Highlight of 2023: Advances in mast cells

In this article for the Highlights of 2023 Series, we consider the growing understanding of mast cell heterogeneity and interactions that has developed from single cell RNA sequencing studies. We also discuss novel concepts concerning mast cell interactions with the central nervous system and evidence for their role in host defense against SARS-CoV-2 infection.

Ketotifen directly modifies the fibrotic response of human skin fibroblasts

Fibrosis is a destructive, end-stage disease process. In the skin, it is associated with systemic sclerosis and scarring with considerable health burden. Ketotifen is a clinical antihistamine and mast cell stabilizer. Studies have demonstrated mast cell-dependent anti-fibrotic effects of ketotifen but direct effects on fibroblasts have not been determined. Human dermal fibroblasts were treated with pro-fibrotic transforming growth factor-β1 (TGFβ) followed by ketotifen or control treatments to determine direct effects on fibrotic fibroblasts. Ketotifen impaired TGFβ-induced α-smooth muscle actin gene and protein responses and decreased cytoskeletal- and contractility-associated gene responses associated with fibrosis. Ketotifen reduced Yes-associated protein phosphorylation, transcriptional coactivator with PDZ binding motif transcript and protein levels, and phosphorylation of protein kinase B. In a fibroblast-populated collagen gel contraction assay, ketotifen reduced the contractile activity of TGFβ-activated fibroblasts. In a murine model of bleomycin-induced skin fibrosis, collagen density and dermal thickness were significantly decreased in ketotifen-treated mice supporting in vitro findings. These results support a novel, direct anti-fibrotic activity of ketotifen, reducing pro-fibrotic phenotypic changes in fibroblasts and reducing collagen fibres in fibrotic mouse skin. Together, these findings suggest novel therapeutic potential and a novel mechanism of action for ketotifen in the context of fibrosis.

Novel inflammatory mediator profile observed during pediatric heart surgery with cardiopulmonary bypass and continuous ultrafiltration

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with systemic inflammation, featuring increased levels of circulating pro-inflammatory cytokines. Intra-operative ultrafiltration extracts fluid and inflammatory factors potentially dampening inflammation-related organ dysfunction and enhancing post-operative recovery. This study aimed to define the impact of continuous subzero-balance ultrafiltration (SBUF) on circulating levels of major inflammatory mediators.

METHODS

Twenty pediatric patients undergoing cardiac surgery, CPB and SBUF were prospectively enrolled. Blood samples were collected prior to CPB initiation (Pre-CPB Plasma) and immediately before weaning off CPB (End-CPB Plasma). Ultrafiltrate effluent samples were also collected at the End-CPB time-point (End-CPB Effluent). The concentrations of thirty-nine inflammatory factors were assessed and sieving coefficients were calculated.

RESULTS

A profound increase in inflammatory cytokines and activated complement products were noted in plasma following CBP. Twenty-two inflammatory mediators were detected in the ultrafiltrate effluent. Novel mediators removed by ultrafiltration included cytokines IL1-Ra, IL-2, IL-12, IL-17A, IL-33, TRAIL, GM-CSF, ET-1, and the chemokines CCL2, CCL3, CCL4, CXCL1, CXCL2 and CXCL10. Mediator extraction by SBUF was significantly associated with molecular mass < 66 kDa (Chi² statistic = 18.8, Chi² with Yates' correction = 16.0, p < 0.0001). There was a moderate negative linear correlation between molecular mass and sieving coefficient (Spearman R = - 0.45 and p = 0.02). Notably, the anti-inflammatory cytokine IL-10 was not efficiently extracted by SBUF.

CONCLUSIONS

CPB is associated with a burden of circulating inflammatory mediators, and SBUF selectively extracts twenty of these pro-inflammatory factors while preserving the key anti-inflammatory regulator IL-10. Ultrafiltration could potentially function as an immunomodulatory therapy during pediatric cardiac surgery. Trial registration ClinicalTrials.gov, NCT05154864. Registered retrospectively on December 13, 2021. https://clinicaltrials.gov/ct2/show/record/NCT05154864 .

Mast cells selectively produce inflammatory mediators and impact the early response to Chlamydia reproductive tract infection

Introduction

Chlamydia trachomatis (C. trachomatis) is a Gram-negative obligate intracellular bacterium that causes reproductive tract complications in women, including ectopic pregnancies and tubal factor infertility. We hypothesized that mast cells, which are common at mucosal barriers, may contribute to responses to Chlamydia infection and aimed to define human mast cell responses to C. trachomatis.

Methods

Human cord blood-derived mast cells (CBMCs) were exposed to C. trachomatis to assess bacterial uptake, mast cell degranulation, gene expression, and production of inflammatory mediators. The role of formyl peptide receptors and Toll-like receptor 2 (TLR2) were investigated using pharmacological inhibitors and soluble TLR2. Mast cell-deficient mice and littermate controls were used to examine the in vivo role of mast cells in influencing the immune response to Chlamydia infection in the female reproductive tract.

Results

C. trachomatis bacteria were taken up by human mast cells but did not replicate efficiently inside CBMCs. C. trachomatis-activated mast cells did not degranulate but maintained viability and exhibited cellular activation with homotypic aggregation and upregulation of ICAM-1. However, they significantly enhanced the gene expression of IL1B, CCL3, NFKB1, CXCL8, and IL6. Inflammatory mediators were produced, including TNF, IL-1β, IL-1RA, IL-6, GM-CSF, IL-23, CCL3, CCL5, and CXCL8. Endocytic blockade resulted in reduced gene expression of IL6, IL1B, and CCL3, suggesting C. trachomatis induced mast cell activation in both extracellular and intracellular locations. The IL-6 response to C. trachomatis was reduced when CBMCs were treated with C. trachomatis coated with soluble TLR2. Mast cells derived from TLR2-deficient mice also demonstrated a reduced IL-6 response to C. muridarum. Five days following C. muridarum infection, mast cell-deficient mice showed attenuated CXCL2 production and significantly reduced numbers of neutrophils, eosinophils, and B cells in the reproductive tract when compared with mast cell-containing littermates.

Discussion

Taken together, these data demonstrate that mast cells are reactive to Chlamydia spp. through multiple mechanisms that include TLR2-dependent pathways. Mast cells also play an important role in shaping in vivo immune responses in Chlamydia reproductive tract infection through both effector cell recruitment and modification of the chemokine microenvironment.

