Azospirillum brasilense AerC and Tlp4b Cytoplasmic Chemoreceptors Are Promiscuous and Interact with the Two Membrane-Bound Chemotaxis Signaling Clusters Mediating Chemotaxis Responses.

Chemotaxis in Bacteria and Archaea depends on the presence of hexagonal polar arrays composed of membrane-bound chemoreceptors that interact with rings of baseplate signaling proteins. In the alphaproteobacterium Azospirillum brasilense, chemotaxis is controlled by two chemotaxis signaling systems (Che1 and Che4) that mix at the baseplates of two spatially distinct membrane-bound chemoreceptor arrays. The subcellular localization and organization of transmembrane chemoreceptors in chemotaxis signaling clusters have been well characterized but those of soluble chemoreceptors remain relatively underexplored. By combining mutagenesis, microscopy, and biochemical assays, we show that the cytoplasmic chemoreceptors AerC and Tlp4b function in chemotaxis and localize to and interact with membrane-bound chemoreceptors and chemotaxis signaling proteins from both polar arrays, indicating that soluble chemoreceptors are promiscuous. The interactions of AerC and Tlp4b with polar chemotaxis signaling clusters are not equivalent and suggest distinct functions. Tlp4b, but not AerC, modulates the abundance of chemoreceptors within the signaling clusters through an unknown mechanism. The AerC chemoreceptor, but not Tlp4b, is able to traffic in and out of chemotaxis signaling clusters depending on its level of expression. We also identify a role of the chemoreceptor composition of chemotaxis signaling clusters in regulating their polar subcellular organization. The organization of chemotaxis signaling proteins as large membrane-bound arrays underlies chemotaxis sensitivity. Our findings suggest that the composition of chemoreceptors may fine-tune chemotaxis signaling not only through their chemosensory specificity but also through their role in the organization of polar chemotaxis signaling clusters. IMPORTANCE Cytoplasmic chemoreceptors represent about 14% of all chemoreceptors encoded in bacterial and archaeal genomes, but little is known about how they interact with and function in large polar assemblies of membrane-bound chemotaxis signaling clusters. Here, we show that two soluble chemoreceptors with a role in chemotaxis are promiscuous and interact with two distinct membrane-bound chemotaxis signaling clusters that control all chemotaxis responses in Azospirillum brasilense. We also found that any change in the chemoreceptor composition of chemotaxis signaling clusters alters their polar organization, suggesting a dynamic interplay between the sensory specificity of chemotaxis signaling clusters and their polar membrane organization.

Kinetic modeling of the chemotactic process in run-and-tumble bacteria.

The chemotactic process of run-and-tumble bacteria results from modulating the tumbling rate in response to changes in chemoattractant gradients felt by the bacteria. The response has a characteristic memory time and is subject to important fluctuations. These ingredients are considered in a kinetic description of chemotaxis, allowing the computation of the stationary mobility and the relaxation times needed to reach the steady state. For large memory times, these relaxation times become large, implying that finite-time measurements give rise to nonmonotonic currents as a function of the imposed chemoattractant gradient, contrary to the stationary regime where the response is monotonic. The case of an inhomogeneous signal is analyzed. Contrary to the usual Keller-Segel model, the response is nonlocal, and the bacterial profile is smoothed with a characteristic length that grows with the memory time. Finally, the case of traveling signals is considered, where appreciable differences appear compared to memoryless chemotactic descriptions.

Computational study of the conformational ensemble of CX3C chemokine receptor 1 (CX3CR1) and its interactions with antagonist and agonist ligands.

The CX3C chemokine receptor 1 (CX3CR1), a member of the class A of G Protein-Coupled Receptors (GPCR) superfamily, and its ligand fractalkine constitute an important biochemical axis that influence many cellular pathways involving homeostatic and inflammatory processes. They participate in the activation, chemotaxis and recruitment of multiple immunological cells such as microglia, macrophages and monocytes, and play a critical role in neuroinflammatory conditions such as Alzheimer's disease and multiple sclerosis, in the recovery from central nervous system injuries, in several chronic, peripheral inflammatory entities and in some infective processes including HIV-AIDS. In this work we present the study of the CX3CR1 receptor employing extensive atomistic Molecular Dynamics (MD) simulations with the aim to characterize the conformational ensemble of the receptor in the presence of its antagonist and agonist ligands. We analyzed the receptor conformational changes and described interactions within its key regions and the bounded ligands to identify their notable differences. Finally, we classify the features that would allow the identification of patterns that characterize a functional state to contribute to the understanding of the complexity of the GPCR superfamily.

