CXCL9 inhibits eosinophil responses by a CCR3- and Rac2-dependent mechanism

Inverse Regulation of C-C Chemokine Receptor 3 Oligomerization by Downstream Proteins Indicates Biased Signal Transduction Pathways

Oligomerization is one of the important mechanisms for G protein-coupled receptors (GPCRs) to modulate their activity in signal transduction. However, details of how and why the oligomerization of GPCRs regulates their functions under physiological conditions remain largely unknown. Here, using single-molecule photobleaching technology, we show that chemokine ligand 5 (CCL5) and chemokine ligand 8 (CCL8) are similar to the previously reported chemokine ligand 11 (CCL11) and chemokine ligand 24 (CCL24), which can regulate the oligomerization of chemokine receptor 3 (CCR3). Our results further demonstrate that downstream proteins, β-arrestin 2 and Gi protein complex, on the CCR3 signal transduction pathway, can inversely regulate the oligomeric states of CCR3 induced by its binding ligands. This unexpected discovery suggests complex relationships between the oligomeric behaviors of CCR3 and the components of ligands-CCR3-downstream proteins, reflecting the potentially functional impact of the oligomerization on the multiple activation pathways of GPCR, such as biased activation.

Origins and functions of eosinophils in two non-mucosal tissues

Eosinophils are a type of granulocyte named after the presence of their eosin-stained granules. Traditionally, eosinophils have been best known to play prominent roles in anti-parasitic responses and mediating allergic reactions. Knowledge of their behaviour has expanded with time, and they are now recognized to play integral parts in the homeostasis of gastrointestinal, respiratory, skeletal muscle, adipose, and connective tissue systems. As such, they are implicated in a myriad of pathologies, and have been the target of several medical therapies. This review focuses on the lifespan of eosinophils, from their origins in the bone marrow, to their tissue-resident role. In particular, we wish to highlight the functions of eosinophils in non-mucosal tissues with skeletal muscle and the adipose tissues as examples, and to discuss the current understanding of their participation in diseased states in these tissues.

Cellular Context Dictates the Suppression or Augmentation of Triple-Negative Mammary Tumor Metastasis by NLRX1

Prior studies have defined multiple, but inconsistent, roles for the enigmatic pattern recognition receptor NLRX1 in regulating several cancer-associated biological functions. In this study, we explore the role of NLRX1 in the highly metastatic murine 4T1 mammary tumor model. We describe a functional dichotomy of NLRX1 between two different cellular contexts: expression in healthy host cells versus expression in the 4T1 tumor cells. Using Nlrx1-/- mice engrafted with 4T1 tumors, we demonstrate that NLRX1 functions as a tumor suppressor when expressed in the host cells. Specifically, NLRX1 in healthy host cells attenuates tumor growth and lung metastasis through suppressing characteristics of epithelial-mesenchymal transition and the lung metastatic niche. Conversely, we demonstrate that NLRX1 functions as a tumor promoter when expressed in 4T1 tumor cells using gain- and loss-of-function studies both in vitro and in vivo. Mechanistically, NLRX1 in the tumor cells augments 4T1 aggressiveness and metastasis through regulating epithelial-mesenchymal transition hallmarks, cell death, proliferation, migration, reactive oxygen species levels, and mitochondrial respiration. Collectively, we provide critical insight into NLRX1 function and establish a dichotomous role of NLRX1 in the 4T1 murine mammary carcinoma model that is dictated by cellular context.

Eosinophil: An innate immune cell with anti-filarial vaccine and biomarker potential

Background

Filarial infections continue to pose a great challenge in endemic countries. One of the central goals in the fight against human filarial infections is the development of strategies that will lead to the inhibition of microfilariae (mf) transmission. Keeping mf under a certain threshold within endemic populations will stop transmission and eliminate the infection.

Method

A narrative review was carried out to identify the possibilities and limitations of exploring the use of eosinophil responses as an anti-filarial vaccine, and biomarker for the detection of filarial infections. An extensive literature search was performed in online scientific databases including PubMed Central, PubMed, BioMed Central, with the use of predefined search terms.

Results

A better understanding of the parasite-host interactions will lead to the development of improved and better treatment or vaccine strategies that could eliminate filariasis as soon as possible. Highlighted in this review is the explorative use of eosinophil-producing CLC/Galectin-10 as a potential biomarker for filarial infections. Also discussed are some genes, and pathways involved in eosinophil recruitments that could be explored for anti-filarial vaccine development.

Conclusion

In this short communication, we discuss how eosinophil-regulated genes, pathways, and networks could be critical in providing more information on how reliably a front-line immune player could be exploited for anti-filarial vaccine development and early infection biomarker.