Peroxisomes Regulate Cellular Free Fatty Acids to Modulate Mast Cell TLR2, TLR4, and IgE-Mediated Activation

Mast cells are specialized, tissue resident, immune effector cells able to respond to a wide range of stimuli. MCs are involved in the regulation of a variety of physiological functions, including vasodilation, angiogenesis and pathogen elimination. In addition, MCs recruit and regulate the functions of many immune cells such as dendritic cells, macrophages, T cells, B cells and eosinophils through their selective production of multiple cytokines and chemokines. MCs generate and release multi-potent molecules, such as histamine, proteases, prostanoids, leukotrienes, heparin, and many cytokines, chemokines, and growth factors through both degranulation dependent and independent pathways. Recent studies suggested that metabolic shifts dictate the activation and granule content secretion by MCs, however the metabolic signaling promoting these events is at its infancy. Lipid metabolism is recognized as a pivotal immunometabolic regulator during immune cell activation. Peroxisomes are organelles found across all eukaryotes, with a pivotal role in lipid metabolism and the detoxification of reactive oxygen species. Peroxisomes are one of the emerging axes in immunometabolism. Here we identified the peroxisome as an essential player in MCs activation. We determined that lack of functional peroxisomes in murine MCs causes a significant reduction of interleukin-6, Tumor necrosis factor and InterleukinL-13 following immunoglobulin IgE-mediated and Toll like receptor 2 and 4 activation compared to the Wild type (WT) BMMCs. We linked these defects in cytokine release to defects in free fatty acids homeostasis. In conclusion, our study identified the importance of peroxisomal fatty acids homeostasis in regulating mast cell-mediated immune functions.

Breastfeeding and the developmental origins of mucosal immunity: how human milk shapes the innate and adaptive mucosal immune systems

PURPOSE OF REVIEW

Breastfeeding provides passive immunity while the neonatal immune system matures, and may also protect against chronic immune-mediated conditions long after weaning. This review summarizes current knowledge and new discoveries about human milk and mucosal immunity.

RECENT FINDINGS

New data suggest that certain microbes in maternal milk may seed and shape the infant gut microbiota, which play a key role in regulating gut barrier integrity and training the developing immune system. Human milk oligosaccharides, best known for their prebiotic functions, have now been shown to directly modulate gene expression in mast and goblet cells in the gastrointestinal tract. Epidemiologic data show a reduced risk of peanut sensitization among infants breastfed by peanut-consuming mothers, suggesting a role for milk-borne food antigens in tolerance development. Cross-fostering experiments in mice suggest the soluble Toll-like receptor 2, found in human milk, may be critical in this process. Finally, interest in human milk antibodies surged during the pandemic with the identification of neutralizing severe acute respiratory syndrome coronavirus 2 antibodies in maternal milk following both natural infection and vaccination.

SUMMARY

Human milk provides critical immune protection and stimulation to breastfed infants. Understanding the underlying mechanisms could identify new therapeutic targets and strategies for disease prevention across the lifespan.

Mast Cell Modulation of B Cell Responses: An Under-Appreciated Partnership in Host Defence

Mast cells are well known to be activated via cross-linking of immunoglobulins bound to surface receptors. They are also recognized as key initiators and regulators of both innate and adaptive immune responses against pathogens, especially in the skin and mucosal surfaces. Substantial attention has been given to the role of mast cells in regulating T cell function either directly or indirectly through actions on dendritic cells. In contrast, the ability of mast cells to modify B cell responses has been less explored. Several lines of evidence suggest that mast cells can greatly modify B cell generation and activities. Mast cells co-localise with B cells in many tissue settings and produce substantial amounts of cytokines, such as IL-6, with profound impacts on B cell development, class-switch recombination events, and subsequent antibody production. Mast cells have also been suggested to modulate the development and functions of regulatory B cells. In this review, we discuss the critical impacts of mast cells on B cells using information from both clinical and laboratory studies and consider the implications of these findings on the host response to infections.

Distinct Metalloproteinase Expression and Functions in Systemic Sclerosis and Fibrosis: What We Know and the Potential for Intervention

Systemic sclerosis (SSc) is a chronic debilitating idiopathic disorder, characterized by deposition of excessive extracellular matrix (ECM) proteins such as collagen which leads to fibrosis of the skin and other internal organs. During normal tissue repair and remodeling, the accumulation and turnover of ECM proteins are tightly regulated by the interaction of matrix metalloproteinases (MMPs) and endogenous tissue inhibitors of metalloproteinases (TIMPs). SSc is associated with dysregulation of the activity of these proteolytic and inhibitory proteins within the tissue microenvironment, tipping the balance toward fibrosis. The resultant ECM accumulation further perpetuates tissue stiffness and decreased function, contributing to poor clinical outcomes. Understanding the expression and function of these endogenous enzymes and inhibitors within specific tissues is therefore critical to the development of therapies for SSc. This brief review describes recent advances in our understanding of the functions and mechanisms of ECM remodeling by metalloproteinases and their inhibitors in the skin and lungs affected in SSc. It highlights recent progress on potential candidates for intervention and therapeutic approaches for treating SSc fibrosis.

Histamine receptor 2 blockade selectively impacts B and T cells in healthy subjects

Histamine receptor 2 (H2R) blockade is commonly used in patients with gastric, duodenal ulcers or gastroesophageal reflux disease. Beyond the gastrointestinal tract, H2R is expressed by multiple immune cells, yet little is known about the immunomodulatory effects of such treatment. Clinical reports have associated H2R blockade with leukopenia, neutropenia, and myelosuppression, and has been shown to provide clinical benefit in certain cancer settings. To systematically assess effects of H2R blockade on key immune parameters, a single-center, single-arm clinical study was conducted in 29 healthy subjects. Subjects received daily high dose ranitidine for 6 weeks. Peripheral blood immunophenotyping and mediator analysis were performed at baseline, 3 and 6 weeks into treatment, and 12 weeks after treatment cessation. Ranitidine was well-tolerated, and no drug related adverse events were observed. Ranitidine had no effect on number of neutrophils, basophils or eosinophils. However, ranitidine decreased numbers of B cells and IL-2Rα (CD25) expressing T cells that remained lower even after treatment cessation. Reduced serum levels of IL-2 were also observed and remained low after treatment. These observations highlight a previously unrecognised immunomodulatory sustained impact of H2R blockade. Therefore, the immune impacts of H2R blockade may require greater consideration in the context of vaccination and immunotherapy.

Mice Heterozygous for the Sodium Channel Scn8a (Nav1.6) Have Reduced Inflammatory Responses During EAE and Following LPS Challenge

Voltage gated sodium (Nav) channels contribute to axonal damage following demyelination in experimental autoimmune encephalomyelitis (EAE), a rodent model of multiple sclerosis (MS). The Nav1.6 isoform has been implicated as a primary contributor in this process. However, the role of Nav1.6 in immune processes, critical to the pathology of both MS and EAE, has not been extensively studied. EAE was induced with myelin oligodendrocyte (MOG35-55) peptide in Scn8admu/+ mice, which have reduced Nav1.6 levels. Scn8admu/+ mice demonstrated improved motor capacity during the recovery and early chronic phases of EAE relative to wild-type animals. In the optic nerve, myeloid cell infiltration and the effects of EAE on the axonal ultrastructure were also significantly reduced in Scn8admu/+ mice. Analysis of innate immune parameters revealed reduced plasma IL-6 levels and decreased percentages of Gr-1high/CD11b+ and Gr-1int/CD11b+ myeloid cells in the blood during the chronic phase of EAE in Scn8admu/+ mice. Elevated levels of the anti-inflammatory cytokines IL-10, IL-13, and TGF-β1 were also observed in the brains of untreated Scn8admu/+ mice. A lipopolysaccharide (LPS) model was used to further evaluate inflammatory responses. Scn8admu/+ mice displayed reduced inflammation in response to LPS challenge. To further evaluate if this was an immune cell-intrinsic difference or the result of changes in the immune or hormonal environment, mast cells were derived from the bone marrow of Scn8admu/+ mice. These mast cells also produced lower levels of IL-6, in response to LPS, compared with those from wild type mice. Our results demonstrate that in addition to its recognized impact on axonal damage, Nav1.6 impacts multiple aspects of the innate inflammatory response.

