Loss of CD34 leads to exacerbated autoimmune arthritis through increased vascular permeability

Mutant Mice and Animal Models of Airway Allergic Disease

Eosinophilia is a hallmark of allergic airway inflammation, and eosinophils represent an integral effector leukocyte through their release of various granule-stored cytokines and proteins. Numerous mouse models have been developed to mimic clinical disease and they have been instrumental in furthering our understanding of the role of eosinophils in disease. Most of these models consist of intranasal (i.n.) administration of antigenic proteases including papain and house dust mite (HDM) or the neo-antigen ovalbumin, with a resulting Th2-biased immune response and airway eosinophilia. These models have been particularly informative when combined with the numerous transgenic mice available that modulate eosinophil frequency or the mechanisms involved in their migration. Here, we describe the current models of allergic airway inflammation and outline some of the transgenic mice available to study eosinophil disease.

Marinoid J, a phenylglycoside from Avicennia marina fruit, ameliorates cognitive impairment in rat vascular dementia: a quantitative iTRAQ proteomic study

CONTEXT

Fruit of Avicennia marina (Forsk.) Vierh. (Acanthaceae) is used as a Chinese herb. Studies have found that it contains marinoid J, a novel phenylethanoid glycoside (PG) compound, but its neuroprotective functions are largely unknown.

OBJECTIVE

This study evaluated the effects of marinoid J on vascular dementia (VD) and determined its potential mechanisms of action.

MATERIALS AND METHODS

The VD model was established by the ligation of the bilateral common carotid artery in Sprague-Dawley rats, who received daily intragastrically administration of saline, marinoid J (125 or 500 mg/kg body weight/d), or oxiracetam (250 mg/kg body weight/d) for 14 days (20 rats in each group). The Morris water maze (MWM) was used to evaluate cognitive performance. The hippocampus was subjected to histological and proteomic analyses.

RESULTS

Marinoid J shortened the escape latency of VD rats (31.07 ± 3.74 s, p < 0.05). It also decreased malondialdehyde (MDA) (27.53%) and nitric oxide (NO) (20.41%) while increasing superoxide dismutase (SOD) (11.26%) and glutathione peroxidase (GSH-Px) (20.38%) content in hippocampus tissues. Proteomic analysis revealed 45 differentially expressed proteins (DEPs) in marinoid J-treated VD rats, which included angiotensin-converting enzyme (ACE), keratin 18 (KRT18), cluster of differentiation 34 (CD34), and synaptotagmin II (SYT2).

CONCLUSIONS

Marinoid J played a role in protecting hippocampal neurons by regulating a set of proteins that influence oxidative stress and apoptosis, this effect may thereby alleviate the symptoms of VD rats. Thus, pharmacological manipulation of marinoid J may offer a novel opportunity for VD treatment.

A sticky wicket: Defining molecular functions for CD34 in hematopoietic cells

The CD34 cell surface antigen is widely expressed in tissues on cells with progenitor-like properties and on mature vascular endothelia. In adult human bone marrow, CD34 marks hematopoietic stem and progenitor cells (HSPCs) starting from the bulk of hematopoietic stem cells with long-term repopulating potential (LT-HSCs) throughout expansion and differentiation of oligopotent and unipotent progenitors. CD34 protein surface expression is typically lost as cells mature into terminal effectors. Because of this expression pattern of HSPCs, CD34 has had a central role in the evaluation or selection of donor graft tissue in HSC transplant (HSCT). Given its clinical importance, it is surprising that the biological functions of CD34 are still poorly understood. This enigma is due, in part, to CD34's context-specific role as both a pro-adhesive and anti-adhesive molecule and its potential functional redundancy with other sialomucins. Moreover, there are also critical differences in the regulation of CD34 expression on HSPCs in humans and experimental mice. In this review, we highlight some of the more well-defined functions of CD34 in HSPCs with a focus on proposed functions most relevant to HSCT biology.

