Development and Function of Arterial and Cardiac Macrophages

Macrophages inhabit all major organs, and are capable of adapting their functions to meet the needs of their home tissues. The recent recognition that tissue macrophages derive from different sources, coupled with the notion that environmental cues and inflammatory stimuli can sculpt and agitate homeostasis, provides a frame of reference from which we can decipher the breadth and depth of macrophage activity. Here we discuss macrophages residing in the cardiovascular system, focusing particularly on their development and function in steady state and disease. Central to our discussion is the tension between macrophage ontogeny as a determinant of macrophage function, and the idea that tissues condition macrophage activities and supplant the influence of macrophage origins in favor of environmental demands.

c-Myb Regulates Proliferation and Differentiation of Adventitial Sca1+ Vascular Smooth Muscle Cell Progenitors by Transactivation of Myocardin

OBJECTIVE

Vascular smooth muscle cells (VSMCs) are believed to dedifferentiate and proliferate in response to vessel injury. Recently, adventitial progenitor cells were implicated as a source of VSMCs involved in vessel remodeling. c-Myb is a transcription factor known to regulate VSMC proliferation in vivo and differentiation of VSMCs from mouse embryonic stem cell-derived progenitors in vitro. However, the role of c-Myb in regulating specific adult vascular progenitor cell populations was not known. Our objective was to examine the role of c-Myb in the proliferation and differentiation of Sca1(+) adventitial VSMC progenitor cells.

APPROACH AND RESULTS

Using mice with wild-type or hypomorphic c-myb (c-myb(h/h)), BrdU (bromodeoxyuridine) uptake and flow cytometry revealed defective proliferation of Sca1(+) adventitial VSMC progenitor cells at 8, 14, and 28 days post carotid artery denudation injury in c-myb(h/h) arteries. c-myb(h/h) cKit(+)CD34(-)Flk1(-)Sca1(+)CD45(-)Lin(-) cells failed to proliferate, suggesting that c-myb regulates the activation of specific Sca1(+) progenitor cells in vivo and in vitro. Although expression levels of transforming growth factor-β1 did not vary between wild-type and c-myb(h/h) carotid arteries, in vitro differentiation of c-myb(h/h) Sca1(+) cells manifested defective transforming growth factor-β1-induced VSMC differentiation. This is mediated by reduced transcriptional activation of myocardin because chromatin immunoprecipitation revealed c-Myb binding to the myocardin promoter only during differentiation of Sca1(+) cells, myocardin promoter mutagenesis identified 2 specific c-Myb-responsive binding sites, and adenovirus-mediated expression of myocardin rescued the phenotype of c-myb(h/h) progenitors.

CONCLUSIONS

These data support a role for c-Myb in the regulation of VSMC progenitor cells and provide novel insight into how c-myb regulates VSMC differentiation through myocardin.

Macrophages and Dendritic Cells

Atherosclerosis is a complex chronic disease. The accumulation of myeloid cells in the arterial intima, including macrophages and dendritic cells (DCs), is a feature of early stages of disease. For decades, it has been known that monocyte recruitment to the intima contributes to the burden of lesion macrophages. Yet, this paradigm may require reevaluation in light of recent advances in understanding of tissue macrophage ontogeny, their capacity for self-renewal, as well as observations that macrophages proliferate throughout atherogenesis and that self-renewal is critical for maintenance of macrophages in advanced lesions. The rate of atherosclerotic lesion formation is profoundly influenced by innate and adaptive immunity, which can be regulated locally within atherosclerotic lesions, as well as in secondary lymphoid organs, the bone marrow and the blood. DCs are important modulators of immunity. Advances in the past decade have cemented our understanding of DC subsets, functions, hematopoietic origin, gene expression patterns, transcription factors critical for differentiation, and provided new tools for study of DC biology. The functions of macrophages and DCs overlap to some extent, thus it is important to reassess the contributions of each of these myeloid cells taking into account strict criteria of cell identification, ontogeny, and determine whether their key roles are within atherosclerotic lesions or secondary lymphoid organs. This review will highlight key aspect of macrophage and DC biology, summarize how these cells participate in different stages of atherogenesis and comment on complexities, controversies, and gaps in knowledge in the field.