Increased mast cell density is associated with decreased fibrosis in human atrial tissue

Fibrotic remodelling of the atria is poorly understood and can be regulated by myocardial immune cell populations after injury. Mast cells are resident immune sentinel cells present in the heart that respond to tissue damage and have been linked to fibrosis in other settings. The role of cardiac mast cells in fibrotic remodelling in response to human myocardial injury is controversial. In this study, we sought to determine the association between mast cells, atrial fibrosis, and outcomes in a heterogeneous population of cardiac surgical patients, including a substantial proportion of coronary artery bypass grafting patients. Atrial appendage from patients was assessed for collagen and mast cell density by histology and by droplet digital polymerase chain reaction (ddPCR) for mast cell associated transcripts. Clinical variables and outcomes were also followed. Mast cells were detected in human atrial tissue at varying densities. Histological and ddPCR assessment of mast cells in atrial tissue were closely correlated. Patients with high mast cell density had less fibrosis and lower severity of heart failure classification or incidence mortality than patients with low mast cell content. Analysis of a homogeneous population of coronary artery bypass graft patients yielded similar observations. Therefore, evidence from this study suggests that increased atrial mast cell populations are associated with decreased clinical cardiac fibrotic remodelling and improved outcomes, in cardiac surgery patients.

Toll-like receptor 2 activation induces C-C chemokine receptor 2-dependent natural killer cell recruitment to the peritoneum

Natural killer (NK) cells are innate effector cells with critical roles not only in tumor immunosurveillance and viral immunity, but also in bacterial and fungal infections. Toll‐like receptor 2 (TLR2) can be important in the early and sustained immune responses to pathogens and tumors through the induction of cytokines and chemokines that recruit and activate immune effector cells. We investigated the role of TLR2 activation in NK cell recruitment with a view to informing approaches to induce or regulate peritoneal NK cell responses therapeutically. Peritoneal injection of TLR2 activators, including peptidoglycan and the lipopeptides FSL‐1 and Pam₃CSK₄, resulted in NK cell recruitment after 16 h with increased NK cell numbers maintained for 48 h. TLR2 activators induced large amounts of CCR2 ligands, but much smaller amounts of CCR5 and CXCR3 ligands. Consistent with this observation, NK cell migration was abrogated in CCR2‐deficient mice after peritoneal FSL‐1 injection. Adoptive transfer of CCR2‐deficient NK cells prior to peritoneal FSL‐1 activation confirmed a cell‐intrinsic component of CCR2‐mediated NK cell migration. TLR2 activation did not induce an activated NK cell phenotype, but significant changes included an increase in the KLRG1⁺ subset and decreased NKG2D expression. Although not activated in vivo, peritoneal NK cells could be activated by interleukin (IL)‐12 and IL‐18 ex vivo to express CD69 and interferonγ. These data demonstrate that TLR2‐mediated immune activation is a potent inducer of NK cell recruitment via a CCR2‐dependent mechanism and that NK cells recruited by this mechanism can respond to additional signals to exert effector cell functions.

Association of a Type 2-Polarized T Cell Phenotype With Methotrexate Nonresponse in Patients With Rheumatoid Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a chronic inflammatory disease mediated through complex immunologic pathways. Among RA patients receiving low-dose methotrexate (MTX) monotherapy, approximately one-half exhibit a meaningful clinical response within the first 6 months of starting treatment. Whether baseline immune phenotypes differ between subsequent MTX responders and nonresponders is unknown. This study utilized comprehensive T cell immunophenotyping to identify specific immunologic pathways associated with MTX-nonresponsive joint inflammation in patients with RA.

METHODS

In total, 32 patients with recent-onset RA were treated with MTX therapy. After 6 months, 15 patients were categorized as responders and 17 as nonresponders. Comprehensive blood T cell immunophenotyping, using multiparameter immunofluorescence flow cytometry analyses, was performed at baseline and following 6 months of treatment.

RESULTS

Baseline measures of disease activity (Disease Activity Score in 28 joints [DAS28], C-reactive protein level, and erythrocyte sedimentation rate) did not differ between MTX responders and nonresponders following MTX treatment. Frequencies of CD4+ and CD8+ T cells were skewed to favor higher CD4:CD8 T cell ratios in MTX responders compared to nonresponders (P < 0.05). The proportion of inducible costimulator-expressing Treg cells was significantly greater among MTX nonresponders. Interleukin-13 (IL-13)-producing, but not interferon-γ- or IL-17-producing, CD4+ effector memory T (Tem) cells were significantly more frequent in MTX nonresponders (P < 0.05). The ratio of IL-13+:IL-17+ Tem cells among CD4+ Tem cells was 1.9-fold higher in MTX nonresponders compared to responders (P < 0.05). Both the CD4:CD8 T cell ratio and the frequency of IL-13+CD4+ Tem cells correlated with changes in the DAS28 score following MTX treatment, whereas T cell expression of immune checkpoint inhibitor markers (CTLA-4, programmed death 1, and T cell immunoglobulin and mucin domain-containing protein 3) did not differ between MTX responders and nonresponders.

CONCLUSION

We observed a bias toward type 2-polarized T cell inflammatory responses in the peripheral blood of MTX-nonresponsive RA patients. Targeting the IL-13+CD4+ T cell pathway could be a new therapeutic strategy in RA patients whose disease remains resistant to MTX.

Nav1.6 promotes inflammation and neuronal degeneration in a mouse model of multiple sclerosis

BACKGROUND

In multiple sclerosis (MS) and in the experimental autoimmune encephalomyelitis (EAE) model of MS, the Nav1.6 voltage-gated sodium (Nav) channel isoform has been implicated as a primary contributor to axonal degeneration. Following demyelination Nav1.6, which is normally co-localized with the Na⁺/Ca²⁺ exchanger (NCX) at the nodes of Ranvier, associates with β-APP, a marker of neural injury. The persistent influx of sodium through Nav1.6 is believed to reverse the function of NCX, resulting in an increased influx of damaging Ca²⁺ ions. However, direct evidence for the role of Nav1.6 in axonal degeneration is lacking.

METHODS

In mice floxed for Scn8a, the gene that encodes the α subunit of Nav1.6, subjected to EAE we examined the effect of eliminating Nav1.6 from retinal ganglion cells (RGC) in one eye using an AAV vector harboring Cre and GFP, while using the contralateral either injected with AAV vector harboring GFP alone or non-targeted eye as control.