Aiolos regulates eosinophil migration into tissues

Expression of Ikaros family transcription factor IKZF3 (Aiolos) increases during murine eosinophil lineage commitment and maturation. Herein, we investigated Aiolos expression and function in mature human and murine eosinophils. Murine eosinophils deficient in Aiolos demonstrated gene expression changes in pathways associated with granulocyte-mediated immunity, chemotaxis, degranulation, ERK/MAPK signaling, and extracellular matrix organization; these genes had ATAC peaks within 1 kB of the TSS that were enriched for Aiolos-binding motifs. Global Aiolos deficiency reduced eosinophil frequency within peripheral tissues during homeostasis; a chimeric mouse model demonstrated dependence on intrinsic Aiolos expression by eosinophils. Aiolos deficiency reduced eosinophil CCR3 surface expression, intracellular ERK1/2 signaling, and CCL11-induced actin polymerization, emphasizing an impaired functional response. Aiolos-deficient eosinophils had reduced tissue accumulation in chemokine-, antigen-, and IL-13-driven inflammatory experimental models, all of which at least partially depend on CCR3 signaling. Human Aiolos expression was associated with active chromatin marks enriched for IKZF3, PU.1, and GATA-1-binding motifs within eosinophil-specific histone ChIP-seq peaks. Furthermore, treating the EOL-1 human eosinophilic cell line with lenalidomide yielded a dose-dependent decrease in Aiolos. These collective data indicate that eosinophil homing during homeostatic and inflammatory allergic states is Aiolos-dependent, identifying Aiolos as a potential therapeutic target for eosinophilic disease.

Analysis of the signal cross talk via CCL26 in the tumor microenvironment in osteosarcoma

Interaction with surrounding healthy cells plays a major role in the growth and metastasis of osteosarcoma. In this study, we hypothesized that humoral factors, which do not require direct contact with cells, are involved in the interaction between osteosarcoma and the surrounding cells. We identified the humoral factor involved in the association between tumor cells and surrounding normal cells using a co-culture model and investigated the significance of our findings. When human osteosarcoma cells (MG63) and human mesenchymal stem cells (hMSCs) were co-cultured and comprehensively analyzed for changes in each culture group, we found that the expression of chemokine (CC motif) ligand 26 (CCL26) was significantly enhanced. We also analyzed the changes in cell proliferation in co-culture, enhanced interaction with administration of recombinant CCL26 (rCCL26), reduced interaction with administration of anti-CCL26 antibodies, changes in invasive and metastatic abilities. CCL26 levels, motility, and invasive capability increased in the co-culture group and the group with added rCCL26, compared to the corresponding values in the MG63 single culture group. In the group with added CCL26 neutralizing antibodies, CCL26 level decreased in both the single and co-culture groups, and motility and invasive ability were also reduced. In a nude mice lung metastasis model, the number of lung metastases increased in the co-culture group and the group with added rCCL26, whereas the number of tumors were suppressed in the group with added neutralizing antibodies compared to those in the MG63 alone. This study identified a possible mechanism by which osteosarcoma cells altered the properties of normal cells to favorably change the microenvironment proximal to tumors and to promote distant metastasis.

Cxcl9l and Cxcr3.2 regulate recruitment of osteoclast progenitors to bone matrix in a medaka osteoporosis model

Bone remodeling requires a balanced interplay of osteoblasts and osteoclasts. While the intercellular signaling that triggers bone cell differentiation is well understood, it remains unclear how bone progenitor cells are recruited to remodeling sites. Various chemokines are upregulated under osteoporotic conditions. However, whether they are involved in progenitor recruitment or instead have inflammatory roles is unknown. Here we used a medaka fish osteoporosis model to identify the chemokine ligand Cxcl9l and receptor Cxcr3.2 as essential to control osteoclast progenitor recruitment and differentiation at bone resorption sites. Cxcr3.2 activity can be blocked by small-molecule inhibitors that protect bone from osteoporotic insult. Our study demonstrates the potential of fish for osteoporosis drug discovery and opens avenues for future osteoporosis therapy.

Bone homeostasis requires continuous remodeling of bone matrix to maintain structural integrity. This involves extensive communication between bone-forming osteoblasts and bone-resorbing osteoclasts to orchestrate balanced progenitor cell recruitment and activation. Only a few mediators controlling progenitor activation are known to date and have been targeted for intervention of bone disorders such as osteoporosis. To identify druggable pathways, we generated a medaka (Oryzias latipes) osteoporosis model, where inducible expression of receptor-activator of nuclear factor kappa-Β ligand (Rankl) leads to ectopic formation of osteoclasts and excessive bone resorption, which can be assessed by live imaging. Here we show that upon Rankl induction, osteoblast progenitors up-regulate expression of the chemokine ligand Cxcl9l. Ectopic expression of Cxcl9l recruits mpeg1-positive macrophages to bone matrix and triggers their differentiation into osteoclasts. We also demonstrate that the chemokine receptor Cxcr3.2 is expressed in a distinct subset of macrophages in the aorta-gonad-mesonephros (AGM). Live imaging revealed that upon Rankl induction, Cxcr3.2-positive macrophages get activated, migrate to bone matrix, and differentiate into osteoclasts. Importantly, mutations in cxcr3.2 prevent macrophage recruitment and osteoclast differentiation. Furthermore, Cxcr3.2 inhibition by the chemical antagonists AMG487 and NBI-74330 also reduced osteoclast recruitment and protected bone integrity against osteoporotic insult. Our data identify a mechanism for progenitor recruitment to bone resorption sites and Cxcl9l and Cxcr3.2 as potential druggable regulators of bone homeostasis and osteoporosis.

