CD16+ monocytes produce IL-6, CCL2, and matrix metalloproteinase-9 upon interaction with CX3CL1-expressing endothelial cells

The CD16+ subset of peripheral blood monocytes (Mo) is expanded dramatically during inflammatory conditions including sepsis, HIV-1 infection, and cancer. CD16+ express high levels of CX3CR1, which mediates arrest onto CX3CL1-expressing endothelial cells (EC) under flow conditions. In contrast, attachment of CD16- Mo onto cytokine-activated EC is independent of CX3CL1. Here, we investigate the ability of CD16+ and CD16- Mo to produce proinflammatory cytokines upon interaction with CX3CL1-expressing HUVEC. We demonstrate that CD16+ but not CD16- Mo produce high levels of IL-6, CCL2, and matrix metalloproteinase (MMP)-9 when cocultured with TNF/IFN-gamma-activated HUVEC or nonactivated HUVEC expressing CX3CL1. Furthermore, supernatants from Mo cocultured with cytokine-activated HUVEC induce neuronal death in vitro. These results suggest that membrane-bound CX3CL1 stimulates production of IL-6, CCL2, and MMP-9 by CD16+ Mo, likely via engagement of CX3CR1. Thus, expansion of CD16+ Mo and their accumulation onto CX3CL1-expressing EC may result in recruitment of Mo and T cell subsets at sites of inflammation in response to CCL2, IL-6-induced cell activation and/or differentiation, and MMP-9-mediated vascular and tissue injury.     

Recruitment of CD16+ monocytes into synovial tissues is mediated by fractalkine and CX3CR1 in rheumatoid arthritis patients

CD16+ monocytes, identified as a minor population of monocytes in human peripheral blood, have been implicated in several inflammatory diseases, including rheumatoid arthritis (RA). Fractalkine (FKN, CX3CL1), a member of the CX3 C subfamily, is induced by pro-inflammatory cytokines, while a receptor for FKN, CX3CR1, is capable of mediating both leukocyte migration and firm adhesion. Here, we investigated the role of FKN and CX3CR1 in activation of CD16+ monocytes and their recruitment into synovial tissues in RA patients. High levels of soluble FKN were detected in the synovial fluid and sera of RA patients. Circulating CD16+ monocytes showed a higher level of CX3CR1 expression than CD16- monocytes in both RA patients and healthy subjects. High level expression of CX3CR1 was also seen in CD16+ monocytes localized to the lining layer in RA synovial tissue. In the in vitro culture experiments, IL-10 induced CX3CR1 expression on the surface of monocytes, and TNFalpha induced membrane-bound FKN as well as soluble FKN expression in synovial fibroblasts. Moreover, soluble FKN was capable of inducing IL-1beta and IL-6 by activated monocytes. These results suggest that FKN might preferentially mediate migration and recruitment of CD16+ monocytes, and might contribute to synovial tissue inflammation.     

Peptidome analysis of human intrauterine adhesion tissues and the identification of antifibrotic peptide

Intrauterine adhesion(IUA) is a common clinical endometrial disease,which can severely damage the fertility and quality of life in women.This study aims to find the differentially expressed endogenous peptides and their possible roles in IUA.Liquid chromatography-mass spectrometry was used to identify the peptidomic profiling of IUA tissues,and the differentially expressed peptides were screened out.Using real-time quantitative PCR,Western blotting,and immunocytochemistry staining,the function o...     