CD34 regulates the skeletal muscle response to hypoxia

Chronic obstructive pulmonary disease (COPD) can sometimes be associated with skeletal muscle atrophy. Hypoxemic episodes, which occur during disease exacerbation and daily physical activity, are frequent in COPD patients. However, the link between hypoxemia and muscle atrophy remains unclear, along with mechanisms of muscle hypoxic stress response. Myogenic progenitors (MPs) and fibro/adipogenic progenitors (FAPs) express CD34 and participate to muscle mass maintenance. Although there is evidence linking CD34 expression and muscle repair, the link between CD34 expression, muscle wasting and the hypoxic stress observed in COPD has never been studied. Using a 2-day model of exposure to hypoxic conditions, we investigated the impact of hypoxia on skeletal muscle wasting and function, and elucidated the importance of CD34 expression in that response. A 2-day exposure to hypoxic conditions induces muscle atrophy, which was significantly worse in Cd34^-/- mice compared to wild type (WT). Moreover, the lack of CD34 expression negatively impacts the maximal strength of the extensor digitorum longus muscle in response to hypoxia. Following exposure to hypoxic conditions, FAPs (which support MPs differentiation and myogenesis) are significantly lower in Cd34^-/- mice compared to WT animals while the expression of myogenic regulatory factors and degradation factors (Atrogin) are similar. CD34 expression is important in the maintenance of muscle mass and function in response to hypoxic stress. These results highlight a new potential role for CD34 in muscle mass maintenance in hypoxic stress such as observed in COPD.

MiR-665 aggravates heart failure via suppressing CD34-mediated coronary microvessel angiogenesis

BACKGROUND

Heart failure (HF) is a major public health problem worldwide. The development of HF was related to coronary microvessel dysfunction. Whether miRNAs participate in HF by regulating coronary microvessel function remain unclear.

METHODS

The potential targets of miR-665 were predicted by rnahybrid software, then verified through anti-Ago2 co-immunoprecipitation, Western blotting and luciferase reporter assays. rAAV9 system was used to manipulate the expression of miR-665 in vivo.

RESULTS

Significant increase of miR-665 was observed in endothelial cells of human heart with heart failure. In vitro over-expression of miR-665 in endothelial cells resulted in decreased proliferation but enhanced apoptosis. rAAV-mediated delivery of miR-665 reduced coronary microvessel angiogenesis and cardiac microvessel density, then further impaired cardiac function in vivo. Furthermore, CD34 was confirmed as one of the miR-665 targets. Consistently, re-expression of CD34 attenuated miR-665-mediated damage effects in vitro and in vivo. We also found that Sp1 regulated miR-665 expression in endothelial cells.

CONCLUSION

Our findings demonstrated that miR-665 played an important role in heart failure via damaging coronary microvessel angiogenesis, and suggested that miRNA-based therapeutics may protect against coronary microvessel dysfunction and heart failure.

CD34 Differentially Regulates Contractile and Noncontractile Elements of Airway Reactivity

Airway hyperresponsiveness (AHR), a major hallmark of asthma, results from alterations of contractile and noncontractile elements of airway reactivity. CD34 is a sialomucin that is expressed on various cells involved in asthma, such as eosinophils and airway smooth muscle precursors, highlighting its potential influence in AHR. To study the role of CD34 in regulating the contractile and noncontractile elements of AHR, AHR was induced by chronic exposure to house dust mite (HDM) antigen. To assess the role of CD34 on the contractile elements of AHR, airway reactivity and airway smooth muscle contractility in response to methacholine were measured. To assess CD34's role in regulating the noncontractile elements of AHR, a chimeric mouse model was used to determine the impact of CD34 expression on inflammatory versus microenvironmental cells in AHR development. Extracellular matrix production, mucus production, and mast cell degranulation were also measured. Whereas wild-type mice developed AHR in response to HDM, a loss of airway reactivity was observed in Cd34^-/- mice 24 hours after the last exposure to HDM compared with naive controls. This was reversed when airway reactivity was measured 1 week after the last HDM exposure. Additionally, mast cell degranulation and mucus production were altered in the absence of CD34 expression. Importantly, simultaneous expression of CD34 on cells originating from the hematopoietic compartment and the microenvironment was needed for expression of this phenotype. These results provide evidence that CD34 is required for AHR and airway reactivity maintenance in the early days after an inflammatory episode in asthma.

