Deficiency in CCR2 increases susceptibility of mice to infection with an intracellular pathogen, Francisella tularensis LVS, but does not impair development of protective immunity

CCR2 is the major chemokine receptor that regulates appropriate trafficking of inflammatory monocytes, but the role of this chemokine receptor and its ligands during primary and secondary infection with intracellular infections remains incompletely understood. Here we used murine infection with the Live Vaccine Strain (LVS) of Francisella tularensis to evaluate the role of CCR2 during primary and secondary parenteral responses to this prototype intracellular bacterium. We find that mice deficient in CCR2 are highly compromised in their ability to survive intradermal infection with LVS, indicating the importance of this receptor during primary parenteral responses. Interestingly, this defect could not be readily attributed to the activities of the known murine CCR2 ligands MCP-1/CCL2, MCP-3/CCL7, or MCP-5/CCL12. Nonetheless, CCR2 knockout mice vaccinated by infection with low doses of LVS generated optimal T cell responses that controlled the intramacrophage replication of Francisella, and LVS-immune CCR2 knockout mice survived maximal lethal Francisella challenge. Thus, fully protective adaptive immune memory responses to this intracellular bacterium can be readily generated in the absence of CCR2.

Macrophages inhibit and enhance endometriosis depending on their origin

Macrophages are intimately involved in the pathophysiology of endometriosis, a chronic inflammatory disorder characterized by the growth of endometrial-like tissue (lesions) outside the uterus. By combining genetic and pharmacological monocyte and macrophage depletion strategies we determined the ontogeny and function of macrophages in a mouse model of induced endometriosis. We demonstrate that lesion-resident macrophages are derived from eutopic endometrial tissue, infiltrating large peritoneal macrophages (LpM) and monocytes. Furthermore, we found endometriosis to trigger continuous recruitment of monocytes and expansion of CCR2+ LpM. Depletion of eutopic endometrial macrophages results in smaller endometriosis lesions, whereas constitutive inhibition of monocyte recruitment significantly reduces peritoneal macrophage populations and increases the number of lesions. Reprogramming the ontogeny of peritoneal macrophages such that embryo-derived LpM are replaced by monocyte-derived LpM decreases the number of lesions that develop. We propose a putative model whereby endometrial macrophages are "proendometriosis" while newly recruited monocyte-derived macrophages, possibly in LpM form, are "antiendometriosis." These observations highlight the importance of monocyte-derived macrophages in limiting disease progression.

MCP-1 promotes detrimental cardiac physiology, pulmonary edema, and death in the cpk model of polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by slowly expanding renal cysts that damage the kidney, typically resulting in renal failure by the fifth decade. The most common cause of death in these patients, however, is cardiovascular disease. Expanding cysts in PKD induce chronic kidney injury that is accompanied by immune cell infiltration, including macrophages, which we and others have shown can promote disease progression in PKD mouse models. Here, we show that monocyte chemoattractant protein-1 [MCP-1/chemokine (C-C motif) ligand 2 (CCL2)] is responsible for the majority of monocyte chemoattractant activity produced by renal PKD cells from both mice and humans. To test whether the absence of MCP-1 lowers renal macrophage concentration and slows disease progression, we generated genetic knockout (KO) of MCP-1 in a mouse model of PKD [congenital polycystic kidney (cpk) mice]. Cpk mice are born with rapidly expanding renal cysts, accompanied by a decline in kidney function and death by postnatal day 21. Here, we report that KO of MCP-1 in these mice increased survival, with some mice living past 3 mo. Surprisingly, however, there was no significant difference in renal macrophage concentration, nor was there improvement in cystic disease or kidney function. Examination of mice revealed cardiac hypertrophy in cpk mice, and measurement of cardiac electrical activity via ECG revealed repolarization abnormalities. MCP-1 KO did not affect the number of cardiac macrophages, nor did it alleviate the cardiac aberrancies. However, MCP-1 KO did prevent the development of pulmonary edema, which occurred in cpk mice, and promoted decreased resting heart rate and increased heart rate variability in both cpk and noncystic mice. These data suggest that in this mouse model of PKD, MCP-1 altered cardiac/pulmonary function and promoted death outside of its role as a macrophage chemoattractant.

MCP-1 deficiency enhances browning of adipose tissue via increased M2 polarization

Obesity is strongly associated with chronic inflammation for which adipose tissue macrophages play a critical role. The objective of this study is to identify monocyte chemoattractant protein-1 (MCP-1, CCL2) as a key player governing M1-M2 macrophage polarization and energy balance. We evaluated body weight, fat mass, adipocyte size and energy expenditure as well as core body temperature of Ccl2 knockout mice compared with wild-type mice. Adipose tissues, differentiated adipocyte and bone marrow-derived macrophages were assessed by qPCR, Western blot analysis and histochemistry. MCP-1 deficiency augmented energy expenditure by promoting browning in white adipose tissue and brown adipose tissue activity via increasing the expressions of Ucp1, Prdm16, Tnfrsf9, Ppargc1a, Nrf1 and Th and mitochondrial DNA copy number. MCP-1 abrogation promoted M2 polarization which is characterized by increased expression of Arg1, Chil3, Il10 and Klf4 whereas it decreased M1 polarization by decreased p65 nuclear translocation and attenuated expression of Itgax, Tnf and Nos2, leading to increased browning of adipocytes. Enhanced M2 polarization and attenuated M1 polarization in the absence of MCP-1 are independent. Collectively, our results suggest that the action of MCP-1 in macrophages modulates energy expenditure by impairing browning in adipose tissue.

CCL2 recruits T cells into the brain in a CCR2-independent manner

CCL2 is a chemokine that can be induced during neuroinflammation to recruit immune cells, but its role in the central nervous system (CNS) is unclear. Our aim was to better understand its role. We induced CCL2 in CNS of naive CCL2-deficient mice using intrathecally administered replication-defective adenovirus and examined cell infiltration by flow cytometry. CCL2 expression induced pronounced and unexpected recruitment of regulatory and IFNγ-producing T cells to CNS from blood, possibly related to defective egress of monocytes from CCL2-deficient bone marrow. Infiltration also occurred in mice lacking CCR2, a receptor for CCL2. Expression of another receptor for CCL2, CCR4, and CXCR3, a receptor for CXCL10, which was also induced, were both increased in CCL2-treated CNS. CCR4 was expressed by neurons and astrocytes as well as CD4 T cells, and CXCR3 was expressed by CD4 and CD8 T cells. Chemokine-recruited T cells did not lead to CNS pathology. Our findings show a role for CCL2 in recruitment of CD4 T cells to the CNS and show that redundancy among chemokine receptors ensures optimal response.

The innate immune response to lower respiratory tract E. Coli infection and the role of the CCL2-CCR2 axis in neonatal mice

Neonates have greater morbidity/mortality from lower respiratory tract infections (LRTI) compared to older children. Lack of conditioning of the pulmonary immune system due to limited environmental exposures and/or infectious challenges likely contributes to the increase susceptibility in the neonate. In this study, we sought to gain insights into the nature and dynamics of the neonatal pulmonary immune response to LRTI using a murine model.

METHODS

Wildtype (WT) and Ccr2^-/- C57BL/6 neonatal and juvenile mice received E. coli or PBS by direct pharyngeal aspiration. Flow cytometry was used to measure immune cell dynamics and identify cytokine-producing cells. Real-time PCR and ELISA were used to measure cytokine/chemokine expression.

RESULTS

Innate immune cell recruitment in response to E. coli-induced LRTI was delayed in the neonatal lung compared to juvenile lung. Lung clearance of bacteria was also significantly delayed in the neonate. Ccr2^-/- neonates, which lack an intact CCL2-CCR2 axis, had higher mortality after E. coli challenged than Ccr2^+/+ neonates. A greater percentage of CD8⁺ T cells and monocytes from WT neonates challenged with E. coli produced TNF compared to controls.

CONCLUSION

The pulmonary immune response to E. coli-induced LRTI differed significantly between neonatal and juvenile mice. Neonates were more susceptible to increasing doses of E. coli and exhibited greater mortality than juveniles. In the absence of an intact CCL2-CCR2 axis, susceptibility to LRTI-induced mortality was further increased in neonatal mice. Taken together these findings underscore the importance of age-related differences in the innate immune response to LRTI during early stages of postnatal life.

CCL2/CCR2 Regulates the Tumor Microenvironment in HER-2/neu-Driven Mammary Carcinomas in Mice

Chronic inflammation is a hallmark of cancer. Inflammatory chemokines, such as C-C chemokine ligand 2 (CCL2), are often present in tumors but their roles in cancer initiation and maintenance are not clear. Here we report that CCL2 promotes mammary carcinoma development in a clinically relevant murine model of breast cancer. Targeted disruption of Ccl2 slowed the growth of activated Her2/neu-driven mammary tumors and prolonged host survival. Disruption of Ccl2 was associated with a decrease in the development and mobilization of endothelial precursor cells (EPCs) which can contribute to tumor neovascularization. In contrast, disruption of Ccr2, which encodes CCL2's sole signaling receptor, accelerated tumor development, shortened host survival, and mobilized EPCs. However, pharmacological inhibition of CCR2 phenocopied Ccl2 disruption rather than Ccr2 disruption, suggesting that the Ccr2-/- phenotype is a consequence of unanticipated alterations not linked to intact CCL2/CCR2 signaling. Consistent with this explanation, Ccr2-/- monocytes are more divergent from wild type monocytes than Ccl2-/- monocytes in their expression of genes involved in key developmental and functional pathways. Taken together, our data suggest a tumor-promoting role for CCL2 acting through CCR2 on the tumor microenvironment and support the targeting of this chemokine/receptor pair in breast cancer.

