Novel Regulator Of Inflammation Research Articles

Etanercept’s Protective Effect Against Lung Inflammation Caused by Polymicrobial Sepsis Induced by CLP in Male Rats

Inflammation and oxidative stress are critical factors leading to sepsis-induced severe lung injury (ALI). This study investigates the regulatory effects of Etanercept (ENT) in an animal model of sepsis-induced ALI. We established a cecal ligation and puncture (CLP) model for ALI in adult rats under anesthesia. Sepsis amplifies pathological lung tissue damage, lung endothelial permeability, serum inflammatory factor production, and the number of inflammatory cells in bronchoalveolar lavage fluid. Furthermore, it enhances the expression of phosphorylated NF-\(\kappa\)B p65, reduces lung superoxide dismutase due to CLP, and elevates lung malondialdehyde levels due to LPS-induced inflammatory factor production. This cascade of events exacerbates the expression of several genes, including TNF-\(\alpha\) and cytokines. LPS-induced inflammatory factor production also enhances the formation of reactive oxygen species in mitochondria. In summary, our current research provides evidence that ENT acts as a novel regulator of inflammation in sepsis-induced ALI in rats. The control of oxidative stress and the modulation of the inflammatory response are two key underlying mechanisms for the effects of ENT.

PTPN21/Pez Is a Novel and Evolutionarily Conserved Key Regulator of Inflammation In Vivo

SummaryDrosophila provides a powerful model in which to study inflammation in vivo, and previous studies have revealed many of the key signaling events critical for recruitment of immune cells to tissue damage. In the fly, wounding stimulates the rapid production of hydrogen peroxide (H2O2).1,2 This then acts as an activation signal by triggering a signaling pathway within responding macrophages by directly activating the Src family kinase (SFK) Src42A,3 which in turn phosphorylates the damage receptor Draper. Activated Draper then guides macrophages to the wound through the detection of an as-yet unidentified chemoattractant.3, 4, 5 Similar H2O2-activated signaling pathways are also critical for leukocyte recruitment following wounding in larval zebrafish,6, 7, 8, 9 where H2O2 activates the SFK Lyn to drive neutrophil chemotaxis. In this study, we combine proteomics, live imaging, and genetics in the fly to identify a novel regulator of inflammation in vivo; the PTP-type phosphatase Pez. Pez is expressed in macrophages and is critical for their efficient migration to wounds. Pez functions within activated macrophages downstream of damage-induced H2O2 and operates, via its band 4.1 ezrin, radixin, and moesin (FERM) domain, together with Src42A and Draper to ensure effective inflammatory cell recruitment to wounds. We show that this key role is conserved in vertebrates, because “crispant” zebrafish larvae of the Draper ortholog (MEGF10) or the Pez ortholog (PTPN21) exhibit a failure in leukocyte recruitment to wounds. This study demonstrates evolutionary conservation of inflammatory signaling and identifies MEGF10 and PTPN21 as potential therapeutic targets for the treatment of inflammatory disorders.

MSP-RON Pathway: Potential Regulator of Inflammation and Innate Immunity

Macrophage-stimulating protein (MSP), a soluble protein mainly synthesized by the liver, is the only known ligand for recepteur d'origine nantais (RON), which is a member of the MET proto-oncogene family. Recent studies show that the MSP-RON signaling pathway not only was important in tumor behavior but also participates in the occurrence or development of many immune system diseases. Activation of RON in macrophages results in the inhibition of nitric oxide synthesis as well as lipopolysaccharide (LPS)-induced inflammatory response. MSP-RON is also associated with chronic inflammatory responses, especially chronic liver inflammation, and might serve as a novel regulator of inflammation, which may affect the metabolism in the body. Another study provided evidence of the relationship between MSP-RON and autoimmune diseases, suggesting a potential role for MSP-RON in the development of drugs for autoimmune diseases. Moreover, MSP-RON plays an important role in maintaining the stability of the tissue microenvironment and contributes to immune escape in the tumor immune microenvironment. Here, we summarize the role of MSP-RON in immunity, based on recent findings, and lay the foundation for further research.