Atheroprotection through SYK inhibition fails in established disease when local macrophage proliferation dominates lesion progression

Macrophages in the arterial intima sustain chronic inflammation during atherogenesis. Under hypercholesterolemic conditions murine Ly6C^high monocytes surge in the blood and spleen, infiltrate nascent atherosclerotic plaques, and differentiate into macrophages that proliferate locally as disease progresses. Spleen tyrosine kinase (SYK) may participate in downstream signaling of various receptors that mediate these processes. We tested the effect of the SYK inhibitor fostamatinib on hypercholesterolemia-associated myelopoiesis and plaque formation in Apoe^−/− mice during early and established atherosclerosis. Mice consuming a high cholesterol diet supplemented with fostamatinib for 8 weeks developed less atherosclerosis. Histologic and flow cytometric analysis of aortic tissue showed that fostamatinib reduced the content of Ly6C^high monocytes and macrophages. SYK inhibition limited Ly6C^high monocytosis through interference with GM-CSF/IL-3 stimulated myelopoiesis, attenuated cell adhesion to the intimal surface, and blocked M-CSF stimulated monocyte to macrophage differentiation. In Apoe^−/− mice with established atherosclerosis, however, fostamatinib treatment did not limit macrophage accumulation or lesion progression despite a significant reduction in blood monocyte counts, as lesional macrophages continued to proliferate. Thus, inhibition of hypercholesterolemia-associated monocytosis, monocyte infiltration, and differentiation by SYK antagonism attenuates early atherogenesis but not established disease when local macrophage proliferation dominates lesion progression.

Interleukin-3 amplifies acute inflammation and is a potential therapeutic target in sepsis

Sepsis is a frequently fatal condition characterized by an uncontrolled and harmful host reaction to microbial infection. Despite the prevalence and severity of sepsis, we lack a fundamental grasp of its pathophysiology. Here we report that the cytokine interleukin-3 (IL-3) potentiates inflammation in sepsis. Using a mouse model of abdominal sepsis, we showed that innate response activator B cells produce IL-3, which induces myelopoiesis of Ly-6C(high) monocytes and neutrophils and fuels a cytokine storm. IL-3 deficiency protects mice against sepsis. In humans with sepsis, high plasma IL-3 levels are associated with high mortality even after adjusting for prognostic indicators. This study deepens our understanding of immune activation, identifies IL-3 as an orchestrator of emergency myelopoiesis, and reveals a new therapeutic target for treating sepsis.

Monocyte fate in atherosclerosis

Monocytes and their descendant macrophages are essential to the development and exacerbation of atherosclerosis, a lipid-driven inflammatory disease. Lipid-laden macrophages, known as foam cells, reside in early lesions and advanced atheromata. Our understanding of how monocytes accumulate in the growing lesion, differentiate, ingest lipids, and contribute to disease has advanced substantially over the last several years. These cells' remarkable phenotypic and functional complexity is a therapeutic opportunity: in the future, treatment and prevention of cardiovascular disease and its complications may involve specific targeting of atherogenic monocytes/macrophages and their products.

Pleural innate response activator B cells protect against pneumonia via a GM-CSF-IgM axis

In response to lung infection, pleural innate response activator B cells produce GM-CSF–dependent IgM and ensure a frontline defense against bacterial invasion.

Pneumonia is a major cause of mortality worldwide and a serious problem in critical care medicine, but the immunophysiological processes that confer either protection or morbidity are not completely understood. We show that in response to lung infection, B1a B cells migrate from the pleural space to the lung parenchyma to secrete polyreactive emergency immunoglobulin M (IgM). The process requires innate response activator (IRA) B cells, a transitional B1a-derived inflammatory subset which controls IgM production via autocrine granulocyte/macrophage colony-stimulating factor (GM-CSF) signaling. The strategic location of these cells, coupled with the capacity to produce GM-CSF–dependent IgM, ensures effective early frontline defense against bacteria invading the lungs. The study describes a previously unrecognized GM-CSF-IgM axis and positions IRA B cells as orchestrators of protective IgM immunity.

Abstract 478: Single-Cell Isolation and Analysis of Viable Proliferating Macrophages From Atherosclerotic Plaques

INTRODUCTION: We have recently shown that the proliferation of macrophages within the atherosclerotic plaque, rather than the recruitment of new monocytes from the blood is the key driver of plaque growth in established atherosclerosis. The study of proliferating macrophages has been hampered by the lack of a technique for identifying proliferating macrophages and isolating them from the atherosclerotic plaque in a viable state.

OBJECTIVE: Develop and validate a process for identifying proliferating macrophages in atherosclerotic lesions, and isolating them as single, viable cells, then perform a molecular characterization of these cells.