Deficiency for the chemokine monocyte chemoattractant protein-1 aggravates tubular damage after renal ischemia/reperfusion injury

Temporal expression of chemokines is a crucial factor in the regulation of renal ischemia/reperfusion (I/R) injury and repair. Beside their role in the migration and activation of inflammatory cells to sites of injury, chemokines are also involved in other processes such as angiogenesis, development and migration of stem cells. In the present study we investigated the role of the chemokine MCP-1 (monocyte chemoattractant protein-1 or CCL2), the main chemoattractant for monocytes, during renal I/R injury. MCP-1 expression peaks several days after inducing renal I/R injury coinciding with macrophage accumulation. However, MCP-1 deficient mice had a significant decreased survival and increased renal damage within the first two days, i.e. the acute inflammatory response, after renal I/R injury with no evidence of altered macrophage accumulation. Kidneys and primary tubular epithelial cells from MCP-1 deficient mice showed increased apoptosis after ischemia. Taken together, MCP-1 protects the kidney during the acute inflammatory response following renal I/R injury.

Absence of CCL2 and CCL3 Ameliorates Central Nervous System Grey Matter But Not White Matter Demyelination in the Presence of an Intact Blood-Brain Barrier

A broad spectrum of diseases is characterized by myelin abnormalities, oligodendrocyte pathology, and concomitant glia activation, among multiple sclerosis (MS). Our knowledge regarding the factors triggering gliosis and demyelination is scanty. Chemokines are pivotal for microglia and astrocyte activation and orchestrate critical steps during the formation of central nervous system (CNS) demyelinating lesions. Redundant functions of chemokines complicate, however, the study of their functional relevance. We used the cuprizone model to study redundant functions of two chemokines, CCL2/MCP1 and CCL3/MIP1α, which are critically involved in the pathological process of cuprizone-induced demyelination. First, we generated a mutant mouse strain lacking functional genes of both chemokines and demonstrated that double-mutant animals are viable, fertile, and do not present with gross abnormalities. Astrocytes and peritoneal macrophages, cultured form tissues of these animals did neither express CCL2 nor CCL3. Exposure to cuprizone resulted in increased CCL2 and CCL3 brain levels in wild-type but not mutant animals. Cuprizone-induced demyelination, oligodendrocyte loss, and astrogliosis were significantly ameliorated in the cortex but not corpus callosum of chemokine-deficient animals. In summary, we provide a novel powerful model to study the redundant function of two important chemokines. Our study reveals that chemokine function in the CNS redounds to region-specific pathophysiological events.

Chemokine mediated monocyte trafficking into the retina: role of inflammation in alteration of the blood-retinal barrier in diabetic retinopathy

Inflammation in the diabetic retina is mediated by leukocyte adhesion to the retinal vasculature and alteration of the blood-retinal barrier (BRB). We investigated the role of chemokines in the alteration of the BRB in diabetes. Animals were made diabetic by streptozotocin injection and analyzed for gene expression and monocyte/macrophage infiltration. The expression of CCL2 (chemokine ligand 2) was significantly up-regulated in the retinas of rats with 4 and 8 weeks of diabetes and also in human retinal endothelial cells treated with high glucose and glucose flux. Additionally, diabetes or intraocular injection of recombinant CCL2 resulted in increased expression of the macrophage marker, F4/80. Cell culture impedance sensing studies showed that purified CCL2 was unable to alter the integrity of the human retinal endothelial cell barrier, whereas monocyte conditioned medium resulted in significant reduction in cell resistance, suggesting the relevance of CCL2 in early immune cell recruitment for subsequent barrier alterations. Further, using Cx3cr1-GFP mice, we found that intraocular injection of CCL2 increased retinal GFP⁺ monocyte/macrophage infiltration. When these mice were made diabetic, increased infiltration of monocytes/macrophages was also present in retinal tissues. Diabetes and CCL2 injection also induced activation of retinal microglia in these animals. Quantification by flow cytometry demonstrated a two-fold increase of CX3CR1⁺/CD11b⁺ (monocyte/macrophage and microglia) cells in retinas of wildtype diabetic animals in comparison to control non-diabetic ones. Using CCL2 knockout (Ccl2^−/−) mice, we show a significant reduction in retinal vascular leakage and monocyte infiltration following induction of diabetes indicating the importance of this chemokine in alteration of the BRB. Thus, CCL2 may be an important therapeutic target for the treatment of diabetic macular edema.

Age- and light-dependent development of localised retinal atrophy in CCL2(-/-)CX3CR1(GFP/GFP) mice

Previous studies have shown that CCL2/CX3CR1 deficient mice on C57BL/6N background (with rd8 mutation) have an early onset (6 weeks) of spontaneous retinal degeneration. In this study, we generated CCL2^−/−CX3CR1^GFP/GFP mice on the C57BL/6J background. Retinal degeneration was not detected in CCL2^−/−CX3CR1^GFP/GFP mice younger than 6 months. Patches of whitish/yellowish fundus lesions were observed in 17∼60% of 12-month, and 30∼100% of 18-month CCL2^−/−CX3CR1^GFP/GFP mice. Fluorescein angiography revealed no choroidal neovascularisation in these mice. Patches of retinal pigment epithelium (RPE) and photoreceptor damage were detected in 30% and 50% of 12- and 18-month CCL2^−/−CX3CR1^GFP/GFP mice respectively, but not in wild-type mice. All CCL2^−/−CX3CR1^GFP/GFP mice exposed to extra-light (∼800lux, 6 h/day, 6 months) developed patches of retinal atrophy, and only 20–25% of WT mice which underwent the same light treatment developed atrophic lesions. In addition, synaptophysin expression was detected in the outer nucler layer (ONL) of area related to photoreceptor loss in CCL2^−/−CX3CR1^GFP/GFP mice. Markedly increased rhodopsin but reduced cone arrestin expression was observed in retinal outer layers in aged CCL2^−/−CX3CR1^GFP/GFP mice. GABA expression was reduced in the inner retina of aged CCL2^−/−CX3CR1^GFP/GFP mice. Significantly increased Müller glial and microglial activation was observed in CCL2^−/−CX3CR1^GFP/GFP mice compared to age-matched WT mice. Macrophages from CCL2^−/−CX3CR1^GFP/GFP mice were less phagocytic, but expressed higher levels of iNOS, IL-1β, IL-12 and TNF-α under hypoxia conditions. Our results suggest that the deletions of CCL2 and CX3CR1 predispose mice to age- and light-mediated retinal damage. The CCL2/CX3CR1 deficient mouse may thus serve as a model for age-related atrophic degeneration of the RPE, including the dry type of macular degeneration, geographic atrophy.

Monocyte chemoattractant protein-1 (MCP-1) deficiency enhances alternatively activated M2 macrophages and ameliorates insulin resistance and fatty liver in lipoatrophic diabetic A-ZIP transgenic mice

AIMS/HYPOTHESIS

Monocyte chemoattractant protein-1 (MCP-1)/chemokine (C-C motif) ligand (CCL) 2 (CCL2) secreted from white adipose tissue (WAT) in obesity has been reported to contribute to tissue macrophage accumulation and insulin resistance by inducing a chronic inflammatory state. MCP-1 has been shown to be elevated in the fatty liver of lipoatrophic A-ZIP-transgenic (A-ZIP-Tg) mice. Treatment of these mice with the CC chemokine receptor (CCR) 2 antagonist has been shown to ameliorate the hyperglycaemia, hyperinsulinaemia and hepatomegaly, in conjunction with reducing liver inflammation. However, since CCR2 antagonists can block not only MCP-1 but also MCP-2 (CCL8) and MCP-3 (CCL7), it remains unclear whether MCP-1 secreted from the liver could contribute to hyperglycaemia, hyperinsulinaemia and hepatomegaly in conjunction with liver inflammation, as well as to the M1 and M2 states of macrophage polarisation.

METHODS

To address these issues, we analysed the effects of targeted disruption of MCP-1 in A-ZIP-Tg mice.

RESULTS

MCP-1 deficiency alone or per se resulted in a significant amelioration of insulin resistance in A-ZIP-Tg mice, which was associated with a suppression of extracellular signal-regulated protein kinase (ERK)-1/2 and p38 mitogen-activated protein kinase (p38MAPK) phosphorylation in liver. Although MCP-1 deficiency did not reduce the expression of macrophage markers, it increased the expression of the genes encoding M2 macrophage markers such as Arg1 and Chi3l3, as well as significantly reducing the triacylglycerol content of livers from A-ZIP-Tg mice. CONCLUSIONS/ INTERPRETATION: Our data clearly indicated that MCP-1 deficiency improved insulin resistance and hepatic steatosis in A-ZIP-Tg mice and was associated with switching macrophage polarisation and suppressing ERK-1/2 and p38MAPK phosphorylation.

Host-derived MCP-1 and MIP-1α regulate protective anti-tumor immunity to localized and metastatic B16 melanoma

Leukocytic infiltration into malignant melanoma lesions is tightly regulated by chemokines. To assess the role of the CC chemokines monocyte chemotactic protein-1 (MCP-1/chemokine ligand 2) and macrophage inflammatory protein-1α (MIP-1α/chemokine ligand 3) in this process, s.c. primary and metastatic B16 F10 melanoma tumor growth levels were examined in mice lacking MCP-1 or MIP-1α. Primary s.c. B16 F10 melanoma growth was augmented by loss of MCP-1 or MIP-1α. Similarly, lung metastasis was enhanced by the deficiency of MCP-1 or MIP-1α. Enhanced tumor outgrowth was associated with decreased percentages of infiltrating CD4(+) T cells, CD8(+) T cells, and natural killer cells. In the absence of MCP-1 or MIP-1α, melanoma outgrowth was correlated with reduced local expression of interferon-γ, IL-6, tumor necrosis factor-α, and transforming growth factor-β. Among these cytokines, reduced expression levels of interferon-γ and tumor necrosis factor-α on leukocytes from the spleen were associated with the development of lung metastasis in chemokine-deficient mice. The local s.c. administration of these four cytokines significantly augmented another chemokine's expression and suppressed primary melanoma growth in mice deficient for MCP-1 or MIP-1α. The s.c. injection of MCP-1 or MIP-1α significantly inhibited the primary tumor growth in wild-type mice. These results indicate that host-derived MCP-1 and MIP-1α regulate protective anti-tumor immunity to B16 F10 melanoma by promoting lymphocyte infiltration into the tumor and subsequent cytokine production.

