Sensitivities of human monocytes and epithelial cells to pneumolysin are different.
(65/970)
The Streptococcus pneumoniae pore-forming toxin, pneumolysin, is an important virulence factor in pneumococcal pneumonia. The effect of pneumolysin on human lung epithelial and monocyte cell viability was compared. Pneumolysin caused a dose-dependent loss of viability of human lung epithelial (A549 and L132) and monocyte (U937 and THP-1) cell lines. Analysis of the dose-response curves revealed similar log 50% inhibitory concentration (pIC(50)) values for A549, L132, and THP-1 of 0.12+/- 0.1, 0.02+/- 0.04, and 0.12+/- 0.13 hemolytic units (HU), respectively, but U937 cells showed a significantly greater pIC(50) of 0.42+/- 0.12 HU. Differentiation of A549 and L132 with phorbol ester or THP-1 with gamma interferon had no effect on their sensitivity to pneumolysin. However, a significant decrease in the potency of pneumolysin against U937 cells followed gamma interferon treatment. The Hill slopes of the inhibition curves were greater than unity, indicating that pneumolysin may act with positive cooperativity. Analysis of pneumolysin-treated THP-1 cells by electron microscopy revealed membrane lesions of between 100 and 200 nm in diameter. (+info)
Glucose-inducible hypertrophy and suppression of anion efflux in rat beta cells.
(66/970)
Hypertrophy of beta cells from obese fa/fa rats is associated with increased sensitivity to basal glucose. Exposure to glucose in culture distorts insulin secretion more in beta cells from large than small islets from fa/fa rats. The aim of the present study is to investigate whether increased beta cell volume is associated with both glucose hypersensitivity and altered activity of the glucose-sensitive anion conductance. Beta cells from fa/fa rats had increased volume compared with those from lean rats after 24 h culture. Three-day exposure to 25 mM glucose in culture induced 10-15% hypertrophy in beta cells from lean rats and basal secretion from intact islets was increased tenfold. Estimates of ion channel activity were made from measurement of radiolabeled ion efflux. Taurine efflux, a marker of glucose-regulated anion channel activity, was reduced after high glucose exposure but no alterations in glucose-dependent K+ efflux were detected. The reverse hemolytic plaque assay was used to determine the contributions of the number of secreting cells (recruitment) versus secretion per cell in beta cells from enlarged (>250 microm diameter), intermediate (125-250 microm) and small (<125 microm) islets from lean and obese rats exposed to conditions mimicking hyperglycemia. After overnight culture, basal secretion was twofold greater from beta cells of large fa/fa islets compared with all other groups. Recruitment at low glucose was increased in all lean or fa/fa beta cells derived from >125 microm islets. When beta cells from small islets were exposed to supra-physiological glucose for 3 days, recruitment was increased at basal glucose and blunted at high glucose. Glucose exposure converts the recruitment profile of beta cells from small islets to resemble that of beta cells from large islets while inducing cellular hypertrophy and reduced anion conductance. However, hypertrophy alone did not predict functional characteristics of overnight-cultured beta cells from fa/fa rats. (+info)
Two diarylurea electron transport inhibitors reduce Staphylococcus aureus hemolytic activity and protect cultured endothelial cells from lysis.
(67/970)
Reduction in electron transport is associated with decreased production in alpha-toxin despite the fact that Staphylococcus aureus is able to grow from 1 CFU to >10(7) CFU. Similarly, under anaerobic conditions, S. aureus does not produce alpha-toxin. Although the pathways that connect oxidative metabolism and toxin production are unknown, agents are available that exhibit greater inhibition of plant versus mammalian electron transport. Herbicides block electron transport in plants by inhibiting the formation of phosphoquinol (QH(2)) in plants. Commercial use in farming is possible because these compounds are much less active against the quinones found mammalian mitochondria. Because bacterial electron transport systems are closer to plant than mammalian systems, we hypothesized that inhibitors of respiration might be able to reduce S. aureus electron transport and block the production of alpha-toxin. We studied two compounds and found that the effective dose for the inhibition of bacterial respiration was 50 to >3,500 times lower than the concentration required to cause similar inhibition of rat mitochondrial respiration. Compounds I and II also reduced toxin production in S. aureus without causing overt toxicity to cultured endothelial cells. Finally, the compounds reduced the damage caused by S. aureus when cocultured with the endothelial cells. This raises the possibility that compounds that inhibit bacterial respiration might be prove valuable for the prevention of toxin production in S. aureus. (+info)
Characterization of pharmacological efficacy of VX-148, a new, potent immunosuppressive inosine 5'-monophosphate dehydrogenase inhibitor.
