The effect of calcium mobilization on LPS-induced IL-1 beta production depends on the differentiation stage of the monocytes/macrophages

Involvement of Rac1 in macrophage activation by brain-derived neurotrophic factor

Brain-derived neurotrophic factor (BDNF) enhances periodontal tissue regeneration. Tissue regeneration is characterized by inflammation, which directs the quality of tissue repair. This study aimed to investigate the effect of BDNF on the phagocytic activity of RAW264.7 cells. In addition, we studied the effect of BDNF on guanosine triphosphatase (GTP)-RAS-related C3 botulinus toxin substrate (Rac)1 and phospho-Rac1 levels in RAW264.7 cells. Rac1 inhibitor inhibited BDNF-induced phagocytosis of latex-beads. In addition, BDNF enhanced Porphyromonas gingivalis (Pg) phagocytosis by RAW264.7 cells as well as latex-beads. We demonstrated for the first time that BDNF enhances phagocytic activity of RAW264.7 cells through Rac1 activation. The present study proposes that BDNF may reduce inflammatory stimuli during BDNF-induced periodontal tissue regeneration through enhanced phagocytic activity of macrophages.

Autocrine activation of cultured macrophages by brain-derived neurotrophic factor

To elucidate a significance of the expression of brain-derived neurotrophic factor (BDNF) in the activated microglia/macrophages of the injured central nervous system, we examined BDNF actions on or BDNF synthesis by macrophages cultured from the mouse peritoneal cavity. They synthesized BDNF and neurotrophin-3 (NT-3) in addition to expressing high-affinity neurotrophin receptors, full-length TrkB (FL), truncated TrkB (TK(-)), and TrkC, thus suggesting an autocrine influence of BDNF and NT-3. BDNF, but not NT-3, enhanced phagocytic activity and stimulated synthesis/secretion of interleukin-1beta in the same manner as lipopolysaccharide (LPS). Furthermore, there was a significant correlation of the phagocytic activity with the expression of BDNF or TrkB (FL). These results imply that the phagocytic activity of macrophages depends on BDNF synthesis and/or TrkB (FL) expression, suggesting that BDNF participates in the activation processes of macrophages by acting in an autocrine manner.

Immuno-regulatory effects of CKBM on the activities of mitogen-activated protein kinases and the release of cytokines in THP-1 monocytic cells

CKBM is an herbal formula composed of five Chinese medicinal herbs (Panax ginseng, Schisandra chinensis, Fructus crataegi, Ziziphus jujube and Glycine Max) supplemented with processed Saccharomyces cerevisiae. Previous studies have demonstrated that CKBM is capable of triggering the release of IL-6 and TNFalpha from human peripheral blood mononuclear cells, and its anti-tumorigenic activity has been demonstrated in nude mice with gastric cancer. In this report, we utilized the THP-1 monocytic cell line as a cellular model to investigate how CKBM regulates the intracellular signaling of monocytes and the subsequent release of the produced cytokines. In terms of mitogen-activated protein kinase (MAPK) cascades, CKBM (20%) had no significant effect on ERK, but was linked to an inhibitory effect on JNK and a stimulatory effect on p38 MAPK. The differential responsiveness of JNK and p38 was dependent on the duration of treatment, as well as on the dosage of CKBM. Treatment of CKBM alone induced the release of IL-10 and IFNgamma, but not IL-1beta, IL-4, IL-6 and TNFbeta, while increase of intracellular Ca2+ concentration by A23187 triggered the release of IL-10 only. Interestingly, A23187 synergized with the activities of CKBM-treated THP-1 cells in terms of IL-1beta and IFNgamma production, while the IL-10 production showed no synergistic relationship between CKBM and A23187. This A23187-induced synergism was associated with a dose-dependent character towards CKBM administration. In view of the intracellular Ca2+ elevation during monocyte activation, our results suggest that CKBM can serve as a promoting agent for modulating the functions of monocytes.