Microbial Regulation of Enteric Eosinophils and Its Impact on Tissue Remodeling and Th2 Immunity

Eosinophils have emerged as multifaceted cells that contribute to tissue homeostasis. However, the impact of the microbiota on their frequency and function at mucosal sites remains unclear. Here, we investigated the role of the microbiota in the regulation of enteric eosinophils. We found that small intestinal (SI) eosinophilia was significantly greater in germ-free (GF) mice compared to specific pathogen free (SPF) controls. This was associated with changes in the production of enteric signals that regulate eosinophil attraction and survival, and was fully reversed by complex colonization. Additionally, SI eosinophils of GF mice exhibited more cytoplasmic protrusions and less granule content than SPF controls. Lastly, we generated a novel strain of eosinophil-deficient GF mice. These mice displayed intestinal fibrosis and were less prone to allergic sensitization as compared to GF controls. Overall, our study demonstrates that commensal microbes regulate intestinal eosinophil frequency and function, which impacts tissue repair and allergic sensitization to food antigens. These data support a critical interplay between the commensal microbiota and intestinal eosinophils in shaping homeostatic, innate, and adaptive immune processes in health and disease.

Rho and Rac, but not ROCK, are required for secretion of human and mouse eosinophil-associated RNases

BACKGROUND

Eosinophil-associated RNases (EARs) are stored preformed in eosinophil cytoplasmic secretory granules and have a key role in eosinophil effector functions in host defence and inflammatory disorders. However, the secretion mechanisms of EARs are poorly understood.

OBJECTIVE

Our study aimed to understand the involvement of cytoskeleton machinery in EAR secretion.

METHODS

Fresh human and mouse eosinophils were stimulated with CCL11, and the secretion of enzymatically active EARs was detected using an RNase activity assay. The involvement of cytoskeletal elements or microtubules was probed using specific inhibitors.

RESULTS

We found that dynamic polymerization of microtubules and cytoskeletal elements, such as Rho and Rac, is required for chemokine-mediated EAR secretion from human and mouse eosinophils. However, inhibition of ROCK (Rho-associated protein kinase) increased EAR secretion in human and mouse eosinophils even in the absence of chemokine stimulation, suggesting ROCK negatively regulates EAR secretion.

CONCLUSIONS

Collectively, these data suggest a cytoskeleton-dependent mechanism of EAR secretion from eosinophils, findings that are pertinent to host defence, allergy and other eosinophil-associated diseases.

Involvement and Possible Role of Eosinophils in Asthma Exacerbation

Eosinophils are involved in the development of asthma exacerbation. Recent studies have suggested that sputum and blood eosinophil counts are important factors for predicting asthma exacerbation. In severe eosinophilic asthma, anti-interleukin (IL)-5 monoclonal antibody decreases blood eosinophil count and asthma exacerbation frequency. However, even in the absence of IL-5, eosinophilic airway inflammation can be sufficiently maintained by the T helper (Th) 2 network, which comprises a cascade of vascular cell adhesion molecule-1/CC chemokines/eosinophil growth factors, including granulocyte-macrophage colony-stimulating factor (GM-CSF). Periostin, an extracellular matrix protein and a biomarker of the Th2 immune response in asthma, directly activates eosinophils in vitro. A major cause of asthma exacerbation is viral infection, especially rhinovirus (RV) infection. The expression of intercellular adhesion molecule (ICAM)-1, a cellular receptor for the majority of RVs, on epithelial cells is increased after RV infection, and adhesion of eosinophils to ICAM-1 can upregulate the functions of eosinophils. The expressions of cysteinyl leukotrienes (cysLTs) and CXCL10 are upregulated in virus-induced asthma. CysLTs can directly provoke eosinophilic infiltration in vivo and activate eosinophils in vitro. Furthermore, eosinophils express the CXC chemokine receptor 3, and CXCL10 activates eosinophils in vitro. Both eosinophils and neutrophils contribute to the development of severe asthma or asthma exacerbation. IL-8, which is an important chemoattractant for neutrophils, is upregulated in some cases of severe asthma. Lipopolysaccharide (LPS), which induces IL-8 from epithelial cells, is also increased in the lower airways of corticosteroid-resistant asthma. IL-8 or LPS-stimulated neutrophils increase the transbasement membrane migration of eosinophils, even in the absence of chemoattractants for eosinophils. Therefore, eosinophils are likely to contribute to the development of asthma exacerbation through several mechanisms, including activation by Th2 cytokines, such as IL-5 or GM-CSF or by virus infection-related proteins, such as CXCL10, and interaction with other cells, such as neutrophils.