METHODS: ApoE-/- and LDLR-/- mice were fed a diet high in fat and cholesterol. Atherosclerotic aortas were collected, and cells were isolated by mechanical and enzymatic dissociation. Cells were stained using fluorescent markers and DNA-binding dyes, then analyzed and isolated by fluorescence-activated cell sorting.

RESULTS: Mincing and enzymatic digestion in collagenase I, collagenase XI, DNAse, and hyaluronidase optimally isolates macrophages from aortic explants. Cell-surface staining with fluorescent antibodies against B220, F4/80, Ly6c, MHC II, and CD11b allows identification of lesional macrophages. DNA staining with Vybrant DyeCycle Violet allows identification of proliferating cells. Combined, these processes allow for the FACS-based sorting of viable proliferating macrophages from atherosclerotic plaque, and subsequent RNA or protein analysis, or culture.

CONCLUSIONS: The process described here allows the first-ever viable isolation of proliferating macrophages from atherosclerotic plaques. This will permit the investigation of molecular targets to interfere with the pathogenesis of atherosclerosis.

Lack of group X secreted phospholipase A₂ increases survival following pandemic H1N1 influenza infection

The role of Group X secreted phospholipase A2 (GX-sPLA2) during influenza infection has not been previously investigated. We examined the role of GX-sPLA2 during H1N1 pandemic influenza infection in a GX-sPLA2 gene targeted mouse (GX(-/-)) model and found that survival after infection was significantly greater in GX(-/-) mice than in GX(+/+) mice. Downstream products of GX-sPLA2 activity, PGD2, PGE2, LTB4, cysteinyl leukotrienes and Lipoxin A4 were significantly lower in GX(-/-) mice BAL fluid. Lung microarray analysis identified an earlier and more robust induction of T and B cell associated genes in GX(-/-) mice. Based on the central role of sPLA2 enzymes as key initiators of inflammatory processes, we propose that activation of GX-sPLA2 during H1N1pdm infection is an early step of pulmonary inflammation and its inhibition increases adaptive immunity and improves survival. Our findings suggest that GX-sPLA2 may be a potential therapeutic target during influenza.

Innate response activator B cells aggravate atherosclerosis by stimulating T helper-1 adaptive immunity

BACKGROUND

Atherosclerotic lesions grow via the accumulation of leukocytes and oxidized lipoproteins in the vessel wall. Leukocytes can attenuate or augment atherosclerosis through the release of cytokines, chemokines, and other mediators. Deciphering how leukocytes develop, oppose, and complement each other's function and shape the course of disease can illuminate our understanding of atherosclerosis. Innate response activator (IRA) B cells are a recently described population of granulocyte macrophage colony-stimulating factor-secreting cells of hitherto unknown function in atherosclerosis.

METHODS AND RESULTS

Here, we show that IRA B cells arise during atherosclerosis in mice and humans. In response to a high-cholesterol diet, IRA B cell numbers increase preferentially in secondary lymphoid organs via Myd88-dependent signaling. Mixed chimeric mice lacking B cell-derived granulocyte macrophage colony-stimulating factor develop smaller lesions with fewer macrophages and effector T cells. Mechanistically, IRA B cells promote the expansion of classic dendritic cells, which then generate interferon γ-producing T helper-1 cells. This IRA B cell-dependent T helper-1 skewing manifests in an IgG1-to-IgG2c isotype switch in the immunoglobulin response against oxidized lipoproteins.

CONCLUSIONS

Granulocyte macrophage colony-stimulating factor-producing IRA B cells alter adaptive immune processes and shift the leukocyte response toward a T helper-1-associated milieu that aggravates atherosclerosis.

Local proliferation dominates lesional macrophage accumulation in atherosclerosis

During the inflammatory response that drives atherogenesis, macrophages accumulate progressively in the expanding arterial wall^1,2. The observation that circulating monocytes give rise to lesional macrophages^3–9 has reinforced the concept that monocyte infiltration dictates macrophage build-up. Recent work indicates, however, that macrophages do not depend on monocytes in some inflammatory contexts¹⁰. We therefore revisited the mechanism of macrophage accumulation in atherosclerosis. We show that murine atherosclerotic lesions experience a surprisingly rapid, 4-week, cell turnover. Replenishment of macrophages in these experimental atheromata depends predominantly on local macrophage proliferation rather than monocyte influx. The microenvironment orchestrates macrophage proliferation via the involvement of scavenger receptor (SR)-A. Our study reveals macrophage proliferation as a key event in atherosclerosis and identifies macrophage self-renewal as a therapeutic target for cardiovascular disease.