Monocyte chemoattractant protein-1-deficiency impairs the expression of IL-6, IL-1β and G-CSF after transient focal ischemia in mice

Monocyte chemoattractant protein-1 (MCP-1), a chemokine secreted by neurons and astrocytes following stroke is known to aggravate ischemia-related damage. Previous studies revealed that MCP-1-deficient mice develop smaller infarcts and have an improved neurological outcome, whereas mice overexpressing MCP-1 show worsened brain damage and impaired neurological function. The aim of the present study was to elucidate the molecular background of the enhanced recovery in MCP-1-deficient mice after stroke. For this purpose, we (1) performed expression analyses on crucial post-stroke related inflammatory genes in MCP-1-deficient mice compared to wildtype controls, (2) analyzed a possible impact of MCP-1 on astrocyte activation (3) investigated the cellular origin of respective inflammatory cytokines and (4) analyzed the impact of MCP-1 secretion on the migration of both neutrophil granulocytes and T-cells. Here we report that MCP-1-deficiency leads to a shift towards a less inflammatory state following experimental occlusion of the middle cerebral artery including an impaired induction of interleukin-6, interleukin-1β and granulocyte-colony stimulating factor expression as well as a subsequent diminished influx of hematogenous cells. Additionally, MCP-1-deficient mice developed smaller infarcts 36 hours after experimental stroke. Investigations revealed no differences in transcription of tumor necrosis factor-α and astrogliosis 12 and 36 hours after onset of ischemia. These novel results help to understand post ischemic, inflammatory mechanisms and might give further arguments towards therapeutical interventions by modulation of MCP-1 expression in post stroke inflammation.

Negative regulation of lung inflammation and immunopathology by TNF-α during acute influenza infection

Lung immunopathology is the main cause of influenza-mediated morbidity and death, and much of its molecular mechanisms remain unclear. Whereas tumor necrosis factor-α (TNF-α) is traditionally considered a proinflammatory cytokine, its role in influenza immunopathology is unresolved. We have investigated this issue by using a model of acute H1N1 influenza infection established in wild-type and TNF-α-deficient mice and evaluated lung viral clearance, inflammatory responses, and immunopathology. Whereas TNF-α was up-regulated in the lung after influenza infection, it was not required for normal influenza viral clearance. However, TNF-α deficiency led not only to a greater extent of illness but also to heightened lung immunopathology and tissue remodeling. The severe lung immunopathology was associated with increased inflammatory cell infiltration, anti-influenza adaptive immune responses, and expression of cytokines such as monocyte chemoattractant protein-1 (MCP-1) and fibrotic growth factor, TGF-β1. Thus, in vivo neutralization of MCP-1 markedly attenuated lung immunopathology and blunted TGF-β1 production following influenza infection in these hosts. On the other hand, in vivo transgenic expression of MCP-1 worsened lung immunopathology following influenza infection in wild-type hosts. Thus, TNF-α is dispensable for influenza clearance; however, different from the traditional belief, this cytokine is critically required for negatively regulating the extent of lung immunopathology during acute influenza infection.

Monocyte chemoattractant protein-1 deficiency does not affect steatosis or inflammation in livers of mice fed a methionine-choline-deficient diet

Monocyte chemoattractant protein-1 (MCP-1, Ccl2) expression is increased in livers of patients with nonalcoholic steatohepatitis and in murine models of steatohepatitis. Several studies in rodents indicate that MCP-1 contributes to liver steatosis induced by feeding a high-fat diet. However, the extent of MCP-1 involvement in the widely utilized methionine-choline-deficient (MCD) diet model of steatohepatitis has not been determined. We tested the hypothesis that MCP-1 contributes to steatohepatitis in mice fed the MCD diet. MCP-1-deficient mice on a C57Bl/6J background and age-matched C57Bl/6J mice were fed either MCD diet or control diet for 4 weeks. MCP-1 deficiency did not affect steatohepatitis, as indicated by liver histopathology, nor did it affect serum alanine aminotransferase activity, hepatic triglyceride levels, hepatic inflammatory gene induction, or macrophage accumulation in mice fed the MCD diet. MCP-1 deficiency reduced the expression of the profibrogenic genes, pro-collagen 1a1, connective tissue growth factor, and transforming growth factor-β, in mice fed the MCD diet. MCP-1 deficiency significantly reduced collagen deposition and α-smooth muscle actin protein levels in the livers of mice fed the MCD diet. The results indicate that MCP-1 does not contribute to liver steatosis or inflammation in the MCD diet model of steatohepatitis. Rather, the data suggest that MCP-1 contributes to fibrosis in mice fed the MCD diet, independent of effects on steatosis and inflammation.

Visualization of chemokine receptor activation in transgenic mice reveals peripheral activation of CCR2 receptors in states of neuropathic pain

CCR2 chemokine receptor signaling has been implicated in the generation of diverse types of neuropathology, including neuropathic pain. For example, ccr2 knock-out mice are resistant to the establishment of neuropathic pain, and mice overexpressing its ligand, monocyte chemoattractant protein-1 (MCP1; also known as CCL2), show enhanced pain sensitivity. However, whether CCR2 receptor activation occurs in the central or peripheral nervous system in states of neuropathic pain has not been clear. We developed a novel method for visualizing CCR2 receptor activation in vivo by generating bitransgenic reporter mice in which the chemokine receptor CCR2 and its ligand MCP1 were labeled by the fluorescent proteins enhanced green fluorescent protein and monomeric red fluorescent protein-1, respectively. CCR2 receptor activation under conditions such as acute inflammation and experimental autoimmune encephalomyelitis could be faithfully visualized by using these mice. We examined the status of CCR2 receptor activation in a demyelination injury model of neuropathic pain and found that MCP1-induced CCR2 receptor activation mainly occurred in the peripheral nervous system, including the injured peripheral nerve and dorsal root ganglia. These data explain the rapid antinociceptive effects of peripherally administered CCR2 antagonists under these circumstances, suggesting that CCR2 antagonists may ameliorate pain by inhibiting CCR2 receptor activation in the periphery. The method developed here for visualizing CCR2 receptor activation in vivo may be extended to G-protein-coupled receptors (GPCRs) in general and will be valuable for studying intercellular GPCR-mediated communication in vivo.

Gr1(+) inflammatory monocytes are required for mucosal resistance to the pathogen Toxoplasma gondii

The enteric pathogen Toxoplasma gondii is controlled by a vigorous innate T helper 1 (Th1) cell response in the murine model. We demonstrated that after oral infection, the parasite rapidly recruited inflammatory monocytes [Gr1(+) (Ly6C(+), Ly6G(-)) F4/80(+)CD11b(+)CD11c(-)], which established a vital defensive perimeter within the villi of the ileum in the small intestine. Mice deficient of the chemokine receptor CCR2 or the ligand CCL2 failed to recruit Gr1(+) inflammatory monocytes, whereas dendritic cells and resident tissue macrophages remained unaltered. The selective lack of Gr1(+) inflammatory monocytes resulted in an inability of mice to control replication of the parasite, high influx of neutrophils, extensive intestinal necrosis, and rapid death. Adoptive transfer of sorted Gr1(+) inflammatory monocytes demonstrated their ability to home to the ileum in infected animals and protect Ccr2(-/-) mice, which were otherwise highly susceptible to oral toxoplasmosis. Collectively, these findings illustrate the critical importance of inflammatory monocytes as a first line of defense in controlling intestinal pathogens.

Monocyte chemoattractant protein deficiency fails to restrain macrophage infiltration into adipose tissue [corrected]

OBJECTIVE

Monocyte chemoattractant protein-1 (MCP-1), a CC-motif chemokine, has been proposed to play critical roles in insulin resistance and recruitment of monocytes into adipose tissue. We hypothesized that the absence of MCP-1 would improve the former and diminish the latter.

RESEARCH DESIGN AND METHODS

We investigated these two hypotheses by quantifying glucose metabolism and the accumulation of macrophages in adipose tissue of control and MCP-1-deficient (Mcp1(-)(/)(-)) mice after feeding the animals a high-fat diet for 10 or 16 weeks.

RESULTS

We first established that the two strains were in the same genetic background and that macrophage recruitment into inflamed peritoneum was markedly reduced in the MCP-1-deficient animals. In striking contrast, independent studies at two different facilities at either an early or late time point failed to detect any impairment in macrophage accumulation in adipose tissue of fat-fed Mcp1(-/-) mice. Immunoblot analysis revealed higher levels of Mac2, a macrophage-specific protein, in multiple fat depots of Mcp1(-/-) mice fed a high-fat diet. These mice also had significantly more adipose tissue than control mice, but their glucose metabolism was similar.

CONCLUSIONS

Our observations suggest that MCP-1 does not play a prominent a role in promoting macrophage recruitment into adipose tissue or in systemic insulin resistance.

