Determination of activation energy distributions for chemisorption of oxygen on carbon: an improved approach

The present paper proposes an approach to obtaining the activation energy distribution for chemisorption of oxygen onto carbon surfaces, while simultaneously allowing for the activation energy dependence of the pre-exponential factor of the rate constant. Prior studies in this area have considered this factor to be uniform, thereby biasing estimated distributions. The results show that the derived activation energy distribution is not sensitive to the chemisorption mechanism because of the step function like property of the coverage. The activation energy distribution is essentially uniform for some carbons, and has two or possibly more discrete stages, suggestive of at least two types of sites, each with its own uniform distribution. The pre-exponential factors of the reactions are determined directly from the experimental data, and are found not to be constant as assumed in earlier work, but correlated with the activation energy. The latter results empirically follow an exponential function, supporting some earlier statistical and experimental work. The activation energy distribution obtained in the present paper permits improved correlation of chemisorption data in comparison to earlier studies. (C) 2000 Elsevier Science Ltd. All rights reserved.

CD40 ligation conditions dendritic cell antigen-presenting function through sustained activation of NF-kappa B

An understanding of the biochemical control of dendritic cell (DC) differentiation/activation is essential for improving T cell immunity by various immunotherapeutic approaches, including DC immunization. Ligation of CD40 enhances DC function, including conditioning for CTL priming. NF-kappaB, and particularly RelB, is an essential control pathway for myeloid DC differentiation. Furthermore, RelB regulates B cell Ag-presenting function. We hypothesized that CD40 ligand (CD40L) and TNF-alpha, which differ in their capacity to condition DC, would also differ in their capacity to activate NF-kappaB. DC differentiated for 2 days from monocytes in the presence of GM-CSF and IL-4 were used as a model, as NF-kappaB activity was constitutively low. The capacity of DC to activate T cells following CD40L treatment was enhanced compared with TNF-alpha treatment, and this was NF-kappaB dependent. Whereas RelB/p50 translocation induced by TNF-alpha was attenuated after 6 h, RelB/p50 nuclear translocation induced by CD40L was sustained for at least 24 h. The mechanism of this difference related to enhanced degradation of IkappaBalpha following CD40L stimulation. However, NF-kappaB activation induced by TNF-alpha could be sustained by blocking autocrine IL-10. These data indicate that NF-kappaB activation is essential for T cell activation by DC, and that this function is enhanced if DC NF-kappaB activation is prolonged. Because IL-10 moderates DC NF-kappaB activation by TNF-alpha, sustained NF-kappaB activation can be achieved by blocking IL-10 in the presence of stimuli that induce TNF-alpha.

p53 Suppresses c-Myb-induced trans-Activation and Transformation by Recruiting the Corepressor mSin3A

p53 is known to repress transcription of a number of genes, but the mechanism of p53 recruitment to these target genes is unknown. The c-myb proto-oncogene product (c-Myb) positively regulates proliferation of immature hematopoietic cells, whereas p53 blocks cell cycle progression. Here, we demonstrate that p53 inhibits c-Myb-induced transcription and transformation by directly binding to c-Myb. The ability of c-Myb to maintain the undifferentiated state of M1 cells was also suppressed by p53. p53 did not affect the ability of c-Myb to bind to DNA but formed a ternary complex with the corepressor mSin3A and c-Myb. Thus, p53 antagonizes c-Myb by recruiting mSin3A to down-regulate specific Myb target genes.