(68/970)
Inosine 5'-monophosphate dehydrogenase (IMPDH) enzyme catalyzes the rate-limiting step in the de novo biosynthesis of guanine nucleotides. Proliferation of lymphocytes is critically dependent on this de novo nucleotide synthesis pathway. Hence, IMPDH is an attractive target for the development of immunosuppressive drugs. VX-148 is a novel, uncompetitive IMPDH inhibitor with a K(i) value of 6 nM against IMPDH type II enzyme. VX-148 is slightly more potent than mycophenolic acid and VX-497 in inhibiting the proliferation of mitogen-stimulated primary human lymphocytes (IC(50) value of ~80 nM). The inhibitory activity of VX-148 is alleviated in the presence of exogenous guanosine. VX-148 does not inhibit proliferation of nonlymphoid cell types such as fibroblasts, indicating selectivity for inhibition of IMPDH activity. VX-148 is orally bioavailable in rats and mice; oral administration of VX-148 inhibits primary antibody response in mice in a dose-dependent manner with an ED(50) value of 38 mg/kg b.i.d. VX-148 significantly prolongs skin graft survival at 100 mg/kg b.i.d. in mice. These results demonstrate that VX-148 is a potent and specific IMPDH inhibitor with a favorable pharmacokinetic profile and good pharmacological activity in mice, and thus support development of VX-148 as an immunosuppressive drug. (+info)
Repertoire of antibody response in bone marrow and the memory response are differentially affected in aging mice.
(69/970)
The primary burst of Ab and germinal center (GC) formation in response to T-dependent Ag is compromised in aging mice. Here we examine the effects of aging on the post-GC phase of memory B cell differentiation and the late Ab repertoire maturation in bone marrow (BM) in mice immunized with a hapten nitrophenyl coupled to chicken gamma-globulin. Specific Ab-forming cells (AFC) with mutated V(H) genes accumulated preferentially in the BM of aged mice, although the AFC numbers and average number of mutations per V(H) were lower, and the D gene usage was less restricted compared with those in the young animals. However, the repertoire of AFC after an Ag boost demonstrated the hallmarks of Ag selection, including the recurrent mutations and canonical VD rearrangements, similar to the late primary response in young animals. It is postulated that the Ab repertoire maturation in aged mice is delayed and may be notably improved by repeated immunizations. (+info)
Single-cell analysis: a novel approach to tumour necrosis factor-alpha synthesis and secretion in sarcoidosis.
(70/970)
Tumour necrosis factor (TNF)-alpha is thought to be a key early cytokine in the pathogenesis of sarcoidosis, despite conflicting data. Largely the product of mononuclear phagocyte activation, it is unclear whether TNF-alpha production at disease sites is a feature of all mononuclear phagocytes that accumulate there or whether it is secreted by a subset of these cells. Using the reverse haemolytic plaque assay, the aims of this study were to determine if the upregulation of TNF-alpha could be confirmed and to investigate whether this was monocyte or macrophage specific. The reverse haemolytic plaque assay allows the measurement of cytokine production at a single cell level. A greater number of alveolar macrophages produced TNF-alpha compared to autologous monocytes in sarcoidosis but not in controls and, based on cell size, it was confirmed that this was the product of more mature macrophages and that the secretion of TNF-alpha by monocytes and macrophages was heterogeneous: not all monocytes and macrophages secrete TNF-alpha. No differences in the average levels of TNF-alpha secretion by peripheral blood monocytes or alveolar macrophages were observed. This study has demonstrated that a subset of mononuclear phagocytes, mature macrophages, are responsible for tumour necrosis factor secretion and this could have implications for targeted management in sarcoidosis in the future. (+info)
Mechanism of action of the growth hormone secretagogue, L-692,585, on isolated porcine somatotropes.
