LPS和CpG寡聚DNA对单核巨噬细胞的效应和作用机制的研究
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摘要
革兰氏阴性细菌胞壁外膜中的脂多糖（LPS）以及细菌DNA和含非甲基化CpG基序
的寡聚脱氧核糖核苷酸（CpG ODN）等都被机体当成危险信号，可激活单核巨噬细胞、
树突状细胞等抗原提呈细胞合成和分泌多种细胞因子及其它炎症介质。本研究主要探讨
了一种新型树突状细胞来源的G蛋白信号转导调节蛋白（DC-RGS）、核受体过氧化体增
殖物激活受体（PPAR）及主要组织相容性复合物Ⅱ类分子（MHC-Ⅱ）在LPS和CpG ODN
活化单核巨噬细胞等抗原提呈细胞产生细胞因子及一氧化氮（NO）过程中的作用。我们
通过基因转染研究发现DC-RGS对LPS诱导人单核细胞THP-1产生细胞因子（TNF-α、
IL-1β、IL-6和IL-12p70）具有微调作用，但不影响IL-8的分泌；CpG ODN也具有与LPS
相似的脱敏现象而且它们可以互相诱导对方脱敏；脱敏时THP-1分泌IL-8不受抑制；用
PPAR的配体和基因转染研究发现PPARα和PPARγ能以配体和转录活性非依赖性机制抑
制巨噬细胞RAW264.7产生IL-12p40和NO，但不影响THP-1细胞产生IL-8；脱敏后PPARγ
表达增高提示其可能反馈性参与LPS和CpG ODN脱敏过程；抗小鼠MHC-Ⅱ的单克隆
抗体B21-2能诱导APCs产生NO，合用LPS、CpG ODN、超抗原SEA或热休克蛋白
HSP60则具有协同效应，表明MHC-Ⅱ的信号转导过程对LPS、CpG ODN、超抗原SEA
和HSP60等危险信号的效应以及信号转导过程具有调节作用。这些发现对炎症感染、动
脉粥样硬化和一些自身免疫性疾病的发病机制的了解以及防治具有一定的意义。
Part I: Identification of a Novel RGS Molecule and Its Tuning
Effects on Cytokine Production by Lipopolysaccharide Treated
THP-1 Monocytes
Regulator of G-protein signaling (RGS) proteins are GTPase
activating proteins that
inhibit signaling in various cellular responses controlled by
heterotrimeric G proteins. Here we
report a novel RGS molecule cloned from human dendritic cells
(DCs), designated DC-RGS,
and its role in regulating the responsiveness of monocytes to
lipopolysaccharide (LPS) in vitro.
We show that DC-RGS is widely distributed and mainly expressed in
myeloid cells. Inhibition
of DC-RGS expression in THP-l cells by antisense technique
differentially sensitized
LPS-induced production of tumor necrosis factor (TNF)-ct,
interleukin (IL)-1 j3, IL-6, IL-8 and
11-12. Moreover, inhibition of DC-RGS expression partially
restored secretion of TNF-ct and
11-6 by LPS desensitized TFW-1 cells. Overexpression of DC-RGS in
THP-1 cells did not
significantly affect cytokine production compared with mock
control. Thus, DC-RGS, a novel
RGS cloned from DCs, plays a fine-timing role in LPS responses
and participates in regulating
responsiveness of monocytes to LPS. We proposed that RGS proteins
together with G proteins
might participate in innate immunity and subsequently affect the
adaptive immune responses.
