Roles of serum in innate immune responses of human leukocytes to synthetic lipopeptide.

Tripalmitoyl-S-glyceryl-l-Cys-Ser-(Lys)4 (Pam3CSK4) is a highly conserved molecular motif found in various classes of lipoproteins. The requirement for leukocyte to respond to synthetic Pam3CSK4 were studied. Pam3CSK4 primed neutrophils for a respiratory burst in a serum-dependent manner. Pam3CSK4 upregulated CD11b, CD14, and cytochrome b558, and downregulated Leu-8. Treatment of neutrophils with anti-CD14 antibodies and treatment of serum with anti-LPS binding protein (LBP) antibodies resulted in the inhibition of priming for respiratory burst by Pam3CSK4. It should be noted that LBP could not replicate the effects of serum in priming of neutrophils for respiratory burst by Pam3CSK4. Serum LBP bound to immobilized Pam3CSK4. Pam3CSK4 induced the interleukin-8 (IL-8) production by leukocytes in a serum-dependent manner. Further, Pam3CSK4-induced priming of neutrophils for respiratory burst was not inhibited by the LPS antagonists LA-14-PP, Rhodobacter sphaeroides LPS, or E5531, and Pam3CSK4-induced IL-8 production by leukocytes was not affected by LPS antagonist, E5531, indicating that Pam3CSK4 was recognized by a different receptor than LPS. Thus, Pam3CSK4 and LPS had similar biological activities and similar requirement to act on leukocytes, but were recognized by different receptors. Serum in the action of Pam3CSK4 on leukocytes was not replicated by LBP, suggesting that Pam3CSK4 might be disaggregated by serum to result in the activation of leukocytes.

Adhesion attenuates respiratory burst induced by different modes of triggering in resting or LPS-primed neutrophils.

The effects of adherence on neutrophil superoxide anion (O2-) generation triggered by surface, soluble ligand, or adherence were studied. Resting-neutrophils adhered to the uncoated tubes resulting in O2- generation, but not on plasma-, fibrinogen-, vitronectin-, fibronectin-, laminin-, collagen-, or poly HEMA-coated surfaces. Enhanced N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated O2- generation by LPS-primed-neutrophils was induced by the incubation on plasma, fibrinogen, vitronectin, fibronectin, or laminin in the absence of Mg2+. In the presence of Mg2+, this response was observed in cells on collagen or poly HEMA. LPS-primed-neutrophils adhered to uncoated, BSA- or IgG-coated tubes and did not respond to fMLP, indicating that the fMLP-response of LPS-primed-neutrophils was suppressed by adherence. Upon incubation on plasma, fibrinogen, vitronectin, fibronectin in the presence of Mg2+, LPS-primed-neutrophils showed O2- generation. Upon incubation on collagen or poly HEMA, the primed-neutrophils neither generated O2- nor adhered. We found that O2- response of LPS-primed-neutrophils was attenuated depending on the time of exposure to plasma-coated surface. This attenuation was evident on plasma or fibrinogen, but not on collagen in the presence of Mg2+, indicating that O2- generation by LPS-primed-neutrophils was attenuated dependent on adherence but not on Mg2+. Thus, adhesion attenuated the O2- generation triggered by both soluble (fMLP) and insoluble (surface) stimuli.

Innate immune-stimulatory activity of Porphyromonas gingivalis fimbriae is eliminated by phase separation using Triton X-114.

Fimbriae are virulence factors of Porphyromonas gingivalis (P. gingivalis). In this study, the action of fimbriae on neutrophil respiratory burst and cytokine production by mononuclear cells (MNC) were investigated. Native or denatured form of purified P. gingivalis fimbriae contained endotoxin at an equivalence of 1-3µglipopolysaccharides(LPS)/mg protein. The endotoxin could be reduced to the equivalent of 1ng-LPS/mg protein by phase separation using Triton X-114. Unfractionated fimbriae caused serum-dependent priming of neutrophils for enhanced respiratory burst, but both native and denatured forms of Triton X-114-fractionated fimbriae were not active at 100µg/mL. Unfractionated fimbriae induced serum-dependent production of IL-1ß by MNC. Triton X-114-fractionated fimbriae (10µg/mL)-induced production of IL-1ß, IL-8 or TNF-α was much lower than that induced by unfractionated fimbriae or 10ng/mL P. gingivalis-LPS preparation. Triton X-114-fractionated fimbriae immobilized on polystyrene tubes induced adhesion-stimulated superoxide release by LPS-primed neutrophils in a ß2 integrin-dependent manner. P. gingivalis cells caused priming of neutrophils; however, Toll-like receptor (TLR) 4 antagonists did not affect this response. Thus, P. gingivalis fimbriae were ineffective in inducing innate immune response in leukocytes; however, they induced ß2 integrin-mediated response by neutrophils. Immune-stimulatory components of P. gingivalis might be recognized by receptors other than TLR4.

