Attenuation of apoptosis underlies B lymphocyte stimulator enhancement of humoral immune response.
(41/729)
B lymphocyte stimulator (BLyS) is a newly identified monocyte-specific TNF family cytokine. It has been implicated in the development of autoimmunity, and functions as a potent costimulator with antiimmunoglobulin M in B cell proliferation in vitro. Here we demonstrate that BLyS prominently enhances the humoral responses to both T cell-independent and T cell-dependent antigens, primarily by attenuation of apoptosis as evidenced by the prolonged survival of antigen-activated B cells in vivo and in vitro. BLyS acts on primary splenic B cells autonomously, and directly cooperates with CD40 ligand (CD40L) in B cell activation in vitro by protecting replicating B cells from apoptosis. Moreover, although BLyS alone cannot activate the cell cycle, it is sufficient to prolong the survival of naive resting B cells in vitro. Attenuation of apoptosis by BLyS correlates with changes in the ratios between Bcl-2 family proteins in favor of cell survival, predominantly by reducing the proapoptotic Bak and increasing its prosurvival partners, Bcl-2 and Bcl-xL. In either resting or CD40L-activated B cells, the NF-kappaB transcription factors RelB and p50 are specifically activated, suggesting that they may mediate BLyS signals for B cell survival. Together, these results provide direct evidence for BLyS enhancement of both T cell-independent and T cell-dependent humoral immune responses, and imply a role for BLyS in the conservation of the B cell repertoire. The ability of BLyS to increase B cell survival indiscriminately, at either a resting or activated state, and to cooperate with CD40L, further suggests that attenuation of apoptosis underlies BLyS enhancement of polyclonal autoimmunity as well as the physiologic humoral immune response. (+info)
Reproducibility of renal length measurements with 99mTc-DMSA SPECT.
(42/729)
Renal length measurements are used in evaluating several abnormalities of the pediatric genitourinary tract. This study assesses reproducibility of renal length measurements obtained with 99mTc-dimercaptosuccinic acid (DMSA) SPECT. METHODS: The lengths of 98 kidneys of 51 children (age range, 1-16 y; mean age, 5.4 y) who underwent 99mTc-DMSA SPECT were measured independently by 2 observers. Renal length was calculated by converting pixels between points at the superior and inferior renal margins on a summated coronal image to centimeters. Lengths were measured for kidneys as they appeared in situ and after realignment along their long axes. SPECT reconstruction, choice of display parameters, positioning of points used for measuring, and alignment were performed independently by each observer. Interobserver variability, interobserver correlation, and mean differences between observers' measurements (expressed as measurement of observer 2 - measurement of observer 1) were calculated. RESULTS: Correlation between the observers' measurements was highly significant for both nonaligned and aligned studies (r = 0.95 and 0.97, respectively; both, P < 0.0001). Interobserver variability expressed as 1 SD was 3.6 mm for nonaligned studies and 2.8 mm for aligned studies. The mean difference between the 2 observers' measurements for nonaligned studies was 2.0 +/- 4.8 mm (P < 0.0001) with a range of -11 to 14 mm. For aligned studies the mean difference between the 2 observers' measurements was -0.1 +/- 4.0 mm (P = 0.88) with a range of -20 to 10 mm. Differences between observers were not dependent on absolute renal length (P = 0.68 for nonaligned studies; P = 0.40 for aligned studies). CONCLUSION: The variability in renal length measurements determined by 99mTc-DMSA SPECT is similar to that reported previously using sonography. Because the interobserver differences in renal length are similar to annual renal growth rates during childhood, caution should be applied when incorporating renal length measurements determined by 99mTc-DMSA SPECT into management algorithms. Additional studies are required to further establish interobserver variability, to assess intraobserver variability, and to evaluate means of improving standardization. (+info)
Commitment of B lymphocytes to a plasma cell fate is associated with Blimp-1 expression in vivo.