(71/970)
The effects of a GH secretagogue, L-692,585 (L-585), and human GH-releasing hormone (hGHRH) on calcium transient and GH release were investigated in isolated porcine pituitary cells using calcium imaging and the reverse hemolytic plaque assay (RHPA). Somatotropes were functionally identified by the application of hGHRH. All cells that responded to hGHRH responded to L-585 application. Perfusion application of 10 microM hGHRH and L-585 for 2 min resulted in an increase in intracellular calcium concentrations ([Ca(2+)](i)) of 53+/-1 nM (mean+/-S.E.M.) (P < 0.01) and 68+/-2 nM (P < 0.01) respectively. The L-585 response was characterized by an initial increase in [Ca(2+)](i) followed by a decline to a plateau level above the baseline. Concurrent calcium imaging with RHPA indicated that the L-585-evoked increase in [Ca(2+)](i) coincided with GH release. L-585 significantly increased the percentage of plaque-forming cells (24+/-3 vs 40+/-6%; P < 0.05) and mean area of plaques (1892+/-177 vs 3641+/-189 micro m(2); P < 0.01) indicating increased GH release. Substance P (SP) analogue ([d -Arg(1),d -Phe(5),d -Trp(7,11)]-SP) blocked, and the hGHRH receptor antagonist ((Phenylac-Tyr(1),d -Arg(2), p-chloro-Phe(6), Homoarg(9), Tyr (Me)(10), Abu(15), Nle(27),d -Arg(28), Homoarg(29))-GRF (1-29) amide) decreased the stimulatory effect of hGHRH. These failed to block the stimulatory effect of L-585, suggesting a different receptor for L-585 from the GHRH receptor. The hGHRH-induced calcium transients and initial peak increase induced by L-585 were significantly decreased by removal of calcium from the bathing medium or the addition of nifedipine, an L-calcium channel blocker. The plateau component of L-585-induced calcium change was abolished by removal of calcium and nifedipine. These results suggest an involvement of calcium channels in GH release. Either SQ-22536, an adenylate cyclase inhibitor, or U73122, a phospholipase C (PLC) inhibitor, blocked the stimulatory effects of hGHRH and L-585 on [Ca(2+)](i) transient, indicating the involvement of adenylate cyclase-cAMP and PLC-inositol triphosphate pathways. These results further suggested that calcium mobilization from internal stores during the first phase of the L-585 response induced an increase in [Ca(2+)](i) whereas calcium influx during the second phase is a consequence of somatotrope depolarization. (+info)
Adjuvant and mitogenic properties of a supernatant fraction of sonically treated Myobacterium bovis (BCG).
(72/970)
A water-soluble, oil-free supernatant fraction of sonically treated BCG (BCG-SS) was shown to be an immunological adjuvant and a mitogen. When BCG-SS and sheep erythrocytes (SRBC) were injected intravenously into mice, the plaque-forming cell (PFC) response was 10 times greater than that induced by injection of SRBC alone. Circulating antibody responses to SRBC and to bovine serum albumin were also enhanced by BCG-SS. The in vitro enhancement of PFC and circulating antibody responses did not require mineral oil or exogenous lipids. In vitro PFC responses by normal mouse spleen cells were also greatly increased in the presence of BCG-SS. Anti-theta serum-treated spleen cells from mice that had been lethally irradiated and reconstituted with normal bone marrow cells also gave a higher PFC response to SRBC in the presence of BCG-SS. This suggests that BCG-SS can stimulate B lymphocytes to develop an immune response when T lymphocytes are severely depleted or absent. BCG-SS also stimulated the uptake of 125IUdR by normal spleen cell cultures, indicating that it is a mitogen. (+info)