Immune spleen cells attenuate the inflammatory profile of the mesenteric perivascular adipose tissue in obese mice.

The perivascular adipose tissue (PVAT) differs from other fat depots and exerts a paracrine action on the vasculature. The spleen has an important role in the immune response, and it was observed to have either a protective role or a contribution to obesity-related diseases. However, the relation between spleen and PVAT is elusive in obesity. We investigated the role of spleen in the inflammatory profile of the mesenteric PVAT (mPVAT) from mice fed a high-fat diet (HFD) for 16 weeks. Male C57Bl/6 mice were sham-operated or splenectomized (SPX) and fed a HFD for 16 weeks. mPVAT morphology was evaluated by hematoxylin and eosin staining, infiltrated immune cells were evaluated by flow cytometry, inflammatory cytokines were evaluated by ELISA and the splenic cell chemotaxis mediated by mPVAT was evaluated using a transwell assay. In SPX mice, HFD induced adipocyte hypertrophy and increased immune cell infiltration and proinflammatory cytokine levels in mPVAT. However, none of these effects were observed in mPVAT from sham-operated mice. Spleen from HFD fed mice presented reduced total leukocytes and increased inflammatory markers when compared to the spleen from control mice. Chemotaxis of spleen cells mediated by mPVAT of HFD fed mice was reduced in relation to standard diet fed mice. The spleen protects mPVAT against the effects of 16-week HFD. This information was missing, and it is important because PVAT is different from other fat depots and data cannot be extrapolated from any type of adipose tissue to PVAT.

Derivation of a bacterial nutrient-taxis system with doubly degenerate cross-diffusion as the parabolic limit of a velocity-jump process.

This paper is devoted to the justification of the macroscopic, mean-field nutrient taxis system with doubly degenerate cross-diffusion proposed by Leyva et al. (Phys A 392:5644-5662, 2013) to model the complex spatio-temporal dynamics exhibited by the bacterium Bacillus subtilis during experiments run in vitro. This justification is based on a microscopic description of the movement of individual cells whose changes in velocity (in both speed and orientation) obey a velocity jump process governed by a transport equation of Boltzmann type. For that purpose, the asymptotic method introduced by Hillen and Othmer (SIAM J Appl Math 61:751-775, 2000; SIAM J Appl Math 62:1222-1250, 2002) is applied, which consists of the computation of the leading order term in a regular Hilbert expansion for the solution to the transport equation, under an appropriate parabolic scaling and a first order perturbation of the turning rate of Schnitzer type (Schnitzer in Phys Rev E 48:2553-2568, 1993). The resulting parabolic limit equation at leading order for the bacterial cell density recovers the degenerate nonlinear cross diffusion term and the associated chemotactic drift appearing in the original system of equations. Although the bacterium B. subtilis is used as a prototype, the method and results apply in more generality.

In vitro chemokine (C-C motif) receptor 6-dependent non-inflammatory chemotaxis during spermatogenesis.

BACKGROUND: Chemokine (C-C motif) receptor 6 (CCR6) is present in sperm and plays a significant role in sperm motility and chemotaxis acting in the reproductive tracts. However, the expression and functional significance of CCR6 in testis are still poorly understood, especially in the process of spermatogenesis. METHODS AND RESULTS: CCR6 was expressed in spermatogenic cell lines and its expression was shown in an age-dependent upregulation manner from puberty to adulthood in mouse testis. Immunostaining results confirmed the localization of CCR 6 in testis. Further chemotaxis assays demonstrated that spermatogenic cells GC-1 and -2 exhibited a directional movement toward CCR6-specific ligand such as CCL20 or Sertoli cells in vitro. CONCLUSIONS: The present findings indicate that CCR6 is involved in the chemotaxis of spermatogenic cells in vitro and promotes chemotaxis under non-inflammatory conditions during normal spermatogenesis.

Is the activity of CGRP and Adrenomedullin regulated by RAMP (-2) and (-3) in Trypanosomatidae? An in-silico approach.

