Arginine deficiency leads to impaired cofilin dephosphorylation in activated human T lymphocytes

The amino acid arginine is fundamentally involved in the regulation of the immune response during infection, inflammatory diseases and tumor growth. Arginine deficiency (e.g. due to the myeloid cell enzyme arginase) inhibits proliferation and effector functions of activated T lymphocytes. Here, we studied intracellular mechanisms mediating this suppression of human T lymphocytes. Our proteomic analysis revealed an impaired dephosphorylation of the actin-binding protein cofilin upon T-cell activation in the absence of arginine. We show that this correlates with alteration of actin polymerization and impaired accumulation of CD2 and CD3 in the evolving immunological synapse in T cell-antigen presenting cells conjugates. In contrast, T-cell cytokine synthesis is differentially regulated in human T lymphocytes in the absence of arginine. While the production of certain cytokines (e.g. IFN-γ) is severely reduced, T lymphocytes produce other cytokines (e.g. IL-2) independent of extracellular arginine. MEK and PI3K activity are reciprocally regulated in association with impaired cofilin dephosphorylation. Finally, we show that impaired cofilin dephosphorylation is also detectable in human T cells activated in a granulocyte-dominated purulent micromilieu due to arginase-mediated arginine depletion. Our novel results identify cofilin as a potential regulator of human T-cell activation under conditions of inflammatory arginine deficiency.     

Lung infection caused by Pseudomonas aeruginosa in a CD26/DPP4 deficient F344 rat model

Background

Pseudomonas aeruginosa (PA) is the most important opportunistic pathogen in causing nosocomial infections and, furthermore, poses a permanent threat for severe chronic infections in patients with cystic fibrosis or COPD. The transmembrane protein CD26 with dipeptidyl peptidase-4 (DPP4) activity shows an increased expression in inflamed tissue. We tested whether CD26/DPP4 deficiency leads to reduced inflammation and decreased structural damage when infected with PA.

Methods

CD26/DPP4⁺ and CD26/DPP4^? rats were instilled intratracheally with NaCl (controls) or with PA. Six hours later, bacterial distribution was detected with the in vivo imaging system 200 (IVIS). Lungs were then processed for molecular biology, light and electron microscopy and analyzed qualitatively, quantitatively and stereologically. Bacterial numbers were determined in homogenized lungs.

Results

Compared to saline treated controls, in both infected groups (1) the acinar airspace was significantly increased, (2) the volume density of the alveolar epithelium was significantly decreased, (3) the septal thickness was significantly reduced, (4) more than 40% of the alveolar epithelial surface was damaged, and up to 36% of the epithelial surface was covered with edema. In infected CD26^? rats, the increase in lung weight was significantly less pronounced, the portion of edematous alveolar airspace was significantly lower and the part of edema interspersed with PA was decreased significantly.

Conclusions

CD26/DPP4 deficiency resulted in reduced pulmonary edema under sublethal PA infection, implicating a role for CD26 in infection progression. The partly pronounced structural damage may mask further possible influences of CD26 on the inflammatory response.

     

Arginase: an emerging key player in the mammalian immune system

The enzyme arginase metabolizes L-arginine to L-ornithine and urea. Besides its fundamental role in the hepatic urea cycle, arginase is also expressed the immune system of mice and man. While significant interspecies differences exist regarding expression, subcellular localization and regulation of immune cell arginase, associated pathways of immunopathology are comparable between species. Arginase is induced in murine myeloid cells mainly by Th2 cytokines and inflammatory agents and participates in a variety of inflammatory diseases by down-regulation of nitric oxide synthesis, induction of fibrosis and tissue regeneration. In humans, arginase I is constitutively expressed in polymorphonuclear neutrophils and is liberated during inflammation. Myeloid cell arginase-mediated L-arginine depletion profoundly suppresses T cell immune responses and this has emerged as a fundamental mechanism of inflammation-associated immunosuppression. Pharmacological interference with L-arginine metabolism is a novel promising strategy in the treatment of cancer, autoimmunity or unwanted immune deviation.     