Loss of Vascular CD34 Results in Increased Sensitivity to Lung Injury

Survival during lung injury requires a coordinated program of damage limitation and rapid repair. CD34 is a cell surface sialomucin expressed by epithelial, vascular, and stromal cells that promotes cell adhesion, coordinates inflammatory cell recruitment, and drives angiogenesis. To test whether CD34 also orchestrates pulmonary damage and repair, we induced acute lung injury in wild-type (WT) and Cd34^-/- mice by bleomycin administration. We found that Cd34^-/- mice displayed severe weight loss and early mortality compared with WT controls. Despite equivalent early airway inflammation to WT mice, CD34-deficient animals developed interstitial edema and endothelial delamination, suggesting impaired endothelial function. Chimeric Cd34^-/- mice reconstituted with WT hematopoietic cells exhibited early mortality compared with WT mice reconstituted with Cd34^-/- cells, supporting an endothelial defect. CD34-deficient mice were also more sensitive to lung damage caused by influenza infection, showing greater weight loss and more extensive pulmonary remodeling. Together, our data suggest that CD34 plays an essential role in maintaining vascular integrity in the lung in response to chemical- and infection-induced tissue damage.

De novo protein sequencing, humanization and in vitro effects of an antihuman CD34 mouse monoclonal antibody

QBEND/10 is a mouse immunoglobulin lambda-chain monoclonal antibody with strict specificity against human hematopoietic progenitor cell antigen CD34. Our in vitro study showed that QBEND/10 impairs the tube formation of human umbilical vein endothelial cells (HUVECs), suggesting that the antibody may be of potential benefit in blocking tumor angiogenesis. We provided a de novo protein sequencing method through tandem mass spectrometry to identify the amino acid sequences in the variable heavy and light chains of QBEND/10. To reduce immunogenicity for clinical applications, QBEND/10 was further humanized using the resurfacing approach. We demonstrate that the de novo sequenced and humanized QBEND/10 retains the biological functions of the parental mouse counterpart, including the binding kinetics to CD34 and blockage of the tube formation of the HUVECs.

CD34 Promotes Pathological Epi-Retinal Neovascularization in a Mouse Model of Oxygen-Induced Retinopathy

The sialomucins CD34 and podocalyxin (PODXL) are anti-adhesive molecules expressed at the luminal membrane of endothelial cells of small blood vessels and facilitate vascular lumen formation in the developing mouse aorta. CD34 transcript and protein levels are increased during human angiogenesis, its expression is particularly enriched on endothelial tip cell filopodia and CD34 is a marker for tip cells in vitro. Here, we investigated whether CD34 merely marks endothelial tip cells or has a functional role in tip cells and angiogenesis. We assessed that silencing CD34 in human microvascular endothelial cells has little effect on endothelial cell migration or invasion, but has a significant effect on vascular-endothelial growth factor-induced angiogenic sprouting activity in vitro. In vivo, the absence of CD34 reduced the density of filopodia on retinal endothelial tip cells in neonatal mice, but did not influence the overall architecture of the retinal vascular network. In oxygen-induced retinopathy, Cd34^-/- mice showed normal intra-retinal regenerative angiogenesis but the number of pathological epi-retinal neovascular tufts were reduced. We conclude that CD34 is not essential for developmental vascularization in the retina, but its expression promotes the formation of pathological, invasive vessels during neovascularization.