In Silico Modeling of Metabolic State in Single Th17 Cells Reveals Novel Regulators of Inflammation and Autoimmunity

Abstract Cellular metabolism is a major regulator of immune response, but it is difficult to study the metabolic status of an individual immune cell using current technologies. Here, we present Compass, an algorithm to characterize the metabolic landscape of single cells in silico based on single-cell RNA-Seq and flux balance analysis. We used Compass to study the landscape of metabolic heterogeneity in Th17 cells and search for novel metabolic regulators of their inflammatory function. In central carbon metabolism, Compass predicted a metabolic switch between glycolysis and fatty acid oxidation that mirrors the Th17 vs. Treg phenotype, which we validated through transcriptomic, metabolic and functional assays. The TCA cycle was predicted to break at two points, both of which have been independently identified by other groups in M1 macrophage polarization. Surprisingly, and contrary to common immunometabolic understanding, Compass predicted that glycolysis too was divided into functional modules, and that one of them supported an anti-inflammatory phenotype. We validate the paradoxical prediction and demonstrate that inhibition of this module promotes a pro-inflammatory transcriptional program in Th17 cells, resulting in neuroinflammation in an adoptive transfer model of autoimmune disease. In conclusion, Compass is a widely applicable algorithm to characterize metabolic states at single cell resolution. It allows associating cellular metabolic states with effector functions and detection of metabolic targets that regulate effector phenotypes. We expect it to become a widely used tool with the increasing availability of single-cell RNA-Seq data, spurred by efforts such as the human cell atlas.

TLR-TRIF signaling induces GLI3 to modulate inflammation

Abstract Chronic inflammation is associated with several disorders and therefore the identification of novel regulators of inflammation is needed. We identified GLI3 as a novel component of the TLR-TRIF signaling. Stimulation of monocytes with LPS increased GLI3 expression in a hedgehog-independent mechanism. We stimulated cells with MPLA, (TLR4 ligand that signals through TRIF) and polyI:C (TLR3 ligand) and found that IRF3 directly binds to the GLI3 promoter and IRF3 increased GLI3 expression. We generated a conditional knockout (cko) mouse where GLI3 was deleted in myeloid cells using LysM-Cre mediated recombination. IFA-elicited macrophages from cko mice stimulated with LPS showed reduced IL-6, CCL2 and TNF-a secretion compared to macrophages from wild-type (wt) littermates. We also performed RNA sequencing of LPS treated or untreated macrophages from GLI3 cko or wt mice. Using a generalized linear model in edgeR, we identified 495 genes with significant interaction effects between genotype and LPS treatment. Ingenuity Pathway Analysis of the interaction genes revealed “Inflammatory Response” and “Immune Cell Trafficking” pathways as most significantly enriched. The 25 significant interaction genes on these pathways included 9 with a positive interaction (Ccl25, Cd226, Cgas, Hmgn5, Il12b, Lrrc8a, Rapgef3, Rnf122, and Tlr8) and 16 with a negative interaction (Acacb, Adipoq, Ccl1, Ccne1, Cx3cl1, Fry, Gstk1, Mertk, Nqo2, Slc6a4, Sort1, Timd4, Tnfrsf18/GITR, Tnfsf13/APRIL, Tnfsf13b/BAFF, and Trem2). Taken together, these results identify a novel role for GLI3 in mediating TLR-TRIF-induced inflammation and identify a novel set of inflammatory genes that are dependent on GLI3 in response to TLR-TRIF signaling.

MicroRNA-129-5p alleviates spinal cord injury in mice via suppressing the apoptosis and inflammatory response through HMGB1/TLR4/NF-κB pathway.

Secondary injury after spinal cord injury (SCI) is one reversible pathological change mainly involving excessive inflammatory response and neuro-apoptosis. Since in recent years, microRNAs (miRNAs) have been proposed as novel regulators of inflammation in different disease conditions. However, the role of miRNAs in the inflammatory response and apoptosis of secondary injury after SCI remains to be fully elucidated. Here, we tried to explore the influence and mechanism of miRNAs on the neuron inflammatory response and apoptosis after SCI. The expression profiles of miRNA were examined using miRNA microarray, and among the candidate miRNAs, miR-129-5p was found to be the most down-regulated miRNA in spinal tissues. Overexpression of miR-129-5p using agomir-miR-129-5p promoted injury mice functional recovery, suppressed the apoptosis and alleviated inflammatory response in spinal tissues. Using LPS-induced BV-2 cell model, we found miR-129-5p was also proved in protecting inflammatory response and cell apoptosis in vitro. High-mobility group protein B1 (HMGB1), a well-known inflammatory mediator, was found to be directly targeted by miR-129-5p and it was associated with the inhibitory effect of miR-129-5p on the activation of toll-like receptor (TLR)-4 (TLR4)/ nuclear factor-κB (NF-κB) pathway in vitro and in vivo. Further experiments revealed that the anti-apoptosis and anti-inflammatory effects of miR-129-5p were reversed by HMGB1 overexpression in BV-2 cells. Collectively, these data revealed that miR-129-5p alleviated SCI in mice via suppressing the apoptosis and inflammatory response through HMGB1//TLR4/NF-κB pathway. Our data suggest that up-regulation of miR-129-5p may be a novel therapeutic target for SCI.