RESULTS

In retinas, the expression of Rbpms, a marker for retinal ganglion cells, was found to be inversely correlated to the expression of Scn8a. Furthermore, the gene expression of the pro-inflammatory cytokines Il6 (IL-6) and Ifng (IFN-γ), and of the reactive gliosis marker Gfap (GFAP) were found to be reduced in targeted retinas. Optic nerves from targeted eyes were shown to have reduced macrophage infiltration and improved axonal health.

CONCLUSION

Taken together, our results are consistent with Nav1.6 promoting inflammation and contributing to axonal degeneration following demyelination.

Extracellular mitochondria Released from Hepatic Ischemia Reperfusion Induce Macrophage activation both in vitro and in vivo

Background

During liver transplantation ischemia and reperfusion injury (IRI), an immune driven inflammatory response provoked by cellular oxygen deprivation, is unavoidable. The inflammatory responses, resulting from acute oxidative stress and consequent hepatocellular death during the early reperfusion phase, cause the release of endogenous danger signals. Recent studies show that the release of free mitochondria (FM) from deceased organ donors is directly linked with functionally important immune activation and early allograft dysfunction (Pollara, et al., 2018). Organs from donors after cardiocirculatory death (DCD) undergo a prolonged warm ischemia process compared with organs from donors after neurological determination of death (NDD), and therefore have more severe IRI. Herein, we investigated the roles of FM in liver IRI, particularly as related to macrophages.

Methods

Liver biopsies were assayed by TEM to assess for FM release. FM were co-cultured with macrophages (cell line, bone marrow derived macrophages, and primary Kupffer cells), and injected i.p. in vivo to explore the recruitment and activation of macrophages. Inflammatory mediators were tested by luminex.

Results

FM levels were significantly higher in IRI. Co-culture of FM with macrophages significantly increased inflammatory mediator release but this process was not Formyl Peptide Receptor 1 dependent. The injection of FM induced significant accumulation of monocyte-derived macrophages and activation of macrophages in the peritoneum.

Conclusion

Our results indicate that IRI can elicit significantly increased FM, and that FM from hepatic IRI can attract and activate macrophages, which may influence the outcome of liver transplantation.

Mast Cells in Cardiac Fibrosis: New Insights Suggest Opportunities for Intervention

Mast cells (MC) are innate immune cells present in virtually all body tissues with key roles in allergic disease and host defense. MCs recognize damage-associated molecular patterns (DAMPs) through expression of multiple receptors including Toll-like receptors and the IL-33 receptor ST2. MCs can be activated to degranulate and release pre-formed mediators, to synthesize and secrete cytokines and chemokines without degranulation, and/or to produce lipid mediators. MC numbers are generally increased at sites of fibrosis. They are potent, resident, effector cells producing mediators that regulate the fibrotic process. The nature of the secretory products produced by MCs depend on micro-environmental signals and can be both pro- and anti-fibrotic. MCs have been repeatedly implicated in the pathogenesis of cardiac fibrosis and in angiogenic responses in hypoxic tissues, but these findings are controversial. Several rodent studies have indicated a protective role for MCs. MC-deficient mice have been reported to have poorer outcomes after coronary artery ligation and increased cardiac function upon MC reconstitution. In contrast, MCs have also been implicated as key drivers of fibrosis. MC stabilization during a hypertensive rat model and an atrial fibrillation mouse model rescued associated fibrosis. Discrepancies in the literature could be related to problems with mouse models of MC deficiency. To further complicate the issue, mice generally have a much lower density of MCs in their cardiac tissue than humans, and as such comparing MC deficient and MC containing mouse models is not necessarily reflective of the role of MCs in human disease. In this review, we will evaluate the literature regarding the role of MCs in cardiac fibrosis with an emphasis on what is known about MC biology, in this context. MCs have been well-studied in allergic disease and multiple pharmacological tools are available to regulate their function. We will identify potential opportunities to manipulate human MC function and the impact of their mediators with a view to preventing or reducing harmful fibrosis. Important therapeutic opportunities could arise from increased understanding of the impact of such potent, resident immune cells, with the ability to profoundly alter long term fibrotic processes.

Cytokines and Soluble Receptors in Breast Milk as Enhancers of Oral Tolerance Development

The postpartum period is an important window during which environmental factors can shape the life-long health of the infant. This time period often coincides with substantial milk consumption either in the form of breast milk or from cow's milk sources, such as infant formulas. Although breast milk is the most beneficial source of nutrients for infants during the first 6 months after birth, its role in regulating food allergy development, through regulation of oral tolerance, is still controversial. Breast milk contains several factors that can impact mucosal immune function, including immune cells, antibodies, microbiota, oligosaccharides, cytokines, and soluble receptors. However, there is considerable variation in the assessed levels of cytokines and soluble receptors between studies and across the lactation period. Most of these cytokines and soluble receptors are absent, or only found in limited quantities, in commercial baby formulas. Differences in content of these pluripotent factors, which impact on both the mother and the neonate, could contribute to the controversy surrounding the role of breast milk regulating oral tolerance. This review highlights current knowledge about the importance of cytokines and soluble receptors in breast milk on the development of oral tolerance and tolerance-relateddisorders. Understanding the mechanisms by which such milk components might promote oral tolerance could aid in the development of improved strategies for allergy prevention.

An introduction to immunology and immunopathology

Beyond structural and chemical barriers to pathogens, the immune system has two fundamental lines of defense: innate immunity and adaptive immunity. Innate immunity is the first immunological mechanism for fighting against an intruding pathogen. It is a rapid immune response, initiated within minutes or hours after aggression, that has no immunologic memory. Adaptive immunity, on the other hand, is antigen-dependent and antigen-specific; it has the capacity for memory, which enables the host to mount a more rapid and efficient immune response upon subsequent exposure to the antigen. There is a great deal of synergy between the adaptive immune system and its innate counterpart, and defects in either system can provoke illness or disease, such as inappropriate inflammation, autoimmune diseases, immunodeficiency disorders and hypersensitivity reactions. This article provides a practical overview of innate and adaptive immunity, and describes how these host defense mechanisms are involved in both heath and illness.

Ranitidine Inhibition of Breast Tumor Growth Is B Cell Dependent and Associated With an Enhanced Antitumor Antibody Response

Background

The histamine receptor 2 antagonist ranitidine is a commonly used, non-prescription, medication. It limits the development, growth, and metastasis of breast cancers in mouse models of disease. In this study, we examined the role of B cells in this response, the impact of ranitidine on the development of antitumor antibodies and subpopulations of natural killer cells using murine breast cancer models.

Methods

Peripheral blood granulocyte populations were assessed in both E0771-GFP and 4T1 orthotopic tumor-bearing mice by evaluation of stained blood smears. Antibody responses were assessed both in terms of the levels of anti-GFP antibodies detected by enzyme-linked immunosorbent assay and also by antibody binding to the surface of tumor cells evaluated by flow cytometry. B cell and NK cell populations were examined in the draining lymph nodes and spleens of tumor-bearing animals, by flow cytometry with and without ranitidine treatment.