Insight on the regulation of chemokine activities

The activity of chemokines is regulated by several mechanisms that control the final cellular response. The present review discusses the complexity of the regulation of the chemokine system, and the novel findings describing how in persistent infections, the expression of chemokine receptors on the surface of T cells does not correlate with their homing potential. Thanks to the latest advances in our comprehension of the chemokine system, novel approaches targeting chemokines, chemokine receptors, or protein of their signaling pathway should be considered in order to achieve a personalized therapy.

Characteristics of Allergic Pulmonary Inflammation in CXCR3Knockout Mice Sensitized and Challenged with House Dust Mite Protein

Chemokine C-X-C motif receptor 3 (CXCR3) is a chemokine receptor that is mainly expressed by activated T lymphocytes. T cells play important roles in allergic pulmonary inflammation, which is a hallmark of asthma and elicits the localized accumulation of activated T cells in the lung. In China, a marked increase in the incidence rate of chronic allergic pulmonary inflammation has made it a major public health threat. In the present study, we investigated the role of CXCR3 and its ligands in airway inflammation induced by house dust mite protein (HDMP) in a CXCR3 knockout (CXCR3KO) asthma mouse model. Pathological manifestations in the lung, cell counts and bronchoalveolar lavage fluid (BALF) classifications were studied using hematoxylin and eosin (H&E) staining. The levels of IL-4 and IFN-γ in the BALF and splenocyte supernatants were measured using ELISA. CD4+ and CD8+ T cells in the lung and spleen were analyzed by flow cytometry. RT-PCR was applied to measure the mRNA transcript levels of monokines induced by IFN-γ(CXCL9) and IFN-γ inducible protein 10(CXCL10). The total cell counts, eosinophil counts, and IL-4 levels in the BALF and cultured splenocyte supernatants were significantly increased, while the levels of IFN-γ were reduced in the HDMP groups(P<0.01). Changes in the total cell counts, eosinophil counts, and lymphocyte counts, as well as the total protein levels in the BALF, the levels of IL-4 in splenocyte supernatants, and the pathological manifestations in the lung, were all greater in CXCR3KO mice than in C57BL/6 wild-type mice. Furthermore, the expression levels of CXCL9 and CXCL10 mRNA transcripts in the lungs of CXCR3KO mice were lower than those in C57BL/6 wild-type mice (P<0.05). CXCR3 and its ligands (i.e., CXCL9 and CXCL10) may play anti-inflammatory roles in this animal model. Promoting the expression of CXCR3 and its ligands may represent a novel therapeutic approach for preventing and curing asthma.

Modulation of Chemokine Responses: Synergy and Cooperativity

Chemokine biology is mediated by more complex interactions than simple monomolecular ligand–receptor interactions, as chemokines can form higher order quaternary structures, which can also be formed after binding to glycosaminoglycans (GAGs) on endothelial cells, and their receptors are found as dimers and/or oligomers at the cell surface. Due to the complexity of the chemokine binding and signaling system, several mechanisms have been proposed to provide an explanation for the synergy observed between chemokines in leukocyte migration. Pioneering studies on interactions between different chemokines have revealed that they can act as antagonists, or synergize with other chemokines. The synergism can occur at different levels, involving either two chemokine receptors triggered simultaneously or sequentially exposed to their agonists, or the activation of one type of chemokine receptor triggered by chemokine heterocomplexes. In addition to the several chemokines that, by forming a heterocomplex with chemokine receptor agonists, act as enhancers of molecules of the same family, we have recently identified HMGB1, an endogenous damage-associated molecular patterns (DAMPs) molecule, as an enhancer of the activity of CXCL12. It is now evident that synergism between chemokines is crucial at the very early stage of inflammation. In addition, the low-affinity interaction with GAGs has recently been shown to induce cooperativity allowing synergy or inhibition of activity by displacement of other ligands.

STAT1 signaling is essential for protection against Cryptococcus neoformans infection in mice

Nonprotective immune responses to highly virulent Cryptococcus neoformans strains, such as H99, are associated with Th2-type cytokine production, alternatively activated macrophages, and inability of the host to clear the fungus. In contrast, experimental studies show that protective immune responses against cryptococcosis are associated with Th1-type cytokine production and classical macrophage activation. The protective response induced during C. neoformans strain H99γ (C. neoformans strain H99 engineered to produce murine IFN-γ) infection correlates with enhanced phosphorylation of the transcription factor STAT1 in macrophages; however, the role of STAT1 in protective immunity to C. neoformans is unknown. The current studies examined the effect of STAT1 deletion in murine models of protective immunity to C. neoformans. Survival and fungal burden were evaluated in wild-type and STAT1 knockout (KO) mice infected with either strain H99γ or C. neoformans strain 52D (unmodified clinical isolate). Both strains H99γ and 52D were rapidly cleared from the lungs, did not disseminate to the CNS, or cause mortality in the wild-type mice. Conversely, STAT1 KO mice infected with H99γ or 52D had significantly increased pulmonary fungal burden, CNS dissemination, and 90-100% mortality. STAT1 deletion resulted in a shift from Th1 to Th2 cytokine bias, pronounced lung inflammation, and defective classical macrophage activation. Pulmonary macrophages from STAT1 KO mice exhibited defects in NO production correlating with inefficient inhibition of fungal proliferation. These studies demonstrate that STAT1 signaling is essential not only for regulation of immune polarization but also for the classical activation of macrophages that occurs during protective anticryptococcal immune responses.