Part II: Evidence for Activation-independent Repression
Mechanism of PPARy in LPS and CpG ODN Responses: Relevance
to Desensitization
Lipopolysaccharide (LPS) desensitization or endotoxin tolerance,
a state of hypo-
responsiveness to LPS induced by pretreatment of low dose of LPS,
is characterized by
decreased proinflammatory factors production in response to
secondary LPS challenge even in
10
high dose. Here we showedoligodeoxynucleotides containing
unmethylated CpG motif (CpG
ODN), similar to LPS, could also resulted in desensitization as
evidenced from reduced nitric
oxide (NO) and cytokine IL-12p40 production by murine macrophage
Raw264.7 cells. LPS
and CpG ODN could cross-desensitize each other to induce NO and
IL-12p40 production but
CpG ODN was more potential. Interestingly, 1-8 production by
THIP-l human monocytes
couldn't be desensitized by LPS or/and CpG ODN. We then tested
the hypothesis that
peroxisome proliferator-activated receptor (PPAR) a and PPARy,
ligand-dependent nuclear
receptors that have been implicated in negative-modulating
macrophage cell activation, might
be involved in desensitization state induction. We showed that
pretreatment with ligands of
PPARcC (agonist Wy-14643) and PPARy (agonist 15-d-PGJ2 and
antagonist BADGE), but not
with PPARy agonist pioglitazone, reduced LPS or CpG ODN-induced
NO and IL-12p4O
production. Further, enhanced expression of PPARQ or PPARy
(including a dominant-negative
PPARy mutant) by transient transfection, mimics desensitization
induction, attenuated LPS or
CpG ODN-induced NO and ]IL-l2p4O production, but did not affect
IL-S production. Western
blot analysis showed that LPS or CpG ODN treatment resulted in
altered kinetics of PPAR7
and NF-icB p50 subunit expression while no alteration of PPARcL
expression in THP-1 cells.
LPS or CpG ODN pretreatment significantly increased expression of
PPART. Thus we suggest
that PPARy might participate in signaling and desensitization
induced by LPS and CpG ODN
in activation-independent manner and constitutively.
Part Ill: Modulating Effects of B21-2, a Monoclonal Antibody
Against MHC class II molecules, on Danger Signals-Induced NO
Production by Antigen-Presenting Cells
Major histocompatibilty complex class II molecules (M1HC II) are
efficiently expressed
by antigen-presenting cells (APCs), including macrophages,
dendritic cells (DCs) and B cells.
Macrophages and DCs could be induced to produce nitric oxide (NO)
by danger signals, such
as bacterial endotoxin lipopolysaccharide (LPS)
的寡聚脱氧核糖核苷酸（CpG ODN）等都被机体当成危险信号，可激活单核巨噬细胞、
树突状细胞等抗原提呈细胞合成和分泌多种细胞因子及其它炎症介质。本研究主要探讨
了一种新型树突状细胞来源的G蛋白信号转导调节蛋白（DC-RGS）、核受体过氧化体增
殖物激活受体（PPAR）及主要组织相容性复合物Ⅱ类分子（MHC-Ⅱ）在LPS和CpG ODN
活化单核巨噬细胞等抗原提呈细胞产生细胞因子及一氧化氮（NO）过程中的作用。我们
通过基因转染研究发现DC-RGS对LPS诱导人单核细胞THP-1产生细胞因子（TNF-α、
IL-1β、IL-6和IL-12p70）具有微调作用，但不影响IL-8的分泌；CpG ODN也具有与LPS
相似的脱敏现象而且它们可以互相诱导对方脱敏；脱敏时THP-1分泌IL-8不受抑制；用
PPAR的配体和基因转染研究发现PPARα和PPARγ能以配体和转录活性非依赖性机制抑
制巨噬细胞RAW264.7产生IL-12p40和NO，但不影响THP-1细胞产生IL-8；脱敏后PPARγ
表达增高提示其可能反馈性参与LPS和CpG ODN脱敏过程；抗小鼠MHC-Ⅱ的单克隆
抗体B21-2能诱导APCs产生NO，合用LPS、CpG ODN、超抗原SEA或热休克蛋白
HSP60则具有协同效应，表明MHC-Ⅱ的信号转导过程对LPS、CpG ODN、超抗原SEA
和HSP60等危险信号的效应以及信号转导过程具有调节作用。这些发现对炎症感染、动
脉粥样硬化和一些自身免疫性疾病的发病机制的了解以及防治具有一定的意义。
Part I: Identification of a Novel RGS Molecule and Its Tuning
Effects on Cytokine Production by Lipopolysaccharide Treated
THP-1 Monocytes
Regulator of G-protein signaling (RGS) proteins are GTPase
activating proteins that
inhibit signaling in various cellular responses controlled by
heterotrimeric G proteins. Here we
report a novel RGS molecule cloned from human dendritic cells
(DCs), designated DC-RGS,
and its role in regulating the responsiveness of monocytes to
lipopolysaccharide (LPS) in vitro.