P14ARF inhibits regional inflammation and vascularization in intervertebral disc degeneration by upregulating TIMP3.

In this study, we identified P14 alternate reading frame (P14ARF) as a novel regulator of inflammation and vascularization in intervertebral disk degeneration (IVDD). We collected IVD tissues from IVDD patients and normal individuals for analysis of P14ARF expression. We also induced experimental IVDD by needle puncture injuries in the caudal intervertebral disks of Sprague-Dawley (SD) rats and achieved recombinant adenovirus-mediated P14ARF overexpression in experimental IVDD rats. Regulation relationships between P14ARF and tissue inhibitors of metalloproteinases-3 (TIMP3) were confirmed in P14ARF-overexpressed and TIMP3-depleted nucleus pulposus (NP) cells. Tube formation in vitro was evaluated in coculture systems of human umbilical vein endothelial cells (HUVECs) and rat degenerated NP cells (DNPCs). Inflammatory response was assessed from levels of TNF-α, IL-1β, and IL-6 and neovascularization from expression of endothelial growth factor (VEGF). The P14ARF and TIMP3 were downregulated in degenerated IVD tissue derived from patients and experimental IVDD rats. Overexpressed P14ARF suppressed inflammatory cytokine levels and vascularization. There was decreased in vitro tube formation in response to P14ARF overexpression and TIMP3 elevation. Finally, attenuated inflammatory responses and suppression of VEGF were achieved by P14ARF-mediated promotion of TIMP3 in rat DNPCs. Taken together, the present study reveals that P14ARF/TIMP3 modulation of inflammatory response and vascularization in the context of IVDD highlights a potential target for future therapeutic strategies.

MicroRNA-182 supplies negative feedback regulation to ameliorate lipopolysaccharide-induced ALI in mice by targeting TLR4.

Acute lung injury (ALI), characterized by increased excessive pulmonary inflammation, is a pervasive inflammatory disease with clinically high incidence. MicroRNA (miRNAs) have been associated with the progression of multiple diseases and are regarded as novel regulators of inflammation. However, it remains largely unknown whether the miRNAs-mediated regulatory mechanism has an effect on lipopolysaccharide (LPS)-induced inflammation in ALI. We discovered that miR-182 distinctly lessened expression in the lung tissue of mice with ALI and macrophages stimulated by LPS. We also found that overexpression of miR-182 significantly cut down the secretion of inflammatory cytokines, while this change was reversed by inhibition of miR-182. In addition, miR-182 suppressed the activation of NF-κB by targeting TLR4 expression. And it was confirmed that miR-182 directly regulated TLR4 expression at the posttranscriptional level by binding to the 3'-UTR of TLR4. Together, these data suggested that inhibition of TLR4 expression assuaged LPS-stimulated inflammation through negative feedback regulation of miR-182.

Interleukin-36 family as a novel regulator of inflammation in the barrier tissues