CX3CR1-deficiency is associated with increased severity of disease in experimental autoimmune uveitis

The role of CX3CR1 in regulating the function of monocytes and microglia was examined in mice in which CX3CR1 had been replaced by green fluorescent protein (GFP). Induction of experimental autoimmune uveitis (EAU) in these mice resulted in increased disease severity at day 23 postimmunization with uveitogenic peptide when compared with CX3CR1-positive mice and increased apoptosis of neuronal cells in the inner nuclear layer. Resident microglia within the retina were activated equally as EAU developed in mice with or without CX3CR1, as determined by changes in morphology, suggesting that the microglial cell response did not account for the differences. Although the inflammatory infiltrate had increased in mice without CX3CR1 at day 23 postimmunization, the percentage of natural killer cells in the infiltrate was not changed in these mice. Similarly, increased disease severity at this stage was not associated with an overall increased percentage of macrophages in the retinal inflammatory infiltrate or in increased activation of these cells. The increased recruitment of monocytes to the retina in response to EAU induction in CX3CR1^GFP/GFP mice compared with CX3CR1^GFP/+ mice was not reflected in increased migration away from vessels, leading to marked clustering of GFP⁺ cells around veins and venules in these mice. It is possible that this monocyte/macrophage clustering leads to the increased severity of disease seen in the mice by focusing and so intensifying the inflammatory response.     

Chemokine receptor CX3CR1 promotes dendritic cell development under steady-state conditions

Expression of CX3CR1 is an attribute of myeloid precursors committed to the monocyte/macrophage (Mφ)/DC lineages and is maintained during all stages of DC differentiation. Nevertheless, the exact role of this molecule during developmental progression of myeloid precursors towards the DC lineage remains elusive. To overcome potential compensatory mechanisms and issues of redundancy, we employed competitive adoptive transfer experiments to assess a possible function of CX3CR1 in DC and monocyte/Mφ differentiation in vivo. We show here that expression of CX3CR1 promotes the generation of DCs and monocytes/Mφ under steady-state conditions and during compensatory expansion after selective depletion of DCs, but not under inflammatory conditions evoked by sub-lethal irradiation. Direct administration of CX3CR1-deficient and CX3CR1-sufficient precursors into the spleen or the thymus resulted in a similar competitive advantage of WT over CX3CR1-deficient precursors as i.v. transfer, suggesting that CX3CR1-mediated survival rather than recruitment to lymphoid organs is critical for DC/Mφ differentiation. In conclusion, our data support the hypothesis that CX3CR1 promotes proper development of myeloid precursors into DCs and monocytes/Mφs under steady-state conditions, possibly by providing survival signals or mediating accessibility to organ-specific niches, rather than acting as a mediator of homing to the spleen or the thymus.     

Analyses of phenotypic and functional characteristics of CX3CR1-expressing natural killer cells

We previously demonstrated a correlation between the frequency of CX3CR1-expressing human natural killer (NK) cells and disease activity in multiple sclerosis and showed that CX3CR1(high) NK cells were more cytotoxic than their CX3CR1(neg/low) counterparts. Here we aimed to determine whether human NK cell fractions defined by CX3CR1 represent distinct subtypes. Phenotypic and functional NK cell analyses revealed that, distinct from CX3CR1(high), CX3CR1(neg/low) NK cells expressed high amounts of type 2 cytokines, proliferated robustly in response to interleukin-2 and promoted a strong up-regulation of the key co-stimulatory molecule CD40 on monocytes. Co-expression analyses of CX3CR1 and CD56 demonstrated the existence of different NK cell fractions based on the surface expression of these two surface markers, the CX3CR1(neg) CD56(bright), CX3CR1(neg) CD56(dim) and CX3CR1(high) CD56(dim) fractions. Additional investigations on the expression of NK cell receptors (KIR, NKG2A, NKp30 and NKp46) and the maturation markers CD27, CD62L and CD57 indicated that CX3CR1 expression of CD56(dim) discriminated between an intermediary CX3CR1(neg) CD56(dim) and fully mature CX3CR1(high) CD56(dim) NK cell fractions. Hence, CX3CR1 emerges as an additional differentiation marker that may link NK cell maturation with the ability to migrate to different organs including the central nervous system.     