Actin cytoskeletal defects in immunodeficiency

The importance of the cytoskeleton in mounting a successful immune response is evident from the wide range of defects that occur in actin-related primary immunodeficiencies (PIDs). Studies of these PIDs have revealed a pivotal role for the actin cytoskeleton in almost all stages of immune system function, from hematopoiesis and immune cell development, through to recruitment, migration, intercellular and intracellular signaling, and activation of both innate and adaptive immune responses. The major focus of this review is the immune defects that result from mutations in the Wiskott-Aldrich syndrome gene (WAS), which have a broad impact on many different processes and give rise to clinically heterogeneous immunodeficiencies. We also discuss other related genetic defects and the possibility of identifying new genetic causes of cytoskeletal immunodeficiency.

Up-regulation of chemokine C-C ligand 2 (CCL2) and C-X-C chemokine 8 (CXCL8) expression by monocytes in chronic idiopathic urticaria

The disturbed cytokine-chemokine network could play an important role in the onset of diseases with inflammatory processes such as chronic idiopathic urticaria (CIU). Our main objectives were to evaluate the relation between proinflammatory chemokine serum levels from CIU patients and their response to autologous skin test (ASST) and basophil histamine release (BHR). We also aimed to assess the chemokine secretion by peripheral blood mononuclear cells (PBMC) upon polyclonal stimulus and to evaluate chemokine C-C ligand 2/C-X-C chemokine 8 (CCL2/CXCL8) and Toll-like receptor-4 (TLR-4) expression in monocytes. We observed significantly higher serum levels of the CXCL8, CXCL9, CXCL10 and CCL2 in CIU patients compared to the healthy group, regardless of the BHR or ASST response. The basal secretion of CCL2 by PBMC or induced by Staphylococcus aureus enterotoxin A (SEA) was higher in CIU patients than in the control group, as well as for CXCL8 and CCL5 secretions upon phytohaemagglutinin stimulation. Also, up-regulation of CCL2 and CXCL8 mRNA expression was found in monocytes of patients upon SEA stimulation. The findings showed a high responsiveness of monocytes through CCL2/CXCL8 expression, contributing to the creation of a proinflammatory environment in CIU.

Agonist activation of f-actin-mediated eosinophil shape change and mediator release is dependent on Rac2

BACKGROUND

Tissue recruitment and activation of eosinophils contribute to allergic symptoms by causing airway hyperresponsiveness and inflammation. Shape changes and mediator release in eosinophils may be regulated by mammalian Rho-related guanosine triphosphatases. Of these, Rac2 is essential for F-actin formation as a central process underlying cell motility, exocytosis, and respiratory burst in neutrophils, while the role of Rac2 in eosinophils is unknown.We set out to determine the role of Rac2 in eosinophil mediator release and F-actin-dependent shape change in response to chemotactic stimuli.

METHODS

Rac2-deficient eosinophils from CD2-IL-5 transgenic mice crossed with rac2 gene knockout animals were examined for their ability to release superoxide through respiratory burst or eosinophil peroxidase by degranulation. Eosinophil shape change and actin polymerization were also assessed by flow cytometry and confocal microscopy following stimulation with eotaxin-2 or platelet-activating factor.

RESULTS

Eosinophils from wild-type mice displayed inducible superoxide release, but at a small fraction (4-5%) of human eosinophils. Rac2-deficient eosinophils showed significantly less superoxide release (p < 0.05, 26% less than wild type). Eosinophils lacking Rac2 had diminished degranulation (p < 0.05, 62% less eosinophil peroxidase) and shape changes in response to eotaxin-2 or platelet-activating factor (with 68 and 49% less F-actin formation, respectively; p < 0.02) compared with wild-type cells.

CONCLUSION

These results demonstrate that Rac2 is an important regulator of eosinophil function by contributing to superoxide production, granule protein release, and eosinophil shape change. Our findings suggest that Rho guanosine triphosphatases are key regulators of cellular inflammation in allergy and asthma.