The interleukin-36 (IL-36) family was discerned in the superfamily of interleukin-1 (IL-1) ten years ago. This family includes three isoforms of IL-36α, IL-36β, IL-36γ, which have pro-inflammatory activity and a specific receptor antagonist, IL-36ra, which implements anti-inflammatory function. All of them bind to the same IL-1R6 receptor. The pro-inflammatory isoforms also involve an accessory IL-1RAcP protein into signaling; resulting into conduction of a signal into the cell via the assembling heterodimer receptor. In contrast, IL-36ra inhibits the formation of a heterodimer and blocks the signal transmission. The cytokines of the IL-36 family and appropriate receptors are normally expressed on epithelial cells in barrier tissues such as the respiratory, intestinal tract and skin. Like all cytokines of the IL-1 superfamily, IL-36 is synthesized as inactive form and requires activation, but not due to caspases, but being mediated by neutrophil enzymes, such as cathepsin G, proteinase-3, and elastase, which are constantly present in barrier tissues. In this regard, IL-36 is involved in homeostasis of barrier tissues. Apparently, the IL-36 cytokine system appeared in response to the developing ability of some microorganisms to avoid immune recognition and activation of innate immune response, and, in particular, the IL-1 pro-inflammatory system. An imbalance between the pro- and anti-inflammatory pathways readily causes inflammation in the corresponding tissue. This review discusses participation of cytokines from the IL-36 family in homeostasis of barrier tissues, as well as potential role of the IL-36 family in pathogenesis of bacterial, viral, and fungal skin diseases, atopic dermatitis, autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjogren's syndrome, ulcerative colitis and Crohn's disease. The role of IL-36 family cytokines in the immunopathogenesis of psoriasis has been well studied. This review is presenting the modern ideas about immune pathogenesis of psoriasis. The special role of cytokines from the IL-36 family was shown both for induction of psoriatic inflammation and evolving a positive feedback loop that supports and enhances the immune component of inflammation, which leads to progression of the disease. Moreover, modern methods of treating psoriasis are discussed, in particular, a possible promising approach to IL-36 blockade, or usage of recombinant IL-36ra for the treatment of psoriatic patients. Experimental studies in this area in mice provide some grounds for optimism.

MicroRNA-106a Provides Negative Feedback Regulation in Lipopolysaccharide-Induced Inflammation by targeting TLR4.

Acute lung injury (ALI) is a common clinical disease with high incidence and mortality rate, which is characterized by severe inflammatory response and tissues damage. MicroRNAs (miRNAs) have been regarded as novel regulators of inflammation, and play an important role in various inflammatory diseases. However, it remains unknown whether the regulatory mechanisms mediated by miR-106a is involved in LPS-induced ALI. In this study, we found that expression of miR-106a was significantly decreased in lung tissues of ALI mice and LPS-stimulated macrophages. We also revealed that over-expression of miR-106a significantly decreased the production of pro-inflammatory cytokines, including IL-1β, IL-6 and TNF-α, whereas this effect was reversed by the inhibition of miR-106a. Moreover, miR-106a inhibits NF-κB activation by targeting TLR4 expression. We further demonstrated that miR-106a inhibited TLR4 expression via binding directly to the 3'-UTR of TLR4. Taken together, the results of the present study illuminated that miR-106a is a negative feedback regulator in LPS-stimulated inflammation through TLR4/NF-κB signaling pathway.

MicroRNA‑93 inhibits chondrocyte apoptosis and inflammation in osteoarthritis by targeting the TLR4/NF‑κB signaling pathway.

Osteoarthritis (OA) is a serious disease of the articular cartilage, and inflammation has been implicated in its pathogenesis. Previously, microRNAs (miRNAs) have been proposed as novel regulators of inflammation, however, the functional role of microRNAs in regulating inflammation in OA remains to be fully elucidated. The aim of the present study was to investigate the roles of miRNAs in OA inflammation and the underlying molecular mechanism. Firstly, the miRNA expression patterns were analyzed in the articular cartilage tissues from experimental OA mice using an miRNA microarray. miRNA (miR)-93 was identified with particular interest due to its reported effects on apoptosis and inflammation suppression. Subsequently, the expression of miR-93 was further validated in the articular cartilage tissues of OA mice and lipopolysaccharide (LPS)-stimulated primary chondrocytes. Using this LPS-induced chondrocyte injury model, the overexpression of miR-93 enhanced cell viability, improved cell apoptosis and attenuated the inflammatory response, as reflected by reductions in pro-inflammatory cytokines, including tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6. In addition, Toll-like receptor 4 (TLR4), an important regulator of the nuclear factor-κB (NF-κB) signaling pathway, was identified as a direct target of miR-93 in chondrocytes. Furthermore, the restoration of TLR4 markedly abrogated the inhibitory effects of miR-93 on the chondrocyte apoptosis and inflammation induced by LPS. In addition, the overexpression of miR-93 by agomir-miR-93 significantly inhibited the levels of pro-inflammatory cytokines and cell apoptosis, whereas antagomir-93 exacerbated apoptosis and inflammation in vivo. Taken together, the results of the study suggested that miR-93 may be a promising therapeutic target for the treatment of human OA.