Immunological protein expression profile in Ccl2/Cx3cr1 deficient mice with lesions similar to age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in the United States. Ccl2 knock-out (KO) mice sporadically develop the cardinal features of AMD in their senescent stage. Humans bearing a loss of function variant or single nucleotide polymorphism (SNP) in CX3CR1 are at increased risk of developing AMD. We recently developed Ccl2(-/-)/Cx3cr1(-/-) mice, which consistently develop retinal degeneration with many AMD features. Since there is strong evidence for an immunological role in AMD pathogenesis, we examined ocular immune protein expression levels in Ccl2(-/-)/Cx3cr1(-/-), Ccl2(-/-), Cx3cr1(-/-), and age-matched wild-type (WT) mice. Immunohistochemistry revealed increased complement C3d in Bruch's membrane, retinal pigment epithelium (RPE), choroidal capillaries, and particularly drusen of the Ccl2(-/-)/Cx3cr1(-/-) mice relative to the WT controls. No change was detected in single KO mice. Real-time RT-PCR revealed a 2.5-fold increase in C3 expression in the Ccl2(-/-)/Cx3cr1(-/-). While the retinas of four month old WT and Ccl2(-/-) showed minimal immunoreactivity for markers of macrophages and microglia, infiltrates of these mononuclear phagocytic cells were detected in the Ccl2(-/-)/Cx3cr1(-/-)retinal lesions and a few foci in the Cx3cr1(-/-) retina. The Ccl2(-/-)/Cx3cr1(-/-) had reduced toll-like receptor 4 (TLR4) expression in the RPE. Following LPS injection, the Ccl2(-/-)/Cx3cr1(-/-) had significantly reduced endotoxin-induced uveitis scores and showed a diminished increase in Tlr4 mRNA expression. No changes in TLR4 expression were detected in either single KO. Autoantibodies against the retina and photoreceptors were also detected in the Ccl2(-/-)/Cx3cr1(-/-) serum. Real-time RT-PCR revealed significant increases in Ccl5 transcript in the Ccl2(-/-)/Cx3cr1(-/-) relative to the WT. These results suggest that innate immunity and possibly adaptive immunity play an important role in Ccl2(-/-)/Cx3cr1(-/-) retinal degeneration. Moreover, since human AMD patients show similar immunopathological profiles, these results support the Ccl2(-/-)/Cx3cr1(-/-) as a suitable model for human AMD.

Absence of CC chemokine ligand 2 does not limit obesity-associated infiltration of macrophages into adipose tissue

Macrophage recruitment to adipose tissue in obesity contributes to enhanced adipose tissue inflammatory activity and thus may underlie obesity-associated metabolic dysfunction. Obese adipose tissue exhibits increases in CC chemokine ligand 2 (CCL2, or monocyte chemoattractant protein-1), an important macrophage-recruiting factor. We therefore hypothesized that elevated CCL2 may contribute to obesity-associated adipose tissue macrophage recruitment. Male 6-week-old CCL2(-/-) and wild-type mice (n = 11-14 per group) were fed standard and high-fat diets until 34 weeks of age. At 12-16 and 25-29 weeks of age, blood was collected for plasma glucose and hormone measurements, and glucose tolerance and insulin tolerance tests were performed. Adipose tissue was collected at 34 weeks for analysis of macrophage infiltration. Surprisingly, CCL2(-/-) mice on high-fat diet showed no reductions in adipose tissue macrophages. CCL2(-/-) mice on standard and high-fat diet were also glucose intolerant and had mildly increased plasma glucose and decreased serum adiponectin levels compared with wild-type mice. On high-fat diet, CCL2(-/-) mice also gained slightly more weight and were hyperinsulinemic compared with wild-type mice. Because macrophage levels were unchanged in CCL2(-/-) mice, the phenotype appears to be caused by lack of CCL2 itself. The fact that metabolic function was altered in CCL2(-/-) mice, despite no changes in adipose tissue macrophage levels, suggests that CCL2 has effects on metabolism that are independent of its macrophage-recruiting capabilities. Importantly, we conclude that CCL2 is not critical for adipose tissue macrophage recruitment. The dominant factor for recruiting macrophages in adipose tissue during obesity therefore remains to be identified.

Organ-Specific Differences in the Function of MCP-1 and CXCR3 During Cardiac and Skin Allograft Rejection

BACKGROUND

Chemokines are well-established to function in the recruitment of leukocytes into allografts in the course of rejection. Moreover, some studies have indicated that there are organ-specific differences in chemokine function, but the mechanism accounting for this difference is not known.

METHODS

Fully major histocompatibility complex-mismatched vascularized cardiac transplants or skin transplants were performed using BALB/c (H-2d), C57BL/6 (H-2b), MCP-1-/- (H-2b) and CXCR3-/- (H-2b) mice as donors or recipients. Also, skin grafts (H-2b) were placed onto SCID mice (H-2d) that received BALB/c splenocytes (H-2d) by adoptive transfer either at the time of transplantation, or after a period of 28 days.

RESULTS

Cardiac allografts in MCP-1-/- recipients survived significantly longer (P<0.0005) than wild-type (WT) controls. However, there was no prolongation of survival when MCP-1-/- grafts were used a donors in WT mice. In contrast, the absence of donor but not recipient MCP-1 prolonged skin allograft survival. WT donor cardiac grafts in CXCR3-/- recipients had a modest prolongation of survival (P<0.0005), whereas CXCR3-/- donor cardiac grafts in WT recipients were rejected similar to controls. Also, while recipient CXCR3 had no effect on the rejection of skin, CXCR3-/- donor skin grafts survived significantly longer than WT controls. This survival advantage was lost when vascularized CXCR3-/- skin grafts were used as donors in the SCID model of rejection.

CONCLUSION

Recipient derived MCP-1 and CXCR3 are functional in the rejection of vascularized, but not nonvascularized, allografts. In contrast, donor-derived MCP-1 and CXCR3 are functional in nonvascularized, but not vascularized grafts.

Proteolytic activation of monocyte chemoattractant protein-1 by plasmin underlies excitotoxic neurodegeneration in mice

Exposure of neurons to high concentrations of excitatory neurotransmitters causes them to undergo excitotoxic death via multiple synergistic injury mechanisms. One of these mechanisms involves actions undertaken locally by microglia, the CNS-resident macrophages. Mice deficient in the serine protease plasmin exhibit decreased microglial migration to the site of excitatory neurotransmitter release and are resistant to excitotoxic neurodegeneration. Microglial chemotaxis can be signaled by the chemokine monocyte chemoattractant protein-1 (MCP-1)/CCL2 (CC chemokine ligand 2). We show here that mice genetically deficient for MCP-1 phenocopy plasminogen deficiency by displaying decreased microglial recruitment and resisting excitotoxic neurodegeneration. Connecting these pathways, we demonstrate that MCP-1 undergoes a proteolytic processing step mediated by plasmin. The processing, which consists of removal of the C terminus of MCP-1, enhances the potency of MCP-1 in in vitro migration assays. Finally, we show that infusion of the cleaved form of MCP-1 into the CNS restores microglial recruitment and excitotoxicity in plasminogen-deficient mice. These findings identify MCP-1 as a key downstream effector in the excitotoxic pathway triggered by plasmin and identify plasmin as an extracellular chemokine activator. Finally, our results provide a mechanism that explains the resistance of plasminogen-deficient mice to excitotoxicity.

CCL2 (Monocyte Chemoattractant Protein-1) in cancer bone metastases

The paradigm of cancer development and metastasis is a comprehensive, complex series of events that ultimately reflects a coordinated interaction between the tumor cell and the microenvironment within which the tumor cell resides. Despite the realization that this relationship has changed the current paradigm of cancer research, the struggle continues to more completely understand the pathogenesis of the disease and the ability to appropriately identify and design novel targets for therapy. A particular area of research that has added a significant understanding to cancer metastasis is the role of chemokines and chemokine receptors. Here we review the current concepts of CCL2 (monocyte chemoattractant protein 1) and its role in tumor metastasis with particular interest to its role in the development of bone metastases.

Critical Role of Monocyte Chemoattractant Protein-1/CC Chemokine Ligand 2 in the Pathogenesis of Ischemic Cardiomyopathy

Background— Cardiac interstitial fibrosis plays an important role in the pathogenesis of ischemic cardiomyopathy, contributing to systolic and diastolic dysfunction. We have recently developed a mouse model of fibrotic noninfarctive cardiomyopathy due to brief repetitive myocardial ischemia and reperfusion. In this model, fibrotic changes are preceded by marked and selective induction of the CC chemokine monocyte chemoattractant protein-1 (MCP-1). We hypothesized that MCP-1 may mediate fibrotic remodeling through recruitment of mononuclear cells and direct effects on fibroblasts.

Methods and Results— Wild-type (WT) and MCP-1-null mice underwent daily 15-minute coronary occlusions followed by reperfusion. Additional WT animals received intraperitoneal injections of a neutralizing anti-MCP-1 antibody after the end of each ischemic episode. Hearts were examined echocardiographically and processed for histological and RNA studies. WT mice undergoing repetitive brief myocardial ischemia and reperfusion protocols exhibited macrophage infiltration after 3 to 5 days and marked interstitial fibrosis in the ischemic area after 7 days, accompanied by ventricular dysfunction. MCP-1-null mice had markedly diminished interstitial fibrosis, lower macrophage infiltration, and attenuated ventricular dysfunction compared with WT animals. MCP-1 neutralization also inhibited interstitial fibrosis, decreasing left ventricular dysfunction and regional hypocontractility. Cardiac myofibroblasts isolated from WT but not from MCP-1-null animals undergoing repetitive myocardial ischemia and reperfusion demonstrated enhanced proliferative capacity. However, MCP-1 stimulation did not induce cardiac myofibroblast proliferation and did not alter expression of fibrosis-associated genes.