Regulation of allergic inflammatory responses by inhibitory receptors

An intricate network of activation and inhibitory signals tightly regulates immune responses. To date, multiple activation receptors have been described. These include receptors that mediate cellular functions such as adhesion, chemotaxis, cytokine signalling, mediator release, survival and phagocytosis. In contrast to these activation pathways, an opposing and suppressive receptor system has evolved. These receptors can override the signals elicited by the activation pathways and are broadly termed inhibitory receptors. Inhibitory receptors share unique intracellular signalling motifs and have key roles in various cellular and pathological conditions. Therefore, such receptors are potential targets for future therapeutics. In this review, we will discuss the structure and function of inhibitory receptors. In particular, we will focus on the expression and function of inhibitory receptors on mast cells and eosinophils and illustrate strategies for their inhibition in the settings of allergic inflammation.

Aberrant inflammatory response to Streptococcus pyogenes in mice lacking myeloid differentiation factor 88

Several in vitro studies have emphasized the importance of toll-like receptor/myeloid differentiation factor 88 (MyD88) signaling in the inflammatory response to Streptococcus pyogenes. Since the extent of inflammation has been implicated in the severity of streptococcal diseases, we have examined here the role of toll-like receptor/MyD88 signaling in the pathophysiology of experimental S. pyogenes infection. To this end, we compared the response of MyD88-knockout (MyD88(-/-)) after subcutaneous inoculation with S. pyogenes with that of C57BL/6 mice. Our results show that MyD88(-/-) mice harbored significantly more bacteria in the organs and succumbed to infection much earlier than C57BL/6 animals. Absence of MyD88 resulted in diminished production of inflammatory cytokines such as interleukin-12, interferon-gamma, and tumor necrosis factor-alpha as well as chemoattractants such as monocyte chemotactic protein-1 (MCP-1) and Keratinocyte-derived chemokine (KC), and hampered recruitment of effector cells involved in bacterial clearance (macrophages and neutrophils) to the infection site. Furthermore, MyD88(-/-) but not C57BL/6 mice exhibited a massive infiltration of eosinophils in infected organs, which can be explained by an impaired production of the regulatory chemokines, gamma interferon-induced monokine (MIG/CXCL9) and interferon-induced protein 10 (IP-10/CXCL10), which can inhibit transmigration of eosinophils. Our results indicate that MyD88 signaling targets effector cells to the site of streptococcal infection and prevents extravasation of cells that can induce tissue damage. Therefore, MyD88 signaling may be important for shaping the quality of the inflammatory response elicited during infection to ensure optimal effector functions.

Rho GTPases in hematopoiesis and hemopathies

Rho family GTPases are intracellular signaling proteins regulating multiple pathways involved in cell actomyosin organization, adhesion, and proliferation. Our knowledge of their cellular functions comes mostly from previous biochemical studies that used mutant overexpression approaches in various clonal cell lines. Recent progress in understanding Rho GTPase functions in blood cell development and regulation by gene targeting of individual Rho GTPases in mice has allowed a genetic understanding of their physiologic roles in hematopoietic progenitors and mature lineages. In particular, mouse gene-targeting studies have provided convincing evidence that individual members of the Rho GTPase family are essential regulators of cell type-specific functions and stimuli-specific pathways in regulating hematopoietic stem cell interaction with bone marrow niche, erythropoiesis, and red blood cell actin dynamics, phagocyte migration and killing, and T- and B-cell maturation. In addition, deregulation of Rho GTPase family members has been associated with multiple human hematologic diseases such as neutrophil dysfunction, leukemia, and Fanconi anemia, raising the possibility that Rho GTPases and downstream signaling pathways are of therapeutic value. In this review we discuss recent genetic studies of Rho GTPases in hematopoiesis and several blood lineages and the implications of Rho GTPase signaling in hematologic malignancies, immune pathology. and anemia.

CCR3 is a target for age-related macular degeneration diagnosis and therapy

Age-related macular degeneration (AMD), a leading cause of blindness worldwide, is as prevalent as cancer in industrialized nations. Most blindness in AMD results from invasion of the retina by choroidal neovascularization (CNV). We report that the eosinophil/mast cell chemokine receptor CCR3 is specifically expressed in CNV endothelial cells in humans with AMD, and that, despite the expression of its ligands eotaxin-1, -2, and -3, neither eosinophils nor mast cells are present in human CNV. Genetic or pharmacological targeting of CCR3 or eotaxins inhibited injury-induced CNV in mice. CNV suppression by CCR3 blockade was due to direct inhibition of endothelial cell proliferation, and was uncoupled from inflammation as it occurred in mice lacking eosinophils or mast cells and was independent of macrophage and neutrophil recruitment. CCR3 blockade was more effective at reducing CNV than vascular endothelial growth factor-A (VEGF-A) neutralization, which is currently in clinical use, and, unlike VEGF-A blockade, not toxic to the mouse retina. In vivo imaging with CCR3-targeting quantum dots located spontaneous CNV invisible to standard fluorescein angiography in mice before retinal invasion. CCR3 targeting might reduce vision loss due to AMD through early detection and therapeutic angioinhibition.