DMSO Represses Inflammatory Cytokine Production from Human Blood Cells and Reduces Autoimmune Arthritis

Dimethyl sulfoxide (DMSO) is currently used as an alternative treatment for various inflammatory conditions as well as for cancer. Despite its widespread use, there is a paucity of data regarding its safety and efficacy as well as its mechanism of action in human cells. Herein, we demonstrate that DMSO has ex-vivo anti-inflammatory activity using Escherichia coli- (E. coli) and herpes simplex virus-1 (HSV-1)-stimulated whole human blood. Specifically, we found that between 0.5%-2%, DMSO significantly suppressed the expression of many pro-inflammatory cytokines/chemokines and prostaglandin E2 (PGE2). However, a significant reduction in monocyte viability was also observed at 2% DMSO, suggesting a narrow window of efficacy. Anti-inflammatory concentrations of DMSO suppressed E. coli-induced ERK1/2, p38, JNK and Akt phosphorylation, suggesting DMSO acts on these signaling pathways to suppress inflammatory cytokine/chemokine production. Although DMSO induces the differentiation of B16/F10 melanoma cells in vitro, topical administration of DMSO to mice subcutaneously implanted with B16 melanoma cells was ineffective at reducing tumor growth, DMSO was also found to block mouse macrophages from polarizing to either an M1- or an M2-phenotype, which may contribute to its inability to slow tumor growth. Topical administration of DMSO, however, significantly mitigated K/BxN serum-induced arthritis in mice, and this was associated with reduced levels of pro-inflammatory cytokines in the joints and white blood cell levels in the blood. Thus, while we cannot confirm the efficacy of DMSO as an anti-cancer agent, the use of DMSO in arthritis warrants further investigation to ascertain its therapeutic potential.

Histamine H3 and H4 receptor ligands modify vascular histamine levels in normal and arthritic large blood vessels in vivo

Growing evidence associates histamine with arthritis, but its implication in shaping vascular function in chronic inflammation remains largely elusive. This study explored the involvement of vascular histamine in the extra-articular responses in peripheral large blood vessels using a rat model of adjuvant-induced arthritis. Histamine levels were increased in the abdominal aorta and the inferior vena cava of arthritic animals. Contrary to the H1 receptor antagonist dimetindene, histamine induction was observed following administration of the H3 and H4 receptor ligands GSK334429 and JNJ7777120, respectively. In arthritis, prophylactic treatment with GSK334429 partially attenuated the clinical signs and restored basal histamine levels only in the abdominal aorta. This study is the first to implicate the H3 and H4 receptors in a concerted constitutive regulation of basal vascular histamine in the rat large blood vessels and to identify the H3 receptor as a component that may influence arterial histamine during the onset of arthritis.

Targeting mechanisms at sites of complement activation for imaging and therapy

The complement system plays a key role in many acute injury states as well as chronic autoimmune and inflammatory diseases. Localized complement activation and alternative pathway-mediated amplification on diverse target surfaces promote local recruitment of pro-inflammatory cells and elaboration of other mediators. Despite a general understanding of the architecture of the system, though, many of the mechanisms that underlie site-specific complement activation and amplification in vivo are incompletely understood. In addition, there is no capability yet to measure the level of local tissue site-specific complement activation in patients without performing biopsies to detect products using immunohistochemical techniques. Herein is reviewed emerging evidence obtained through clinical research studies of human rheumatoid arthritis along with translational studies of its disease models which demonstrate that several parallel mechanisms are involved in site-specific amplification of activation of the complement system in vivo. Among these processes are de-regulation of the alternative pathway, effector pathway-catalyzed amplification of proximal complement activation, recognition of injury-associated ligands by components of the lectin pathway, and engagement of pathogenic natural antibodies that recognize a limited set of injury-associated neoepitopes. Studies suggest that each of these inter-related processes can play key roles in amplification of complement-dependent injury on self-tissues in vivo. These findings, in addition to development of an imaging strategy described herein designed to quantitatively measure local complement C3 fixation, have relevance to therapeutic and diagnostic strategies targeting the complement system.