Conclusions— Defective MCP-1 signaling inhibits the development of ischemic fibrotic cardiomyopathy in mice. The profibrotic actions of MCP-1 are associated with decreased macrophage recruitment and may not involve direct effects on cardiac fibroblasts.

Monocyte chemoattractant protein-1-induced tissue inflammation is critical for the development of renal injury but not type 2 diabetes in obese db/db mice

AIMS/HYPOTHESIS

Tissue macrophage accumulation is thought to induce insulin resistance during obesity and stimulate the progression of diabetic nephropathy. Monocyte chemoattractant protein-1 (MCP-1) is a potent stimulator of macrophage recruitment. It is increased in adipose tissue during obesity and in diabetic kidneys, suggesting that inflammation of these tissues may be MCP-1-dependent. Based on these findings, the aim of this study was to examine whether a deficiency in MCP-1 would alter the development of type 2 diabetes and its renal complications.

MATERIALS AND METHODS

The role of MCP-1 in the progression of type 2 diabetes and its associated renal injury was assessed in obese db/db mice that were deficient in the gene encoding MCP-1 (Ccl2).

RESULTS

The incidence and development of type 2 diabetes were similar in Ccl2(+/+) and Ccl2(-/-) db/db mice between 8 and 32 weeks of age. Body mass, hyperglycaemia, hyperinsulinaemia, glucose and insulin tolerance, plasma triacylglycerol and serum NEFA were not different between these strains. Pathological changes in epididymal adipose tissue, including increases in macrophage accumulation and Tnfa mRNA and reductions in Adipoq mRNA, were unaffected by the absence of MCP-1. In contrast, kidney macrophage accumulation and the progression of diabetic renal injury (albuminuria, histopathology, renal fibrosis) were substantially reduced in Ccl2(-/-) compared with Ccl2(+/+) db/db mice with equivalent diabetes.

CONCLUSIONS/INTERPRETATION

Our study demonstrates that MCP-1 promotes type 2 diabetic renal injury but does not influence the development of obesity, insulin resistance or type 2 diabetes in db/db mice. MCP-1 plays a critical role in inflammation of the kidney, but not adipose tissue, during the progression of type 2 diabetes.

Chemokines in the MPTP model of Parkinson’s disease: Absence of CCL2 and its receptor CCR2 does not protect against striatal neurodegeneration

Recent studies have invoked inflammation as a major contributor to the pathogenesis of Parkinson's disease (PD). We determined the role of members of the chemokine system, key inflammatory mediators, in PD pathogenesis. In the MPTP model of murine PD, several chemokines, including CC chemokine ligand 2 (CCL2, Monocyte Chemoattractant Protein-1) and CCL3 (Macrophage Inflammatory Protein-1alpha), were upregulated in the striatum and the ventral midbrain. Astrocytes were the predominant source of CCL2 and CCL3 in the striatum and the substantia nigra, and dopaminergic neurons in the substantia nigra constitutively expressed these two chemokines. MPTP treatment resulted in decreased CCL2 expression and increased CCL3 expression in the surviving dopaminergic neurons. Because we found that CCL2 induced production of TNF-alpha in microglial cells, a cytokine known to play a detrimental role in PD, we anticipated that deletion of the genes encoding CCL2 and CCR2, its major receptor, would confer a protective phenotype. However, MPTP-induced striatal dopamine depletion was comparable in double knockout and wild-type mice. Our results demonstrate that chemokines such as CCL2 are induced following MPTP treatment, but that at least within the context of this PD model, the absence of CCL2 and CCR2 does not protect against striatal dopamine loss.

MCP-1 deficiency causes altered inflammation with impaired skeletal muscle regeneration

We examined the role of MCP-1, a potent chemotactic and activating factor for macrophages, in perfusion, inflammation, and skeletal muscle regeneration post-ischemic injury. MCP-1-/- or C57Bl/6J control mice [wild-type (WT)] underwent femoral artery excision (FAE). Muscles were collected for histology, assessment of tissue chemokines, and activity measurements of lactate dehydrogenase (LDH) and myeloperoxidase. In MCP-1-/- mice, restoration of perfusion was delayed, and LDH and fiber size, indicators of muscle regeneration, were decreased. Altered inflammation was observed with increased neutrophil accumulation in MCP-1-/- versus WT mice at Days 1 and 3 (P< or =0.003), whereas fewer macrophages were present in MCP-1-/- mice at Day 3. As necrotic tissue was removed in WT mice, macrophages decreased (Day 7). In contrast, macrophage accumulation in MCP-1-/- was increased in association with residual necrotic tissue and impaired muscle regeneration. Consistent with altered inflammation, neutrophil chemotactic factors (keratinocyte-derived chemokine and macrophage inflammatory protein-2) were increased at Day 1 post-FAE. The macrophage chemotactic factor MCP-5 was increased significantly in WT mice at Day 3 compared with MCP-1-/- mice. However, at post-FAE Day 7, MCP-5 was significantly elevated in MCP-1-/- mice versus WT mice. Addition of exogenous MCP-1 did not induce proliferation in murine myoblasts (C2C12 cells) in vitro. MCP-1 is essential for reperfusion and the successful completion of normal skeletal muscle regeneration after ischemic tissue injury. Impaired muscle regeneration in MCP-1-/- mice suggests an important role for macrophages and MCP-1 in tissue reparative processes.

Critical role of MCP-1 in the pathogenesis of experimental colitis in the context of immune and enterochromaffin cells

Mucosal changes in inflammatory bowel disease (IBD) are characterized by ulcerative lesions accompanied by a prominent infiltrate of inflammatory cells including lymphocytes, macrophages, and neutrophils and alterations in 5-hydroxytryptamine (5-HT)-producing enterochromaffin (EC) cells. Mechanisms involved in recruiting and activating these cells are thought to involve a complex interplay of inflammatory mediators. Studies in clinical and experimental IBD have shown the upregulation of various chemokines including monocyte chemoattractant protein (MCP)-1 in mucosal tissues. However, precise information on the roles of this chemokine or the mechanisms by which it takes part in the pathogenesis of IBD are not clear. In this study, we investigated the role of MCP-1 in the development of hapten-induced experimental colitis in mice deficient in MCP-1. Our results showed a significant reduction in the severity of colitis both macroscopically and histologically along with a decrease in mortality in MCP-1-deficient mice compared with wild-type control mice. This was correlated with a downregulation of myeloperoxidase activity, IL-1beta, IL-12p40, and IFN-gamma production, and infiltration of CD3+ T cells and macrophages in the colonic mucosa. In addition, we observed significantly lower numbers of 5-HT-expressing EC cells in the colon of MCP-1-deficient mice compared with those in wild-type mice after dinitrobenzenesulfonic acid. These results provide evidence for a critical role of MCP-1 in the development of colonic inflammation in this model in the context of immune and enteric endocrine cells.

Depletion of MCP-1 increases development of herpetic stromal keratitis by innate immune modulation

Chemokines are important chemoattractant inflammatory molecules, but their interdependent network in disease pathogenesis remains unclear. Studies in mouse models have shown that herpetic stromal keratitis (SK) is produced by the consequence of a tissue-destructive immunoinflammatory reaction involving herpes simplex virus type 1 (HSV) infection. Here we found that ocular HSV infection leads to increased expression of monocyte chemoattractant protein-1 (MCP-1), one of the major chemoattractants for immune cells that express CCR2, in the SK cornea. However, MCP-1 is unlikely to be a chemoattractant for infiltrating Gr-1(+), CD11b(+) cells in SK, as these cells are found to be CCR2 negative. Nevertheless, infection of MCP-1(-/-) mice resulted in more severe SK lesion severity compared with WT mice (P<0.01). We demonstrated that the loss of MCP-1 in the SK cornea caused a significant overexpression of macrophage inflammatory protein-2 (MIP-2) (P<0.01) on days 2 and 4 postinfection and increased infiltration of inflammatory cells (Gr-1-high and CD11b(+)) expressing CXCR2, a receptor for MIP-2, into the cornea. Subsequently, increased infiltration of inflammatory cells accelerated by MIP-2 overexpression might result in the high production of inflammatory molecules, including vascular endothelial growth factor (VEGF) and IL-1beta in SK, as well as CpG oligodeoxynucleotide (ODN)-implanted eyes of MCP-1(-/-) mice. These results indicate that MCP-1 in the SK cornea might regulate the expression of other chemokines, as well as the infiltration of inflammatory cells and control development of SK.

Abnormal monocyte recruitment and collateral artery formation in monocyte chemoattractant protein-1 deficient mice

Monocyte chemoattractant protein 1 (MCP-1) has been shown to be effective for the stimulation of collateral artery formation in small and large animal models. The availability of a genetic knockout mouse enables evaluation of the importance of the role of MCP-1 in the natural course of collateral artery growth. In a total of 21 MCP-1 -/- as well as 13 of the appropriate genetic background controls ([129Sv/J X C57BI/6J]F1), a femoral artery ligation was performed. Subsequently, a polyethylene catheter, connected to an osmotic minipump, was inserted retrogradely into the occluded femoral artery with the tip pointing upstream. Using this technique, PBS (MCP-1 -/-: n = 13 and C57BI/6J: n = 13) or MCP-1 (JE; MCP-1 -/-: n = 8) was delivered intra-arterially. Seven days after ligation, determination of hind limb flow was assessed by controlled tissue perfusion using differently labeled fluorescent microspheres. MCP-1 -/- mice exhibited a reduction of hind limb flow of 32.9 +/- 9.2% of the unligated hind limb, compared with 55.4 +/- 6.8% in C57BI/6J mice (p<0.01). MCP-1 -/- mice that underwent a subsequent 'rescue' treatment with MCP-1 showed a restoration of flow to a level of 47.4 +/- 9.8% (p = NS compared with PBS-treated C57BI/6J). Specific immunohistochemical staining for monocytes (MOMA-2: MCP-1 -/-, n = 5 and C57BI/6J, n = 5) showed a reduced number of monocytes around developing collateral arteries in the MCP-1 -/- mice. In conclusion, our data show that the absence of MCP-1 causes a strong reduction in flow restoration after femoral artery occlusion, coinciding with a reduced monocyte attraction, emphasizing the central role of this chemokine in the multifactorial process of collateral artery formation.