CX3CL1 up-regulation is associated with recruitment of CX3CR1+ mononuclear phagocytes and T lymphocytes in the lungs during cigarette smoke-induced emphysema

CX3CR1 is expressed on monocytes, dendritic cells, macrophages, subsets of T lymphocytes, and natural killer cells and functions in diverse capacities such as leukocyte adhesion, migration, and cell survival on ligand binding. Expression of the CX3CL1 gene, whose expression product is the sole ligand for CX3CR1, is up-regulated in human lungs with chronic cigarette smoke-induced obstructive lung disease. At present, it is unknown whether CX3CL1 up-regulation is associated with the recruitment and accumulation of immune cells that express CX3CR1. We show that mice chronically exposed to cigarette smoke up-regulate CX3CL1 gene expression, which is associated with an influx of CX3CR1⁺ cells in the lungs. The increase in CX3CR1⁺ cells is primarily comprised of macrophages and T lymphocytes and is associated with the development of emphysema. In alveolar macrophages, cigarette smoke exposure increased the expression of both CX3CR1 and CX3CL1 genes. The inducibility of CX3CR1 expression was not solely dependent on a chronic stimulus because lipopolysaccharide up-regulated CX3CR1 in RAW264.7 cells in vitro and in mononuclear phagocytes in vivo. Our findings suggest a mechanism by which macrophages amplify and promote CX3CR1⁺ cell accumulation within the lungs during both acute and chronic inflammatory stress. We suggest that one function of the CX3CR1-CX3CL1 pathway is to recruit and sustain divergent immune cell populations implicated in the pathogenesis of cigarette smoke-induced emphysema.     

Non-redundant role of the chemokine receptor CX3CR1 in the anti-inflammatory function of gut macrophages

Mucosal immunity at the intestinal level is constantly challenged by the presence of external food and microbial antigens and must be kept under strict control to avoid the rise of aberrant inflammation. Among cells of the innate immunity, macrophages expressing the chemokine receptor CX3CR1 are strategically located near the gut epithelial barrier. These cells contribute to the maintenance of homeostasis by producing the anti-inflammatory cytokine IL-10; however, their role in the control of full blown inflammation and tissue injury is controversial. In this study we investigated mice proficient or deficient for the expression of the CX3CR1 receptor in a model of dextran sulphate sodium (DSS) induced acute colitis. We found that KO mice (CX3CR1^GFP/GFP) had a more severe disease compared to WT mice (CX3CR1^GFP/+), both in terms of histological examination of colonic tissues and leukocyte infiltration, with an expansion of macrophages and CD4-Th17 lymphocytes. The expression of several inflammatory mediators (IL-1β, IL-6, IFNγ, iNOS) was also significantly upregulated in KO mice, despite higher IL-10 production. Overall, our study demonstrates that macrophages expressing a functional CX3CR1 receptor have an important and non-redundant role in controlling the abnormal intestinal inflammation that may lead to tissue damage.     