Overexpression of ADAMTS-7 leads to accelerated initiation and progression of collagen-induced arthritis in mice

The aim of the present study is to determine whether ADAMTS-7 contributes to the onset and severity of joint inflammation in the pathogenesis of inflammatory arthritis. ADAMTS-7 was found to be elevated in the course of collagen-induced arthritis (CIA). ADAMTS-7 transgenic (TG) mice were more susceptible to the induction of CIA. The onset of CIA was accelerated and the arthritic severity was increased in TG mice compared to wild-type mice. The overall incidence was also significantly higher in TG mice. In addition, arthritic TG mice displayed significantly higher clinical and histological arthritis scores. The COMP degradative fragments were significantly elevated in articular cartilage and sera in CIA models of TG mice. Furthermore, the production of tumor necrosis factor-alpha and interleukin-17 was also increased in serum and draining lymph nodes of arthritic TG mice. Therefore, these data provided the in vivo evidence, suggesting that ADAMTS-7 may play an important role in the pathogenesis of inflammatory arthritis, and that inhibition of ADAMTS-7 may be a potential target to ameliorate the severity of inflammatory arthritis.

Podocalyxin regulates murine lung vascular permeability by altering endothelial cell adhesion

Despite the widespread use of CD34-family sialomucins (CD34, podocalyxin and endoglycan) as vascular endothelial cell markers, there is remarkably little known of their vascular function. Podocalyxin (gene name Podxl), in particular, has been difficult to study in adult vasculature as germ-line deletion of podocalyxin in mice leads to kidney malformations and perinatal death. We generated mice that conditionally delete podocalyxin in vascular endothelial cells (Podxl(ΔEC) mice) to study the homeostatic role of podocalyxin in adult mouse vessels. Although Podxl(ΔEC) adult mice are viable, their lungs display increased lung volume and changes to the matrix composition. Intriguingly, this was associated with increased basal and inflammation-induced pulmonary vascular permeability. To further investigate the etiology of these defects, we isolated mouse pulmonary endothelial cells. Podxl(ΔEC) endothelial cells display mildly enhanced static adhesion to fibronectin but spread normally when plated on fibronectin-coated transwells. In contrast, Podxl(ΔEC) endothelial cells exhibit a severely impaired ability to spread on laminin and, to a lesser extent, collagen I coated transwells. The data suggest that, in endothelial cells, podocalyxin plays a previously unrecognized role in maintaining vascular integrity, likely through orchestrating interactions with extracellular matrix components and basement membranes, and that this influences downstream epithelial architecture.

SAP domain-dependent Mkl1 signaling stimulates proliferation and cell migration by induction of a distinct gene set indicative of poor prognosis in breast cancer patients

Background

The main cause of death of breast cancer patients is not the primary tumor itself but the metastatic disease. Identifying breast cancer-specific signatures for metastasis and learning more about the nature of the genes involved in the metastatic process would 1) improve our understanding of the mechanisms of cancer progression and 2) reveal new therapeutic targets. Previous studies showed that the transcriptional regulator megakaryoblastic leukemia-1 (Mkl1) induces tenascin-C expression in normal and transformed mammary epithelial cells. Tenascin-C is known to be expressed in metastatic niches, is highly induced in cancer stroma and promotes breast cancer metastasis to the lung.

Methods

Using HC11 mammary epithelial cells overexpressing different Mkl1 constructs, we devised a subtractive transcript profiling screen to identify the mechanism by which Mkl1 induces a gene set co-regulated with tenascin-C. We performed computational analysis of the Mkl1 target genes and used cell biological experiments to confirm the effect of these gene products on cell behavior. To analyze whether this gene set is prognostic of accelerated cancer progression in human patients, we used the bioinformatics tool GOBO that allowed us to investigate a large breast tumor data set linked to patient data.

Results

We discovered a breast cancer-specific set of genes including tenascin-C, which is regulated by Mkl1 in a SAP domain-dependent, serum response factor-independent manner and is strongly implicated in cell proliferation, cell motility and cancer. Downregulation of this set of transcripts by overexpression of Mkl1 lacking the SAP domain inhibited cell growth and cell migration. Many of these genes are direct Mkl1 targets since their promoter-reporter constructs were induced by Mkl1 in a SAP domain-dependent manner. Transcripts, most strongly reduced in the absence of the SAP domain were mechanoresponsive. Finally, expression of this gene set is associated with high-proliferative poor-outcome classes in human breast cancer and a strongly reduced survival rate for patients independent of tumor grade.

