TNF alpha primes polymorphonuclear leukocytes for an enhanced respiratory burst to a similar extent as bacterial lipopolysaccharide

Porphyromonas gingivalis Outer Membrane Vesicles Induce Selective Tumor Necrosis Factor Tolerance in a Toll-Like Receptor 4- and mTOR-Dependent Manner

Porphyromonas gingivalis is an important member of the anaerobic oral flora. Its presence fosters growth of periodontal biofilm and development of periodontitis. In this study, we demonstrated that lipophilic outer membrane vesicles (OMV) shed from P. gingivalis promote monocyte unresponsiveness to live P. gingivalis but retain reactivity to stimulation with bacterial DNA isolated from P. gingivalis or AIM2 ligand poly(dA·dT). OMV-mediated tolerance of P. gingivalis is characterized by selective abrogation of tumor necrosis factor (TNF). Neutralization of interleukin-10 (IL-10) during OMV challenge partially restores monocyte responsiveness toP. gingivalis; full reactivity toP. gingivalis can be restored by inhibition of mTOR signaling, which we previously identified as the major signaling pathway promoting Toll-like receptor 2 and Toll-like receptor 4 (TLR2/4)-mediated tolerance in monocytes. However, despite previous reports emphasizing a central role of TLR2 in innate immune recognition of P. gingivalis, our current findings highlight a selective role of TLR4 in the promotion of OMV-mediated TNF tolerance: only blockade of TLR4-and not of TLR2-restores responsiveness toP. gingivalis Of further note, OMV-mediated tolerance is preserved in the presence of cytochalasin B and chloroquine, indicating that triggering of surface TLR4 is sufficient for this effect. Taking the results together, we propose that P. gingivalis OMV contribute to local immune evasion of P. gingivalis by hampering the host response.

Lipopolysaccharide-binding protein- and CD14-dependent activation of mitogen-activated protein kinase p38 by lipopolysaccharide in human neutrophils is associated with priming of respiratory burst

Neutrophil (PMN) functions can be primed for greatly increased oxidative radical release by exposure to certain agents such as lipopolysaccharide (LPS). Although a variety of signaling pathways involving both tyrosine kinases and mitogen-activated protein (MAP) kinases may be operative, the mechanisms of PMN priming are still not understood. We found that PMN priming was not achieved by treatment of cells with a very low concentration (5 ng/ml) of LPS unless additional "helper" factors were present in plasma (5%). Under these conditions, LPS induced tyrosine phosphorylation of a 38-kDa protein, which was coincident with the MAP kinase p38 action in this situation. LPS-mediated activation of p38 in human PMNs was dependent on the presence of LPS binding protein from plasma and CD14 on the surfaces of the cells. Phosphorylation of p38 was highly correlated with LPS priming of a formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMN respiratory burst. Treatment of PMN with the p38-specific inhibitor SB203580 significantly attenuated the respiratory burst in cells primed by LPS and stimulated by fMLP. These results suggest that the LPS signaling pathway leading to p38 activation may be an important mechanism in regulation of PMN priming. The mediator(s) linking CD14 to p38 involves proteins that are functionally sensitive to genistein but insensitive to tyrphostin AG126 and to Src- and Syk-family kinase, protein kinase C, and phosphatidylinositol 3-kinase inhibitors. Elucidating this pathway will provide insight into possible regulation of PMN priming by LPS.

Lipopolysaccharide-binding protein- and CD14-dependent activation of mitogen-activated protein kinase p38 by lipopolysaccharide in human neutrophils is associated with priming of respiratory burst

Neutrophil (PMN) functions can be primed for greatly increased oxidative radical release by exposure to certain agents such as lipopolysaccharide (LPS). Although a variety of signaling pathways involving both tyrosine kinases and mitogen-activated protein (MAP) kinases may be operative, the mechanisms of PMN priming are still not understood. We found that PMN priming was not achieved by treatment of cells with a very low concentration (5 ng/ml) of LPS unless additional "helper" factors were present in plasma (5%). Under these conditions, LPS induced tyrosine phosphorylation of a 38-kDa protein, which was coincident with the MAP kinase p38 action in this situation. LPS-mediated activation of p38 in human PMNs was dependent on the presence of LPS binding protein from plasma and CD14 on the surfaces of the cells. Phosphorylation of p38 was highly correlated with LPS priming of a formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMN respiratory burst. Treatment of PMN with the p38-specific inhibitor SB203580 significantly attenuated the respiratory burst in cells primed by LPS and stimulated by fMLP. These results suggest that the LPS signaling pathway leading to p38 activation may be an important mechanism in regulation of PMN priming. The mediator(s) linking CD14 to p38 involves proteins that are functionally sensitive to genistein but insensitive to tyrphostin AG126 and to Src- and Syk-family kinase, protein kinase C, and phosphatidylinositol 3-kinase inhibitors. Elucidating this pathway will provide insight into possible regulation of PMN priming by LPS.