中国HIV-1暴露未感染者及感染者趋化因子受体CX3CR1的表达研究

目的 通过分析中国HIV-1暴露未感者（exposed semnegative individuals，ESN）及HIV-1感染者外周血中CX3C1^＋CD8^＋／CD3^＋、CX3CR1^＋CD16^＋／CD3^-、CX3CR1^＋CD56^＋／CD3^-细胞百分率及绝对值的变化，探讨CX3CR1受体与HIV-1感染及疾病进展的关系。方法 采集19例ESN、34例未经治疗的HIV-1感染者及18例健康人抗凝静脉血，采用流式细胞仪检测技术，分析计算三色荧光抗体标记的全血中CX3CR1^＋CD8^＋／CD3^＋、CX3CR1^＋CD16^＋／CD3^-、CX3CR1^＋CD56^＋／CD3^-细胞百分率及绝对值。结果 ESNCX3CR1^＋CD8^＋／CD3^＋细胞的百分率是11．05％±6．52％，绝对值是81．16±13．67个／山，显著高于正常对照组（百分率是5．69％±3．94％，绝对值是37．36±8．28个/μl）；HIV-1感染组CX3CR1^＋CD8^＋／CD3^＋细胞的百分率是20．98％±11．88％，绝对值是166．38±138．38个/μl，显著高于正常对照组。ESN的CX3CR1^＋CD16^＋／CD3^-细胞的绝对值是312．49±159．45个／m，显著高于HIV-1感染组（108．83±119．35个／ta）。ESN的CX3CR1^＋CD56^＋／CD3^-细胞的绝对值是316．98±162．56个叫，显著高于HIV-1感染组（100．27±114．57个／ta）。HIV．1感染者的CX3CR1^＋CD16^＋／CD3^-、CX3CR1^＋CD56^＋／CD3^-细胞的绝对值与CIM^＋T淋巴细胞的绝对值呈明显正相关（P〈0．05）。结论CX3CR1^＋CD8^＋／CD3^＋细胞在中国ESN体内起保护作用，而在HIV-1感染者体内发挥有限的保护作用。表达CX3CR1受体的NK细胞可以作为监测HIV-1感染者免疫状况的一个指标。     

Blood monocytes consist of two principal subsets with distinct migratory properties

Peripheral blood monocytes are a heterogeneous population of circulating leukocytes. Using a murine adoptive transfer system to probe monocyte homing and differentiation in vivo, we identified two functional subsets among murine blood monocytes: a short-lived CX(3)CR1(lo)CCR2(+)Gr1(+) subset that is actively recruited to inflamed tissues and a CX(3)CR1(hi)CCR2(-)Gr1(-) subset characterized by CX(3)CR1-dependent recruitment to noninflamed tissues. Both subsets have the potential to differentiate into dendritic cells in vivo. The level of CX(3)CR1 expression also defines the two major human monocyte subsets, the CD14(+)CD16(-) and CD14(lo)CD16(+) monocytes, which share phenotype and homing potential with the mouse subsets. These findings raise the potential for novel therapeutic strategies in inflammatory diseases.     

The impact of chemokine receptor CX3CR1 deficiency during respiratory infections with Mycobacterium tuberculosis or Francisella tularensis

Recruitment of immune cells to infection sites is a critical component of the host response to pathogens. This process is facilitated partly through interactions of chemokines with cognate receptors. Here, we examine the importance of fractalkine (CX3CL1) receptor, CX3CR1, which regulates function and trafficking of macrophages and dendritic cells, in the host''s ability to control respiratory infections with Mycobacterium tuberculosis or Francisella tularensis. Following low-dose aerosol challenge with M. tuberculosis, CX3CR1^−/− mice were no more susceptible to infection than wild-type C57BL/6 mice as measured by organ burden and survival time. Similarly, following inhalation of F. tularensis, CX3CR1^−/− mice displayed similar organ burdens to wild-type mice. CX3CR1^−/− mice had increased recruitment of monocytes and neutrophils in the lung; however, this did not result in increased abundance of infected monocytes or neutrophils. We conclude that CX3CR1-deficiency affects immune-cell recruitment; however, loss of CX3CR1 alone does not render the host more susceptible to M. tuberculosis or F. tularensis.     

CX3CR1参与雷公藤内酯对MPP~+帕金森病大鼠多巴胺能神经元的保护作用

目的:探讨雷公藤内酯对1-甲基-4-苯基吡啶(MPP+)帕金森病模型大鼠的保护作用及其可能机制。方法:采用MPP+黑质内注射建立帕金森病大鼠模型。实验分为假手术组、模型组、雷公藤内酯组及其溶剂对照组,利用酪氨酸羟化酶(TH)免疫荧光强度测定多巴胺神经元存活率、小胶质细胞标记物OX-42免疫荧光强度测定小胶质细胞激活程度、Western blotting测定趋化因子受体CX3CR1表达量。结果:免疫组化结果表明,MPP+黑质内注射可使模型组OX-42免疫荧光强度增高,DA神经元进行性变性死亡。雷公藤内酯组OX-42免疫荧光强度较模型组低(P0.01),TH阳性神经元数量较模型组多(P0.01)。Western blotting结果提示雷公藤内酯组CX3CR1表达量较模型组低(P0.05)。结论:雷公藤内酯对MPP+帕金森病大鼠模型具有神经保护作用,其机制可能与抑制小胶质细胞激活有关,抑制CX3CR1可能是其抑制小胶质细胞的途径之一。     