Biology of the eosinophil

In this review, we aim to put in perspective the biology of a multifunctional leukocyte, the eosinophil, by placing it in the context of innate and adaptive immune responses. Eosinophils have a unique contribution in initiating inflammatory and adaptive responses, due to their bidirectional interactions with dendritic cells and T cells, as well as their large panel of secreted cytokines and soluble mediators. The mechanisms and consequences of eosinophil responses in experimental inflammatory models and human diseases are discussed.

2007 E. Mead Johnson award: scientific pursuit of the allergy problem

My research has focused on elucidating the allergy problem over the past two decades. The primary approach has been to uncover critical mechanisms of allergic inflammation, with particular focus on eosinophils, a hallmark cellular constituent of allergic responses. Molecular processes that bridge T helper cell type 2 (TH2) immunity with eosinophilia and key checkpoints for regulating eosinophilia have been uncovered. Notably, interleukin (IL)-5 (derived from TH2 cells) has been identified as the chief hematopoietin responsible for eosinophil expansion in the circulation. Pathways for selective eosinophil mobilization from the blood stream to the tissue have been uncovered by defining the role of the eotaxin subfamily of chemokines in eosinophil chemoattraction and activation. Finally, TH2 cell derived IL-4 and IL-13 have been defined as chief inducers of the eotaxins, and upstream orchestrators of eosinophilic inflammation. These translational studies have formulated novel therapeutic strategies (currently being tested) for a variety of eosinophilic conditions, with particular attention on hypereosinophilic syndromes and eosinophil-associated gastrointestinal disorders such as eosinophilic esophagitis.

Eosinophilia during intestinal infection

Eosinophilia is a common finding in tropical developing countries, and is mainly caused by chronic helminth infections, predominantly of the gut. Although only a minority of infections is symptomatic, development during childhood can be impaired, and in some patients serious complications and sequelae may occur. Eosinophilia in helminth infection is typically associated with a strong Th2 immune response, and eosinophils can effectively kill or damage larvae and adult worms in vitro. However, in vivo, eosinophils are only partly effective in the control of helminth infection, and recent research has shown that eosinophils are involved in a range of immunomodulatory effects, such as increased production of the down-modulatory cytokines interleukin 10 and tumour growth factor beta, as well as stimulation of regulatory T cells and alternatively activated macrophages. Increasing evidence suggests that immunomodulation favours parasite survival and reduces immune pathology. On the other hand, immunomodulation induced by helminth infections may contribute to protection from allergic and autoimmune responses, as proposed by the 'hygiene hypothesis' to explain the increase in allergic diseases in the industrialised world. The predictive value of eosinophilia for the presence of helminth infections is limited and depends on the epidemiological background and the extent of the eosinophilia. It increases considerably in populations with a high prevalence of parasitic infections, as in developing tropical countries or in travellers to those areas.

Eosinophils: biological properties and role in health and disease

Eosinophils are pleiotropic multifunctional leukocytes involved in initiation and propagation of diverse inflammatory responses, as well as modulators of innate and adaptive immunity. In this review, the biology of eosinophils is summarized, focusing on transcriptional regulation of eosinophil differentiation, characterization of the growing properties of eosinophil granule proteins, surface proteins and pleiotropic mediators, and molecular mechanisms of eosinophil degranulation. New views on the role of eosinophils in homeostatic function are examined, including developmental biology and innate and adaptive immunity (as well as their interaction with mast cells and T cells) and their proposed role in disease processes including infections, asthma, and gastrointestinal disorders. Finally, strategies for targeted therapeutic intervention in eosinophil-mediated mucosal diseases are conceptualized.

Rho GTPases and regulation of hematopoietic stem cell localization

Bone marrow engraftment in the context of hematopoietic stem cell and progenitor (HSC/P) transplantation is based on the ability of intravenously administered cells to lodge in the medullary cavity and be retained in the appropriate marrow space, a process referred to as homing. It is likely that homing is a multistep process, encompassing a sequence of highly regulated events that mimic the migration of leukocytes to inflammatory sites. In leukocyte biology, this process includes an initial phase of tethering and rolling of cells to the endothelium via E- and P-selectins, firm adhesion to the vessel wall via integrins that appear to be activated in an "inside-out" fashion, transendothelial migration, and chemotaxis through the extracellular matrix (ECM) to the inflammatory nidus. For HSC/P, the cells appear to migrate to the endosteal space of the bone marrow. A second phase of engraftment involves the subsequent interaction of specific HSC/P surface receptors, such as alpha(4)beta(1) integrin receptors with vascular cell-cell adhesion molecule-1 and fibronectin in the ECM, and interactions with growth factors that are soluble, membrane, or matrix bound. We have utilized knockout and conditional knockout mouse lines generated by gene targeting to study the role of Rac1 and Rac2 in blood cell development and function. We have determined that Rac is activated via stimulation of CXCR4 by SDF-1, by adhesion via beta(1) integrins, and via stimulation of c-kit by the stem cell factor-all of which involved in stem cell engraftment. Thus Rac proteins are key molecular switches of HSC/P engraftment and marrow retention. We have defined Rac proteins as key regulators of HSC/P cell function and delineated key unique and overlapping functions of these two highly related GTPases in a variety of primary hematopoietic cell lineages in vitro and in vivo. Further, we have begun to define the mechanisms by which each GTPase leads to specific functions in these cells. These studies have led to important new understanding of stem cell bone marrow retention and trafficking in the peripheral circulation and to the development of a novel small molecule inhibitor that can modulate stem cell functions, including adhesion, mobilization, and proliferation. This chapter describes the biochemical footprint of stem cell engraftment and marrow retention related to Rho GTPases. In addition, it reviews abnormalities of Rho GTPases implicated in human immunohematopoietic diseases and in leukemia/lymphoma.