The Calcitonin-Like Receptor (CLR) belongs to the classical seven-transmembrane segment molecules coupled to heterotrimeric G proteins. Its pharmacology depends on the simultaneous expression of the so-called Receptor Activity Modifier Proteins (RAMP-) -1, -2 and -3. RAMP-associated proteins modulate glycosylation and cellular traffic of CLR, therefore determining its pharmacodynamics. In higher eukaryotes, the complex formed by CLR and RAMP-1 is more akin to bind Calcitonin Gene-Related Peptide (CGRP), whereas those formed by CLR and RAMP-2 or RAMP-3, bind preferentially Adrenomedullin (AM). In lower eukaryotes, RAMPs, or any homologous protein, have not been identified until now. Herein we demonstrated a negative chemotactic response elicited by CGRP (10-9 and 10-8 M) and AM (10-9 to 10-5 M). Whether or not this response is receptor mediated should be verified, as well as the expression of a 24 kDa band in Leishmania, recognized by western blot analysis by the use of (human-)-RAMP-2 antibodies as detection probes. Queries with human RAMP-2 and RAMP-3 protein sequences in blastp against Leishmania (Viannia) braziliensis predicted proteome, allowed us to detect two sequence alignments in the parasite: A RAMP-2-aligned sequence corresponding to Leishmania folylpolyglutamate synthase (FPGS), and a RAMP-3 aligned protein, a hypothetical Leishmania protein with yet unknown function. The presence of homologous of these proteins was described in-silico in other members of the Trypanosomatidae. These preliminary and not yet complete data suggest the feasibility that both CGRP and Adrenomedullin activities may be regulated by homologs of RAMP- (-2) and (-3) in these parasites.

In vitro chemokine (C-C motif) receptor 6-dependent non-inflammatory chemotaxis during spermatogenesis

BACKGROUND: Chemokine (C-C motif) receptor 6 (CCR6) is present in sperm and plays a significant role in sperm motility and chemotaxis acting in the reproductive tracts. However, the expression and functional significance of CCR6 in testis are still poorly understood, especially in the process of spermatogenesis. METHODS AND RESULTS: CCR6 was expressed in spermatogenic cell lines and its expression was shown in an age-dependent upregulation manner from puberty to adulthood in mouse testis. Immunostaining results confirmed the localization of CCR 6 in testis. Further chemotaxis assays demonstrated that spermatogenic cells GC-1 and -2 exhibited a directional movement toward CCR6-specific ligand such as CCL20 or Sertoli cells in vitro. CONCLUSIONS: The present findings indicate that CCR6 is involved in the chemotaxis of spermatogenic cells in vitro and promotes chemotaxis under non-inflammatory conditions during normal spermatogenesis.

Chemotaxis detection towards chlorophenols using video processing analysis.

To our knowledge, this communication is the first report of chemotaxis towards chlorophenols by any bacteria. We used a recently published method based on the agarose in-plug assay combined with video processing analysis and we also present a new index of bacterial mean speed for these assays.

Identification of chemotaxis operon cheYZA and cheA gene expression under stressful conditions in Piscirickettsia salmonis.

Piscirickettsia salmonis is the etiological agent of piscirickettsiosis, which, as the main systemic disease in the Chilean salmon industry, causes significant economic losses. This bacterium can produce biofilm as a persistence and survival strategy in adverse conditions. In other bacteria, cheA is a key gene for modulating the onset of bacterial chemotaxis, as well as having a secondary role in biofilm production. Notwithstanding this association, the potential relationships between biofilm formation and genes involved in P. salmonis chemotaxis are poorly understood. This study aimed to determine P. salmonis cheA gene expression when grown in different culture media known to induce biofilm production. Piscirickettsia salmonis AUSTRAL-005 produced moderate/high biofilm levels after 144 h of incubation in the AUSTRAL-SRS and marine broths. In contrast, LF-89 biofilm production was weak/nonexistent in the aforementioned broths. Both assessed P. salmonis strains contained the cheYZA operon. Additionally, AUSTRAL-005 cheA transcripts increased in both culture media. In conclusion, these results suggest potential relationships between biofilm formation and genes related to chemotaxis in the fish pathogen P. salmonis.

Distinct Domains of CheA Confer Unique Functions in Chemotaxis and Cell Length in Azospirillum brasilense Sp7.