Alveolar Epithelial Cells Direct Monocyte Transepithelial Migration upon Influenza Virus Infection: Impact of Chemokines and Adhesion Molecules

Influenza A virus pneumonia is characterized by severe lung injury and high mortality. Early infection elicits a strong recruitment of monocytes from the peripheral blood across the endo-/epithelial barrier into the alveolar air space. However, it is currently unclear which of the infected resident lung cell populations, alveolar epithelial cells or alveolar macrophages, elicit monocyte recruitment during influenza A virus infection. In the current study, we investigated whether influenza A virus infection of primary alveolar epithelial cells and resident alveolar macrophages would elicit a basal-to-apical monocyte transepithelial migration in vitro. We found that infection of alveolar epithelial cells with the mouse-adapted influenza A virus strain PR/8 strongly induced the release of monocyte chemoattractants CCL2 and CCL5 followed by a strong monocyte transepithelial migration, and this monocytic response was strictly dependent on monocyte CCR2 but not CCR5 chemokine receptor expression. Analysis of the adhesion molecule pathways demonstrated a role of ICAM-1, VCAM-1, integrin-associated protein (CD47), and junctional adhesion molecule-c on the epithelial cell surface interacting with monocyte beta(1) and beta(2) integrins and integrin-associated protein in the monocyte transmigration process. Importantly, addition of influenza A virus-infected alveolar macrophages further enhanced monocyte transmigration across virus-infected epithelium in a TNF-alpha-dependent manner. Collectively, the data show an active role for virus-infected alveolar epithelium in the regulation of CCL2/CCR2-dependent monocyte transepithelial migration during influenza infection that is essentially dependent on both classical beta(1) and beta(2) integrins but also junctional adhesion molecule pathways.

Diminished induction of skin fibrosis in mice with MCP-1 deficiency

Scar and fibrosis are often the end result of mechanical injury and inflammatory diseases. One chemokine that is repeatedly linked to fibrotic responses is monocyte chemoattractant protein-1 (MCP-1). We utilized a murine fibrosis model that produces dermal lesions similar to scleroderma to evaluate collagen fibrillogenesis in the absence of MCP-1. Dermal fibrosis was induced by subcutaneous injection of bleomycin into the dorsal skin of MCP-1-/- and wild-type C57BL/6 mice. After 4 weeks of daily injections, bleomycin treatment led to thickened collagen bundles with robust inflammation in the lesional dermis of wild-type mice. In contrast, the lesional skin of MCP-1-/- mice exhibited a dermal architecture similar to phosphate-buffered saline (PBS)-injected control and normal skin, with few inflammatory cells. Ultrastructural analysis of the lesional dermis from bleomycin-injected wild-type mice revealed markedly abnormal arrangement of collagen fibrils, with normal large diameter collagen fibrils replaced by small collagen fibrils of 41.5 nm. In comparison, the dermis of bleomycin-injected MCP-1-/- mice displayed a uniform pattern of fibril diameters that was similar to normal skin (average diameter 76.7 nm). The findings implicate MCP-1 as a key determinant in the development of skin fibrosis induced by bleomycin, and suggest that MCP-1 may influence collagen fiber formation in vivo.

Tetrapeptide AcSDKP Induces Postischemic Neovascularization Through Monocyte Chemoattractant Protein-1 Signaling

BACKGROUND

We investigated the putative proangiogenic activity and molecular pathway(s) of the tetrapeptide acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) in a model of surgically induced hindlimb ischemia.

METHODS AND RESULTS

Hindlimb ischemia was induced by femoral artery ligature and an osmotic minipump was implanted subcutaneously to deliver low (0.12 mg/kg per day) or high (1.2 mg/kg per day) doses of AcSDKP, for 7 or 21 days. Angiography scores, arteriole density, capillary number, and foot perfusion were increased at day 21 in the high-dose AcSDKP-treated mice (by 1.9-, 1.8-, 1.3-, and 1.6-fold, respectively) compared with control animals (P<0.05, P<0.01, P<0.01, respectively). AcSDKP treatment for 24 hours upregulated the monocyte chemoattractant protein-1 (MCP-1) mRNA and protein levels by 1.5-fold in cultured endothelial cells (P<0.01). In the ischemic hindlimb model, administration of AcSDKP also enhanced MCP-1 mRNA levels by 90-fold in ischemic leg (P<0.001) and MCP-1 plasma levels by 3-fold (P<0.001 versus untreated ischemic control mice). MCP-1 levels upregulation were associated with a 2.3-fold increase in the number of Mac3-positive cells in ischemic area of AcSDKP-treated mice (P<0.001 versus untreated animals). Interestingly, AcSDKP-induced monocyte/macrophage infiltration and postischemic neovascularization was fully blunted in MCP-1-deficient animals.

CONCLUSIONS

AcSDKP stimulates postischemic neovascularization through activation of a proinflammatory MCP-1-related pathway.

Exacerbation of retinal degeneration and choroidal neovascularization induced by subretinal injection of Matrigel in CCL2/MCP-1-deficient mice

This study presents a mouse model for human age-related macular degeneration (AMD) as characterized by subretinal deposit and choroidal neovascularization. Matrigel, a basement membrane extract, solidifies after implantation in tissue and can stimulate local angiogenesis. This study demonstrates the induction of neovascularization and focal retinal degeneration following subretinal Matrigel injection in mice. In senescent mice, the normal functioning of CC chemokine CCL2/MCP-1 and its receptor CCR2 confers protection against age-related retinal degeneration, a disease that shares many similar features with human AMD. Our data shows that CCL2-deficient mice develop more severe disease as compared to the wild-type controls. These findings suggest that Matrigel subretinal injection could be used to generate AMD-like pathological changes. The data support the previously proposed role of CCL2 in AMD pathogenesis.

Cellular Events in the Normal and Inflamed Cornea

PURPOSE

Although normal cornea is an avascular transparent structure, bone marrow (BM)-derived cells exist in situ even in noninflamed conditions. We evaluated constitutive cellular trafficking into the cornea in the naive state and investigated how corneal inflammation may be initiated by various stimuli.

METHODS

BM chimeric mice were generated using BM from enhanced green fluorescent protein (eGFP) transgenic mice. Corneas of chimeric mice were carefully studied by fluorescent biomicroscopy until 6 months after transplantation. To analyze initiation of cellular events in corneal immune response, we cauterized the center of the cornea or inoculated IL-1 beta into the corneal micropocket. Cellular events were analyzed by flow cytometry.

RESULTS

At 2 weeks after BM transplantation, GFP cells gradually migrated into the cornea from the limbal area and were distributed over the entire cornea at 6 months. In both the cauterization and micropocket assays, infiltration of neutrophils and macrophages occurred on days 2 and 4, respectively. Depletion of neutrophils by anti-Gr-1 Ab significantly reduced corneal edema/opacity induced by cauterization. IL-1 beta-induced angiogenesis was markedly reduced in monocyte chemoattractant protein-1 knockout mice.

CONCLUSIONS

BM-derived cells are recruited into the normal cornea and may be essential to maintain corneal clarity. In the inflamed cornea, neutrophils might be responsible for acute corneal edema/opacity and macrophages for corneal angiogenesis and chronic inflammation.

Infiltration of COX-2-expressing macrophages is a prerequisite for IL-1 beta-induced neovascularization and tumor growth

Inflammatory angiogenesis is a critical process in tumor progression and other diseases. The inflammatory cytokine IL-1beta promotes angiogenesis, tumor growth, and metastasis, but its mechanisms remain unclear. We examined the association between IL-1beta-induced angiogenesis and cell inflammation. IL-1beta induced neovascularization in the mouse cornea at rates comparable to those of VEGF. Neutrophil infiltration occurred on day 2. Macrophage infiltration occurred on days 4 and 6. The anti-Gr-1 Ab-induced depletion of infiltrating neutrophils did not affect IL-1beta- or VEGF-induced angiogenesis. The former was reduced in monocyte chemoattractant protein-1-deficient (MCP-1(-/-)) mice compared with wild-type mice. After day 4, clodronate liposomes, which kill macrophages, reduced IL-1beta-induced angiogenesis and partially inhibited VEGF-induced angiogenesis. Infiltrating macrophages near the IL-1beta-induced neovasculature were COX-2 positive. Lewis lung carcinoma cells expressing IL-1beta (LLC/IL-1beta) developed neovasculature with macrophage infiltration and enhanced tumor growth in wild-type but not MCP-1(-/-) mice. A COX-2 inhibitor reduced tumor growth, angiogenesis, and macrophage infiltration in LLC/IL-1beta. Thus, macrophage involvement might be a prerequisite for IL-1beta-induced neovascularization and tumor progression.