ERK signaling mediates the induction of inflammatory cytokines by bufalin in human monocytic cells

Treatment of human leukemia THP-1 cells with bufalin, a specific inhibitor of Na(+)-K(+)-ATPase, sequentially induces c-fos and inflammatory cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) gene expressions before the appearance of mature phenotypes of monocytic cells. In this study we examined the signal transduction leading to bufalin-induced gene expressions. Bufalin selectively activated extracellular signal-regulated kinase (ERK), compared with other mitogen-activated protein (MAP) kinase family members. Pretreatment of THP-1 cells with PD-98059, an inhibitor of the ERK-kinase cascade, abolished bufalin-induced c-fos and IL-1 beta gene expressions, indicating that the ERK-kinase cascade mediates the induction of inflammatory cytokines by bufalin. Inhibition of the Na(+)/Ca(2+) exchanger by KB-R7943 and of protein kinase C (PKC) by Ro-31-8220 suppressed ERK activation and gene expressions of c-fos and IL-1 beta. These findings suggest that Na(+)-K(+)-ATPase inhibition by bufalin induces calcium influx and thereby activates PKC and ERK. In cells treated with an inhibitor of p38 MAP kinases, SB-203580, bufalin-mediated ERK activation became persistent and the induction of IL-1 beta and TNF-alpha expressions was significantly augmented. These results suggest that cross talk in bufalin-mediated ERK activation is negatively regulated by endogenous p38 MAP kinase activations.

Differential responses of human mononuclear phagocytes to mycobacterial lipoarabinomannans: role of CD14 and the mannose receptor

CD14 is a signaling receptor for both gram-negative bacterial lipopolysaccharide (LPS) and mycobacterial lipoarabinomannan (LAM) that lacks terminal mannosyl units (AraLAM). In contrast, terminally mannosylated LAM (ManLAM) binds the macrophage mannose receptor (MMRc), although the ability of the MMRc to serve as a signaling receptor has not been previously reported. We compared the abilities of AraLAM and ManLAM to induce distinct responses in two monocytic cell populations, freshly isolated human peripheral blood monocytes (PBM) and monocyte-derived macrophages (MDM). The responses examined were chemotaxis and transient changes in free cytosolic calcium ([Ca2+]in). We found that AraLAM but not ManLAM was chemotactic for both PBM and MDM. Migration of these cells in vitro to AraLAM was specifically blocked by an anti-CD14 monoclonal antibody, suggesting that CD14 mediates the chemotactic response to AraLAM. Subsequently, we found that AraLAM induced a transient rise in [Ca2+]in levels within a subpopulation of PBM but not MDM. This response was blocked by anti-CD14 antibodies. In contrast, ManLAM induced a transient rise in [Ca2+]in levels within a subpopulation of MDM but not PBM. This response was blocked by either anti-CD14 or anti-MMRc antibodies. These data suggest that the MMRc can serve as a signaling receptor and that coligation of both CD14 and the MMRc is required to elicit a specific response. Thus, one response to LAM (chemotaxis) can be elicited solely by engaging CD14, whereas a different response (changes in [Ca2+]in levels) depends on both the differentiation state of the cells and concomitant engagement of CD14 and the MMRc.

Adherence-dependent calcium signaling in monocytes: induction of a CD14-high phenotype, stimulus-responsive subpopulation