Activation of NK cell cytotoxicity

Natural killer (NK) cells are innate effector lymphocytes necessary for defence against stressed, microbe-infected, or malignant cells. NK cells kill target cells by either of two major mechanisms that require direct contact between NK cells and target cells. In the first pathway, cytoplasmic granule toxins, predominantly a membrane-disrupting protein known as perforin, and a family of structurally related serine C, proteases (granzymes) with various substrate specificities, are secreted by exocytosis and together induce apoptosis of the target cell. The granule-exocytosis pathway potently activates cell-death mechanisms that operate through the activation of apoptotic cysteine proteases (caspases), but can also cause cell death in the absence of activated caspases. The second pathway involves the engagement of death receptors (e.g. Fas/CD95) on target cells by their cognate ligands (e.g. FasL on NK cells, resulting in classical caspase-dependent apoptosis. The comparative role of these pathways in the pathophysiology of many diseases is being dissected by analyses of gene-targeted mice that lack these molecules, and humans who have genetic mutations affecting these pathways. We are also now learning that the effector function of NK cells is controlled by interactions involving specific NK cell receptors and their cognate ligands, either on target cells, or other cells of the immune system. This review will discuss the functional importance of NK cell cytotoxicity and the receptor/ligand interactions that control these processes. (C) 2004 Elsevier Ltd. All rights reserved.

Activation of visual areas during the attentional blink

When two targets are presented in rapid succession, identification of the first target is nearly perfect while identification of the second is severely impaired at shorter inter-target lags, and then gradually improves as lag increases. This second-target deficit is known as the attentional blink (AB). Numerous studies have implicated competition for access to higher-order processing mechanisms as the primary cause of the AB. However, relatively few studies have directly examined how the AB modulates activity in specific brain areas. To this end, we used fMRI to measure activation in the occipital and parietal cortices (including V1, V2, and area MT) during an AB task. Participants were presented with an initial target of oriented line segments embedded in a central stream of letter distractors. This central target was followed 100 - 700 ms later by a peripheral ‘X’ presented at one of four locations along with three ‘+’ distractors. All peripheral items were presented in the centre of a small field of moving dots. Participants made non-speeded judgments about line-segment orientation and the location of the second target at the end of a trial and to ignore all other stimuli. The results showed a robust AB characterised by a linear improvement in second-target accuracy as lag increased. This pattern of behavioural results was mirrored by changes in activation patterns across a number of visual areas indicating robust modulation of brain activity by the AB.

Midazolam reduces the selective activation of the rhinal cortex by contextual fear stimuli

Independent brain circuits appear to underlie different forms of conditioned fear, depending on the type of conditioning used, such as a context or explicit cue paired with footshocks. Several clinical reports have associated damage to the medial temporal lobe (MTL) with retrograde amnesia. Although a number of studies have elucidated the neural circuits underlying conditioned fear, the involvement of MTL components in the aversive conditioning paradigm is still unclear. To address this issue, we assessed freezing responses and Fos protein expression in subregions of the rhinal cortex and ventral hippocampus of rats following exposure to a context, light or tone previously paired with footshock (Experiment 1). A comparable degree of freezing was observed in the three types of conditioned fear, but with distinct patterns of Fos distribution. The groups exposed to cued fear conditioning did not show changes in Fos expression, whereas the group subjected to contextual fear conditioning showed selective activation of the ectorhinal (Ect), perirhinal (Per), and entorhinal (Ent) cortices, with no changes in the ventral hippocampus. We then examined the effects of the benzodiazepine midazolam injected bilaterally into these three rhinal subregions in the expression of contextual fear conditioning (Experiment 2). Midazolam administration into the Ect, Per, and Ent reduced freezing responses. These findings suggest that contextual and explicit stimuli endowed with aversive properties through conditioning recruit distinct brain areas, and the rhinal cortex appears to be critical for storing context-, but not explicit cue-footshock, associations. (C) 2010 Elsevier B.V. All rights reserved.

Fronto-parietal activation in attention-deficit hyperactivity disorder, combined type: functional magnetic resonance imaging study

A functional magnetic resonance imaging mental rotation paradigm was used to investigate the patterns of activation of fronto-parietal brain areas in male adolescents with attention-deficit hyperactivity disorder, combined type (ADHD-CT) compared with age-, gender-, handedness- and performance IQ-matched healthy controls. The ADHD-CT group had (a) decreased activation of the 'action-attentional' system (including Brodmann's areas (BA) 46, 39,40) and the superior parietal (BA7) and middle frontal (BA10) areas and (b) increased activation of the posterior midline attentional system. These different neuroactivation patterns indicate widespread frontal, striatal and parietal dysfunction in adolescents with ADHD-CT. Declaration of interest None.