Treatment of psoriasis with the chimeric monoclonal antibody against tumor necrosis factor alpha, infliximab

BACKGROUND

Psoriatic skin lesions in patients with Crohn's disease or psoriatic arthritis have shown improvement during infliximab treatment.

OBJECTIVE

The purpose of our study was to systematically assess the effects of infliximab in patients with psoriatic skin lesions.

METHODS

Eight patients with severe psoriasis were enrolled in an open-label clinical trial. Patients received infliximab, 5 mg/kg, intravenously at weeks 0, 2, and 6. The Psoriasis Area and Severity Index (PASI) was used to monitor disease activity at weeks 0, 2, 4, 6, 8, 10, and 14. Week 10 was the end point of the treatment phase; week 14 was the follow-up end point. Pruritus was assessed on a scale of 0 to 3. Histologic sections were prepared from biopsy specimens of uninvolved skin and of psoriatic lesions at weeks 0, 1, and 10 to measure epidermal thickness with the use of a microscopic micrometer grid.

RESULTS

The PASI diminished from 21.8 +/- 4.2 (mean +/- SE) at week 0 to 3.4 +/- 2.0 at week 10, corresponding to 10.7% +/- 4.3% of the original values (100%); on follow-up at week 14, the PASI was 7.1 +/- 2.7 (or still 33.3% +/- 11.3% of the values at week 0). Pruritus decreased from 2.5 +/- 0.26 at week 0 to 0.43 +/- 0.2 at week 10 and to 0.83 +/- 11.3 at week 14. Likewise, epidermal thickness (acanthosis) tended to normalize from 0.41 +/- 0.06 mm at week 0 to 0.14 +/- 0.02 mm at week 10. No adverse effects other than fatigue during infusion on some occasions were reported.

CONCLUSION

Although psoriasis tends to recur beyond 2 months of the infusions, this open study provides evidence that infliximab is an effective treatment.

Activation of extracellular signal-related protein kinases 1 and 2 of the mitogen-activated protein kinase family by lipopolysaccharide requires plasma in neutrophils from adults and newborns

Neutrophils exposed to low concentrations of gram-negative lipopolysaccharide (LPS) become primed and have an increased oxidative response to a second stimulus (e.g., formyl-methionyl-leucyl-phenylalanine [fMLP]). In studies aimed at understanding newborn sepsis, we have shown that neutrophils of newborns are not primed in response to LPS. To further understand the processes involved in LPS-mediated priming of neutrophils, we explored the role of extracellular signal-related protein kinases (ERK 1 and 2) of the mitogen-activated protein kinase family. We found that LPS activated ERK 1 and 2 in cells of both adults and newborns and that activation was plasma dependent (maximal at > or =5%) through LPS-binding protein. Although fibronectin in plasma is required for LPS-mediated priming of neutrophils of adults assessed by fMLP-triggered oxidative burst, it was not required for LPS-mediated activation of ERK 1 and 2. LPS-mediated activation was dose and time dependent; maximal activation occurred with approximately 5 ng of LPS per ml and at 10 to 40 min. We used the inhibitor PD 98059 to study the role of ERK 1 and 2 in the LPS-primed fMLP-triggered oxidative burst. While Western blotting showed that 100 microM PD 98059 completely inhibited LPS-mediated ERK activation, oxidative response to fMLP by a chemiluminescence assay revealed that the same concentration inhibited the LPS-primed oxidative burst by only 40%. We conclude that in neutrophils, LPS-mediated activation of ERK 1 and 2 requires plasma and that this activation is not dependent on fibronectin. In addition, we found that the ERK pathway is not responsible for the lack of LPS priming in neutrophils of newborns but may be required for 40% of the LPS-primed fMLP-triggered oxidative burst in cells of adults.