Results

Oral ranitidine treatment was not associated with changes in peripheral blood granulocyte populations in tumor-bearing mice. However, ranitidine treatment was associated with the development of enhanced antitumor antibody responses. This was not limited to the tumor setting since ranitidine-treated mice immunized with ovalbumin also demonstrated increased IgG antibody responses. Analysis of B cell populations indicated that while B1 cell populations remained unchanged there was a significant decrease in B2 cells in the tumor-draining inguinal lymph nodes. Notably, ranitidine did not significantly inhibit primary tumor growth in B cell-deficient animals. Examination of NK cell populations revealed a significant decrease in the proportion of intermediately functionally mature NK cells populations (CD27⁺CD11b⁻) in ranitidine-treated tumor-bearing mice compared with untreated tumor-bearing controls.

Conclusion

These data demonstrate an important role for B cells in the enhanced antitumor immune response that occurs in response to ranitidine treatment. Our findings are consistent with a model, whereby ranitidine reduces tumor-associated immune suppression allowing for the development of more effective antitumor responses mediated by B cells which may include the participation of NK cells. These data underline the importance of considering widely used histamine receptor antagonists as modulators of antitumor immunity to breast cancer.

Interferon α2 and interferon γ induce the degranulation independent production of VEGF-A and IL-1 receptor antagonist and other mediators from human mast cells

Background

Mast cells are resident immune effector cells, often studied in the context of allergic disease. Found in substantial numbers at sites of potential infection they are increased at sites of angiogenesis and can be pivotal for the sensing and clearance of a variety of pathogens. Interferons (IFNs) are cytokines that are critical for host defence against intracellular pathogens. Increased levels of IFNs are observed during viral infection and in autoimmune diseases. IFNs are also widely used therapeutically and have been examined in the therapy of severe asthma.

Objective

To define the selective human mast cell cytokine and chemokine response following activation with type I or type II IFN's.

Methods

The ability of both IFNα2 and IFNγ to induce cytokine production by human cord blood‐derived mast cells was examined in vitro. Cytokine and chemokine production at 6 and 24 h was assessed by multiplex protein analysis. Degranulation was assessed by β‐hexosaminidase release. Mast cells were also treated with reovirus or respiratory syncytial virus and their production of CXCL10, IL‐1 receptor antagonist (IL‐1Ra), and vascular endothelial growth factor (VEGF) examined after 24 h.

Results

In addition to increased expression of classical IFN response genes, such as CXCL10, small but significant increases in CCL5 and IL‐17 production were observed following IFN activation. Notably, human mast cells produced both VEGF and IL‐1Ra in a dose dependent manner. These responses occurred in the absence of mast cell degranulation by a mechanism consistent with classical IFN signaling. Both reovirus and respiratory syncytial virus infection of mast cells, were also associated with IFN‐dependent IL‐1Ra expression.

Conclusion and Clinical Relevance

Our findings demonstrate that IFNs have profound impact on cytokine and chemokine expression by human mast cells, alone or in the context of viral infection. Mast cell VEGF and IL‐1Ra responses to IFNs could impact the regulation of local inflammatory responses and subsequent tissue remodeling.

VEGF-A is increased in exogenous endophthalmitis

OBJECTIVE

Exogenous endophthalmitis is an ophthalmologic emergency defined by panocular inflammation. Vascular endothelial growth factor A (VEGF-A) contributes to inflammation by promoting chemotaxis of monocytes and granulocytes and by increasing vascular permeability. The purpose of this article is to determine if VEGF-A is elevated in the vitreous samples obtained from individuals with exogenous endophthalmitis.

METHODS

Vitreous samples from individuals with exogenous endophthalmitis (n = 18) were analyzed via Luminex assay and enzyme-linked immunosorbent assay for the cytokines VEGF-A, tumor necrosis factor (TNF), interleukin 6 (IL-6), IL-8 (chemokine [CXCL]-8), IL-1β, IL-10, IL-12p70, IL-33, interferon (IFN)-γ, IFN-α, IFN-β, chemokine ligand (CCL)-3, IL-2, IL-5, IL-15, CXCL-10, CCL-2, IL-1Ra, CCL-5, IL-17, and CCL-11. Vitreous samples obtained at the time of macular hole surgery served as controls (n = 8).

RESULTS

Concentrations of VEGF-A were significantly elevated in vitreous samples from individuals with exogenous endophthalmitis compared with macular hole (p < 0.001). VEGF-A was significantly upregulated in individuals with exogenous endophthalmitis after cataract surgery (p = 0.001), vitrectomy (p = 0.024), and intravitreal injection (p = 0.012). VEGF-A concentrations were similar in both culture-positive and culture-negative populations (p > 0.05). In a linear regression model, levels of VEGF-A correlated significantly with the chemokine CXCL-8 (p = 0.028).

CONCLUSIONS

We demonstrate that VEGF-A is potently upregulated in exogenous endophthalmitis. This observation provides a foundation for future studies of targeted VEGF-A blockade in the management of endophthalmitis.

Virus-Infected Human Mast Cells Enhance Natural Killer Cell Functions

Mucosal surfaces are protected from infection by both structural and sentinel cells, such as mast cells. The mast cell's role in antiviral responses is poorly understood; however, they selectively recruit natural killer (NK) cells following infection. Here, the ability of virus-infected mast cells to enhance NK cell functions was examined. Cord blood-derived human mast cells infected with reovirus (Reo-CBMC) and subsequent mast cell products were used for the stimulation of human NK cells. NK cells upregulated the CD69 molecule and cytotoxicity-related genes, and demonstrated increased cytotoxic activity in response to Reo-CBMC soluble products. NK cell interferon (IFN)-γ production was also promoted in the presence of interleukin (IL)-18. In vivo, SCID mice injected with Reo-CBMC in a subcutaneous Matrigel model, could recruit and activate murine NK cells, a property not shared by normal human fibroblasts. Soluble products of Reo-CBMC included IL-10, TNF, type I and type III IFNs. Blockade of the type I IFN receptor abrogated NK cell activation. Furthermore, reovirus-infected mast cells expressed multiple IFN-α subtypes not observed in reovirus-infected fibroblasts or epithelial cells. Our data define an important mast cell IFN response, not shared by structural cells, and a subsequent novel mast cell-NK cell immune axis in human antiviral host defense.

Air Pollution During Pregnancy and Cord Blood Immune System Biomarkers

OBJECTIVES

We aimed to determine whether average and trimester-specific exposures to ambient measures of nitrogen dioxide (NO2) and particular matter (PM2.5) were associated with elevated cord blood concentrations of immunoglobulin E (IgE) and two epithelial cell produced cytokines: interleukin-33 (IL-33) and thymic stromal lymphopoietin (TSLP).