Chemotaxis is the movement of cells in response to gradients of diverse chemical cues. Motile bacteria utilize a conserved chemotaxis signal transduction system to bias their motility and navigate through a gradient. A central regulator of chemotaxis is the histidine kinase CheA. This cytoplasmic protein interacts with membrane-bound receptors, which assemble into large polar arrays, to propagate the signal. In the alphaproteobacterium Azospirillum brasilense, Che1 controls transient increases in swimming speed during chemotaxis, but it also biases the cell length at division. However, the exact underlying molecular mechanisms for Che1-dependent control of multiple cellular behaviors are not known. Here, we identify specific domains of the CheA1 histidine kinase implicated in modulating each of these functions. We show that CheA1 is produced in two isoforms: a membrane-anchored isoform produced as a fusion with a conserved seven-transmembrane domain of unknown function (TMX) at the N terminus and a soluble isoform similar to prototypical CheA. Site-directed and deletion mutagenesis combined with behavioral assays confirm the role of CheA1 in chemotaxis and implicate the TMX domain in mediating changes in cell length. Fluorescence microscopy further reveals that the membrane-anchored isoform is distributed around the cell surface while the soluble isoform localizes at the cell poles. Together, the data provide a mechanism for the role of Che1 in controlling multiple unrelated cellular behaviors via acquisition of a new domain in CheA1 and production of distinct functional isoforms.IMPORTANCE Chemotaxis provides a significant competitive advantage to bacteria in the environment, and this function has been transferred laterally multiple times, with evidence of functional divergence in different genomic contexts. The molecular principles that underlie functional diversification of chemotaxis in various genomic contexts are unknown. Here, we provide a molecular mechanism by which a single CheA protein controls two unrelated functions: chemotaxis and cell length. Acquisition of this multifunctionality is seemingly a recent evolutionary event. The findings illustrate a mechanism by which chemotaxis function may be co-opted to regulate additional cellular functions.

An intact acrosome is required for the chemotactic response to progesterone in mouse spermatozoa.

Mammalian sperm become fertilization-competent in the oviduct, during a process known as capacitation that involves the acquisition of the ability to exocytose the acrosome but also the chemotactic responses-both of which contribute to successful fertilization. Chemotaxis is used by spermatozoa to orient and to locate the egg; the acrosome reaction facilitates sperm binding to and fusing with the egg membrane. Mammalian spermatozoa are able to sense picomolar concentrations of progesterone, which drives chemotactic behavior. The state of the acrosome during the chemotactic response, however, is unknown. Genetically modified mouse spermatozoa were employed in a chemotaxis assay under fluorescence microscopy to evaluate their acrosome status while swimming, allowing us to elucidate the acrosome integrity of sperm responding to progesterone-induced chemotaxis. We first showed that wild-type mouse spermatozoa chemotactically respond to a gradient of progesterone, and that the genetic modifications employed do not affect the chemotactic behavior of sperm to progesterone. Next, we found that acrosome-intact, but not acrosome-reacted, spermatozoa orient and respond to picomolar concentrations of progesterone and that chemotaxis normally occurs prior to the acrosome reaction. Our results suggest that premature commitment to acrosome exocytosis leads to navigation failure, so proper control and timing of the acrosome reaction is required for fertilization success and male fertility.

The Master Regulators of the Fla1 and Fla2 Flagella of Rhodobacter sphaeroides Control the Expression of Their Cognate CheY Proteins.

Rhodobacter sphaeroides is an alphaproteobacterium that has two complete sets of flagellar genes. The fla1 set was acquired by horizontal transfer from an ancestral gammaproteobacterium and is the only set of flagellar genes that is expressed during growth under standard laboratory conditions. The products of these genes assemble a single, subpolar flagellum. In the absence of the Fla1 flagellum, a gain-of-function mutation in the histidine kinase CckA turns on the expression of the fla2 flagellar genes through the response regulator CtrA. The rotation of the Fla1 and Fla2 flagella is controlled by different sets of chemotaxis proteins. Here, we show that the expression of the chemotaxis proteins that control Fla2, along with the expression of the fla2 genes, is coordinated by CtrA, whereas the expression of the chemotaxis genes that control Fla1 is mediated by the master regulators of the Fla1 system. The coordinated expression of the chemosensory proteins with their cognate flagellar genes highlights the relevance of integrating the expression of the horizontally acquired fla1 genes with a chemosensory system independently of the regulatory proteins responsible for the expression of fla2 and its cognate chemosensory system. IMPORTANCE Gene acquisition via horizontal transfer represents a challenge to the recipient organism to adjust its metabolic and genetic networks to incorporate the new material in a way that represents an adaptive advantage. In the case of Rhodobacter sphaeroides, a complete set of flagellar genes was acquired and successfully coordinated with the native flagellar system. Here we show that the expression of the chemosensory proteins that control flagellar rotation is dependent on the master regulators of their corresponding flagellar system, minimizing the use of transcription factors required to express the native and horizontally acquired genes along with their chemotaxis proteins.

