (NODAT) - A new therapeutic option?

Metabolic derangements including new-onset diabetes after transplantation (NODAT) or transplant-associated hyperglycemia (TAH) are common after solid organ transplantation. In the fi st year after kidney transplantation the incidence of diabetes is increased by twoto three-fold and disturbed glucose metabolism is observed in the vast majority of patients in the fi st week after transplantation [1, 2]. While advances in the quality and quantity of immunosuppressive drugs have been made over the recent decades, no specifi c therapeutic regimens have been developed for the treatment of TAH/NODAT. Diabetes after transplantation constitutes a major risk factor for cardiovascular disease and is strongly associated not only with excessive morbidity and mortality but also with inferior graft survival [3]. While graft survival rates have steadily improved over time mainly through advancements of immunosuppressive therapy, further progress in the fi elds of solid organ transplantation can only be expected, if modifi able risk factors can be positively infl uenced. As the majority of registry data indicate that TAH/NODAT is a relevant and common condition in a signifi cant proportion of transplant patients, it seems prudent to suggest that prevention and/or adequate treatment of this metabolic disorder holds the promise to further improve the success of transplantation as both graft and patient survival might be positively aff ected by such measures. Th e selection of antihyperglycemic agents can be based on their eff ectiveness in lowering glucose, extraglycemic eff ects that may reduce long-term complications, safety profi les, tolerability, ease of use, and expense. Unfortunately, even in the fi eld of type 2 diabetes the lack of clinical trials that directly compare diff erent treatment regimens makes it diffi cult to recommend one class of drugs over another [4]. Because of the increased risks of side-eff ects including hypoglycemia secondary to drug accumulation and lactate acidosis in the case of metformin most glucose lowering drugs are contraindicated in patients with impaired renal function. Th iazolidinediones (TZDs or glitazones) belong to the few orally available drugs that are approved for patients with glomerular fi ltration rates below 30 ml/min. Th erefore, the current perspective is intended to review the current data on this class of antihyperglycemic agents and to discuss the potential roles of TZDs in the treatment of TAH/NODAT after renal transplantation.

Induction of alloantigen-specific hyporesponsiveness in vitro by n-butyrate: antagonistic effect of cyclosporin A.

Abstract  The short‐chain fatty acid n‐butyrate has recently been shown in vitro to specifically downregulate Tcell reactivity to nominal antigen or to alloantigen, which possibly results from inhibition of cell cycle progression in early G1 phase during antigen contact. In the present study, we investigated the effect of cyclosporin A (CyA) on the modulation of alloreactivity in human mixed lymphocyte culture (MLC) by n‐butyrate. Whereas in primary culture, CyA additively enhanced inhibition of DNA synthesis by n‐butyrate, the effect of this agent on secondary Tcell reactivity was clearly antagonized by CyA. Thus, specific downregulation of prolifer‐ative responsiveness to restimula‐tion with antigen from the original donor, observed in cultures pre‐treated with n‐butyrate alone, was at least partially prevented by the addition of CyA to the primary culture. Our in vitro finding indicates that specific downregulation of Tcell alloreactivity by n‐butyrate might depend on a calcium‐dependent Tcell receptor (TCR)‐medi‐ated signal sensitive to the immuno‐suppressive action of CyA.

Diabetische Nephropathie – Update 2012

SummaryDiabetes mellitus is the leading single cause for renal replacement therapy. Its development and progression, however, can be ameliorated by adequate therapy. The present article represents the recommendations of the Austrian Diabetes Association and the Austrian Society for Nephrology for the prevention and treatment of diabetic nephropathy.ZusammenfassungDiabetische Nephropathie ist die führende Ursache der Nierenersatztherapie und die häufigste Nierenkrankheit geworden. Die Entwicklung und das Fortschreiten kann durch optimierte Therapie beeinflusst werden. Im vorliegenden Artikel werden die gemeinsamen Empfehlungen der Österreichischen Diabetesgesellschaft und der Österreichischen Gesellschaft für Nephrologie dargestellt.

[Diabetic nephropathy--update 2012].

SummaryDiabetes mellitus is the leading single cause for renal replacement therapy. Its development and progression, however, can be ameliorated by adequate therapy. The present article represents the recommendations of the Austrian Diabetes Association and the Austrian Society for Nephrology for the prevention and treatment of diabetic nephropathy.ZusammenfassungDiabetische Nephropathie ist die führende Ursache der Nierenersatztherapie und die häufigste Nierenkrankheit geworden. Die Entwicklung und das Fortschreiten kann durch optimierte Therapie beeinflusst werden. Im vorliegenden Artikel werden die gemeinsamen Empfehlungen der Österreichischen Diabetesgesellschaft und der Österreichischen Gesellschaft für Nephrologie dargestellt.