METHODS

This study utilized data and biospecimens from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study. There were 2001 pregnant women recruited between 2008 and 2011 from 10 Canadian cities. Maternal exposure to NO2 and PM2.5 was estimated using land use regression and satellite-derived models.

RESULTS

We observed statistically significant associations between maternal NO2 exposure and elevated cord blood concentrations of both IL-33 and TSLP among girls but not boys.

CONCLUSIONS

Maternal NO2 exposure may impact the development of the newborn immune system as measured by cord blood concentrations of two cytokines.

Toll-like receptor 2 activators modulate oral tolerance in mice

BACKGROUND

Toll-like receptor 2 (TLR2) is a widely expressed pattern recognition receptor critical for innate immunity. TLR2 is also a key regulator of mucosal immunity implicated in the development of allergic disease. TLR2 activators are found in many common foods, but the role of TLR2 in oral tolerance and allergic sensitization to foods is not well understood.

OBJECTIVE

The purpose of this study was to evaluate the impacts of TLR2 expression and TLR2 activation on oral tolerance to food antigens in a murine model.

METHODS

Mice were fed ovalbumin (OVA) or peanut butter with or without the addition of low doses of TLR2 activators Pam3 CSK4 or FSL-1. Oral tolerance was assessed by analysing antibody responses after a systemic antigen challenge. OVA-specific Tregs were assessed in the Peyer's patches, mesenteric lymph nodes, and spleen in wild-type and TLR2(-/-) mice. Low-dose Pam3 CSK4 was also tested as an oral adjuvant.

RESULTS

Oral tolerance was successfully induced in both wild-type and TLR2(-/-) recipient mice, with an associated regulatory T-cell response. Oral TLR2 activation, with low-dose Pam3 CSK4 or FSL-1, during oral antigen exposure was found to alter oral tolerance and was associated with the development of substantial IgE and IgA responses to foods upon systemic challenge. Low-dose oral Pam3 CSK4 treatment also selectively enhanced antigen-specific IgA responses to oral antigen exposure.

CONCLUSIONS AND CLINICAL RELEVANCE

TLR2 is not necessary for oral tolerance induction, but oral TLR2 activation modulates humoral IgE and IgA responses during tolerance development. Low-dose Pam3 CSK4 is also an effective oral adjuvant that selectively enhances IgA production. These observations are pertinent to the optimization of oral allergen immunotherapy and oral vaccine development.

Proceedings of the Canadian society of allergy and clinical immunology annual scientific meeting 2015

A1 Role of fibrocytes in allergic rhinitis

Marie-Ève Côté, Marie-Ève Boulay, Sophie Plante, Jamila Chakir, Louis-Philippe Boulet

A2 Patterns of aeroallergens sensitization in Northern Alberta

Hanan Ahmed, Maria-Beatriz Ospina, Kyriaki Sideri, Harissios Vliagoftis

A3 Addressing acceptable risk for adolescents with Food-Induced Anaphylaxis (FIA)

Sara F. Johnson, Roberta L. Woodgate

A4 Outcomes of matched related and unrelated bone marrow transplantation after reduced-toxicity conditioning for children suffering from Chronic Granulomatous Disease

Guilhem Cros, Pierre Teira, Sonia Cellot, Henrique Bittencourt, Helene Decaluwe, Marie France Vachon, Michel Duval, Elie Haddad

A5 Outcomes of patients with severe combined immunodeficiency (SCID) prior to and after initiation of newborn screening for SCID in Ontario

Vy H.D. Kim, Anne Pham-Huy, Eyal Grunebaum

A6 Detection of regulatory B cells in the airways of subjects with asthma

John-Paul Oliveria, Stephanie Phan, Mark W. Tenn, Damian Tworek, Steven G. Smith, Adrian J. Baatjes, Caitlin D. Obminski, Caroline E. Munoz, Tara X. Scime, Roma Sehmi, Gail M Gauvreau

A7 Characterization of IgE-expressing B cells in the airways and peripheral blood of allergic asthmatic subjects

John-Paul Oliveria, Stephanie Phan, Mark W. Tenn, Brittany M Salter, Steven G Smith, Caitlin D Obminski, Caroline E Munoz, Abbey Schlatman, Tara X Scime, Rick Watson, Roma Sehmi, Gail M Gauvreau

A8 Pregnancy: could it be a risk factor for primary immunodeficient patients

Roya Sherkat, Razieh Khoshnevisan, Saba Sheikhbahaei

A9 Clinical experience with Octagam: a Canadian retrospective chart review

Stephen Betschel, Richard Warrington, Robert Schellenberg

A10 Kounis syndrome secondary to contrast media with inferior ST elevations and bilateral ischemic stroke

Michael N Fein, Jean-Philippe Pelletier

A11 Honey bee venom immunotherapy ineffective in bumble bee-induced anaphylaxis: case report and review of literature

Manstein Kan, Robert Schellenberg

A12 Delayed immune reconstitution occurring after multiple immune complications of hematological stem cell transplantation for a leaky SCID

Roxane Labrosse, Guilhem Cros, Pierre Teira, Henrique Bittencourt, Helene Decaluwe, Michel Duval, Elie Haddad

A13 Comparison of Three Case Reports of Acquired Angioedema: presentation, management and outcome

Raymond Mak, James Loh, Amin Kanani

A14 Sitagliptin-associated angioedema not related to concurrent use of ARB or ACE inhibitor

Dominik A. Nowak, Paul K. Keith

A15 Sneddon-Wilkinson subcorneal pustular dermatosis associated with an IgA monoclonal gammopathy

Daniel Pannozzo, Dominik A. Nowak, Hermenio C. Lima

A16 Omalizumab can be effective in patients with allergic bronchopulmonary aspergillosis

Diana Pham, Hoang Pham, Gonzalo G. Alvarez, Istvan T. Bencze, Krishna B. Sharma, Mark Smith, Shawn Aaron, Jennifer Block, Tara Keays, Judith Leech, David Schneidermen, Jodi Cameron, Jennifer Forgie, Alicia Ring, John W. O’Quinn, Stephanie Santucci, William H. Yang

A17 Efficacious use of omalizumab in the treatment of cystic fibrosis

Diana Pham, Hoang Pham, Ena Gaudet, Shawn Aaron, Stephanie Santucci, William H. Yang

A18 HAE with normal C1-INH with inconsistent response to C1 esterase inhibitor infusion but reliably responsive to icatibant

Hoang Pham, Stephanie Santucci, William H. Yang

A19 Anaphylaxis reaction to lactase enzyme

Mathew R. Voisin, Rozita Borici-Mazi

A20 Risk of solid tumor malignancies in patients with primary immune deficiency

Kateryna Vostretsova, Donald F. Stark

A21 Is it time to adopt the chromogenic assay for measuring C1 esterase inhibitor function in patients with HAE Type 2?