Isolation of monocytes by plastic adherence alters cell morphology and function. In order to study the effects of cell isolation procedures and subsequent culture on monocyte function, we examined cytoplasmic calcium concentration changes (delta[Ca2+]in) in human monocytes isolated by either negative (magnetic bead) or positive (plastic adherence) selection then stimulated with formyl-Met-Leu-Phe (fMLP), either immediately after isolation, or after 48 h in culture. We have previously shown that fresh adherence-isolated monocytes respond to fMLP with small delta[Ca2+]in and oxidative burst responses, exhibiting larger responses following 48 h of incubation. We now demonstrate that fresh monocytes, prevented from adhering by negative selection, exhibit an even smaller fMLP-induced delta[Ca2+]in, which does not increase during 48 h in culture if cells are kept nonadherent, in Teflon. Calcium responses of adherent, fresh monocytes do not increase if cells are subsequently placed into suspension and maintained nonadherent, but increase if nonadherent cells are permitted to adhere to plastic. Furthermore, augmented fMLP-[Ca2+]in and oxidative burst responses in plastic-adherent cells are restricted to a CD14-high phenotype subpopulation. The CD14-high phenotype also describes a subpopulation of cells that responds to CD4 crosslinking with a rapid delta[Ca2+]in. Induction of a subpopulation of CD14-high expressing cells by adherence may explain in part maturation-induced response changes observed in macrophage but not in monocyte in vitro systems.

Increased IL-1, IL-6 and TNF alpha secretion and mRNA levels in WEHI-3 cells exposed to cyclopiazonic acid

The effects of the mycotoxin cyclopiazonic acid (CPA) on cytokine secretion and gene expression were evaluated in the WEHI-3 murine macrophage cell line. Lipopolysaccharide (LPS)-stimulated and non-stimulated cells were exposed to various concentrations of CPA and culture supernatants were assessed for interleukin (IL)-1 beta, IL-6 and TNFalpha by ELISA. Without LPS stimulation, only IL-6 was increased by CPA at 5000 ng/ml after 1, 2 and 3 days. With LPS stimulation, IL-1 beta was elevated in the presence of 500 and 1000 ng/ml of CPA at 1 day and 500, 1000 and 5000 ng/ml at 2 days and 3 days. TNF alpha was increased by 1000 ng/ml CPA at 12 h and by 500, 1000 and 5000 ng/ml CPA at 1-3 days. IL-6 levels were increased in the presence of 100, 500 and 1000 CPA ng/ml at both 12 h and 3 days and in the presence of 100, 500, 1000 and 5000 ng/ml CPA at both 1 day and 2 days. The cytokine effects were further related to proliferation and cell viability using the MTT [3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide] assay. Proliferation was increased relative to controls in the presence of 50-1000 ng/ml of CPA in LPS-stimulated cells and in the presence of 500-1000 ng/ml CPA in unstimulated cells. In contrast, proliferation was markedly inhibited by 5000 ng/ml CPA in both stimulated and unstimulated cells. To relate the effect of CPA on IL secretion to mRNA transcript levels, LPS-stimulated cells were incubated with 1000 ng/ml of CPA for 2, 4, 8, 12 and 24 h and cytokine mRNA levels were evaluated using RT-PCR in combination with Southern hybridization analysis. In the presence of LPS only, IL-1 beta and IL-6 mRNA peaked at 8 h and 4 h, respectively, and then decreased whereas TNF alpha mRNA was strongly expressed from 2-8 h and markedly decreased at 12 h. In the presence of LPS and CPA, however, IL-1 beta and IL-6 mRNA levels gradually increased up to 24 h reaching 2.5 and 29-fold higher than controls, respectively. In contrast, TNF alpha mRNA levels slowly decreased after 8 h but remained markedly elevated relative to controls. Taken together, these results suggest that CPA can superinduce both secretion and mRNA levels of proinflammatory cytokines associated with macrophage activation. Cytokine upregulation was not always consistent with proliferative effects.

Bacterial stimulators of macrophages

Our current understanding of the interaction between bacteria and macrophages, cells of the immune system that play a major role in the defense against infection, is summarized. Cell-surface structures of Gram-negative and Gram-positive bacteria that account for these interactions are described in detail. Besides surface structures, soluble bacterial molecules, toxins that are derived from pathogenic bacteria, are also shown to modulate macrophage functions. In order to affect macrophage functions, bacterial surface structures have to be recognized by the macrophage and toxins have to be taken up. Subsequently, signal transduction mechanisms are initiated that enable the macrophage to respond to the invading bacteria. To destroy bacteria, macrophages employ many strategies, among which antigen processing and presentation to T cells, phagocytosis, chemotaxis, and different bactericidal mechanisms are considered to be the main weapons.