Perturbation of chemokine networks by gene deletion alters the reinforcing actions of ethanol

Microarray analysis of human alcoholic brain and cultured cells exposed to ethanol showed significant changes in expression of genes related to immune or inflammatory responses, including chemokines and chemokine receptors. To test the hypothesis that chemokines exhibit previously undiscovered pleiotropic effects important for the behavioral actions of ethanol, we studied mutant mice with deletion of the Ccr2, Ccr5, Ccl2 or Ccl3 genes. Deletion of Ccr2, Ccl2 (females) or Ccl3 in mice resulted in lower preference for alcohol and consumption of lower amounts of alcohol in a two-bottle choice test as compared with wild-type mice. Ethanol treatment (2.5 g/kg, i.p.) induced stronger conditioned taste aversion in Ccr2, Ccl2 or Ccl3 null mutant mice than in controls. Ccr2 and Ccr5 null mutant mice did not differ from wild-type mice in ethanol-induced loss of righting reflex (LORR), but mice lacking Ccl2 or Ccl3 showed longer LORR than wild-type mice. There were no differences between mutant strains and wild-type mice in severity of ethanol-induced withdrawal. Genetic mapping of chromosome 11 for the Ccl2 and Ccl3 genes (46.5 and 47.6 cM, respectively) revealed that an alcohol-induced LORR QTL region was contained within the introgressed region derived from 129/SvJ, which may cause some behavioral phenotypes observed in the null mice. On the contrary, known QTLs on Chr 9 are outside of 129/SvJ region in Ccr2 and Ccr5 (71.9 and 72.0 cM, respectively) null mutant mice. These data show that disruption of the chemokine network interferes with motivational effects of alcohol.

Monocyte chemoattractant protein-1 and CCR2 interactions are required for IFN-alpha/beta-induced inflammatory responses and antiviral defense in liver

IFN-alpha/beta-mediated functions promote production of MIP-1alpha (or CCL3) by mediating the recruitment of MIP-1alpha-producing macrophages to the liver during early infection with murine CMV. These responses are essential for induction of NK cell inflammation and IFN-gamma delivery to support effective control of local infection. Nevertheless, it remains to be established if additional chemokine functions are regulated by IFN-alpha/beta and/or play intermediary roles in supporting macrophage trafficking. The chemokine MCP-1 (or CCL2) plays a distinctive role in the recruitment of macrophages by predominantly stimulating the CCR2 chemokine receptor. Here, we examine the roles of MCP-1 and CCR2 during murine CMV infection in liver. MCP-1 production preceded that of MIP-1alpha during infection and was dependent on IFN-alpha/beta effects for induction. Resident F4/80(+) liver leukocytes were identified as primary IFN-alpha/beta responders and major producers of MCP-1. Moreover, MCP-1 deficiency was associated with a dramatic reduction in the accumulation of macrophages and NK cells, as well as decreased production of MIP-1alpha and IFN-gamma in liver. These responses were also markedly impaired in mice with a targeted disruption of CCR2. Furthermore, MCP-1- and CCR2-deficient mice exhibited increased viral titers and elevated expression of the liver enzyme alanine aminotransferase in serum. These mice also had widespread virus-induced liver pathology and succumbed to infection. Collectively, these results establish MCP-1 and CCR2 interactions as factors promoting early liver inflammatory responses and define a mechanism for innate cytokines in regulation of chemokine functions critical for effective localized antiviral defenses.

Impairment in postischemic neovascularization in mice lacking the CXC chemokine receptor 3

Inflammatory cell infiltration is a feature of postischemic neovascularization. However, mechanisms leading to leukocyte attraction to the site of neovascularization are still undefined. We hypothesized that the CXC chemokine receptor 3 (CXCR3) may contribute to leukocyte accumulation and subsequently to blood vessel growth in the ischemic area. Ischemia induced by femoral artery ligature improved the number of CXCR3-expressing cells and the level of its ligand, CXCL10. Angiographic score, blood flow recovery measurement, and capillary density analysis showed a significant decrease of ischemic/nonischemic leg ratio in CXCR3-deficient mice when compared with controls (P<0.05), at day 21 after ischemia. Interestingly, this impairment was as important as that observed in mice deficient for the well known CC-chemokine monocyte chemoattractant protein-1 (MCP-1). At day 7 of ischemic injury, the number of CD3-positive T cells and Mac-3-positive monocytes/macrophages was 38% and 45% lower, respectively, in the ischemic leg of CXCR3-deficient mice compared with the control group (P<0.05), suggesting an important role for CXCR3 in leukocyte recruitment into the ischemic area. VEGF protein content, a classical proangiogenic factor, was also markedly reduced (80% reduction) in ischemic leg of CXCR3-deficient mice (P<0.01). Injection of bone marrow-derived mononuclear cells (BM-MNCs) isolated from wild-type animals restored the neovascularization reaction in CXCR3-deficient mice whereas BM-MNCs from CXCR3-deficient mice was ineffective. In conclusion, CXCR3 plays a key role in neovascularization and provides novel information on the mechanisms leading to leukocyte infiltration in the vessel growth area.

Differential roles of CCL2 and CCR2 in host defense to coronavirus infection

The CC chemokine ligand 2 (CCL2, monocyte chemoattractant protein-1) is important in coordinating the immune response following microbial infection by regulating T cell polarization as well as leukocyte migration and accumulation within infected tissues. The present study examines the consequences of mouse hepatitis virus (MHV) infection in mice lacking CCL2 (CCL2(-/-)) in order to determine if signaling by this chemokine is relevant in host defense. Intracerebral infection of CCL2(-/-) mice with MHV did not result in increased morbidity or mortality as compared to either wild type or CCR2(-/-) mice and CCL2(-/-) mice cleared replicating virus from the brain. In contrast, CCR2(-/-) mice displayed an impaired ability to clear virus from the brain that was accompanied by a reduction in the numbers of antigen-specific T cells as compared to both CCL2(-/-) and wild-type mice. The paucity in T cell accumulation within the central nervous system (CNS) of MHV-infected CCR2(-/-) mice was not the result of either a deficiency in antigen-presenting cell (APC) accumulation within draining cervical lymph nodes (CLN) or the generation of virus-specific T cells within this compartment. A similar reduction in macrophage infiltration into the CNS was observed in both CCL2(-/-) and CCR2(-/-) mice when compared to wild-type mice, indicating that both CCL2 and CC chemokine receptor 2 (CCR2) contribute to macrophage migration and accumulation within the CNS following MHV infection. Together, these data demonstrate that CCR2, but not CCL2, is important in host defense following viral infection of the CNS, and CCR2 ligand(s), other than CCL2, participates in generating a protective response.

Role of CC chemokines in skeletal muscle functional restoration after injury

The purpose of this study was to determine whether certain chemokines, which are highly expressed in injured skeletal muscle, are involved in the repair and functional recovery of the muscle after traumatic injury. In wild-type control mice, mRNA transcripts of macrophage inflammatory protein (MIP)-1α, MIP-1β, and monocyte chemoattractant protein (MCP)-1 as well as their major receptors, CCR5 and CCR2, increased after freeze injury and gradually returned to control (uninjured) levels by 14 days. Muscle function and histological characteristics were monitored in injured mice that were genetically deficient for the CCR5 receptor (a major receptor for MIP-1α and MIP-1β) and also rendered MCP-1 deficient with neutralizing antibodies. To dissect the role of these chemokines, additional studies were conducted in CCR5- and CCR2-deficient mice. CCR5-/- mice injected with MCP-1 antiserum for the first 3 days after injury exhibited a twofold greater maximal isometric tetanic torque deficit at 14 days after injury than did controls (i.e., 33% vs. 17%; P = 0.002). The impaired functional recovery was accompanied with an increased fat infiltration within the regenerating muscle without a significant difference in the influx of inflammatory cells, including macrophages. Strength recovery was also impaired in mice deficient for the receptor of MCP-1, CCR2, but not in CCR5-/- mice that were not injected with MCP-1 antiserum. The data suggest that MCP-1/CCR2 plays a role in the regeneration and recovery of function after traumatic muscle injury.

Role of Monocyte Chemotactic Protein-1/CC Chemokine Ligand 2 on γδ T Lymphocyte Trafficking during Inflammation Induced by Lipopolysaccharide orMycobacterium bovisBacille Calmette-Guérin

Gammadelta T lymphocytes are involved in a great variety of inflammatory and infectious responses. However, the mechanisms by which gammadelta T lymphocytes migrate to inflamed sites are poorly understood. In this study we investigate the role of monocyte chemotactic protein (MCP)-1 in regulating gammadelta T cell migration after LPS or Mycobacterium bovis bacille Calmette-Guérin (BCG) challenge. LPS-induced gammadelta T cell influx was significantly inhibited by either pretreatment with dexamethasone or vaccinia virus Lister 35-kDa chemokine binding protein, vCKBP, a CC chemokine neutralizing protein, suggesting a role for CC chemokines in this phenomenon. LPS stimulation increased the expression of MCP-1 mRNA and protein at the inflammation site within 6 h. It is noteworthy that LPS was unable to increase MCP-1 production or gammadelta T cell recruitment in C3H/HeJ, indicative of the involvement of Toll-like receptor 4. Gammadelta T cells express MCP-1 receptor CCR2. Pretreatment with anti-MCP-1 mAb drastically inhibited LPS-induced in vivo gammadelta T cell mobilization. Indeed, MCP-1 knockout mice were unable to recruit gammadelta T cells to the pleural cavity after LPS stimulation, effect that could be restored by coadministration of MCP-1. In addition, BCG-induced gammadelta lymphocyte accumulation was significantly reduced in MCP-1 knockout mice when compared with wild-type mice. In conclusion, our results indicate that LPS-induced gammadelta T lymphocyte migration is dependent on Toll-like receptor 4 and sensitive to both dexamethasone and CC chemokine-binding protein inhibition. Moreover, by using MCP-1 neutralizing Abs and genetically deficient mice we show that LPS- and BCG-induced gammadelta T lymphocyte influx to the pleural cavity of mice is mainly orchestrated by the CC chemokine MCP-1.