(43/729)
B lymphocyte-induced maturation protein-1 (Blimp-1) is a transcriptional repressor that is sufficient to trigger terminal differentiation in the B cell lymphoma BCL-1. In this study, we have determined the expression pattern of Blimp-1 in vivo in primary and secondary lymphoid organs of humans and immunized mice. Blimp-1 is expressed in plasma cells derived from either a T-independent or T-dependent response in plasma cells that have undergone isotype switching and those resulting from secondary immunization. Blimp-1 is also present in long-lived plasma cells residing in the bone marrow. However, Blimp-1 was not detected in memory B cells. This expression pattern provides further evidence of a critical role for Blimp-1 in plasma cell development, supporting earlier studies in cultured lines. Significantly, Blimp-1 was also found in a fraction (4-15%) of germinal center B cells in murine spleen and human tonsils. Blimp-1 expression in the germinal center is associated with an interesting subset of cells with a phenotype intermediate between germinal center B cells and plasma cells. In the mouse, Blimp-1(+) germinal center B cells peak at day 12 postimmunization and disappear soon thereafter. They are not apoptotic, some are proliferating, they express germinal center markers peanut agglutinin or CD10 but not Bcl-6, and most express CD138 (syndecan-1), IRF4, and cytoplasmic Ig. Together, these data support a model in which B cell fate decisions occur within the germinal center and Blimp-1 expression is critical for commitment to a plasma cell, rather than a memory cell, fate. (+info)
TGF-beta receptor controls B cell responsiveness and induction of IgA in vivo.
(44/729)
To determine the role of the pleiotropic cytokine TGF-beta in B cells, we generated mice lacking the TGF-beta receptor (TbetaR) type II selectively in this cell type through conditional mutagenesis (Cre/loxP). The absence of TbetaRII in B cells leads to a reduced life span of conventional B cells, expansion of peritoneal B-1 cells, B cell hyperplasia in Peyer's patches, elevated serum immunoglobulin, and substantial IgG3 responses to a normally weak immunogen. This B cell hyperresponsiveness is associated with a virtually complete serum IgA deficiency. The data reveal differential roles of TbetaR in homeostasis and antigen responsiveness of B cell subpopulations and establish a critical function of the TGF-beta receptor ligand pair in the induction of IgA responses in vivo. (+info)
Conversion of 4-hydroxyacetophenone into 4-phenyl acetate by a flavin adenine dinucleotide-containing Baeyer-Villiger-type monooxygenase.
(45/729)
An arylketone monooxygenase was purified from Pseudomonas putida JD1 by ion exchange and affinity chromatography. It had the characteristics of a Baeyer-Villiger-type monooxygenase and converted its substrate, 4-hydroxyacetophenone, into 4-hydroxyphenyl acetate with the consumption of one molecule of oxygen and oxidation of one molecule of NADPH per molecule of substrate. The enzyme was a monomer with an M(r) of about 70,000 and contained one molecule of flavin adenine dinucleotide (FAD). The enzyme was specific for NADPH as the electron donor, and spectral studies showed rapid reduction of the FAD by NADPH but not by NADH. Other arylketones were substrates, including acetophenone and 4-hydroxypropiophenone, which were converted into phenyl acetate and 4-hydroxyphenyl propionate, respectively. The enzyme displayed Michaelis-Menten kinetics with apparent K(m) values of 47 microM for 4-hydroxyacetophenone, 384 microM for acetophenone, and 23 microM for 4-hydroxypropiophenone. The apparent K(m) value for NADPH with 4-hydroxyacetophenone as substrate was 17.5 microM. The N-terminal sequence did not show any similarity to other proteins, but an internal sequence was very similar to part of the proposed NADPH binding site in the Baeyer-Villiger monooxygenase cyclohexanone monooxygenase from an Acinetobacter sp. (+info)
Selective mGluR5 antagonists MPEP and SIB-1893 decrease NMDA or glutamate-mediated neuronal toxicity through actions that reflect NMDA receptor antagonism.