Myocardial infarction accelerates atherosclerosis

During progression of atherosclerosis, myeloid cells destabilize lipid-rich plaque in the arterial wall and cause its rupture, thus triggering myocardial infarction and stroke. Survivors of acute coronary syndromes have a high risk of recurrent events for unknown reasons. Here we show that the systemic response to ischemic injury aggravates chronic atherosclerosis. After myocardial infarction or stroke, apoE^−/− mice developed larger atherosclerotic lesions with a more advanced morphology. This disease acceleration persisted over many weeks and was associated with markedly increased monocyte recruitment. When seeking the source of surplus monocytes in plaque, we found that myocardial infarction liberated hematopoietic stem and progenitor cells from bone marrow niches via sympathetic nervous system signaling. The progenitors then seeded the spleen yielding a sustained boost in monocyte production. These observations provide new mechanistic insight into atherogenesis and provide a novel therapeutic opportunity to mitigate disease progression.

Demyelinating diseases: myeloperoxidase as an imaging biomarker and therapeutic target

PURPOSE

To evaluate myeloperoxidase (MPO) as a newer therapeutic target and bis-5-hydroxytryptamide-diethylenetriaminepentaacetate-gadolinium (Gd) (MPO-Gd) as an imaging biomarker for demyelinating diseases such as multiple sclerosis (MS) by using experimental autoimmune encephalomyelitis (EAE), a murine model of MS.

MATERIALS AND METHODS

Animal experiments were approved by the institutional animal care committee. EAE was induced in SJL mice by using proteolipid protein (PLP), and mice were treated with either 4-aminobenzoic acid hydrazide (ABAH), 40 mg/kg injected intraperitoneally, an irreversible inhibitor of MPO, or saline as control, and followed up to day 40 after induction. In another group of SJL mice, induction was performed without PLP as shams. The mice were imaged by using MPO-Gd to track changes in MPO activity noninvasively. Imaging results were corroborated by enzymatic assays, flow cytometry, and histopathologic analyses. Significance was computed by using the t test or Mann-Whitney U test.

RESULTS

There was a 2.5-fold increase in myeloid cell infiltration in the brain (P = .026), with a concomitant increase in brain MPO level (P = .0087). Inhibiting MPO activity with ABAH resulted in decrease in MPO-Gd-positive lesion volume (P = .012), number (P = .009), and enhancement intensity (P = .03) at MR imaging, reflecting lower local MPO activity (P = .03), compared with controls. MPO inhibition was accompanied by decreased demyelination (P = .01) and lower inflammatory cell recruitment in the brain (P < .0001), suggesting a central MPO role in inflammatory demyelination. Clinically, MPO inhibition significantly reduced the severity of clinical symptoms (P = .0001) and improved survival (P = .0051) in mice with EAE.

CONCLUSION

MPO may be a key mediator of myeloid inflammation and tissue damage in EAE. Therefore, MPO could represent a promising therapeutic target, as well as an imaging biomarker, for demyelinating diseases and potentially for other diseases in which MPO is implicated.

Innate response activator B cells protect against microbial sepsis

Recognition and clearance of a bacterial infection are a fundamental properties of innate immunity. Here, we describe an effector B cell population that protects against microbial sepsis. Innate response activator (IRA) B cells are phenotypically and functionally distinct, develop and diverge from B1a B cells, depend on pattern-recognition receptors, and produce granulocyte-macrophage colony-stimulating factor. Specific deletion of IRA B cell activity impairs bacterial clearance, elicits a cytokine storm, and precipitates septic shock. These observations enrich our understanding of innate immunity, position IRA B cells as gatekeepers of bacterial infection, and identify new treatment avenues for infectious diseases.

Extramedullary hematopoiesis generates Ly-6C(high) monocytes that infiltrate atherosclerotic lesions

BACKGROUND

Atherosclerotic lesions are believed to grow via the recruitment of bone marrow-derived monocytes. Among the known murine monocyte subsets, Ly-6C(high) monocytes are inflammatory, accumulate in lesions preferentially, and differentiate. Here, we hypothesized that the bone marrow outsources the production of Ly-6C(high) monocytes during atherosclerosis.