人早孕蜕膜间充质干细胞移植治疗大鼠宫腔粘连

目的:探讨人早孕蜕膜间充质干细胞(hDMSCs)治疗大鼠宫腔粘连(IUA)的可行性和有效性。方法:体外分离、培养、纯化、鉴定h DMSCs。将30只雌性SD大鼠随机分为3组:蜕膜间充质干细胞治疗组(IUA+hDMSCs)、IUA模型组和假手术(sham)组,每组各10只。IUA+hDMSCs组和IUA组复制IUA模型后10 min内,IUA+hDMSCs组经尾静脉注射2×10~6个Dio标记的hDMSCs,每3天补充1次,连续注射3次;IUA组经尾静脉注射相同容量的PBS;sham组仅行开腹手术。3个动情周期后取子宫行HE染色和Masson染色,测量子宫内膜厚度、子宫内膜腺体数目、子宫内膜小血管数目和纤维化面积比率,并行免疫组化检测子宫内膜组织细胞角蛋白、波形蛋白、转化生长因子(TGF)-β1及整合素αγβ3的表达量,q PCR检测IUA相关基因含量,免疫荧光观察h DMSCs在内膜中的分布情况,并评估大鼠的生育能力。结果:IUA组部分子宫腔闭锁,内膜萎缩,腺体减少,大量纤维化改变。IUA+hDMSCs组与IUA组相比子宫间质厚度明显增加(P0.05),大量腺体增生和小血管新生(P0.05),纤维化程度减小(P0.05),与sham组比较无统计学差异。IUA+hDMSCs组细胞角蛋白、波形蛋白和整合素αγβ3表达量明显高于IUA组(P0.05),而TGF-β1表达量低于IUA组(P0.05)。qPCR结果显示与IUA组相比,除TNF-α和结缔组织生长因子下调外,IUA+hDMSCs组的干细胞因子、血管内皮生长因子、碱性成纤维细胞生长因子和thrombospondin-1均明显上调。免疫荧光结果显示Dio- DMSCs主要分布于腔上皮层,部分位于间质。IUA+hDMSCs组大鼠双侧子宫均妊娠,平均胎鼠数量与IUA组相比有统计学差异(P0.05)。结论:hDMSCs可在受损的大鼠子宫内膜中存活、增殖,有效修复大鼠的子宫内膜,抑制IUA。     

Glucocorticoids induce an activated, anti-inflammatory monocyte subset in mice that resembles myeloid-derived suppressor cells