Ex vivo induction of apoptosis in lymphocytes is mediated by oxidative stress: role for lymphocyte loss in HIV infection

Programmed cell death (apoptosis) of T-lymphocytes observed in human immunodeficiency virus (HIV) infected individuals could be linked to oxidative stress. Therefore, we have investigated whether reactive oxygen species (ROS) induce apoptosis, which might contribute to the cell loss during progression of HIV-1 infection. ROS were generated in peripheral blood mononuclear cells (PBMC) obtained from HIV-1-positive patients and from healthy controls by stimulation with bacteria or by treatment with hypoxanthine/xanthine oxidase, which has been shown to generate ROS without direct involvement of cytokines. A dose-dependent inhibition of ROS formation correlated with the reduction of apoptosis induced by both bacterial and hypoxanthine/xanthine oxidase stimulation, suggesting that ROS generation was responsible for the induction of apoptosis. In addition, hydrogen peroxide (H2O2) rather than superoxide (O2.-) was observed to induce apoptosis. ROS-dependent apoptosis was shown to be independent of cytokines such as tumor necrosis factor-alpha (TNF-alpha). ROS-induced apoptosis was significantly enhanced in HIV-infected subjects even in the very early stages after infection. Moreover, ROS-mediated apoptosis was not restricted to a particular lymphocyte subset. In view of the diminished oxidative resistance of HIV-infected individuals, our results suggest that ROS-mediated apoptosis might contribute to the deletion of lymphocytes and to the pathogenesis of the disease.

Diminished priming of neonatal polymorphonuclear leukocytes by lipopolysaccharide is associated with reduced CD14 expression

Previous research in our laboratory has shown that polymorphonuclear leukocytes (PMN) from neonates are not primed effectively in vitro with lipopolysaccharide (LPS) (from Escherichia coli 0111:B4) compared with priming of adult PMN. This finding led us to speculate that differences between neonatal and adult LPS receptors may account for the lower response by neonatal PMN to LPS. In these experiments, we investigated if CD14 or other LPS receptors contribute to the priming activity of PMN by LPS. We found that unprimed neonatal and adult PMN expressed similar numbers of CD14 (11.6 +/- 9.2 versus 18.6 +/- 2.7 fluorescence units [FlU]; P > 0.05) and LPS-binding sites (2.94 +/- 1.4 versus 4.94 +/- 0.79 FlU; P > 0.05). Monoclonal antibody against CD14 (MY4) did not significantly change the binding of LPS to adult unprimed PMN, suggesting that LPS receptors other than CD14 receptors are predominant on PMN. However, when PMN were pretreated with LPS (10 ng/ml) for 45 min at 37 degrees C, expression of CD14 on adult PMN increased to 33.8 +/- 4.9 FlU (P < 0.05 versus unprimed adult PMN) while that on neonatal PMN showed little change, increasing to 17.2 +/- 10.3 FlU (P > 0.05 versus unprimed neonatal PMN; P < 0.05 versus primed adult PMN). Furthermore, MY4 specifically blocked oxidative-radical production from PMN primed with LPS (10 ng/ml) compared with that from control PMN (P < 0.01). These studies suggest that LPS primes PMN by activating CD14 expression. We conclude that lower expression of CD14 or failure to up-regulate CD14 after LPS pretreatment contributes to the inability of neonatal PMN to be primed by LPS.

Indomethacin-induced gastrointestinal ulcers in rats: effects of dietary fatty acids and endotoxin

The purpose of this study was to determine how dietary n-3 and n-6 polyunsaturated fatty acids (PUFA) affected the gastrointestinal response to lipopolysaccharide (LPS) and indomethacin (INDO) in the rat. Rats were fed diets containing 12.5% linseed oil (LO-enriched in short-chain n-3 PUFA) or corn oil (CO-enriched in n-6 PUFA). After 30 days on the diets, rats were given one of three treatments 1:10 mg/kg O55:B5 Escherichia coli LPS intraperitoneally (i.p.), 2:25 mg/kg INDO subcutaneously (s.c.), 3: a combination of 10 mg/kg i.p. LPS and 25 mg/kg (s.c.) INDO given 30 min before LPS. 20 h after challenge, rats were given an intravenous injection of Monastral Blue B to stain ulcer areas in the gastrointestinal tract. Lipopolysaccharide did not result in any Monastral Blue B vascular leakage in the gastrointestinal tract. Rats on the LO diet had significantly increased stomach and intestinal ulcers compared to CO fed rats. When rats were challenged with LPS and INDO, the LPS almost completely eliminated small intestinal ulcers, but enhanced ulcer development in the stomach.