Conclusions

This study highlights a crucial role for the transcriptional regulator Mkl1 and its SAP domain during breast cancer progression. We identified a novel gene set that correlates with bad prognosis and thus may help in deciding the rigor of therapy.

Mutant mice and animal models of airway allergic disease

Eosinophilia is a hallmark of allergic airway inflammation, and eosinophils represent an integral effector leukocyte through their release of various granule-stored cytokines and proteins. Numerous mouse models have been developed to mimic clinical disease and they have been instrumental in furthering our understanding of the role of eosinophils in disease. Most of these models consist of intranasal (i.n.) administration of antigenic proteases including papain and house dust mite (HDM) or the neo-antigen ovalbumin, with a resulting Th2-biased immune response and airway eosinophilia. These models have been particularly informative when combined with the numerous transgenic mice available that modulate eosinophil frequency or the mechanisms involved in their migration. Here, we describe the current models or allergic airway inflammation and outline some of the transgenic mice available to study eosinophils in disease.

Requirement for core 2 O-glycans for optimal resistance to helminth infection

The migration of lymphocytes to the small intestine is controlled by expression of the integrin α4β7 and the chemokine receptor CCR9. However, the molecules that specifically regulate migration to the large intestine remain unclear. Immunity to infection with the large intestinal helminth parasite Trichuris muris is dependent upon CD4⁺ T cells that migrate to the large intestine. We examine the role of specific chemokine receptors, adhesion molecules and glycosyltransferases in the development of protective immunity to Trichuris. Mice deficient in expression of the chemokine receptors CCR2 or CCR6 were resistant to infection with Trichuris. Similarly, loss of CD34, CD43, CD44 or PSGL-1 had no effect on resistance to infection. In contrast, simultaneous deletion of the Core2 β1,6-N-acetylglucosaminyltransferase (C2GnT) enzymes C2GnT1 and C2Gnt2 resulted in delayed expulsion of worms. These results suggest that C2GnT-dependent modifications may play a role in migration of protective immune cells to the large intestine.

An in vivo assay to test blood vessel permeability

This method is based on the intravenous injection of Evans Blue in mice as the test animal model. Evans blue is a dye that binds albumin. Under physiologic conditions the endothelium is impermeable to albumin, so Evans blue bound albumin remains restricted within blood vessels. In pathologic conditions that promote increased vascular permeability endothelial cells partially lose their close contacts and the endothelium becomes permeable to small proteins such as albumin. This condition allows for extravasation of Evans Blue in tissues. A healthy endothelium prevents extravasation of the dye in the neighboring vascularized tissues. Organs with increased permeability will show significantly increased blue coloration compared to organs with intact endothelium. The level of vascular permeability can be assessed by simple visualization or by quantitative measurement of the dye incorporated per milligram of tissue of control versus experimental animal/tissue. Two powerful aspects of this assay are its simplicity and quantitative characteristics. Evans Blue dye can be extracted from tissues by incubating a specific amount of tissue in formamide. Evans Blue absorbance maximum is at 620 nm and absorbance minimum is at 740 nm. By using a standard curve for Evans Blue, optical density measurements can be converted into milligram dye captured per milligram of tissue. Statistical analysis should be used to assess significant differences in vascular permeability.

Mouse models to evaluate the function of genes associated with allergic airway disease

PURPOSE OF REVIEW

In recent years, considerable effort has been invested in developing mouse models of allergic airway disease, as a means of evaluating the role of select genes in its pathophysiology. Here, we review the principal models used in this field, including models of allergic asthma and hypersensitivity pneumonitis. As an example of how these models can reveal novel functional roles for genes, we review our work showing a role for the stem-cell-associated gene, Cd34. Through this example, we illustrate the genetic and immunological strategies available in the field to better understand allergic airway inflammation.