Glucocorticoids (GC) are still the most widely used immunosuppressive agents in clinical medicine. Surprisingly, little is known about the mechanisms of GC action on monocytes, although these cells exert pro- and anti-inflammatory effects. We have shown recently that GC induce a specific monocyte phenotype with anti-inflammatory properties in humans. We now investigated whether this also applies for the murine system and how this subset would relate to recently defined murine subtypes. After treatment with dexamethasone for 48 h, monocytes up-regulated scavenger receptor CD163 and Gr-1, down-regulated CX(3)CR1, and shared with human GC-treated monocytes functional features such as low adhesiveness but high migratory capacity. They specifically up-regulated anti-inflammatory IL-10, but not TGF-beta, and in contrast to their human counterparts, they down-regulated IL-6. Although GC-induced monocytes down-regulated CX(3)CR1, a distinctive marker for classical/proinflammatory human and murine monocytes (CX(3)CR1(lo)CCR2(+)Ly6C(hi)), they differed from this physiologically occurring subset, as they remained Ly6C(med) and unactivated (CD62 ligand(++)). In addition to their immunosuppressive effects, they were CD11b(+)Gr-1(+) and expressed the IL-4Ralpha chain (CD124), a recently described, signature molecule of tumor-induced myeloid-derived suppressor cells (MDSC). We therefore generated murine MDSC in B16 melanoma-bearing mice and indeed found parallel up-regulation of CD11b(+)Gr-1(+) and CD124 on GC-induced monocytes and MDSC. These data allow us to speculate that the GC-induced subtype shares with inflammatory monocytes the ability to migrate quickly into inflamed tissue, where they, however, exert anti-inflammatory effects and that similarities between GC-induced monocytes and MDSC may be involved in progression of some tumors observed in patients chronically treated with GC.     

Human intestinal pro-inflammatory CD11chighCCR2+CX3CR1+ macrophages,but not their tolerogenic CD11c−CCR2−CX3CR1− counterparts,are expanded in inflammatory bowel disease

Although macrophages (Mϕ) maintain intestinal immune homoeostasis, there is not much available information about their subset composition, phenotype and function in the human setting. Human intestinal Mϕ (CD45⁺HLA-DR⁺CD14⁺CD64⁺) can be divided into subsets based on the expression of CD11c, CCR2 and CX3CR1. Monocyte-like cells can be identified as CD11c^highCCR2⁺CX3CR1⁺ cells, a phenotype also shared by circulating CD14⁺ monocytes. On the contrary, their Mϕ-like tissue-resident counterparts display a CD11c⁻CCR2⁻CX3CR1⁻ phenotype. CD11c^high monocyte-like cells produced IL-1β, both in resting conditions and after LPS stimulation, while CD11c⁻ Mϕ-like cells produced IL-10. CD11c^high pro-inflammatory monocyte-like cells, but not the others, were increased in the inflamed colon from patients with inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis. Tolerogenic IL-10-producing CD11c⁻ Mϕ-like cells were generated from monocytes following mucosal conditioning. Finally, the colonic mucosa recruited circulating CD14⁺ monocytes in a CCR2-dependent manner, being such capacity expanded in IBD. Mϕ subsets represent, therefore, transition stages from newly arrived pro-inflammatory monocyte-like cells (CD11c^highCCR2⁺CX3CR1⁺) into tolerogenic tissue-resident (CD11c⁻CCR2⁻CX3CR1⁻) Mϕ-like cells as reflected by the mucosal capacity to recruit circulating monocytes and induce CD11c⁻ Mϕ. The process is nevertheless dysregulated in IBD, where there is an increased migration and accumulation of pro-inflammatory CD11c^high monocyte-like cells.     

CX3CR1通过调节Ca2+内流介导神经元凋亡影响缺血性卒中小鼠预后

目的观察脑缺血后趋化因子受体1(CX3CR1)在神经元上的表达变化,并探讨其作用及机制。方法将野生型C57/BL6小鼠和CX3CR1基因敲除小鼠,分别设置对照组(假手术组)和小鼠中动脉永久闭塞(pMCAO)模型,用磁共振成像(MRI)检测30 min后脑缺血范围和24 h后梗死面积;免疫荧光三重染色法检测凋亡;Western blot检测CX3CR1蛋白的表达。在体外,培养原代神经元,建立氧糖剥离(OGD)细胞缺血模型;用MTT法检测细胞存活率;免疫荧光检测神经元CX3CR1的表达;激光共聚焦显微镜观察神经元内Ca^2+浓度变化。结果在野生型小鼠中,与对照组和健侧相比,pMACO后,患侧CX3CR1表达显著升高(P<0.05),且CX3CR1与凋亡蛋白caspase-3在神经元上共表达;与野生型小鼠相比,CX3CR1基因敲除小鼠pMACO 30 min后缺血损伤面积相似,但24 h后CX3CR1基因敲除小鼠梗死面积小于对照组(P<0.05);在体外,原代神经元OGD后CX3CR1表达显著升高(P<0.05),敲除神经元上CX3CR1,可减轻谷氨酸介导的兴奋性损伤,细胞存活率显著上升,同时观察到,敲除CX3CR1可降低谷氨酸介导的Ca^2+内流到神经元的速度和总量。结论缺血可诱导神经元CX3CR1的表达,且神经元CX3CR1可以通过调节Ca^2+内流来介导神经元的凋亡。     