Elizabeth Yeboah, Paul K. Keith

A22 Emergency department visits for anaphylaxis and allergic reactions

Michelle Martin-Rhee, Cheryl Gula, Clare Cheng, Geoff Paltser

A23 START: Susceptibility To food Allergies in a Registry of Twins

Alizée Dery, Ann Clarke, Kari Nadeau, Laurie Harada, Kimberley Weatherall, Celia Greenwood, Denise Daley, Yuka Asai, Moshe Ben-Shoshan

A24 Qualifying the diagnostic approach employed by allergists when managing patients with self-diagnosed non-celiac gluten sensitivity (NCGS)

Lee Horgan, Teresa Pun

A25 Retrospective analysis on the agreement between skin prick test and serum food specific IgE antibody in adults with suspected food allergy

Ling Ling, Maria B. Ospina, Kyriaki Sideri, Harissios Vliagoftis

A26 Staple food hypersensitivity from infancy to adolescence: a report from the BAMSE cohort

Jennifer L.P. Protudjer, Mirja Vetander, Marianne van Hage, Ola Olén, Magnus Wickman, Anna Bergström

A27 Evaluating the impact of supervised epinephrine autoinjector administration during food challenges on perceived parent confidence

Timothy Teoh, Christopher Mill, Tiffany Wong, Ingrid Baerg, Angela Alexander, Kyla J. Hildebrand, John Dean, Boris Kuzeljevic, Edmond S. Chan

A28 Local immunoglobulin production to Aspergillus fumigatus cystic fibrosis

Jonathan Argeny, Mia Gona-Hoepler, Petra Fucik, Edith Nachbaur, Saskia Gruber, Reto Crameri, Andreas Glaser, Zsolt Szépfalusi, Claudio Rhyner, Thomas Eiwegger

A29 Extract consumption with skin prick test (SPT) devices

Greg. Plunkett, Brad Mire

A30 Evaluation of our cases with nonsteroidal anti-inflammatory drug reactions

Mehtap Yazicioglu, Ceren Can, Gokce Ciplak

A31 Reasons for referral and final diagnoses in a tertiary care pediatric allergy clinic

Victoria E. Cook, Kyla J. Hildebrand, Elodie Portales-Casamar, Christopher Mill, Edmond S. Chan

A32 Internist referral practices for inpatients with self-reported penicillin allergies at a tertiary care teaching hospital

Michael N Fein, Emil P Nashi

A33 Assessing the risk of reactions in children with a negative oral challenge after a subsequent use of amoxicillin

Sofianne Gabrielli, Christopher Mill, Marie-Noel Primeau, Christine Lejtenyi, Elena Netchiporouk, Alizee Dery, Greg Shand, Moshe Ben-Shoshan

A34 Validity of self-reported penicillin allergies

Erica Hoe, Joel Liem

A35 Effectiveness of allergy-test directed elimination diets in eosinophilic esophagitis

Jason K. Ko, David J.T. Huang, Jorge A. Mazza

A36 Allergy testing and dietary management in pediatric eosinophilic esophagitis (EoE): A retrospective review of a tertiary Canadian centre’s experience

Mary McHenry, Anthony Otley,Wade Watson

A37 Visualizing the impact of atopic and allergic skin disease

Dominik A. Nowak, John N. Kraft

A38 Cystic fibrosis with and without nasal polyposis in pediatric patients: a cross-sectional comparative study

Mihaela Paina, Ahmed A. Darwish Hassan, Delia Heroux, Lynn Crawford, Gail Gauvreau, Judah Denburg, Linda Pedder, Paul K. Keith

A39 Evaluation of macrolide antibiotic hypersensitivity: the role of oral challenges in children

Bahar Torabi, Marie-Noel Primeau, Christine Lejtenyi, Elaine Medoff, Jennifer Mill, Moshe Ben-Shoshan

A40 Venom allergy testing: is a graded approach necessary?

Jaclyn A. Quirt, Xia Wen, Jonathan Kim, Angel Jimenez Herrero, Harold L. Kim

A41 The role of oral challenges in evaluating cephalosporin hypersensitivity reactions in children

Magdalena J. Grzyb, Marie-Noël Primeau, Christine Lejtenyi, Elaine Medoff, Jennifer Mill, Moshe Ben-Shoshan

A42 Breastfeeding and infant wheeze, atopy and atopic dermatitis: findings from the Canadian Healthy Infant Longitudinal Development Study

Meghan B. Azad, Zihang Lu, Allan B. Becker, Padmaja Subbarao, Piushkumar J. Mandhane, Stuart E. Turvey, Malcolm R. Sears, the CHILD Study Investigators

A43 IL33 DNA methylation in bronchial epithelial cells is associated to asthma

Anne-Marie Boucher-Lafleur, Valérie Gagné-Ouellet, Éric Jacques, Sophie Plante, Jamila Chakir, Catherine Laprise

A44 NRF2 mediates the antioxidant response to organic dust-induced oxidative stress in bronchial epithelial cells

Michael Chen, Toby McGovern, Mikael Adner, James G. Martin

A45 The effects of perinatal distress, immune biomarkers and mother-infant interaction quality on childhood atopic dermatitis (rash) at 18 months

Nela Cosic, Henry Ntanda, Gerald Giesbrecht, Anita Kozyrskyj, Nicole Letourneau

A46 Examining the immunological mechanisms associated with cow’s milk allergy

Bassel Dawod, Jean Marshall

A47 Tryptase levels in children presenting with anaphylaxis to the Montréal Children’s Hospital

Sarah De Schryver, Michelle Halbrich, Ann Clarke, Sebastian La Vieille, Harley Eisman, Reza Alizadehfar, Lawrence Joseph, Judy Morris, Moshe Ben-Shoshan

A48 Secondhand tobacco smoke exposure in infancy and the development of food hypersensitivity from childhood to adolescence

Laura Y. Feldman, Jesse D. Thacher, Inger Kull, Erik Melén, Göran Pershagen, Magnus Wickman, Jennifer L. P. Protudjer, Anna Bergström

A49 Combined exposure to diesel exhaust and allergen enhances allergic inflammation in the bronchial submucosa of atopic subjects

Ali Hosseini, Tillie L. Hackett, Jeremy Hirota, Kelly McNagny, Susan Wilson, Chris Carlsten

A50 Comparison of skin-prick test measurements by an automated system against the manual method

Saiful Huq, Rishma Chooniedass, Brenda Gerwing, Henry Huang, Diana Lefebvre, Allan Becker

A51 The accurate identification and quantification of urinary biomarkers of asthma and COPD through the use of novel DIL- LC-MS/MS methods

Mona M. Khamis, Hanan Awad, Kevin Allen, Darryl J. Adamko, Anas El-Aneed

A52 Systemic immune pathways associated with the mechanism of Cat-Synthetic Peptide Immuno-Regulatory Epitopes, a novel immunotherapy, in whole blood of cat-allergic people

Young Woong Kim, Daniel R. Gliddon, Casey P. Shannon, Amrit Singh, Pascal L. C. Hickey, Anne K. Ellis, Helen Neighbour, Mark Larche, Scott J. Tebbutt

A53 Reducing the health disparities: online support for children with asthma and allergies from low-income families