(46/729)
1. The metabotropic glutamate receptors (mGluRs) are a family of G-protein linked receptors that can be divided into three groups (group I, II and III). A number of studies have implicated group I mGluR activation in acute neuronal injury, but until recently it was not possible to pharmacologically differentiate the roles of the two individual subunits (mGluR1 and mGluR5) in this group. 2. We investigated the role of mGluR5 in acute NMDA and glutamate mediated neurodegeneration in cultured rat cortical cells using the mGluR5 antagonists MPEP and SIB-1893, and found that they provide significant protection at concentrations of 20 or 200 microM. 3. These compounds act as effective mGluR5 antagonists in our cell culture system, as indicated by the ability of SIB-1893 to prevent phosphoinositol hydrolysis induced by the specific mGluR5 agonist, (RS)-2-chloro-5-hydroxyphenylglycine (CHPG). 4. However, they also significantly reduce NMDA evoked current recorded from whole cells voltage clamped at -60 mV, and significantly decrease the duration of opening of NMDA channels recorded in the outside out patch configuration. 5. This suggests that although MPEP and SIB-1893 are effective mGluR5 antagonists, they also act as noncompetitive NMDA receptor antagonists. Therefore, the neuroprotective effects of these compounds are most likely mediated through their NMDA receptor antagonist action, and caution should be exercised when drawing conclusions about the roles of mGluR5 based on their use. (+info)
Endotoxin-induced myocardial tumor necrosis factor-alpha synthesis depresses contractility of isolated rat hearts: evidence for a role of sphingosine and cyclooxygenase-2-derived thromboxane production.
(47/729)
BACKGROUND: Although endotoxin (lipopolysaccharides, LPS) is recognized as a mediator of septic cardiodepression, its cardiac effects are still not fully elucidated. METHODS AND RESULTS: Perfusion of isolated rat hearts with LPS for 180 minutes resulted in a decline of left ventricular contractility after 90 minutes, whereas coronary perfusion pressure remained unaffected. This cardiodepression was paralleled by a release of tumor necrosis factor (TNF)-alpha into the perfusate and preceded by myocardial TNF-alpha mRNA upregulation as quantified by real-time polymerase chain reaction. The cardiodepression was abrogated when LPS was perfused with a TNF-alpha antiserum or the ceramidase inhibitor N:-oleoylethanolamine. In contrast, the cardiac release of nitric oxide (NO) was not augmented by LPS. Immunohistochemical studies of LPS-perfused hearts revealed a positive staining for the constitutive (NOSIII) but not for the inducible NO synthase (NOSII). Accordingly, NOSII mRNA levels commenced to increase only at the very end of the LPS perfusion period. Progressive liberation of thromboxane (Tx) A(2) and prostacyclin was induced by LPS together with myocardial cyclooxygenase (Cox)-2 mRNA expression. Both nonselective inhibition of Cox by indomethacin and selective inhibition of the inducible Cox-2 by NS-398 abolished prostanoid release. Interestingly, the generation of TNF-alpha and the associated cardiodepression caused by LPS were reduced by indomethacin, NS-398 and the Tx-receptor antagonist daltroban. CONCLUSIONS: LPS depresses contractility of isolated rat hearts by inducing TNF-alpha synthesis and subsequently activating the sphingomyelinase pathway, whereas no evidence for a role of NOSII- or NOSIII-generated NO was found. Moreover, Cox-2-derived TxA(2) appears to facilitate TNF-alpha synthesis in response to LPS. (+info)
Urinary homovanillic acid, dopamine and norepinephrine excretion in patients with essential hypertension.
(48/729)
Urinary excretion of dopamine, norepinephrine and homovanillic acid was measured in normotensive subjects and in patients with either labile of stable hypertension under conditions controlled for posture, sodium and potassium intake and time of day. Mean homovanillic acid excretion was 313.5 plus or minus 77.7 (SE) mug/4h in the normotensive patients. Mean values for the patients with labile or stable hypertension were significantly greater, at 2506 plus or minus 476 mug/4 h (P smaller than 0.001) and 795 plus or minus 170 mug/4 h (P smaller than 0.01), respectively. Urinary excretion of dopamine and norepinephrine tended to be elevated in patients with labile hypertension when compared with values in the control subjects and the patients with stable hypertension. The data are compatible with the hypothesis of adrenergic hyperactivity in labile hypertension and underline the biochemical heterogeneity of essential hypertension. Because the overlapping of values between control subjects and patients with labile hypertension was minimal, it is proposed that an elevated valve for urinary homovanillic acid could be used as a biochemical marker to identify the patients with labile hypertension. (+info)