NLRP3 Inflammasome as a Molecular Marker in Diabetic Cardiomyopathy.

Diabetic cardiomyopathy (DCM), a common consequence of longstanding diabetes mellitus, is initiated by death of cardiomyocyte. Hyperglycemia-induced reactive oxygen species (ROS) overproduction is a major contributor of the chronic low-grade inflammation that characterizes as the DCM. ROS may promote the activation of nucleotide-binding oligomerization domain like receptor (NLR) pyrin domain containing 3 (NLRP3) inflammasome, a novel regulator of inflammation and cell death, by nuclear factor-kB (NF-κB) and thioredoxin interacting/inhibiting protein (TXNIP). NLRP3 inflammasome regulates the death of cardiomyocyte and activation of fibroblast in DCM, which is involved in the structural and functional disorder of DCM. However, comprehensive understanding of molecular mechanisms linking NLRP3 inflammasome and disorder of cardiomyocyte and fibroblast in DCM is lacking. Here, we review the molecular mechanism(s) of NLRP3 inflammasome activation in response to hyperglycemia in DCM.

Immune modulatory mechanisms of lanthionine synthetase C-like protein 2 (IRM12P.656)

Abstract Lanthionine synthetase C-like protein 2 (LANCL2) has emerged as a novel therapeutic target for metabolic, infectious and immune-mediated diseases. We previously demonstrated that directly targeting LANCL2 through treatment with abscisic acid or 61610 results in efficacious anti-inflammatory responses during DSS-induced colitis however molecular mechanisms underlying this immunomodulatory function remain elusive. Here we report for the first time the use of LANCL2-deficient mice to investigate the mechanism of action and cell specificity of the protein. At the cellular level, bone marrow derived macrophages (BMDM), RAW cells, and gastric epithelial cells express comparable levels of basal LANCL2 mRNA. LPS-mediated inflammation in BMDM increased both mRNA and protein levels of LANCL2 that peaked 6 hours post-challenge and subsequently returned to normal levels after 12 hours. Similarly, DSS-induced colitis induced expression of LANCL2 in the colons of wild-type (WT) mice and correlated with elevated levels of proinflammatory cytokines. Interestingly, the absence of LANCL2 did not cause significant alterations in infiltrating cellular phenotypes however LANCL2-deficiency permitted exaggerated IL17 and IFNγ expression in colonic tissue when compared to WT counterparts at day 7 post-challenge. In conclusion, our findings indicate that LANCL2 is a novel regulator of inflammation that functions predominantly at the molecular level to down-regulate excessive inflammatory responses.

LpPLA2 and Sirt1 – Novel regulators of inflammation in placental tissue in diabetes and obesity?

LpPLA2 and Sirt1 – Novel regulators of inflammation in placental tissue in diabetes and obesity?

MicroRNA‐93 inhibits inflammatory cytokine production in LPS‐stimulated murine macrophages by targeting IRAK4

Endotoxin-induced uveitis (EIU) is an animal model of acute ocular inflammation for the study of human endogenous anterior uveitis. The mechanisms accounting for the development of ocular inflammation remain hazy. MicroRNAs (mi-RNAs) have been proposed as novel regulators of inflammation. It remains unclear whether a microRNA-mediated regulatory mechanism is involved in LPS-induced EIU. In this study, we report that miR-93 expression in the eyes of EIU rats and LPS-stimulated macrophages is significantly decreased. We also show that miR-93 inhibits NF-κB activation and pro-inflammatory cytokines by targeting IRAK4 expression. We further demonstrate that miR-93 inhibits IRAK4 expression by binding directly to the 3'-UTR of IRAK4. Our findings suggest that miR-93 is a negative regulator of the immune response in EIU.

Modulation of p75NTR prevents diabetes- and proNGF-induced retinal inflammation and blood–retina barrier breakdown in mice and rats