RECENT FINDINGS

CD34 was found to play an important role in the development of two different models of allergic disease, that is, Th2-driven allergic asthma and Th17-driven hypersensitivity pneumonitis. Using a combination of genetically modified mice as well as cell transfers and chimeric mice, we showed that CD34 is important for the efficient trafficking of hematopoietic subsets into and out of the lung, including mast cells, eosinophils and dendritic cells.

SUMMARY

The currently available array of mutant mice and animal models of allergic disease now offers an opportunity to make profound insights into these diseases and provide preclinical models for the development of therapeutics.

Mast cell activation and neutrophil recruitment promotes early and robust inflammation in the meninges in EAE

The meninges are often considered inert tissues that house the CSF and provide protection for the brain and spinal cord. Yet emerging data demonstrates that they are also active sites of immune responses. Furthermore, the blood-CSF barrier surrounding meningeal blood vessels, together with the blood-brain barrier (BBB), is postulated to serve as a gateway for the pathological infiltration of immune cells into the CNS in multiple sclerosis (MS). Our previous studies using mast cell-deficient (Kit(W/Wv)) mice demonstrated that mast cells resident in the dura mater and pia mater exacerbate experimental autoimmune encephalomyelitis (EAE), a rodent model of MS, by facilitating CNS inflammatory cell influx. Here we examined the underlying mechanisms that mediate these effects. We demonstrate that there are dramatic alterations in immune associated gene expression in the meninges in pre-clinical disease, including those associated with mast cell and neutrophil function. Meningeal mast cells are activated within 24 h of disease induction, but do not directly compromise CNS vascular integrity. Rather, through production of TNF, mast cells elicit an early influx of neutrophils, cells known to alter vascular permeability, into the meninges. These data add to the growing evidence that inflammation in the meninges precedes CNS immune cell infiltration and establish that mast cells are among the earliest participants in these disease-initiating events. We hypothesize that mast cell-dependent neutrophil recruitment and activation in the meninges promotes early breakdown of the local BBB and CSF-blood barrier allowing initial immune cell access to the CNS.

IL-7Rα and L-selectin, but not CD103 or CD34, are required for murine peanut-induced anaphylaxis

Background

Allergy to peanuts results in severe anaphylactic responses in affected individuals, and has dramatic effects on society and public policy. Despite the health impacts of peanut-induced anaphylaxis (PIA), relatively little is known about immune mechanisms underlying the disease. Using a mouse model of PIA, we evaluated mice with deletions in four distinct immune molecules (IL7Rα, L-selectin, CD34, CD103), for perturbed responses.

Methods

PIA was induced by intragastric sensitization with peanut antigen and cholera toxin adjuvant, followed by intraperitoneal challenge with crude peanut extract (CPE). Disease outcome was assessed by monitoring body temperature, clinical symptoms, and serum histamine levels. Resistant mice were evaluated for total and antigen specific serum IgE, as well as susceptibility to passive systemic anaphylaxis.

Results

PIA responses were dramatically reduced in IL7Rα^−/− and L-selectin^−/− mice, despite normal peanut-specific IgE production and susceptibility to passive systemic anaphylaxis. In contrast, CD34^−/− and CD103^−/− mice exhibited robust PIA responses, indistinguishable from wild type controls.

Conclusions

Loss of L-selectin or IL7Rα function is sufficient to impair PIA, while CD34 or CD103 ablation has no effect on disease severity. More broadly, our findings suggest that future food allergy interventions should focus on disrupting sensitization to food allergens and limiting antigen-specific late-phase responses. Conversely, therapies targeting immune cell migration following antigen challenge are unlikely to have significant benefits, particularly considering the rapid kinetics of PIA.