Differential expression of the chemokine receptors CX3CR1 and CCR1 by microglia and macrophages in myelin-oligodendrocyte-glycoprotein-induced experimental autoimmune encephalomyelitis

Chemokines are important for the recruitment of immune cells into sites of inflammation. To better understand their functional roles during inflammation we have here studied the in vivo expression of receptors for the chemokines CCL3/CCL5/CCL7 (MIP-1alpha/RANTES/MCP-3) and CX3CL1 (fractalkine), CCR1 and CX3CR1, respectively, in rat myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis. Combined in situ hybridization and immunohistochemistry demonstrated intensely upregulated CCR1 mRNA expression in early, actively demyelinating plaques, whereas CX3CR1 displayed a more generalized expression pattern. CX3CR1 mRNA expressing cells were identified as microglia on the basis of their cellular morphology and positive GSA/B4 lectin staining. In contrast, CCR1 mRNA was preferentially expressed by ED1+ GSA/B4+ macrophages. The notion of differential chemokine receptor expression in microglia and monocyte-derived macrophages was corroborated at the protein level by extraction and flow cytometric sorting of cells infiltrating the spinal cord using gating for the surface markers CD45, ED-2 and CD11b. These observations suggest a differential receptor expression between microglia and monocyte-derived macrophages and that mainly the latter cell type is responsible for active demyelination. This has great relevance for the possibility of therapeutic intervention in demyelinating diseases such as multiple sclerosis, for example by targeting signaling events leading to monocyte recruitment.     

Pivotal Advance: Th-1 cytokines inhibit, and Th-2 cytokines promote fibrocyte differentiation

CD14+ peripheral blood monocytes can differentiate into fibroblast-like cells called fibrocytes, which are associated with and are at least partially responsible for wound healing and fibrosis in multiple organ systems. Signals regulating fibrocyte differentiation are poorly understood. In this study, we find that when added to human PBMCs cultured in serum-free medium, the profibrotic cytokines IL-4 and IL-13 promote fibrocyte differentiation without inducing fibrocyte or fibrocyte precursor proliferation. We also find that the potent, antifibrotic cytokines IFN-gamma and IL-12 inhibit fibrocyte differentiation. In our culture system, IL-1beta, IL-3, IL-6, IL-7, IL-16, GM-CSF, M-CSF, fetal liver tyrosine kinase 3, insulin growth factor 1, vascular endothelial growth factor, and TNF-alpha had no significant effect on fibrocyte differentiation. IL-4, IL-13, and IFN-gamma act directly on monocytes to regulate fibrocyte differentiation, and IL-12 acts indirectly, possibly through CD16-positive NK cells. We previously identified the plasma protein serum amyloid P (SAP) as a potent inhibitor of fibrocyte differentiation. When added together, the fibrocyte-inhibitory activity of SAP dominates the profibrocyte activities of IL-4 and IL-13. The profibrocyte activities of IL-4 and IL-13 and the fibrocyte-inhibitory activities of IFN-gamma and IL-12 counteract each other in a concentration-dependent manner. These results indicate that the complex mix of cytokines and plasma proteins present in inflammatory lesions, wounds, and fibrosis will influence fibrocyte differentiation.