LPS-Induced Murine Systemic Inflammation Is Driven by Parenchymal Cell Activation and Exclusively Predicted by Early MCP-1 Plasma Levels

Systemic inflammation remains a major cause of morbidity and mortality in the United States, across many disease processes. One classic murine model to study this syndrome is lipopolysaccharide (LPS)–induced Toll-like receptor 4 (TLR4)–dependent systemic inflammation. Although most studies have focused on inflammatory cell TLR4 responses, parenchymal cells also express TLR4. Our objective was to define the in vivo role of parenchymal- versus marrow-derived cell activation via TLR4 during LPS-induced inflammation. Mice bearing TLR4 on parenchymal cells only, marrow-derived cells only, both, or neither were generated using bone marrow transplantation. Mortality occurred only in mice that had TLR4 expression on their parenchymal cells. Before onset, virtually all major plasma cytokines and blood neutrophil responses were related to marrow-derived cell activation via TLR4. The only cytokine predictive of oncoming systemic inflammation was the chemokine monocyte chemoattractant protein-1. Late blood neutrophil responses were related to the presence of TLR4 on either parenchymal or marrow cells, whereas plasma cytokine elevations late in LPS-induced systemic inflammation were dependent on mice having TLR4 in both cell compartments. Parenchymal cell activation via TLR4 is a key component of LPS-induced systemic inflammation and mortality, although most plasma cytokine levels and blood neutrophil responses were not key components. Given its unique role, future studies into monocyte chemoattractant protein-1's exact role during systemic inflammation are warranted. Systemic inflammation remains a major cause of morbidity and mortality in the United States, across many disease processes. One classic murine model to study this syndrome is lipopolysaccharide (LPS)–induced Toll-like receptor 4 (TLR4)–dependent systemic inflammation. Although most studies have focused on inflammatory cell TLR4 responses, parenchymal cells also express TLR4. Our objective was to define the in vivo role of parenchymal- versus marrow-derived cell activation via TLR4 during LPS-induced inflammation. Mice bearing TLR4 on parenchymal cells only, marrow-derived cells only, both, or neither were generated using bone marrow transplantation. Mortality occurred only in mice that had TLR4 expression on their parenchymal cells. Before onset, virtually all major plasma cytokines and blood neutrophil responses were related to marrow-derived cell activation via TLR4. The only cytokine predictive of oncoming systemic inflammation was the chemokine monocyte chemoattractant protein-1. Late blood neutrophil responses were related to the presence of TLR4 on either parenchymal or marrow cells, whereas plasma cytokine elevations late in LPS-induced systemic inflammation were dependent on mice having TLR4 in both cell compartments. Parenchymal cell activation via TLR4 is a key component of LPS-induced systemic inflammation and mortality, although most plasma cytokine levels and blood neutrophil responses were not key components. Given its unique role, future studies into monocyte chemoattractant protein-1's exact role during systemic inflammation are warranted. Systemic inflammation remains a major cause of morbidity and mortality in the United States because it is involved in a host of different infectious and noninfectious diseases.1Bhatia M. Acute pancreatitis as a model of SIRS.Front Biosci. 2009; 14: 2042-2050Crossref PubMed Scopus (70) Google Scholar, 2Bhatia M. He M. Zhang H. Moochhala S. Sepsis as a model of SIRS.Front Biosci. 2009; 14: 4703-4711Crossref PubMed Scopus (67) Google Scholar, 3Dahiya P. Burns as a model of SIRS.Front Biosci. 2009; 14: 4962-4967Crossref PubMed Scopus (71) Google Scholar One classic animal model for this process is triggered by lipopolysaccharide (LPS), a Gram-negative bacterial toxin recognized solely by Toll-like receptor 4 (TLR4).4Thomas L. The physiological disturbances produced by endotoxins.Annu Rev Physiol. 1954; 16: 467-490Crossref PubMed Scopus (60) Google Scholar The role of TLR4 as the much-sought LPS receptor was made over a decade ago through the serendipitous discovery of mouse substrains completely resistant to this toxin.5Poltorak A. He X. Smirnova I. Liu M.Y. Van Huffel C. Du X. Birdwell D. Alejos E. Silva M. Galanos C. Freudenberg M. Ricciardi-Castagnoli P. Layton B. Beutler B. Defective LPS signaling in C3H/HeJ and C57BL/10ScCr mice: mutations in Tlr4 gene.Science. 