Defective NF-kappaB Activation in Response to LPS in Type 1 Diabetes Dendritic Cells

Dendritic cells (DC) are the potent antigen presenting cells which modulate T cell responses to self or non-self antigens. DC play a significant role in the pathogenesis of autoimmune diseases, inflammation and infection, but also in the maintenance of tolerance. NF-kappaB, particularly RelB is a crucial pathway for myeloid DC differentiation and functional maturation. While the current paradigm is that mature, nuclear RelB+ DC prime T cells for immunity/autoimmunity and immature DC for tolerance, RelB-deficient mice paradoxically develop generalised systemic autoimmune inflammatory disease with myelopoiesis and splenomegaly. Previous studies suggested abnormal DC differentiation in healthy relatives of type 1 diabetes (t1dm) patients. Therefore, we compared NF- kB activation in monocyte-derived DC from t1dm and non-t1dm controls in response to LPS. While resting DC appeared normal, DC from 6 out of 7 t1dm patients but no t2dm or rheumatoid arthritis patients failed to translocate NF- kB subunits to the nucleus in response to LPS, along with a failure to up-regulate expression of cell surface CD40 and MHC class I. NF- kB subunit mRNA increased normally in t1dm DC after LPS. Both the classical or non-canonical NF- kB pathways were affected as both TNF-a and CD40 stimulation led to a similarly abnormal NF- kB response. In contrast, expression of phosphorylated p38 MAPK and pro-inflammatory cytokine production was intact. These abnormalities in NF- kB activation appear to be generally and specifically applicable at a post-translational level in t1dm, and have the capacity to profoundly influence immunoregulation in affected individuals.

Timing of rotator cuff activation during shoulder external rotation in throwers with and without symptoms of pain

Study Design: Fine-wire EMG rotator cuff onset time analysis in 2 matched groups of throwers with and without pain. Objective: To identify if there is a difference in the activation patterns of the rotator cuff muscles during a rapid shoulder external rotation task between throwers with and without pain. Background: The coordinated action of the rotator cuff is recognized as essential for glenohumeral joint control in the throwing athlete. Identification of abnormalities occurring in muscle activation patterns for injured athletes is relevant when prescribing rehabilitative exercises. Methods and Measures: Twelve throwers with shoulder pain were compared to a matched group of 11 asymptomatic throwers. Participants were matched for age, height, body mass, and habitual activity. Fine-wire EMG electrodes were inserted into the subscapularis, supraspinatus, and infraspinatus. EMG activity was measured during a reaction time task of rapid shoulder external rotation in a seated position. The timing of onset of EMG activity was analyzed in relation to visualization of a light (reaction time) and to the onset of infraspinatus activity (relative latency). Results: In the group with shoulder pain, the onset of subscapularis activity was found to be significantly delayed (reaction time, P = .0018; relative latency, P = .0005) from the onset of infraspinatus activity when compared to the control group. Conclusions: The presence of shoulder pain in these athletes was associated with a difference in the onset of subscapularis EMG activity during a rapid shoulder external rotation movement. This was an initial step in the understanding of the joint protection mechanisms of the glenohumeral joint and the problems that occur in throwers. This information may assist in providing future guidelines for more effective rehabilitation and prevention strategies for this condition.

CR3 (CD11b/CD18) activation of nasal neutrophils: a measure of upper airway endotoxin exposure

Inhaled endotoxin (lipopolysaccharide, LPS) initiates an inflammatory response and leads to the expression of CR3 (CD11b/CD18) receptors on polymorphonuclear leukocytes (PMNs). We determined if PMN activation in nasal lavage fluid (NLF) is a possible biomarker of occupational endotoxin exposure. Seven subjects exposed to endotoxin provided NLF samples that were split into three aliquots (negative control - 1 M nicotinamide; sham; positive control - 11 eta g of exogenous LPS) and PMN activation was measured using a chemiluminometer. Differences in mean PMN activation were apparent, negative control: 548 +/- 15.65 RLU 100 mu l(-1); sham: 11469 +/- 2582 RLU 100 mu l(-1); positive control: 42026 +/- 16659 RLU 100 mu l (n = 7; p < 0.05). This technique shows promise as a diagnostic method for measuring upper airway LPS exposure.