MCP-1 deficiency is associated with reduced intimal hyperplasia after arterial injury

Monocyte chemoattractant protein (MCP)-1 is abundant in smooth muscle cells (SMC) and macrophages of atherosclerotic plaques and in the injured arterial wall. MCP-1 and its receptor, CCR2, are important mediators of macrophage accumulation and atherosclerotic plaque progression. We have recently reported that CCR2(-/-) mice have a approximately 60% decrease in intimal hyperplasia and medial DNA synthesis in response to femoral arterial injury. We have now examined the response to femoral arterial injury in MCP-1(-/-) mice. MCP-1 deficiency was associated with a approximately 30% reduction in intimal hyperplasia at 4 weeks and was not associated with diminished medial DNA synthesis. Despite inducing tissue factor in SMC culture, MCP-1 deficiency was not associated with a decrease in neointimal tissue factor after injury. These data suggest that MCP-1 and CCR2 deficiencies have distinct effects on arterial injury. The effects of MCP-1 on intimal hyperplasia may be mediated largely through SMC migration.

CC Chemokine Ligand 2 and Its Receptor Regulate Mucosal Production of IL-12 and TGF-β in High Dose Oral Tolerance

Oral tolerance is the result of a complex immunoregulatory strategy used by the gut and its associated lymphoid tissues to render the peripheral immune system unresponsive to nonpathogenic proteins, such as food or commensal bacteria. The mechanism of oral tolerance induction and maintenance is not well understood. We have previously shown that the chemokine, CC chemokine ligand 2 (CCL2), is important for the induction and maintenance of oral tolerance. To address the role CCL2 plays in oral tolerance, we used both CCL2(-/-) and CCR2(-/-) mice. Cells from the spleen, mesenteric lymph nodes, and peripheral lymph nodes of CCL2(-/-) and CCR2(-/-) mice fed high doses of OVA showed robust proliferative responses compared with cells from Ag-fed wild-type mice. CCL2(-/-) and CCR2(-/-) mice also produced high amounts of Th1 cytokines such as IL-2 and IFN-gamma and very low amounts of IL-4 and IL-10. The ability of APCs from the gut of CCL2(-/-) and CCR2(-/-) OVA-fed mice to stimulate an indicator T cell line was evaluated. APCs from the Peyer's patch of OVA-fed knockout animals could induce a T cell response measured by an increase in proliferation and generation of IL-12 and IFN-gamma with a concomitant reduction of TGF-beta compared with wild-type controls that did not induce a Th1 response. These data indicate that CCL2 and signaling through its receptor CCR2 is critical for the induction of oral tolerance by regulating Ag presentation leading to a disruption in the balance of inflammatory and regulatory cytokines.

The role of G-protein signaling in hematopoietic stem/progenitor cell mobilization

The directed migration of mature leukocytes to inflammatory sites and the lymphocyte trafficking in vivo are dependent on G protein-coupled receptors and delivered through pertussis toxin (Ptx)-sensitive Gi-protein signaling. In the present study, we explored the in vivo role of G-protein signaling on the redistribution or mobilization of hematopoietic stem/progenitor cells (HPCs). A single injection of Ptx in mice elicits a long-lasting leukocytosis and a progressive increase in circulating colony-forming unit-culture (CFU-C) and colony-forming unit spleen (CFU-S). We found that the prolonged effect is sustained by a continuous slow release of Ptx bound to red blood cells or other cells and is potentially enhanced by an indirect influence on cell proliferation. Plasma levels of certain cytokines (interleukin 6 [IL-6], granulocyte colony-stimulating factor [G-CSF]) increase days after Ptx treatment, but these are unlikely initiators of mobilization. In addition to normal mice, mice genetically deficient in monocyte chemotactic protein 1 (MCP-1), matrix metalloproteinase 9 (MMP-9), G-CSF receptor, beta2 integrins, or selectins responded to Ptx treatment, suggesting independence of Ptx-response from the expression of these molecules. Combined treatments of Ptx with anti-very late activation antigen (anti-VLA-4), uncovered potentially important insight in the interplay of chemokines/integrins, and the synergy of Ptx with G-CSF appeared to be dependent on MMP-9. As Ptx-mobilized kit+ cells display virtually no response to stromal-derived factor 1 (SDF-1) in vitro, our data suggest that disruption of CXCR4/SDF-1 signaling may be the underlying mechanism of Ptx-induced mobilization and indirectly reinforce the notion that active signaling through this pathway is required for continuous retention of cells within the bone marrow. Collectively, our data unveil a novel example of mobilization through pharmacologic modulation of signaling.

Monocytes are potent facilitators of alveolar neutrophil emigration during lung inflammation: role of the CCL2-CCR2 axis

Coordinated neutrophil and monocyte recruitment is a characteristic feature of acute lung inflammatory responses. We investigated the role of monocyte chemotactic protein-1 (CCL2, JE) and the chemokine receptor CCR2 in regulating alveolar leukocyte traffic. Groups of wild-type (WT) mice, CCR2-deficient mice, lethally irradiated CCR2-deficient and WT mice that were reciprocally bone marrow transplanted (chimeric CCR2 deficient and WT, respectively), chimeric CCR2-deficient mice with an enriched CCR2(+) alveolar macrophage population, and CCR2-deficient mice transfused with CCR2(+) mononuclear cells were treated with intratracheal CCL2 and/or Escherichia coli endotoxin. Our data show that alveolar monocyte recruitment is strictly dependent on CCR2. LPS-induced neutrophil migration to the lungs is CCR2 independent. However, when CCR2-bearing blood monocytes are present, alveolar neutrophil accumulation is accelerated and drastically amplified. We suggest that this hitherto unrecognized cooperativity between monocytes and neutrophils contributes to the strong, coordinated leukocyte efflux in lung inflammation.

Induction of low dose oral tolerance in monocyte chemoattractant protein-1- and CCR2-deficient mice

The chemokine monocyte chemoattractant protein-1 (MCP-1) and its receptor CCR2 have been shown to play an important role in the migration and trafficking of macrophages and Th1 effector cells in experimental autoimmune encephalomyelitis. Also, MCP-1 has been reported to regulate oral tolerance induction by inhibition of Th1 cell-related cytokines and by the ability of Abs to MCP-1 to inhibit oral tolerance. This study demonstrates that neither MCP-1 nor its receptor CCR2 is required for the induction of oral tolerance. Mice deletional for either MCP-1 or CCR2 had suppressed cell-proliferative and Th1 responses following oral administration and immunization with myelin oligodendrocyte glycoprotein (MOG(35-55)). TGF-beta was up-regulated in fed and immunized deletional mice, while IL-4 was absent from deletional mice, but up-regulated in controls. Decreased experimental autoimmune encephalomyelitis severity was found in MOG(35-55)-fed MCP-1 deletional mice, indicating induction of oral tolerance. These results demonstrate that MCP-1 is not required for induction of oral tolerance and that MCP-1 and CCR2 are essential for up-regulation of IL-4 in tolerized mice.

Targeting monocyte chemoattractant protein-1 signalling in disease

Monocyte chemoattractant protein-1 (MCP-1) has been implicated in many inflammatory and autoimmune diseases. The G-protein-coupled receptor CCR-2B is probably the most important MCP-1 receptor in vivo, and loss of MCP-1 effector function alone is sufficient to impair monocytic trafficking in inflammation models. MCP-1 signalling appears to be a relevant target, especially in rheumatoid arthritis (RA). In RA patients, MCP-1 is produced by synovial cells and infiltrating monocytes, plasma MCP-1 concentrations correlate with swollen joint count, and elevated serum MCP-1 concentrations were found in juvenile RA in patients with active disease. Modulation of MCP-1 signalling in experimental RA showed beneficial effects on inflammation and joint destruction. With respect to chronic neuroinflammation, a critical role for MCP-1 has been established in animal models for multiple sclerosis. In acute neuroinflammation, experimental evidence for a detrimental role of MCP-1 in stroke and excitotoxic injury has been found. Several selective small molecular weight CCR-2B antagonists and MCP-1-blocking antibodies have been described. The proof for the validity of targeting MCP-1 signalling in disease, however, has yet to be established in clinical trials.

Developmentally regulated monocyte recruitment and bone resorption are modulated by functional deletion of the monocytic chemoattractant protein-1 gene

Tooth eruption involves the movement of a tooth from its site of development within the alveolar bone to its functional position in the oral cavity. Because this process is dependent upon monocytes and formation of osteoclasts, it represents an excellent model for examination of these processes under developmental regulation. We investigated the functional role of monocyte chemoattractant protein-1 (MCP-1) in monocyte recruitment and its impact on bone resorption by examining each parameter in MCP-1(-/-) mice as compared with wild-type controls during tooth eruption. The peak number of monocytes occurred on day 5 in the MCP-1(-/-) mice and on day 9 in the wild-type mice. The peak number of osteoclasts followed the same pattern, occurring sooner in the MCP-1(-/-) (day 5) than in wild-type mice (day 9). Consistent with this, MCP-1(-/-) mice had an accelerated rate of tooth eruption in the early phase when the teeth first entered the oral cavity as compared with the wild-type mice. However, there was accelerated eruption in the wild-type group in the later phase of tooth eruption. When examined at the molecular level, inducible nitric oxide synthase (iNOS) and interleukin-11 and -6 were expressed at considerably higher levels in the experimental group with accelerated tooth eruption. This is the first report identifying these factors as potential modulators of bone resorption that can accelerate the rate of tooth eruption. We conclude that, at early timepoints, monocyte recruitment occurs by MCP-1-independent mechanisms. However, at a later timepoint, MCP-1 may play a contributory role in the recruitment of monocytic cells, allowing the wild-type animals to catch up.