Human breast cancer-derived soluble factors facilitate CCL19-induced chemotaxis of human dendritic cells.

Breast cancer remains as a challenging disease with high mortality in women. Increasing evidence points the importance of understanding a crosstalk between breast cancers and immune cells, but little is known about the effect of breast cancer-derived factors on the migratory properties of dendritic cells (DCs) and their consequent capability in inducing T cell immune responses. Utilizing a unique 3D microfluidic device, we here showed that breast cancers (MCF-7, MDA-MB-231, MDA-MB-436 and SK-BR-3)-derived soluble factors increase the migration of DCs toward CCL19. The enhanced migration of DCs was mainly mediated via the highly activated JNK/c-Jun signaling pathway, increasing their directional persistence, while the velocity of DCs was not influenced, particularly when they were co-cultured with triple negative breast cancer cells (TNBCs or MDA-MB-231 and MDA-MB-436). The DCs up-regulated inflammatory cytokines IL-1ß and IL-6 and induced T cells more proliferative and resistant against activation-induced cell death (AICD), which secret high levels of inflammatory cytokines IL-1ß, IL-6 and IFN-γ. This study demonstrated new possible evasion strategy of TNBCs utilizing their soluble factors that exploit the directionality of DCs toward chemokine responses, leading to the building of inflammatory milieu which may support their own growth.

Two-Swim Operators in the Modified Bacterial Foraging Algorithm for the Optimal Synthesis of Four-Bar Mechanisms.

This paper presents two-swim operators to be added to the chemotaxis process of the modified bacterial foraging optimization algorithm to solve three instances of the synthesis of four-bar planar mechanisms. One swim favors exploration while the second one promotes fine movements in the neighborhood of each bacterium. The combined effect of the new operators looks to increase the production of better solutions during the search. As a consequence, the ability of the algorithm to escape from local optimum solutions is enhanced. The algorithm is tested through four experiments and its results are compared against two BFOA-based algorithms and also against a differential evolution algorithm designed for mechanical design problems. The overall results indicate that the proposed algorithm outperforms other BFOA-based approaches and finds highly competitive mechanisms, with a single set of parameter values and with less evaluations in the first synthesis problem, with respect to those mechanisms obtained by the differential evolution algorithm, which needed a parameter fine-tuning process for each optimization problem.

Orthodontic movement in deciduous teeth.

Deciduous teeth exfoliate as a result of apoptosis induced by cementoblasts, a process that reveals the mineralized portion of the root while attracting clasts. Root resorption in deciduous teeth is slow due to lack of mediators necessary to speed it up; however, it accelerates and spreads in one single direction whenever a permanent tooth pericoronal follicle, rich in epithelial growth factor (EGF), or other bone resorption mediators come near. The latter are responsible for bone resorption during eruption, and deciduous teeth root resorption and exfoliation. Should deciduous teeth be subjected to orthodontic movement or anchorage, mediators local levels will increase. Thus, one should be fully aware that root resorption in deciduous teeth will speed up and exfoliation will early occur. Treatment planning involving deciduous teeth orthodontic movement and/or anchorage should consider: Are clinical benefits relevant enough as to be worth the risk of undergoing early inconvenient root resorption?

Treatment with sulphated galactan inhibits macrophage chemotaxis and reduces intraplaque macrophage content in atherosclerotic mice.

Experimental data from animal models and clinical studies support connections between the haemostasis and inflammation in atherogenesis. These interfaces among inflammation and thrombogenesis have been suggested as targets for pharmacological intervention to reduce disease progression. We hypothesize that the recently discovered antithrombotic drug Sulphated Galactan (SG) (isolated from the red marine alga Acanthophora muscoides) might reduce atherosclerotic plaque vulnerability and inflammatory gene expression in 10-week aged apolipoprotein E deficient (ApoE-/-) mice under high-cholesterol diet for additional 11weeks. Then, the underlying cellular mechanisms were investigated in vitro. SG (10mg/kg) or Vehicle was subcutaneously injected from week 6 until week 11 of the diet. Treatment with SG reduced intraplaque macrophage and Tissue Factor (TF) content as compared to Vehicle-treated animals. Intraplaque TF co-localized and positively correlated with macrophage rich-areas. No changes on atherosclerotic plaque size, and other intraplaque features of vulnerability (such as lipid, neutrophil, MMP-9 and collagen contents) were observed. Moreover, mRNA expression of MMPs, chemokines and genetic markers of Th1/2/reg/17 lymphocyte polarization within mouse aortic arches and spleens was not affected by SG treatment. In vitro, treatment with SG dose-dependently reduced macrophage chemotaxis without affecting TF production. Overall, the chronic SG treatment was well tolerated. In conclusion, our results indicate that SG treatment reduced intraplaque macrophage content (by impacting on cell recruitment) and, concomitantly, intraplaque TF content of potential macrophage origin in atherosclerotic mice.