We show that DC-RGS is widely distributed and mainly expressed in
myeloid cells. Inhibition
of DC-RGS expression in THP-l cells by antisense technique
differentially sensitized
LPS-induced production of tumor necrosis factor (TNF)-ct,
interleukin (IL)-1 j3, IL-6, IL-8 and
11-12. Moreover, inhibition of DC-RGS expression partially
restored secretion of TNF-ct and
11-6 by LPS desensitized TFW-1 cells. Overexpression of DC-RGS in
THP-1 cells did not
significantly affect cytokine production compared with mock
control. Thus, DC-RGS, a novel
RGS cloned from DCs, plays a fine-timing role in LPS responses
and participates in regulating
responsiveness of monocytes to LPS. We proposed that RGS proteins
together with G proteins
might participate in innate immunity and subsequently affect the
adaptive immune responses.
Part II: Evidence for Activation-independent Repression
Mechanism of PPARy in LPS and CpG ODN Responses: Relevance
to Desensitization
Lipopolysaccharide (LPS) desensitization or endotoxin tolerance,
a state of hypo-
responsiveness to LPS induced by pretreatment of low dose of LPS,
is characterized by
decreased proinflammatory factors production in response to
secondary LPS challenge even in
10
high dose. Here we showedoligodeoxynucleotides containing
unmethylated CpG motif (CpG
ODN), similar to LPS, could also resulted in desensitization as
evidenced from reduced nitric
oxide (NO) and cytokine IL-12p40 production by murine macrophage
Raw264.7 cells. LPS
and CpG ODN could cross-desensitize each other to induce NO and
IL-12p40 production but
CpG ODN was more potential. Interestingly, 1-8 production by
THIP-l human monocytes
couldn't be desensitized by LPS or/and CpG ODN. We then tested
the hypothesis that
peroxisome proliferator-activated receptor (PPAR) a and PPARy,
ligand-dependent nuclear
receptors that have been implicated in negative-modulating
macrophage cell activation, might
be involved in desensitization state induction. We showed that
pretreatment with ligands of
PPARcC (agonist Wy-14643) and PPARy (agonist 15-d-PGJ2 and
antagonist BADGE), but not
with PPARy agonist pioglitazone, reduced LPS or CpG ODN-induced
NO and IL-12p4O
production. Further, enhanced expression of PPARQ or PPARy
(including a dominant-negative
PPARy mutant) by transient transfection, mimics desensitization
induction, attenuated LPS or
CpG ODN-induced NO and ]IL-l2p4O production, but did not affect
IL-S production. Western
blot analysis showed that LPS or CpG ODN treatment resulted in
altered kinetics of PPAR7
and NF-icB p50 subunit expression while no alteration of PPARcL
expression in THP-1 cells.
LPS or CpG ODN pretreatment significantly increased expression of
PPART. Thus we suggest
that PPARy might participate in signaling and desensitization
induced by LPS and CpG ODN
in activation-independent manner and constitutively.
Part Ill: Modulating Effects of B21-2, a Monoclonal Antibody
Against MHC class II molecules, on Danger Signals-Induced NO
Production by Antigen-Presenting Cells
Major histocompatibilty complex class II molecules (M1HC II) are
efficiently expressed
by antigen-presenting cells (APCs), including macrophages,
dendritic cells (DCs) and B cells.