1998; 282: 2085-2088Crossref PubMed Scopus (6583) Google Scholar, 6Qureshi S.T. Lariviere L. Leveque G. Clermont S. Moore K.J. Gros P. Malo D. Endotoxin-tolerant mice have mutations in Toll-like receptor 4 (Tlr4).J Exp Med. 1999; 189: 615-625Crossref PubMed Scopus (1365) Google Scholar Since then, TLR4 mutant or knockout mice have been used to study global TLR4 dependence in a host of other systemic inflammatory diseases.7Barsness K.A. Arcaroli J. Harken A.H. Abraham E. Banerjee A. Reznikov L. McIntyre R.C. Hemorrhage-induced acute lung injury is TLR-4 dependent.Am J Physiol Regul Integr Comp Physiol. 2004; 287: R592-R599Crossref PubMed Scopus (118) Google Scholar, 8Levy R.M. Prince J.M. Yang R. Mollen K.P. Liao H. Watson G.A. Fink M.P. Vodovotz Y. Billiar T.R. Systemic inflammation and remote organ damage following bilateral femur fracture requires Toll-like receptor 4.Am J Physiol Regul Integr Comp Physiol. 2006; 291: R970-R976Crossref PubMed Scopus (89) Google Scholar, 9Breslin J.W. Wu M.H. Guo M. Reynoso R. Yuan S.Y. Toll-like receptor 4 contributes to microvascular inflammation and barrier dysfunction in thermal injury.Shock. 2008; 29: 349-355Crossref PubMed Scopus (60) Google Scholar Investigations into the host systemic inflammatory response have focused largely on the actions of inflammatory cells, in part because these cells are easily accessible for study. Responses of these cells to LPS have been well documented, along with their roles in acute and chronic tissue injury.10Beutler B. Rietschel E.T. Innate immune sensing and its roots: the story of endotoxin.Nat Rev Immunol. 2003; 3: 169-176Crossref PubMed Scopus (1078) Google Scholar It is known, however, that TLR4 is also widely expressed by many different types of parenchymal cells.11Zarember K.A. Godowski P.J. Tissue expression of human Toll-like receptors and differential regulation of Toll-like receptor mRNAs in leukocytes in response to microbes, their products, and cytokines.J Immunol. 2002; 168: 554-561Crossref PubMed Scopus (1071) Google Scholar It remains unclear what role parenchymal cell activation via such receptors plays in the pathophysiological characteristics of systemic inflammation. Previous studies12Andonegui G. Bonder C.S. Green F. Mullaly S.C. Zbytnuik L. Raharjo E. Kubes P. Endothelium-derived Toll-like receptor-4 is the key molecule in LPS-induced neutrophil sequestration into lungs.J Clin Invest. 2003; 111: 1011-1020Crossref PubMed Scopus (352) Google Scholar, 13Tavener S.A. Long E.M. Robbins S.M. McRae K.M. Van Remmen H. Kubes P. Immune cell Toll-like receptor 4 is required for cardiac myocyte impairment during endotoxemia.Circ Res. 2004; 95: 700-707Crossref PubMed Scopus (138) Google Scholar, 14Zhou H. Andonegui G. Wong C.H. Kubes P. Role of endothelial TLR4 for neutrophil recruitment into central nervous system microvessels in systemic inflammation.J Immunol. 2009; 183: 5244-5250Crossref PubMed Scopus (131) Google Scholar, 15Zhou H. Lapointe B.M. Clark S.R. Zbytnuik L. Kubes P. A requirement for microglial TLR4 in leukocyte recruitment into brain in response to lipopolysaccharide.J Immunol. 2006; 177: 8103-8110Crossref PubMed Scopus (142) Google Scholar into the roles of these cells in response to LPS have focused on one particular organ or tissue, as opposed to the global host response. The objective of these studies was to determine whether and to what extent parenchymal cell activation by TLR4 contributes to LPS-induced systemic inflammation in terms of both early events (onset and neutropenia) and late events (neutrophilia, organ neutrophil infiltration, and mortality).4Thomas L. The physiological disturbances produced by endotoxins.Annu Rev Physiol. 1954; 16: 467-490Crossref PubMed Scopus (60) Google Scholar Determining the kinetics of these changes is key to this inquiry because some of the most prominent changes could be the consequence, rather than the cause. Hence, within the context of these studies, we also tested various cytokines and chemokines early and late in the disease process to determine which (if any) are crucial to systemic inflammation. Our hypothesis is that systemic inflammation is actually driven by parenchymal cell activation via TLR4 while plasma cytokine levels are driven instead by marrow-derived cell activation via TLR4. All studies were approved by Mayo Clinic's institutional animal care and use committee. Bone marrow transplantations were conducted between C57BL TLR4 wild-type and/or knockout mice (Jackson Laboratories, Bar Harbor, ME) using previously published methods.16Spangrude G.J. Assessment of lymphocyte development in radiation bone marrow chimeras.Curr Protoc Immunol. 