Inhibitory receptors on eosinophils: a direct hit to a possible Achilles heel?

Since their discovery, much data have been accumulated on eosinophil differentiation, morphology, trafficking, and anatomical location(s) in health and disease. Although "classic" activation pathways (such as cytokines, chemokines, proinflammatory components, and adhesion molecules) regulating eosinophil activation have been widely explored, the presence of other activation molecules that might be disease specific is limited. Furthermore, the expression and function of inhibitory receptors on eosinophils have received scant attention. The need to identify new pathways that regulate eosinophil activation is a crucial goal as it can expand our knowledge on this peculiar cell and provide insights into important queries regarding the physiologic function of eosinophils. Over the past several years, it has become increasingly apparent that eosinophils express several receptors belonging to the immunoglobulin superfamily. In this review, we summarize the current knowledge on the expression and function of new pathways that govern eosinophil activation. In addition, we will propose some hypotheses regarding the ability to use these pathways as a future therapeutic approach. In conclusion, we assume that targeting inhibitory receptors on eosinophils may provide opportunities for immunoregulatory therapy in the near future.

LTP consolidation: Substrates, explanatory power, and functional significance

Long-term potentiation (LTP) resembles memory in that it is initially unstable and then, over about 30 min, becomes increasingly resistant to disruption. Here we present an hypothesis to account for this initial consolidation effect and consider implications that follow from it. Anatomical studies indicate that LTP is accompanied by changes in spine morphology and therefore likely involves cytoskeletal changes. Accordingly, theta bursts initiate calpain-mediated proteolysis of the actin cross-linking protein spectrin and trigger actin polymerization in spine heads, two effects indicative of cytoskeletal reorganization. Polymerization occurs within 2 min, has the same threshold as LTP, is dependent on integrins, and becomes resistant to disruption over 30 min. We propose that the stabilization of the new cytoskeletal organization, and thus of a new spine morphology, underlies the initial phase of LTP consolidation. This hypothesis helps explain the diverse array of proteins and signaling cascades implicated in LTP, as well as the often-contradictory results about contributions of particular molecules. It also provides a novel explanation for why LTP is potently modulated by factors likely to be released during theta trains (e.g., BDNF). Finally, building on evidence that normal patterns of activity reverse LTP, we suggest that consolidation provides a delay that allows brain networks to sculpt newly formed memories.

The role of chemokine activation of Rac GTPases in hematopoietic stem cell marrow homing, retention, and peripheral mobilization

Signaling downstream from the chemokine receptor CXCR4, the tyrosine kinase receptor c-kit and beta1-integrins has been shown to be crucial in the regulation of migration, homing, and engraftment of hematopoietic stem cells and progenitors. Each of these receptors signal through Rac-type Rho guanosine triphosphatases (GTPases). Rac GTPases play a major role in the organization of the actin cytoskeleton and also in the control of gene expression and the activation of proliferation and survival pathways. Here we review the specific roles of the members of the Rac subfamily of the Rho GTPase family in regulating the intracellular signaling of hematopoietic cells responsible for regulation of homing, marrow retention, and peripheral mobilization.

The eosinophil

Eosinophils have been considered end-stage cells involved in host protection against parasites. However, numerous lines of evidence have now changed this perspective by showing that eosinophils are pleiotropic multifunctional leukocytes involved in initiation and propagation of diverse inflammatory responses, as well as modulators of innate and adaptive immunity. In this review, we summarize the biology of eosinophils, focusing on the growing properties of eosinophil-derived products, including the constituents of their granules as well as the mechanisms by which they release their pleiotropic mediators. We examine new views on the role of eosinophils in homeostatic function, including developmental biology and innate and adaptive immunity (as well as interaction with mast cells and T cells). The molecular steps involved in eosinophil development and trafficking are described, with special attention to the important role of the transcription factor GATA-1, the eosinophil-selective cytokine IL-5, and the eotaxin subfamily of chemokines. We also review the role of eosinophils in disease processes, including infections, asthma, and gastrointestinal disorders, and new data concerning genetically engineered eosinophil-deficient mice. Finally, strategies for targeted therapeutic intervention in eosinophil-mediated mucosal diseases are conceptualized.