Macrophages and DCs could be induced to produce nitric oxide (NO)
by danger signals, such
as bacterial endotoxin lipopolysaccharide (LPS)
引文
1． Kehrl, J. H. 1998． Heterotrimeric G protein signaling: roles in immune function and fine-tuning by RGS proteins. Immunity 8:1
2． Hornquist, C. E., X. Lu. P. M. Rogers-Fani, U. Rudolph, S. Shappell, L. Birnbaumer. and G. R. Harriman. 1997． G(alpha)i2-deficient mice with colitis exhibit a local increase in memory CD4+ T cells and proinflammatory Thl-type cytokines. J. Immunol. 158:1068
3． He, J., S. Gurunathan, A. Iwasaki, B. Ash-Shaheed, and B. L. Kelsall. 2000． Primary role for Gi protein signaling in the regulation of interleukin 12 production and the induction of T helper cell type 1 responses. J. Exp. Med. 191:1605
4． Dohlman, H. G. and J. Thorner. 1997． RGS proteins and signaling by heterotrimeric G proteins. J. Biol. Chem. 272:3871．
5． Herman, D. M. and A. G. Oilman. 1998． Mammalian RGS proteins: barbarians at the gate. J. Biol. Chem. 273:1269
6． De Vries, L., and M. G. Farquhar. 1999． RGS proteins: more than just GAPs for heterotrimeric G proteins. Trends. Cell. Biol. 9:138
7． Hong, J. X., G. L. Wilson, C. H. .Fox, and J. H. Kehrl. 1993． Isolation and characterization of a novel B cell activation gene. J. Immunol. 150:3895．
8． Newton, J. S., R. W. Deed, E. L. Mitchell, J. J. Murphy, and J. D. Norton. 1993． A B cell specific immediate early human gene is located on chromosome band 1q31 and encodes an a helical basic phosphoprotein. Biochim. Biophys. Acta. 1216: 314
9． Siderovski, D. P., S. P. Heximer, and D. R. Forsdyke. 1994． A human gene encoding a putative basic helix-loop-helix phosphoprotein whose mRNA increases rapidly in cycloheximide-treated blood mononuclear cells. DNA Cell. Biol. 12:125
10． Beadling, C., K. M. Druey, G. Richter, J. H. Kehrl, and K. A. Smith. 1999． Regulators of G protein signaling exhibit distinct patterns of gene expression and target G protein specificity in human lymphocytes. J. Immunol. 162:2677
11． Bowman, E. P., J. J. Campbell, K. M. Druey, A. Scheschonka, J. H. Kehrl, and E. C. Butcher. 1998． Regulation of chemotactic and proadhesive responses to chemoattractant receptors by RGS (regulator of G-protein signaling) family members. J. Biol. Chem. 273:28040
12． Denecke, B., A. Meyerdierks, and E. C. Bottger. 1999． RGS1 is expressed in monocytes and acts as a GTPase-activating protein for G-protein-coupled chemoattractant receptors. J. Biol. Chem. 274:26860
13． Moratz, C., V H. Kang, K. M. Druey, C. S. Shi, A. Scheschonka, P. M. Murphy, T. Kozasa, and J.H. Kehrl. 2000． Regulator of G protein signaling 1 (RGS1) markedly impairs Gi alpha signaling responses of B lymphocytes. J. Immunol. 164:1829
14． Reif, K., and J. G. Cyster. 2000． RGS molecule expression in murine B lymphocytes and ability to down-regulate chemotaxis to lymphoid chemokines. J. Immunol. 164:4720
15． Panetta, R., Y. Guo, S. Magder, and M. T. Greenwood. 1999． Regulators of G-protein signaling (RGS) 1 and 16 are induced in response to bacterial lipopolysaccharide and stimulate c-fos promoter expression. Biochem. Biophys. Res. Commun. 259:550
16． Benzing, T., R. Brandes, L. Sellin, B. Schermer, S. Lecker, G. Walz, and E. Kim. 1999． Upregulation of RGS7 may contribute to tumor necrosis factor-induced changes in central nervous function. Nat. Med. 5:913