Anti-CD14 Antibody-treated Neutrophils Respond to LPS: Possible Involvement of CD14 Upregulated by Anti-CD14 Antibody Binding.

CD14 and Toll-like receptor 4/MD2 (TLR4/MD2) mediate the action of LPS on neutrophils. The anti-CD14 antibody and the TLR4/MD2-antagonist, synthetic lipid IVa (LA-14-PP), are known to inhibit the response of neutrophils to LPS. We studied the role of CD14 in LPS-induced priming of neutrophils for enhanced release of the superoxide anion. The anti-CD14 antibody at much higher concentrations than required to saturate CD14 was required to inhibit priming by LPS. The inhibitory effect of the anti-CD14 antibody was overcome by LPS. After washing, anti-CD14-treated neutrophils showed upregulated CD14 upon incubation at 37°C and responded to LPS with a delayed time-course. Thus, CD14-blocked neutrophils gained responsiveness to LPS through newly upregulated CD14. These results suggested that the unbound/free anti-CD14 antibody was essential to inhibit LPS-induced priming by blocking CD14 that were newly expressed during incubation at 37°C. LA-14-PP inhibited the response of neutrophils to LPS in an anti-CD14 antibody sensitive manner. When neutrophils were treated with LA-14-PP followed by treatment with the anti-CD14 antibody, CD14 was upregulated upon warming, but priming was blocked, suggesting that TLR4/MD2 was not newly expressed by warming in association with CD14 molecules. Thus, in addition to blocking CD14, the anti-CD14 antibody was found to induce the expression of new CD14.

Mechanisms of the Macrolide-Induced Inhibition of Superoxide Generation by Neutrophils.

The effect of macrolides on the superoxide (O2 (-)) production by neutrophils was studied. Resting neutrophils become primed by lipopolysaccharide (LPS) or N-formyl-methionyl-leucyl-phenylalanine (fMLP), and primed neutrophils generate O2 (-) in response to fMLP or adhesion, respectively. Both LPS-primed fMLP-stimulated O2 (-) generation by macrolide-treated neutrophils and adhesion-stimulated O2 (-) generation by macrolide-treated fMLP-primed neutrophils were inhibited. Macrolide inhibition of O2 (-) generation was dependent on serum or pH. Serum could be substituted by NaHCO3. The intensity of inhibition was azithromycin = roxithromycin > clarithromycin > erythromycin, in that order. Non-antimicrobial derivatives of erythromycin, that is, EM703 and EM900, inhibited O2 (-) generation at pH 7.4. NH4Cl abolished the activity of azithromycin (AZ) only when added to neutrophils with AZ but not after incubation with AZ, suggesting that NH4Cl prevented the influx of AZ. AZ did not affect the expression of alkaline phosphatase, CD11b, and cytochrome b558 in both resting and LPS-primed neutrophils. These results suggested that macrolides did not affect granule mobilization but inhibited O2 (-) generation selectively.

Disaggregation of lipopolysaccharide by albumin, hemoglobin or high-density lipoprotein, forming complexes that prime neutrophils for enhanced release of superoxide.