2008; (Chap 4:Unit 4.6)Crossref Google Scholar In brief, recipient mice were administered neomycin (4 mg/mL in drinking water) for 24 hours and then irradiated twice using 5-Gy doses 3 hours apart in a Cs137 irradiator (J.L. Shepard & Associates, San Fernando, CA). Donor mice were euthanized, and bone marrow was sterilely extracted from excised femurs and tibia. Eight million bone marrow cells, suspended in sterile PBS, were introduced into each recipient mouse via jugular vein injection under general anesthesia. Recipient mice continued to receive 4 mg/mL neomycin for 2 weeks, followed by an additional 6- to 8-week recovery period, to reconstitute immunity with donor bone marrow. Throughout the process, mice were given standard chow and water ad libitum. In this manner, two different types of chimeric TLR4 mice, marrow TLR4−/− (transplant of TLR4−/− bone marrow cells into a TLR4+/+ mouse) and parenchymal TLR4−/− (transplant of TLR4+/+ bone marrow cells into a TLR4−/− mouse), along with two types of transplant control mice, TLR4+/+ (transplant of TLR4+/+ bone marrow cells into a TLR4+/+ mouse) and TLR4−/− (transplant of TLR4−/− bone marrow cells into a TLR4−/− mouse), were generated for all experiments. By using this procedure, it was previously demonstrated that 99% of leukocytes and all tissue macrophages are replaced from the donor bone marrow.12Andonegui G. Bonder C.S. Green F. Mullaly S.C. Zbytnuik L. Raharjo E. Kubes P. Endothelium-derived Toll-like receptor-4 is the key molecule in LPS-induced neutrophil sequestration into lungs.J Clin Invest. 2003; 111: 1011-1020Crossref PubMed Scopus (352) Google Scholar, 13Tavener S.A. Long E.M. Robbins S.M. McRae K.M. Van Remmen H. Kubes P. Immune cell Toll-like receptor 4 is required for cardiac myocyte impairment during endotoxemia.Circ Res. 2004; 95: 700-707Crossref PubMed Scopus (138) Google Scholar, 16Spangrude G.J. Assessment of lymphocyte development in radiation bone marrow chimeras.Curr Protoc Immunol. 2008; (Chap 4:Unit 4.6)Crossref Google Scholar We confirmed engraftment of donor bone marrow at 7 weeks after transplantation using the presence or absence of peripheral blood mononuclear cell production of tumor necrosis factor (TNF)-α in response to LPS ex vivo (data not shown). To induce systemic inflammation, ultra-pure Escherichia coli LPS (Invitrogen, San Diego, CA) was dissolved in PBS and injected i.p. To adjust for variations in LPS biological activity between lots, each lot's LPS activity was quantitated using a chromogenic Limulus amoebocyte lysate kit (GenScript, Piscataway, NJ). A dose of approximately 1.5 × 1015 endotoxin units per kg was selected based on pilot studies demonstrating that this dose achieved systemic inflammation with high mortality in TLR4+/+ mice. A matching volume of PBS injected i.p. was used as a vehicle control. Eighteen mice that underwent transplantation (four TLR4+/+, five marrow TLR4−/−, four parenchymal TLR4−/−, and five TLR4−/−) were injected with i.p. LPS for this experiment. These mice were then monitored for onset of systemic inflammation and mortality. Murine systemic inflammation induced by LPS was defined as previously in a L. The physiological disturbances produced by endotoxins.Annu Rev Physiol. 1954; 16: 467-490Crossref PubMed Scopus (60) Google Scholar of LPS-induced systemic inflammation in In brief, murine LPS-induced systemic inflammation mice to and and this also in the process, mice and to with and and to Mice also and peripheral blood at this Mice were by an was to the of the for to for development of the of murine LPS-induced systemic inflammation. A of mice that underwent TLR4 transplantation TLR4+/+, marrow TLR4−/−, parenchymal TLR4−/−, and TLR4−/−) were used for this experiment. of each and one vehicle via i.p. each of these mice, blood was at after injection for plasma cytokine and blood neutrophil blood and and were then at the of based on the of the experiment. of murine systemic inflammation were at hours using all of the previously defined a of these mice, was confirmed by via for were injection and for All blood