METHODS AND RESULTS

Using murine models of atherosclerosis and fate-mapping approaches, we show that hematopoietic stem and progenitor cells progressively relocate from the bone marrow to the splenic red pulp, where they encounter granulocyte macrophage colony-stimulating factor and interleukin-3, clonally expand, and differentiate to Ly-6C(high) monocytes. Monocytes born in such extramedullary niches intravasate, circulate, and accumulate abundantly in atheromata. On lesional infiltration, Ly-6C(high) monocytes secrete inflammatory cytokines, reactive oxygen species, and proteases. Eventually, they ingest lipids and become foam cells.

CONCLUSIONS

Our findings indicate that extramedullary sites supplement the hematopoietic function of the bone marrow by producing circulating inflammatory cells that infiltrate atherosclerotic lesions.

Detection of macrophages in aortic aneurysms by nanoparticle positron emission tomography-computed tomography

OBJECTIVE

Current management of aortic aneurysms (AAs) relies primarily on size criteria to determine whether invasive repair is indicated to preempt rupture. We hypothesized that emerging molecular imaging tools could be used to more sensitively gauge local inflammation. Because macrophages are key effector cells that destabilize the extracellular matrix in the arterial wall, it seemed likely that they would represent suitable imaging targets. We here aimed to develop and validate macrophage-targeted nanoparticles labeled with fluorine-18 ((18)F) for positron emission tomography-computed tomography (PET-CT) detection of inflammation in AAs.

METHODS AND RESULTS

Aneurysms were induced in apolipoprotein E-/- mice via systemic administration of angiotensin II. Mice were imaged using PET-CT and a monocyte/macrophage-targeted nanoparticle. AAs were detected by contrast-enhanced micro-CT and had a mean diameter of 1.85 ± 0.08 mm, whereas normal aortas measured 1.07 ± 0.03 (P < 0.05). The in vivo PET signal was significantly higher in aneurysms (standard uptake value, 2.46 ± 0.48) compared with wild-type aorta (0.82 ± 0.05, P < 0.05). Validation with scintillation counting, autoradiography, fluorescence, and immunoreactive histology and flow cytometry demonstrated that nanoparticles localized predominantly to monocytes and macrophages within the aneurysmatic wall.

CONCLUSIONS

PET-CT imaging with (18)F-labeled nanoparticles allows quantitation of macrophage content in a mouse model of AA.

The multiple roles of monocyte subsets in steady state and inflammation

Monocytes participate importantly in immunity. Produced in the bone marrow and released into the blood, they circulate in blood or reside in a spleen reservoir before entering tissue and giving rise to macrophages or dendritic cells. Monocytes are more than transitional cells that adapt to a particular tissue environment indiscriminately. Accumulating evidence now indicates that monocytes are heterogeneous in several species and are themselves predetermined for particular function in the steady state and inflammation. Future therapeutics may harness this heterogeneity to target harmful functions while sparing those that are beneficial. Here, we review recent advances on the ontogeny and function of monocytes and their subsets in humans and mice.

Cigarette smoke exposure impairs dendritic cell maturation and T cell proliferation in thoracic lymph nodes of mice

Respiratory tract dendritic cells (DCs) are juxtaposed to directly sample inhaled environmental particles. Processing and presentation of these airborne Ags could result in either the development of immunity or tolerance. The purpose of this study was to determine the consequences of cigarette smoke exposure on DC function in mice. We demonstrate that while cigarette smoke exposure decreased the number of DCs in the lungs, Ag-induced DC migration to the regional thoracic lymph nodes was unaffected. However, cigarette smoking suppressed DC maturation within the lymph nodes as demonstrated by reduced cell surface expression of MHC class II and the costimulatory molecules CD80 and CD86. Consequently, DCs from cigarette smoke-exposed animals had a diminished capacity to induce IL-2 production by T cells that was associated with diminished Ag-specific T cell proliferation in vivo. Smoke-induced defects in DC function leading to impaired CD4(+) T cell function could inhibit tumor surveillance and predispose patients with chronic obstructive pulmonary disease to infections and exacerbations.

Impact of cigarette smoke on T and B cell responsiveness

Although its direct effects cannot be discounted, tobacco's effects on the immune system have been proposed to play a key role in mediating its deleterious health impact. Studies in rats using high levels of smoke exposure have suggested that tobacco smoke exhausts cellular signal transduction cascades, making lymphocytes unresponsive to stimulation. In the present study, we show that purified B or T cells, and total lymphocytes from the lungs, lymph nodes and spleens of smoke-exposed mice fluxed calcium, proliferated, and secreted immunoglobulin or IFN-gamma similarly to control mice when stimulated with ligands including anti-IgM, and anti-CD3. Importantly, we recapitulated these findings in PBMCs from human smokers; cells from long-term smokers and never-smokers proliferated equivalently when stimulated ex vivo. Previous reports of lymphocyte unresponsiveness in rats are inconsistent with these findings, and may reflect a phenomenon observed only at levels of smoke exposure well above those seen in actual human smokers.