17． Cao, X., W. Zhang, T. Wan, L. He, T. Chen, Z. Yuan, S. Ma, Y. Yu, and G. Chen. 2000． Molecular cloning and characterization of a novel CXC chemokine MIP-2gamma chemoattractant for human neutrophils and dendritic cells. J. Immunol. 165: 2588
18． LaRue, K. E., and C. E. McCall. 1994． A labile transcriptional represser modulates endotoxin tolerance. J. Exp. Med 180:2269
19． Hart, D. N. J. 1997． Dendritic cells: unique leukocyte populations which control the primary immune response. Blood. 90:3245
20． Jakway, J. P., and A. L DeFranco. 1986． Pertussis toxin inhibition of B cell and macrophage responses to bacterial lipopolysaccharide. Science. 234:743
21． Zhang, X., and D. C. Morrison. 1993． Pertussis toxin-sensitive factor differentially regulates lipopolysaccharide-induced tumor necrosis factor-alpha and nitric oxide production in mouse peritoneal macrophages. J. Immunol. 150:1011
22． Daniel-Issakani, S., A. M. Spiegel, and B. Strulovici. 1989． Lipopolysaccharide response is linked to the GTP binding protein, Gi2, in the promonocytic cell line U937． J. Biol. Chem. 264:20240
23． Durando, M. M., K. E. Meier, and J. A. Cook. 1998． Endotoxin activation of mitogen-activated protein kinase in THP-1 cells; diminished activation following endotoxin desensitization. J. Leukoc. Biol. 64:259
24． Yasui, K., E. L. Becker, and R. I. Sha'afi. 1992． Lipopolysaccharide and serum cause the translocation of G-protein to the membrane and prime neutrophils via CD14． Biochem. Biophys. Res. Commun. 183:1280
25． Kugi, M., K. Kitamura, G. L. Cottam, and R. T. Miller. 1995． Expression of G alpha i2 mimics several aspects of LPS priming in a murine macrophage-like cell line. J. Inflamm. 45:175
26． Solomon, K. R., E. A. Kurt-Jones, R. A. Saladino, A. M. Stack, I. F. Dunn, M. Ferretti, D. Golenbock, G. R. Fleisher, and R. W. Finberg. 1998． Heterotrimeric G proteins physically associated with the lipopolysaccharide receptor CD14 modulate both in vivo and in vitro responses to lipopolysaccharide. J. Clin. Invest. 102:2019
27． Straub, R. H., and D. N. Mannel. 1999． How the immune system puts the brain to sleep? Nat. Med. 5:877
28． Cook, J. A. 1998． Molecular basis of endotoxin tolerance. Ann. N. Y. Acad. Sci. 851:426
29． Yoza, B., K. LaRue, and C. McCall. 1998． Molecular mechanisms responsible for endotoxin tolerance. Prog. Clin. Biol. Res. 397:209
30． Fernando, L. P., M. Makhlouf, A. N. Fernando, S. Ashton, P. V. Halushka, and J. A. Cook. 1999． Tolerance to LPS decreases macrophage G protein content. Shock. 11:330
31． Rieser. C, C. Papesh, M. Herold, G. Bock, R Ramoner, H. Klocker, G. Bartsch, and M. Thurnher. 1998 Differential deactivation of human dendritic cells by endotoxin desensitization: role of tumor necrosis factor-alpha and prostaglandin E2． Blood 91:3112
32． Karp, C. L., M. Wysocka, X. Ma, M. Marovich, R. E. Factor, T. Nutman, M. Armant, L. Wahl. P. Cuomo, and G. Trinchien. 1998． Potent suppression of IL-12 production from monocytes and dendritic cells during endotoxin tolerance. Eur. J. Immunol. 28:3128
33． Wittmann, M., V. A. Larsson, P. Schmidt, G. Begemann, A. Kapp, and T. Werfel. 1999． Suppression of interleukin-12 production by human monocytes after preincubation with lipopolysaccharide. Blood 94:1717