was in was from each blood and along with at for The blood cells were using neutrophil at for San Diego, the blood cells were and the cells were and using a blood kit of the cells was conducted using a San CA). blood cells were from using standard and were then based on and from the and then confirmed using the neutrophil The of was using of of blood cells. and was using a murine as cytokines were using the mouse cytokine on a as (Invitrogen, CA). and induced by were not for these per because plasma was were for to LPS-induced mortality. of between the four TLR4 transplantation were conducted using LPS-induced plasma cytokine blood neutrophil and tissue were across all four TLR4 transplantation using of and then the for all to for The of oncoming murine systemic inflammation using plasma cytokine was using and under the The for and were using the exact was To whether parenchymal- or marrow-derived cell activation via TLR4 was to the pathophysiological of systemic inflammation, we injected LPS into the i.p. of mice that underwent transplantation (four TLR4+/+, five marrow TLR4−/−, four parenchymal TLR4−/−, and five mortality was dependent on whether TLR4 was expressed on parenchymal cells TLR4+/+ mice having mortality than marrow TLR4−/− mice, this was not In this murine systemic inflammation to between 2 and hours after injection in the TLR4+/+ and marrow TLR4−/− mice. of murine LPS-induced systemic inflammation in the parenchymal TLR4−/− and TLR4−/− mice, to after injection (data not shown). To cell roles on neutrophil responses early and we injected mice that underwent TLR4 transplantation with LPS or vehicle control and blood neutrophil L. The physiological disturbances produced by endotoxins.Annu Rev Physiol. 1954; 16: 467-490Crossref PubMed Scopus (60) Google Scholar We these responses both early in the process after LPS-induced systemic inflammation had and late in the process hours after TLR4+/+ and marrow TLR4−/− mice of systemic inflammation, We also and activity late in murine LPS-induced systemic inflammation by organ to the role such activity in this In this of TLR4+/+, of marrow TLR4−/−, of parenchymal TLR4−/−, and of TLR4−/− mice given LPS of murine systemic inflammation by hours was also at hours in TLR4+/+, marrow TLR4−/−, and parenchymal TLR4−/− mice given LPS with TLR4−/− mice given LPS of of Mice that TLR4 and Given LPS or at after TLR4−/− TLR4−/− systemic by animal based on published of murine LPS-induced systemic and for the of mice in this as by animal based on published of murine LPS-induced systemic L. The physiological disturbances produced by endotoxins.Annu Rev Physiol. 1954; 16: 467-490Crossref PubMed Scopus (60) Google and for the of mice in this as in a TLR4+/+ and parenchymal TLR4−/− mice after LPS injection with marrow TLR4−/− and TLR4−/− mice of Late in the disease process, was in all mice given the TLR4−/− mice of was at hours after LPS in TLR4+/+, marrow TLR4−/−, and parenchymal TLR4−/− mice with TLR4−/− mice of lung and at hours after injection with LPS was in TLR4+/+ and marrow TLR4−/− mice with TLR4−/− mice, whereas parenchymal TLR4−/− mice had levels and of and To define the role of marrow-derived versus parenchymal cell in the development and of systemic inflammation, we early and late plasma cytokine levels to determine which to LPS-induced systemic inflammation 3 and In terms of early after plasma cytokine levels and endothelial factor were all than the of the (data not shown). were in early plasma levels of or of the (data not shown). and elevations to marrow TLR4 expression were not with oncoming development of LPS-induced systemic inflammation of A and chemokine levels had a of different expression inflammatory followed the expression in and whereas chemoattractant and plasma levels were in TLR4+/+, marrow TLR4−/−, and parenchymal TLR4−/− mice given LPS with TLR4−/− mice given LPS of the cytokines and chemokines monocyte chemoattractant followed an expression that oncoming disease of In plasma levels murine systemic inflammation at hours of their transplant with a of to a of to and an under the of levels at hours after injection of and for four of mice that underwent TLR4 transplantation and were given LPS or TLR4+/+, marrow TLR4−/−, parenchymal TLR4−/−, and TLR4−/− mice were used for this experiment. are as the The the for the versus marrow TLR4−/−, parenchymal TLR4−/−, and TLR4−/− mice given Late hours after plasma cytokine and