Lipopolysaccharide-mediated signal transduction through phospholipase D activation in monocytic cell lines

Lipopolysaccharide (LPS)-induced phospholipase D (PLD) activation was investigated in undifferentiated monocytic leukemic cell lines THP-1 and U-937. Treatment of THP-1 or U-937 cells labelled with [32P]orthophosphate, [32P]acyl GPC or [3H]alkyl GPC with LPS, in the presence of 0.5% ethanol, resulted in the accumulation of labelled phosphatidylethanol (PEt) through PLD activation. LPS-mediated PLD activation of THP-1 or U-937 was inhibited by staurosporine (2 microM) and by protein kinase C (PKC) down-regulation with 12-O-tetradecanoylphorbol 13-acetate (TPA) suggesting a role for PKC. In addition to LPS, TPA, ionomycin and cell-permeant analogs of diacylglycerol also stimulated [3H]PEt accumulation. The TPA-induced PEt accumulation was also completely abolished by staurosporine or down-regulation of PKC (> 95% inhibition). Furthermore, the LPS-mediated [32P]PEt formation was attenuated by either depletion of extracellular Ca2+ with EGTA (5 mM) or chelation of intracellular Ca2+ by BAPTA (30 microM). These results indicate that an increase in intracellular Ca2+ is necessary for LPS-mediated PLD activation. Further support for PKC activation by LPS was obtained by determining PKC activity in an in vitro assay of histone H1 phosphorylation using [gamma-32P]ATP. In untreated THP-1 cells, approximately 64% of the PKC activity was localized in the cytosol and 36% in the membrane fraction. Treatment of the cells with LPS (10 micrograms/ml, for 2 h) resulted in an increase of 10% of the membrane-associated PKC activity and a corresponding decrease in the cytosol fraction. These data provide evidence that one of the mechanisms of LPS-mediated signal transduction in human monocytic cell lines involves activation of PLD.

Macrophage activation by T cells: cognate and non-cognate signals

Both tumor necrosis factor-alpha and interferon-gamma are involved in the activation of macrophage cytocidal/cytostatic effector function. Recent studies provide evidence that, in non-septic inflammatory disease, T cells may activate macrophages primed by interferon-gamma either by providing tumor necrosis factor-alpha (in soluble or membrane-anchored form) or by inducing macrophage tumor necrosis factor-alpha production by antigen-non-specific cognate interactions. Conversely, T cells may inhibit macrophage activation by producing cytokines that inhibit either tumor necrosis factor-alpha production or interferon-gamma receptor signaling.

Effect of pteridine derivatives on intracellular calcium concentration in human monocytic cells

Pteridines are heterocyclic compounds which are synthesized and released by human monocytes/macrophages following stimulation by interferon-gamma. Their concentration in various body fluids proved to be indicative for the stimulation of the cellular immune system, and determination of pteridines has become an important diagnostic tool. We show that pteridine derivatives, namely neopterin (N), 7,8-dihydroneopterin (NH2), and 5,6,7,8-tetrahydrobiopterin (BH4) increase intracellular calcium (Cai) in human monocytic cells. Significant increases of Cai are observed at 10 nmol/l NH2, at 100 nmol/l BH4 and at 1 mol/l N, i.e. at concentrations encountered in vivo. At a concentration of 1 mumol/l, Cai is increased (from a control value of 145 +/- 7 nmol/l) to 464 +/- 62 nmol/l (NH2), 340 +/- 41 nmol/l (BH4) and 344 +/- 46 nmol/l (N), respectively. The increase of Cai depends on the presence of extracellular calcium and is likely to be due to activation of a calcium channel. We show that the absence of extracellular calcium or the addition of lanthanum ions to the extracellular fluid fully reverses the pteridine-induced increase of Cai. According to these observations, pteridines may mimic the effects of other inflammatory mediators on monocytic cells and seem to be involved in the crosstalk of immunocompetent cells.