Orthodontic movement in deciduous teeth

Deciduous teeth exfoliate as a result of apoptosis induced by cementoblasts, a process that reveals the mineralized portion of the root while attracting clasts. Root resorption in deciduous teeth is slow due to lack of mediators necessary to speed it up; however, it accelerates and spreads in one single direction whenever a permanent tooth pericoronal follicle, rich in epithelial growth factor (EGF), or other bone resorption mediators come near. The latter are responsible for bone resorption during eruption, and deciduous teeth root resorption and exfoliation. Should deciduous teeth be subjected to orthodontic movement or anchorage, mediators local levels will increase. Thus, one should be fully aware that root resorption in deciduous teeth will speed up and exfoliation will early occur. Treatment planning involving deciduous teeth orthodontic movement and/or anchorage should consider: Are clinical benefits relevant enough as to be worth the risk of undergoing early inconvenient root resorption?.

O dente decíduo é esfoliado graças à apoptose em seus cementoblastos, que desnuda a parte mineralizada da raiz e atrai os clastos. A rizólise é lenta, pois faltam mediadores em quantidade para acelerar o processo, mas ela se acelera e unidireciona quando se aproxima um folículo pericoronário de dente permanente rico em EGF e outros mediadores da reabsorção óssea - os responsáveis pelas reabsorções óssea na erupção e dentária decídua na rizólise e esfoliação. Se houver movimentação ortodôntica ou ancoragem em dentes decíduos, aumenta-se, também, o nível local desses mesmos mediadores, devendo-se estar bem consciente de que haverá uma aceleração da rizólise e, em decorrência, uma antecipação de sua esfoliação. No planejamento de casos em que dentes decíduos estejam envolvidos na movimentação ortodôntica e/ou ancoragem, deve-se ponderar: o benefício clínico para o paciente será relevante, a ponto de valer o risco de uma rizólise abreviada e inconveniente?.

CCR2 Expression in Neutrophils Plays a Critical Role in Their Migration Into the Joints in Rheumatoid Arthritis.

OBJECTIVE: Infiltration of neutrophils into the joints plays an important role in bone erosion and articular destruction in rheumatoid arthritis (RA). Neutrophil trafficking during inflammation is a process that involves activation of chemotactic receptors. Recent findings suggest that changes in chemotactic receptor patterns could occur in neutrophils under certain inflammatory conditions. The aim of this study was to evaluate the gain of responsiveness of neutrophils to CCL2 in RA patients and to assess the role of CCL2 in driving neutrophil infiltration into the joints. METHODS: Neutrophils were purified from the peripheral blood of patients with RA or from mice with antigen-induced arthritis (AIA). Expression of CCR2 was evaluated using polymerase chain reaction, flow cytometry, and immunofluorescence analyses. In vitro chemotaxis to CCL2 was assayed to evaluate the functional significance of de novo CCR2 expression. The murine AIA model was used to evaluate the in vivo role of CCR2 in neutrophil infiltration into the joints. RESULTS: High CCR2 expression and responsiveness to CCL2 were observed in neutrophils from the blood of patients with early RA and in neutrophils from the blood and bone marrow of mice with AIA. Genetic deficiency or pharmacologic inhibition of CCR2 protected against the infiltration of neutrophils into the joints. This protection was not associated with an impairment of the neutrophil chemotactic ability or CXC chemokine production in the joints. Moreover, adoptive transfer of wild-type mouse neutrophils to CCR2-deficient mice restored neutrophil infiltration and the articular mechanical hyperalgesia associated with joint inflammation. CONCLUSION: These findings suggest that CCR2 is directly involved in the detrimental infiltration of neutrophils into the joints in patients with RA, showing a new inflammatory role of CCR2 during RA flares or active disease.