chemokine levels followed a expression and factor plasma levels than the of the (data not shown). was in plasma levels of the (data not shown). and endothelial factor all demonstrated the plasma levels in TLR4+/+ mice, with or levels in the mice that underwent transplantation and were given LPS of endothelial factor not shown). chemokine levels and also this expression the given LPS of These that parenchymal cell activation via TLR4 mortality from murine LPS-induced systemic inflammation marrow-derived cell activation via TLR4 a role in LPS-induced systemic inflammation. These with of organ using chimeric TLR4 mice, in that parenchymal TLR4 both into the during LPS-induced inflammation and leukocyte recruitment to the brain after LPS G. Bonder C.S. Green F. Mullaly S.C. Zbytnuik L. Raharjo E. Kubes P. Endothelium-derived Toll-like receptor-4 is the key molecule in LPS-induced neutrophil sequestration into lungs.J Clin Invest. 2003; 111: 1011-1020Crossref PubMed Scopus (352) Google Scholar, 15Zhou H. Lapointe B.M. Clark S.R. Zbytnuik L. Kubes P. A requirement for microglial TLR4 in leukocyte recruitment into brain in response to lipopolysaccharide.J Immunol. 2006; 177: 8103-8110Crossref PubMed Scopus (142) Google Scholar parenchymal TLR4 expression not cause mortality in a Gram-negative model coli could be because of the host responses that an systemic response to an with systemic G. H. D. Mullaly S.C. B. Long E.M. Robbins S.M. Kubes P. Mice that express TLR4 on endothelial cells a systemic Gram-negative bacterial Clin Invest. 2009; Google of for Systemic in Mice that TLR4 TLR4−/− TLR4−/− inflammation and cytokines in this under mice with control with control mice. in a The in this under mice with control mice. with control mice. and are to be to tissue damage during the systemic inflammatory response. We that early is related to marrow-derived cell TLR4 that TLR4 activation of these cells instead early and in the disease process, TLR4 activation of parenchymal and/or marrow-derived cells to bone marrow of In terms of activity by lung and activity levels were in the TLR4+/+ and marrow TLR4−/− mice given LPS and had elevations in the parenchymal TLR4−/− mice given LPS and These with the of LPS-induced murine systemic inflammation in the TLR4+/+ and marrow TLR4−/− mice. in lung and is with G. Bonder C.S. Green F. Mullaly S.C. Zbytnuik L. Raharjo E. Kubes P. Endothelium-derived Toll-like receptor-4 is the key molecule in LPS-induced neutrophil sequestration into lungs.J Clin Invest. 2003; 111: 1011-1020Crossref PubMed Scopus (352) Google Scholar, 15Zhou H. Lapointe B.M. Clark S.R. Zbytnuik L. Kubes P. A requirement for microglial TLR4 in leukocyte recruitment into brain in response to lipopolysaccharide.J Immunol. 2006; 177: 8103-8110Crossref PubMed Scopus (142) Google Scholar chimeric TLR4 mice, which that neutrophil and in the brain and lung in response to LPS were solely driven by parenchymal TLR4. the between TLR4+/+, marrow TLR4−/−, and parenchymal TLR4−/− organ are not as as the in LPS-induced murine systemic inflammation, mortality, and blood neutrophil responses 2 and on these we that it is that activation of either via TLR4 the and/or activation of in these neutrophil to the of systemic inflammation be of and TLR4 expression in is in the be because of in endothelial is organ from the activation could then be driven by blood neutrophil responses as as TLR4 Given the of cytokines and chemokines in the systemic inflammatory we whether these were to the of LPS-induced systemic inflammation and mortality. The we between early plasma cytokine levels and of LPS-induced systemic inflammation is These that most early cytokine production is marrow-derived cell in is with previously of these classic cytokines and endothelial cell leukocyte and with J. & Scholar we high plasma levels of these in one of chimeric TLR4 mice TLR4−/−) with cytokine signaling that not of systemic inflammation and plasma levels of these in of chimeric TLR4 mice TLR4−/−) that of systemic inflammation and Given the in these cytokines based on such as LPS-induced systemic inflammation, to their as and in the because their role in a classic model of systemic inflammation not be as crucial as C. Sepsis a 14: PubMed Scopus Google Scholar, E. A. G. S. San G. R. A. S. S. R. H. R. M. L. R. J. J. S. of to human necrosis factor in of 1998; PubMed Scopus Google Scholar, of endotoxin for the study of PubMed Scopus