Induced arginine transport via cationic amino acid transporter‐1 is necessary for human T‐cell proliferation

Availability of the semiessential amino acid arginine is fundamental for the efficient function of human T lymphocytes. Tumor‐associated arginine deprivation, mainly induced by myeloid‐derived suppressor cells, is a central mechanism of tumor immune escape from T‐cell‐mediated antitumor immune responses. We thus assumed that transmembranous transport of arginine must be crucial for T‐cell function and studied which transporters are responsible for arginine influx into primary human T lymphocytes. Here, we show that activation via CD3 and CD28 induces arginine transport into primary human T cells. Both naïve and memory CD4⁺ T cells as well as CD8⁺ T cells specifically upregulated the human cationic amino acid transporter‐1 (hCAT‐1), with an enhanced and persistent expression under arginine starvation. When hCAT‐1 induction was suppressed via siRNA transfection, arginine uptake, and cellular proliferation were impaired. In summary, our results demonstrate that hCAT‐1 is a key component of efficient T‐cell activation and a novel potential target structure to modulate adaptive immune responses in tumor immunity or inflammation.     

Influence of platelet activating factor and a nonmetabolizable analogue on superoxide production by bone marrow derived macrophages

Serum-free cultured macrophages could be stimulated for lucigenin-dependent chemiluminescence by platelet activating factor (PAF) and phorbol myristate acetate (PMA). Stimulation with PMA resulted in a desensitization against PAF, whereas prestimulation with PAF had no influence on a following response caused by PMA. The PAF analogue, 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (Et-18-OCH3), did not induce chemiluminescence by itself and desensitized the cells against PAF, like substimulating concentrations of PAF. PAF and PMA responsiveness was rapidly modulated in a similar manner during adherence of the cells to polystyrene tubes. At higher concentrations, Et-18-OCH3 as well as lysophosphatidylcholines potentiated PMA-induced chemiluminescence. The PAF analogue was most effective. Although PMA-induced chemiluminescence was stimulated at least 5-fold by Et-18-OCH3, this compound increased the PMA-induced activation of protein kinase C only 1.39-fold. The priming effect of Et-18-OCH3 was not reduced in the absence of extracellular Ca2+ and after cell membrane depolarisation.     

Subcutaneous versus intravenous bortezomib in two different induction therapies for newly diagnosed multiple myeloma: an interim analysis from the prospective GMMG-MM5 trial

We investigated the impact of subcutaneous versus intravenous bortezomib in the MM5 trial of the German-Speaking Myeloma Multicenter Group which compared bortezomib, doxorubicin, and dexamethasone with bortezomib, cyclophosphamide, and dexamethasone induction therapy in newly diagnosed multiple myeloma. Based on data from relapsed myeloma, the route of administration for bortezomib was changed from intravenous to subcutaneous after 314 of 604 patients had been enrolled. We analyzed 598 patients who received at least one dose of trial medication. Adverse events were reported more frequently in patients treated with intravenous bortezomib (intravenous=65%; subcutaneous=56%, P=0.02). Rates of grade 2 or more peripheral neuropathy were higher in patients treated with intravenous bortezomib during the third cycle (intravenous=8%; subcutaneous=2%, P=0.001). Overall response rates were similar in patients treated intravenously or subcutaneously. The presence of International Staging System stage III disease, renal impairment or adverse cytogenetic abnormalities did not have a negative impact on overall response rates in either group. To our knowledge this is the largest study to present data comparing subcutaneous with intravenous bortezomib in newly diagnosed myeloma. We show better tolerance and similar overall response rates for subcutaneous compared to intravenous bortezomib. The clinical trial is registered at eudract.ema.europa.eu as n. 2010-019173-16.     

Pretreatment and process predictors of nonresponse at different stages of inpatient psychotherapy

Objective: Up to 50% of psychotherapeutic treatments end without significant improvements. While there is first evidence about predictors of nonresponse in outpatient psychotherapy, there are currently no studies investigating predictors of nonresponse in inpatient settings. Based upon a previous systematic literature review, we analyzed the predictive value of initial patient characteristics on nonresponse in symptom distress. Methods: Treatment episodes from 546 patients, treated for at least 4 weeks, were assessed under naturalistic conditions. Nonresponse status (i.e., lack of a reliable improvement in symptom distress) was investigated at four different time points: at week 4, at discharge, and at a two follow-ups (3 and 12 months after discharge). Hierarchical binary logistic regression models were used to predict nonresponse. Sociodemographic data, clinical variables, and the previous response status were entered subsequently in the model. Results: A moderate or functional level of initial symptom distress, a comorbid personality disorder, and previous nonresponse were the most consistent predictors of nonresponse. Conclusions: The results point to the importance of early outcome assessment and suggest the implementation of more symptom-specific treatments.