We studied the interaction of LPS with albumin, hemoglobin or high-density lipoprotein (HDL), and whether the interaction affected the activity of LPS on neutrophils. These proteins disaggregated LPS, depending upon temperature and LPS:protein ratio. Albumin-treated LPS was absorbed by immobilized anti-albumin antibody and was eluted with Triton X-100, indicating that LPS formed a hydrophobic complex with albumin. Rd mutant LPS was not disaggregated by the proteins, and did not form a complex with the proteins. But triethylamine-treated Rd mutant LPS formed complexes. When LPS was incubated with an equal concentration of albumin and with polymyxin B (PMXB), PMXB-LPS-protein three-way complexes were formed. After removal of PMXB, the complexes consisted of 11-15 LPS monomers bound to one albumin or hemoglobin molecule. LPS primed neutrophils for enhanced release of formyl peptide-stimulated superoxide, in a serum- and LPS-binding protein (LBP)-dependent manner. Although LPS plus LBP alone did not prime neutrophils, albumin-, hemoglobin- or HDL-treated LPS primed neutrophils when added with LBP. Triethylamine-treated Rd mutant LPS primed neutrophils only when incubated with one of the proteins and with LBP. Thus, in addition to LBP, disaggregation and complex formation of LPS with one of these proteins is required for LPS to prime neutrophils.

Local anesthetics inhibit priming of neutrophils by lipopolysaccharide for enhanced release of superoxide: suppression of cytochrome b558 expression by disparate mechanisms.

Local anesthetics have anti-inflammatory effects in vivo and inhibit neutrophil functions in vitro, but how these agents act on neutrophils remains unclear. Phagocytosis and bactericidal activity of neutrophils are enhanced by exposure to bacterial components such as lipopolysaccharide (LPS); this process is termed priming, which for enhanced release of superoxide (O2-) causes mobilization of intracellular granules that contain cytochrome b558, a component of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. We studied whether local anesthetics affected LPS priming for enhanced release of O2- in response to triggering by the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP), and we investigated which element in the LPS signaling pathway might be the target of local anesthetics. Neutrophils were incubated with 10 ng/ml LPS and 1% plasma+/-local anesthetics, washed, and triggered with fMLP. Local anesthetics all inhibited LPS priming, and 50% inhibition was at 0.1 mM tetracaine, 0.5 mM bupivacaine, 3.0 mM lidocaine, or 4.0 mM procaine. Local anesthetics inhibited LPS-induced mobilization of specific granules and secretory vesicles. Local anesthetics inhibited LPS-induced up-regulation of cytochrome b558 but not LPS-induced translocation of p47phox. Inhibition of priming by local anesthetics was reversed by washing and incubating for 5 min. Tetracaine alone, but not the other local anesthetics, inhibited LPS activation of p38 mitogen-activated protein kinase (MAPK) and MAPK kinase 3 (kinases in the LPS signaling pathway). The p38 MAPK inhibitors SB203580 and PD169316 also blocked LPS priming. Thus, tetracaine and the other local anesthetics inhibit by disparate mechanisms, but all the local anesthetics impaired up-regulation of cytochrome b558 and all impaired priming of NADPH oxidase by LPS.

Follistatin restricts bone morphogenetic protein (BMP)-2 action on the differentiation of osteoblasts in fetal rat mandibular cells.

UNLABELLED: We tested whether FS secretion might modulate BMP-2 actions by measuring FS levels and counting bone numbers of rat mandibular cells. In the presence of Dex, BMP-2 stimulated FS secretion at the early phase and augmented bone nodule by neutralizing with FS antibody. We concluded that BMP-2 facilitates FS secretion, and the FS restricts BMP-2 action on osteoblastogenesis. INTRODUCTION: Bone morphogenetic proteins (BMPs) promote the differentiation of osteoprogenitor cells into osteoblasts. Activin A is involved in the regulation of bone formation. Follistatin (FS) antagonizes the bioactivities of BMP and activin A extracellularly. MATERIALS AND METHODS: In this study, we tested whether the induction of FS secretion might modulate the effects of BMP-2 on osteoblast development, using the bone nodule-forming cultures of fetal rat mandibular cells. RESULTS AND CONCLUSIONS: In the presence of dexamethasone (Dex), BMP-2 stimulated the secretion of FS at the early phase (days 3-9) of the culture. Dex alone had no effect, and BMP-2 alone was less effective than the combination of the two. BMP-4 and -6 had little effect on FS secretion. Activin A inhibited the early upregulation of FS secretion when added with BMP-2 and Dex. In the presence of Dex, BMP-2 increased bone nodule numbers when added to early cultures. The addition of anti-FS antibody to cultures with BMP-2 and Dex augmented bone nodule formation. These results show that BMP-2 facilitates the secretion of FS in the presence of Dex, and the increased FS secretion restricts the action of BMP-2 on osteoblast differentiation.