34． Kaufmann, A., D. Gemsa, and H. Sprenger. 2000． Differential desensitization of lipopolysaccharide-inducible chemokine gene expression in human monocytes and macrophages. Eur. J. Immunol. 30:1562
35． Shu, H., B. Wong, G. Zhou, Y. Li, J. Berger, J. W. Woods, S. D. Wright, and T. Q. Cai. 2000． Activation of PPARalpha or gamma Reduces Secretion of Matrix Metalloproteinase 9 but Not Interleukin 8 from Human Monocytic THP-1 Cells. Biochem. Biophys. Res. Commun. 267:345
36． Hepler, J. R., D. M. Berman, A. G. Gilman, and T. Kozasa. 1997． RGS4 and GAIP are GTPase-activating proteins for Gq alpha and block activation of phospholipase C beta by gamma-thio-GTP-Gq alpha. Proc. Natl. Acad Sci. U. S. A. 94:428
37． Bunemann M. and M. M. Hosey. 1998． Regulators of G protein signaling (RGS) proteins constitutively activate Gbeta gamma-gated potassium channels. J. Biol. Chem. 273:31186
38． Ferrari D., P. Chiozzi, S. Falzoni, S. Hanau, and F. D. Virgilio. 1997． Purinergic modulation of interleukin-1 release from microglial cells stimulated with bacterial endotoxin. J. Exp. Med. 185, 579
39． Petrova T.V., K. T. Akama, and L. J. Van Eldik. 1999． Selective modulation of BV-2 microglial activation by prostaglandin E(2) . Differential effects on endotoxin-stimulated cytokine induction. J. Biol. Chem. 274:28823
40． Hoffmann, J. A., F. C. Kafatos, C. A. Janeway, and R. A. Ezekowitz. 1999． Phylogenetic perspectives in innate immunity. Science. 284:1313
41． Fearon, D. T., and R. M. Locksley. 1996． The instructive role of innate immunity in the acquired immune response. Science. 272:50
42． Trinchieri, G. 1995． Interleukin-12: A proinflammatory cytokine with immunoregulatory functions that bridge innate resistance and antigen-specific adaptive immunity. Annu. Rev. Immunol. 13:251
43． Park IK, Klug CA, Li K, Jerabek L, Li L, Nanamori M, Neubig RR, Hood L, Weissman IL, Clarke MF. Molecular cloning and characterization of a novel regulator of G-protein signaling from mouse hematopoietic stem cells. J Biol Chem 2001;276(2) :915-923
2． Hornquist, C. E., X. Lu. P. M. Rogers-Fani, U. Rudolph, S. Shappell, L. Birnbaumer. and G. R. Harriman. 1997． G(alpha)i2-deficient mice with colitis exhibit a local increase in memory CD4+ T cells and proinflammatory Thl-type cytokines. J. Immunol. 158:1068
3． He, J., S. Gurunathan, A. Iwasaki, B. Ash-Shaheed, and B. L. Kelsall. 2000． Primary role for Gi protein signaling in the regulation of interleukin 12 production and the induction of T helper cell type 1 responses. J. Exp. Med. 191:1605
4． Dohlman, H. G. and J. Thorner. 1997． RGS proteins and signaling by heterotrimeric G proteins. J. Biol. Chem. 272:3871．
5． Herman, D. M. and A. G. Oilman. 1998． Mammalian RGS proteins: barbarians at the gate. J. Biol. Chem. 273:1269
6． De Vries, L., and M. G. Farquhar. 1999． RGS proteins: more than just GAPs for heterotrimeric G proteins. Trends. Cell. Biol. 9:138
7． Hong, J. X., G. L. Wilson, C. H. .Fox, and J. H. Kehrl. 1993． Isolation and characterization of a novel B cell activation gene. J. Immunol. 150:3895．
8． Newton, J. S., R. W. Deed, E. L. Mitchell, J. J. Murphy, and J. D. Norton. 1993． A B cell specific immediate early human gene is located on chromosome band 1q31 and encodes an a helical basic phosphoprotein. Biochim. Biophys. Acta. 1216: 314