Diabetic retinopathy is characterised by early blood-retina barrier (BRB) breakdown and neurodegeneration. Diabetes causes imbalance of nerve growth factor (NGF), leading to accumulation of the NGF precursor (proNGF), as well as the NGF receptor, p75 neurotrophin receptor (p75(NTR)), suggesting a possible pathological role of the proNGF-p75(NTR) axis in the diabetic retina. To date, the role of this axis in diabetes-induced retinal inflammation and BRB breakdown has not been explored. We hypothesised that modulating p75(NTR) would prevent diabetes- and proNGF-induced retinal inflammation and BRB breakdown. Diabetes was induced by streptozotocin in wild-type and p75(NTR) knockout (p75KO) mice. After 5 weeks, the expression of inflammatory mediators, ganglion cell loss and BRB breakdown were determined. Cleavage-resistant proNGF was overexpressed in rodent retinas with and without p75(NTR) short hairpin RNA or with pharmacological inhibitors. In vitro, the effects of proNGF were investigated in retinal Müller glial cell line (rMC-1) and primary Müller cells. Deletion of p75(NTR) blunted the diabetes-induced decrease in retinal NGF expression and increases in proNGF, nuclear factor κB (NFκB), p-NFκB and TNF-α. Deletion of p75(NTR) also abrogated diabetes-induced glial fibrillary acidic protein expression, ganglion cell loss and vascular permeability. Inhibited expression or cleavage of p75(NTR) blunted proNGF-induced retinal inflammation and vascular permeability. In vitro, proNGF induced p75(NTR)-dependent production of inflammatory mediators in primary wild-type Müller and rMC-1 cultures, but not in p75KO Müller cells. The proNGF-p75(NTR) axis contributes to retinal inflammation and vascular dysfunction in the rodent diabetic retina. These findings underscore the importance of p75(NTR) as a novel regulator of inflammation and potential therapeutic target in diabetic retinopathy.

GSNOR:a Novel Regulator of Inflammation

GSNOR:a Novel Regulator of Inflammation

Keratin intermediate filament proteins – novel regulators of inflammation and immunity in skin

Inflammation is a complex biological response, protecting the host and promoting homeostasis following mechanical, chemical or microbial insults. Epithelia are strategically located at the interface between the external and internal milieu where, collectively, their ability to establish a

Unraveling Inflammatory Responses using Systems Genetics and Gene-Environment Interactions in Macrophages

Many common diseases have an important inflammatory component mediated in part by macrophages. Here we used a systems genetics strategy to examine the role of common genetic variation in macrophage responses to inflammatory stimuli. We examined genome-wide transcript levels in macrophages from 92 strains of the Hybrid Mouse Diversity Panel. We exposed macrophages to control media, bacterial lipopolysaccharide (LPS), or oxidized phospholipids. We performed association mapping under each condition and identified several thousand expression quantitative trait loci (eQTL), gene-by-environment interactions, and eQTL "hot spots" that specifically control LPS responses. We used siRNA knockdown of candidate genes to validate an eQTL hot spot in chromosome 8 and identified the gene 2310061C15Rik as a regulator of inflammatory responses in macrophages. We have created a public database where the data presented here can be used as a resource for understanding many common inflammatory traits that are modeled in the mouse and for the dissection of regulatory relationships between genes.

Membrane-associated CD93 regulates leukocyte migration and C1q-hemolytic activity during murine peritonitis.

CD93 is emerging as a novel regulator of inflammation; however, its molecular function is unknown. CD93 exists as a membrane-associated glycoprotein on the surface of cells involved in the inflammatory cascade, including endothelial and myeloid cells. A soluble form (sCD93) is detectable in blood and is elevated with inflammation. In this study, we demonstrate heightened susceptibility to thioglycollate-induced peritonitis in CD93(-/-) mice. CD93(-/-) mice showed a 1.6-1.8-fold increase in leukocyte infiltration during thioglycollate-induced peritonitis between 3 and 24 h that returned to wild type levels by 96 h. Impaired vascular integrity in CD93(-/-) mice during peritonitis was demonstrated using fluorescence multiphoton intravital microscopy; however, no differences in cytokine or chemokine levels were detected with Luminex Multiplex or ELISA analysis. C1q-hemolytic activity in CD93(-/-) mice was decreased by 22% at time zero and by 46% 3 h after thioglycollate injection, suggesting a defect in the classical complement pathway. Leukocyte recruitment and C1q-hemolytic activity was restored to wild type levels when CD93 was expressed on either hematopoietic cells or nonhematopoietic cells in bone marrow chimeric mice. However, elevated levels of sCD93 in inflammatory fluid were observed only when CD93 was expressed on nonhematopoietic cells. Because cell-associated CD93 was sufficient to restore a normal inflammatory response, these data suggest that cell-associated CD93, and not sCD93, regulates leukocyte recruitment and complement activation during murine peritonitis.