DNA binding-independent transcriptional activation of the vascular endothelial growth factor gene (VEGF) by the Myb oncoprotein

Myb is a key transcription factor that can regulate proliferation, differentiation, and apoptosis, predominantly in the haemopoietic system. Abnormal expression of Myb is associated with a number of cancers, both haemopoietic and non-haemopoietic. In order to better understand the role of Myb in normal and tumorigenic processes, we undertook a cDNA array screen to identify genes that are regulated by this factor. In this way, we identified the gene encoding vascular endothelial growth factor (VEGF) as being potentially regulated by the Myb oncoprotein in myeloid cells. To determine whether this was a direct effect on VEGF gene transcription, we examined the activity of the murine VEGF promoter in the presence of either wild-type (WT) or mutant forms of Myb. It was found that WT Myb was able to activate the VEGF promoter and that a minimal promoter region of 120 bp was sufficient to confer Myb responsiveness. Surprisingly, activation of the VEGF promoter was independent of DNA binding by Myb. This was shown by the use of DNA binding-defective Myb mutants and by mutagenesis of a potential Myb-binding site in the minimal promoter. Mutation of Sp1 sites within this region abolished Myb-mediated regulation of a reporter construct, suggesting that Myb DNA binding-independent activation of VEGF expression occurs via these Sp1 binding elements. Regulation of VEGF production by Myb has implications for the potential role of Myb in myeloid leukaemias and in solid tumours where VEGF may be functioning as an autocrine growth factor. (c) 2006 Elsevier Inc. All rights reserved.

Protein disulfide isomerase redox-dependent association with p47(phox): evidence for an organizer role in leukocyte NADPH oxidase activation

Mechanisms of leukocyte NADPH oxidase regulation remain actively investigated. We showed previously that vascular and macrophage oxidase complexes are regulated by the associated redox chaperone PDI. Here, we investigated the occurrence and possible underlying mechanisms of PDI-mediated regulation of neutrophil NADPH oxidase. In a semirecombinant cell-free system, PDI inhibitors scrRNase (100 mu g/mL) or bacitracin (1 mM) near totally suppressed superoxide generation. Exogenously incubated, oxidized PDI increased (by similar to 40%), whereas PDIred diminished (by similar to 60%) superoxide generation. No change occurred after incubation with PDI serine-mutated in all four redox cysteines. Moreover, a mimetic CxxC PDI inhibited superoxide production by similar to 70%. Thus, oxidized PDI supports, whereas reduced PDI down-regulates, intrinsic membrane NADPH oxidase complex activity. In whole neutrophils, immunoprecipitation and colocalization experiments demonstrated PDI association with membrane complex subunits and prominent thiol-mediated interaction with p47(phox) in the cytosol fraction. Upon PMA stimulation, PDI was mobilized from azurophilic granules to cytosol but did not further accumulate in membranes, contrarily to p47(phox). PDI-p47(phox) association in cytosol increased concomitantly to opposite redox switches of both proteins; there was marked reductive shift of cytosol PDI and maintainance of predominantly oxidized PDI in the membrane. Pulldown assays further indicated predominant association between PDIred and p47(phox) in cytosol. Incubation of purified PDI (> 80% reduced) and p47(phox) in vitro promoted their arachidonate-dependent association. Such PDI behavior is consistent with a novel cytosolic regulatory loop for oxidase complex (re) cycling. Altogether, PDI seems to exhibit a supportive effect on NADPH oxidase activity by acting as a redox-dependent enzyme complex organizer. J. Leukoc. Biol. 90: 799-810; 2011.

Macrophage Activation Syndrome Associated with Etanercept in a Child with Systemic Onset juvenile Idiopathic Arthritis

Fundacao de Amparo a Pesquisa do Estado de Sao Paulo - FAPESP[06/61303-7]