CD34 promotes satellite cell motility and entry into proliferation to facilitate efficient skeletal muscle regeneration

Expression of the cell surface sialomucin CD34 is common to many adult stem cell types, including muscle satellite cells. However, no clear stem cell or regeneration-related phenotype has ever been reported in mice lacking CD34, and its function on these cells remains poorly understood. Here, we assess the functional role of CD34 on satellite cell-mediated muscle regeneration. We show that Cd34(-/-) mice, which have no obvious developmental phenotype, display a defect in muscle regeneration when challenged with either acute or chronic muscle injury. This regenerative defect is caused by impaired entry into proliferation and delayed myogenic progression. Consistent with the reported antiadhesive function of CD34, knockout satellite cells also show decreased motility along their host myofiber. Altogether, our results identify a role for CD34 in the poorly understood early steps of satellite cell activation and provide the first evidence that beyond being a stem cell marker, CD34 may play an important function in modulating stem cell activity.

CD34 is required for dendritic cell trafficking and pathology in murine hypersensitivity pneumonitis

RATIONALE

Although recent work has shown that CD34 plays an important role in the trafficking of inflammatory cells during Th2-biased inflammatory responses, its role in Th1/Th17-biased disease as well as dendritic cell (DC) trafficking is unknown.

OBJECTIVES

We used CD34-deficient mice (Cd34(-/-)) to investigate the role of CD34 in the Th1/Th17-biased lung inflammatory disease, hypersensitivity pneumonitis (HP).

METHODS

HP was induced in wild-type (wt) and Cd34(-/-) mice by repeated intranasal administration of Saccharopolyspora rectivirgula antigen. Lung inflammation was assessed by histology and analysis of bronchoalveolar lavage cells. Primary and secondary immune responses were evaluated by cytokine recall responses of pulmonary inflammatory cells as well as draining lymph node cells.

MEASUREMENTS AND MAIN RESULTS

Cd34(-/-) mice were highly resistant to the development of HP and exhibited an inflammatory pattern more reflective of a primary response to S. rectivirgula rather than the chronic lymphocytosis that is typical of this disease. Cytokine recall responses from Cd34(-/-) lymph node cells were dampened and consistent with a failure of antigen-loaded Cd34(-/-) DCs to deliver antigen and prime T cells in the draining lymph nodes. In agreement with this interpretation, adoptive transfer of wt DCs into Cd34(-/-) mice was sufficient to restore normal sensitivity to HP. CD34 was found to be expressed by wt DCs, and Cd34(-/-) DCs exhibited an impaired ability to chemotax toward a subset of chemokines in vitro. Finally, expression of human CD34 in Cd34(-/-) mice restored normal susceptibility to HP.

CONCLUSIONS

We conclude that CD34 is expressed by mucosal DCs and plays an important role in their trafficking through the lung and to the lymph nodes. Our data also suggest that CD34 may play a selective role in the efficient migration of these cells to a subset of chemokines.

Opposing roles for CD34 in B16 melanoma tumor growth alter early stage vasculature and late stage immune cell infiltration

Tumor growth and metastasis are determined by the complex interplay of factors, including those intrinsic to tumor cells and extrinsic factors associated with the tumor microenvironment. Our previous work demonstrated key roles for CD34 in the maintenance of vascular integrity and eosinophil and mast cell homing. Since both of these functions affect tumor development, we characterized the effect of CD34 ablation on tumor growth using the B16F1 melanoma model. Intriguingly, we found that CD34 plays a biphasic role in tumor progression. In early growth, both subcutaneous-injected tumors and intravenous-injected lung metastases grew more slowly in Cd34^−/− mice. This correlated with abnormal vessel morphology and increased vascular permeability in these mice. Bone marrow transplantation experiments confirmed that this reflects a non-hematopoietic function of CD34. At later stages, subcutaneous tumor growth was accelerated in Cd34^−/− mice and surpassed growth in wildtype mice. Bone marrow chimera experiments demonstrated this difference was due to a hematopoietic function for CD34 and, correspondingly we found reduced intra-tumor mast cell numbers in Cd34^−/− mice. In aggregate, our analysis reveals a novel role for CD34 in both early and late tumor growth and provides novel insights into the role of the tumor microenvironment in tumor progression.