Cigarette smoke exposure attenuates cytokine production by mouse alveolar macrophages

Alveolar macrophages (aMs) play a central role in respiratory host defense by sensing microbial antigens and initiating immune-inflammatory responses early in the course of an infection. The purpose of this study was to investigate the effect of cigarette smoke exposure on aMs after stimulation of innate pattern recognition receptors (PRRs) in a murine model. To accomplish this, C57BL/6 mice were exposed for 8 weeks using two models of cigarette smoke exposure, nose-only or whole-body exposure, and aMs isolated from the bronchoalveolar lavage. After stimulation of aMs with pI:C, a mimic of viral replication, and bacterial cell-wall constituent LPS, aMs from cigarette smoke-exposed mice produced significantly attenuated levels of the inflammatory cytokines TNF-alpha and IL-6, and the chemokine RANTES. This attenuation was specific to the aM compartment, and not related to changes in aM viability or expression of Toll-like receptor (TLR)3 or TLR4 between groups. Furthermore, aMs from smoke-exposed mice had decreased cytokine RNA as compared with aMs from sham-exposed mice. Mechanistically, this was associated with decreased nuclear translocation of the proinflammatory transcription factor NF-kappaB, and increased activator protein-1 nuclear translocation, in aMs from smoke-exposed mice. Attenuated cytokine production was reversible after smoking cessation. Cigarette smoke exposure also attenuated TNF-alpha production after stimulation with nucleotide-oligomerization domain-like receptor agonists, showing that the effect applies more broadly to other PRR pathways. Our data demonstrate that cigarette smoke exposure attenuates aM responses after innate stimulation, including pathways typically associated with bacterial and viral infections.

Cigarette smoke impacts immune inflammatory responses to influenza in mice

RATIONALE

Studies have shown that cigarette smoke impacts respiratory host defense mechanisms; however, it is poorly understood how these smoke-induced changes impact the overall ability of the host to deal with pathogenic agents.

OBJECTIVE

The objective of this study was to investigate the impact of mainstream cigarette smoke exposure on immune inflammatory responses and viral burden after respiratory infection with influenza A.

METHODS

C57BL/6 mice were sham- or smoke-exposed for 3 to 5 mo and infected with either 2.5 x 10(3) pfu (low dose) or 2.5 x 10(5) pfu (high dose) influenza virus.

MEASUREMENTS AND MAIN RESULTS

Although smoke exposure attenuated the airway's inflammatory response to low-dose infection, we observed increased inflammation in smoke-exposed compared with sham-exposed mice after infection with high-dose influenza, despite a similar rate of viral clearance. The heightened inflammatory response was associated with increased expression of tumor necrosis factor-alpha, interleukin-6, and type 1 IFN in the airway, and increased mortality. Importantly, smoke exposure did not interfere with the development of influenza-specific memory responses; sham- and smoke-exposed animals were equally protected upon viral rechallenge.

CONCLUSION

Our study suggests that, in mice, cigarette smoke affects primary antiviral immune-inflammatory responses, whereas secondary immune protection remains intact.

Mainstream cigarette smoke exposure attenuates airway immune inflammatory responses to surrogate and common environmental allergens in mice, despite evidence of increased systemic sensitization

The purpose of this study was to investigate the impact of mainstream cigarette smoke exposure (MTS) on allergic sensitization and the development of allergic inflammatory processes. Using two different experimental murine models of allergic airways inflammation, we present evidence that MTS increased cytokine production by splenocytes in response to OVA and ragweed challenge. Paradoxically, MTS exposure resulted in an overall attenuation of the immune inflammatory response, including a dramatic reduction in the number of eosinophils and activated (CD69+) and Th2-associated (T1ST2+) CD4 T lymphocytes in the lung. Although MTS did not impact circulating levels of OVA-specific IgE and IgG1, we observed a striking reduction in OVA-specific IgG2a production and significantly diminished airway hyperresponsiveness. MTS, therefore, plays a disparate role in the development of allergic responses, inducing a heightened state of allergen-specific sensitization, but dampening local immune inflammatory processes in the lung.