Google Scholar studies are to define by which TLR4 signaling within parenchymal cells the of systemic inflammation. The one early plasma cytokine to have was is a chemokine that cells, and to the of inflammation and be produced by both immune and monocyte chemoattractant PubMed Scopus Google Scholar, L. Van J. levels of the chemokines monocyte and are in human PubMed Google Scholar, J. K.A. expression in J Physiol Physiol. PubMed Scopus Google Scholar been in response to LPS in mice, and although the of its role in this systemic inflammatory response is J. is during and in PubMed Scopus Google Scholar, I. and monocyte chemoattractant in human of lipopolysaccharide on and immune Immunol. PubMed Google Scholar Previous R.M. J. mice in Clin Invest. PubMed Scopus Google Scholar, A. M. Role of in and 2008; PubMed Scopus Google Scholar of in murine LPS-induced systemic inflammation have demonstrated both and to Although the studies exact role or it is that its role in the development of LPS-induced systemic inflammation and mortality be unique with other inflammatory and be It is well that a systemic inflammatory response introduced into mice, a role in this disease R. S.A. recruitment of and macrophages to through expression of monocyte chemoattractant Immunol. PubMed Google Scholar, L. monocyte chemoattractant in by a systemic Immunol. PubMed Google Scholar, Liao X. chemoattractant is for the of and in mice requires an additional for inflammatory Immunol. PubMed Google Scholar, monocyte chemoattractant in a model and cells to PubMed Scopus (138) Google Scholar Given the morbidity and mortality with systemic inflammation in many disease the of a plasma molecule predictive of oncoming systemic inflammation be in in which the development of systemic inflammation only in a of of its exact in the B. Rietschel E.T. Innate immune sensing and its roots: the story of endotoxin.Nat Rev Immunol. 2003; 3: 169-176Crossref PubMed Scopus (1078) Google Scholar, G.J. and tumor necrosis levels following with volume and of J 1999; PubMed Scopus Google Scholar, The inflammatory response to PubMed Scopus Google Scholar late in LPS-induced systemic inflammation, plasma cytokine to be with and plasma cytokines in the TLR4+/+ mice to an or between marrow-derived cell and parenchymal cell activation during LPS-induced systemic inflammation. late plasma cytokine levels and in the two chimeric TLR4 mouse TLR4−/− and parenchymal these two have different responses to this is that late in the systemic inflammatory disease process, plasma cytokines and chemokines a for systemic inflammation, as in In that expression of TLR4 by parenchymal cells is for the development of LPS-induced systemic inflammation and mortality. In this both early and late blood neutrophil responses and plasma cytokine levels not the development of systemic inflammation, of such as in wild-type mice of signaling via TLR4 in both parenchymal and bone systemic inflammation via K.J. Beutler B. J. S. A. A. and tissue injury induced by human PubMed Scopus Google Scholar Our study that to be in future of systemic inflammation on Although the onset of systemic inflammation was with mortality, the of systemic inflammation onset could be through of and Although TLR4 signaling in parenchymal cells the development of LPS-induced systemic inflammation, that marrow-derived cell activation via TLR4 or an systemic inflammatory was unique in its expression early and was the only chemokine to the onset of LPS-induced systemic inflammation with high Given that of not systemic inflammation in the role of in this process R. S.A. recruitment of and macrophages to through expression of monocyte chemoattractant Immunol. PubMed Google Scholar, L. monocyte chemoattractant in by a systemic Immunol. PubMed Google Scholar, Liao X. chemoattractant is for the of and in mice requires an additional for inflammatory Immunol. PubMed Google Scholar, monocyte chemoattractant in a model and cells to PubMed Scopus (138) Google Scholar The parenchymal cell of not been These studies are because studies of the role of in or host systemic inflammatory responses to LPS are which TLR4 activation in parenchymal cells and bone cells, be as in that TLR4 signaling in both is during human systemic inflammation. this model related to TLR4 signaling in systemic studies with this model plasma chemokine levels to during systemic inflammation processes. We for and for with the plasma cytokine