9． Siderovski, D. P., S. P. Heximer, and D. R. Forsdyke. 1994． A human gene encoding a putative basic helix-loop-helix phosphoprotein whose mRNA increases rapidly in cycloheximide-treated blood mononuclear cells. DNA Cell. Biol. 12:125
10． Beadling, C., K. M. Druey, G. Richter, J. H. Kehrl, and K. A. Smith. 1999． Regulators of G protein signaling exhibit distinct patterns of gene expression and target G protein specificity in human lymphocytes. J. Immunol. 162:2677
11． Bowman, E. P., J. J. Campbell, K. M. Druey, A. Scheschonka, J. H. Kehrl, and E. C. Butcher. 1998． Regulation of chemotactic and proadhesive responses to chemoattractant receptors by RGS (regulator of G-protein signaling) family members. J. Biol. Chem. 273:28040
12． Denecke, B., A. Meyerdierks, and E. C. Bottger. 1999． RGS1 is expressed in monocytes and acts as a GTPase-activating protein for G-protein-coupled chemoattractant receptors. J. Biol. Chem. 274:26860
13． Moratz, C., V H. Kang, K. M. Druey, C. S. Shi, A. Scheschonka, P. M. Murphy, T. Kozasa, and J.H. Kehrl. 2000． Regulator of G protein signaling 1 (RGS1) markedly impairs Gi alpha signaling responses of B lymphocytes. J. Immunol. 164:1829
14． Reif, K., and J. G. Cyster. 2000． RGS molecule expression in murine B lymphocytes and ability to down-regulate chemotaxis to lymphoid chemokines. J. Immunol. 164:4720
15． Panetta, R., Y. Guo, S. Magder, and M. T. Greenwood. 1999． Regulators of G-protein signaling (RGS) 1 and 16 are induced in response to bacterial lipopolysaccharide and stimulate c-fos promoter expression. Biochem. Biophys. Res. Commun. 259:550
16． Benzing, T., R. Brandes, L. Sellin, B. Schermer, S. Lecker, G. Walz, and E. Kim. 1999． Upregulation of RGS7 may contribute to tumor necrosis factor-induced changes in central nervous function. Nat. Med. 5:913
17． Cao, X., W. Zhang, T. Wan, L. He, T. Chen, Z. Yuan, S. Ma, Y. Yu, and G. Chen. 2000． Molecular cloning and characterization of a novel CXC chemokine MIP-2gamma chemoattractant for human neutrophils and dendritic cells. J. Immunol. 165: 2588
18． LaRue, K. E., and C. E. McCall. 1994． A labile transcriptional represser modulates endotoxin tolerance. J. Exp. Med 180:2269
19． Hart, D. N. J. 1997． Dendritic cells: unique leukocyte populations which control the primary immune response. Blood. 90:3245
20． Jakway, J. P., and A. L DeFranco. 1986． Pertussis toxin inhibition of B cell and macrophage responses to bacterial lipopolysaccharide. Science. 234:743
21． Zhang, X., and D. C. Morrison. 1993． Pertussis toxin-sensitive factor differentially regulates lipopolysaccharide-induced tumor necrosis factor-alpha and nitric oxide production in mouse peritoneal macrophages. J. Immunol. 150:1011
22． Daniel-Issakani, S., A. M. Spiegel, and B. Strulovici. 1989． Lipopolysaccharide response is linked to the GTP binding protein, Gi2, in the promonocytic cell line U937． J. Biol. Chem. 264:20240
23． Durando, M. M., K. E. Meier, and J. A. Cook. 1998． Endotoxin activation of mitogen-activated protein kinase in THP-1 cells; diminished activation following endotoxin desensitization. J. Leukoc. Biol. 64:259
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