Erika Ladouceur, Miriam Stewart, Josh Evans, Jeff Masuda, Nicole Letourneau, Teresa To, Malcolm King

A54 Epigenetic association of PSORS1C1 and asthma in the Saguenay-Lac-Saint-Jean asthma study

Miriam Larouche, Liming Liang, Catherine Laprise

A55 IL-33 induces cytokine and chemokine production in human mast cells

Stephanie A. Legere, Ian D. Haidl, Jean-Francois Legaré, Jean S. Marshall

A56 Reference ranges for lung clearance index from infancy to adolescence for Canadian population

Zihang Lu, Malcolm Sears, Theo J. Moraes, Felix Ratjen, Per Gustafsson, Wendy Lou, Padmaja Subbarao

A57 Kingston Allergy Birth Cohort: cohort profile and mother/child characteristics to age 2

Michelle L. North, Elizabeth Lee, Vanessa Omana, Jenny Thiele, Jeff Brook, Anne K. Ellis

A58 Cow’s milk protein specific IgE, IgA and IgG4 as a predictor of outcome in oral immunotherapy

Tanvir Rahman, Duncan Lejtenyi, Sarah De Schryver, Ryan Fiter, Ciriaco Piccirillo, Moshe Ben-Shoshan, Bruce Mazer

A59 Age of peanut introduction and development of reactions and sensitization to peanut

Elinor Simons, Allan B. Becker, Rishma Chooniedass, Kyla Hildebrand, Edmond S. Chan, Stuart Turvey, Padmaja Subbarao, Malcolm Sears

A60 Multi-omic blood biomarker signatures of the late phase asthmatic response

Amrit Singh, Casey P. Shannon, Young Woong Kim, Mari DeMarco, Kim-Anh Le Cao, Gail M. Gauvreau, J. Mark FitzGerald, Louis-Philippe Boulet, Paul M. O’Byrne, Scott J. Tebbutt

A61 Early life gut microbial alterations in children diagnosed with asthma by three years of age

Leah T. Stiemsma, Marie-Claire Arrieta, Jasmine Cheng, Pedro A. Dimitriu, Lisa Thorson, Sophie Yurist, Boris Kuzeljevic, Diana L. Lefebvre, Padmaja Subbarao, Piush Mandhane, Allan Becker, Malcolm R. Sears, Kelly M. McNagny, Tobias Kollmann, the CHILD Study Investigators, William W. Mohn, B. Brett Finlay, Stuart E. Turvey

A62 The relationship between food sensitization and atopic dermatitis at age 1 year in a Canadian birth cohort

Maxwell M. Tran, Diana L. Lefebvre, Chinthanie F. Ramasundarahettige, Allan B. Becker, Wei Hao Dai, Padmaja Subbarao, Piush J. Mandhane, Stuart E. Turvey, Malcolm R. Sears

A63 Allergen inhalation enhances Toll-like receptor-induced thymic stromal lymphopoietin receptor expression by hematopoietic progenitor cells in mild asthmatics

Damian Tworek, Delia Heroux, Seamus N. O’Byrne, Paul M. O’Byrne, Judah A. Denburg

A64 The Allergic Rhinitis Clinical Investigator Collaborative – replicated eosinophilia on repeated cumulative allergen challenges in nasal lavage samples

Laura Walsh, Mena Soliman, Jenny Thiele, Lisa M. Steacy, Daniel E. Adams, Anne K. Ellis

A65 The CHILD Study: optimizing subject retention in pediatric longitudinal cohort research

Linda Warner, Mary Ann Mauro, Robby Mamonluk, Stuart E. Turvey

A66 Differential expression of C3a and C5a in allergic asthma

ChenXi Yang, Amrit Singh, Casey P. Shannon, Young Woong Kim, Ed M. Conway, Scott J. Tebbutt

Ranitidine modifies myeloid cell populations and inhibits breast tumor development and spread in mice

Histamine receptor 2 (H2) antagonists are widely used clinically for the control of gastrointestinal symptoms, but also impact immune function. They have been reported to reduce tumor growth in established colon and lung cancer models. Histamine has also been reported to modify populations of myeloid-derived suppressor cells (MDSCs). We have examined the impact of the widely used H2 antagonist ranitidine, on both myeloid cell populations and tumor development and spread, in three distinct models of breast cancer that highlight different stages of cancer progression. Oral ranitidine treatment significantly decreased the monocytic MDSC population in the spleen and bone marrow both alone and in the context of an orthotopic breast tumor model. H2 antagonists ranitidine and famotidine, but not H1 or H4 antagonists, significantly inhibited lung metastasis in the 4T1 model. In the E0771 model, ranitidine decreased primary tumor growth while omeprazole treatment had no impact on tumor development. Gemcitabine treatment prevented the tumor growth inhibition associated with ranitidine treatment. In keeping with ranitidine-induced changes in myeloid cell populations in non-tumor-bearing mice, ranitidine also delayed the onset of spontaneous tumor development, and decreased the number of tumors that developed in LKB1^−/−/NIC mice. These results indicate that ranitidine alters monocyte populations associated with MDSC activity, and subsequently impacts breast tumor development and outcome. Ranitidine has potential as an adjuvant therapy or preventative agent in breast cancer and provides a novel and safe approach to the long-term reduction of tumor-associated immune suppression.

Prenatal exposure to phthalates, bisphenol A and perfluoroalkyl substances and cord blood levels of IgE, TSLP and IL-33

The fetal time period is a critical window of immune system development and resulting heightened susceptibility to the adverse effects of environmental exposures. Epidemiologists and toxicologists have hypothesized that phthalates, bisphenol A (BPA) and perfluoroalkyl substance have immunotoxic properties. Immunotoxic effects of chemicals may manifest in an altered immune system profile at birth. Immunoglobulin E, thymic stromal lymphopoietin (TSLP), and interleukin-33 (IL-33) are integral in the etiology of childhood allergy and detectable at birth. The objective of this study was to determine the association between maternal levels of phthalates, bisphenol A (BPA), and perfluoroalkyl substances and elevated umbilical cord blood levels of IgE, TSLP, and IL-33. This study utilized data collected in the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a trans-Canada cohort study of 2001 pregnant women. Of these women, 1258 had a singleton, term birth and cord blood sample. A Bayesian hierarchical model was employed to determine associations between log-transformed continuous variables and immune system biomarkers while adjusting for potential confounding from correlated environmental contaminants. Inverse, nonlinear associations were observed between maternal urinary MCPP levels and elevated levels of both IL-33/TSLP and IgE and between maternal urinary BPA levels and elevated levels of IL-33/TSLP. In this primarily urban Canadian population of pregnant women and their newborns, maternal urinary and plasma concentrations of phthalate metabolites, BPA, and perfluoroalkyl substances were not associated with immunotoxic effects that manifest as increased odds of elevated levels of IgE, TSLP or IL-33.

Maternal exposure to metals and persistent pollutants and cord blood immune system biomarkers

BACKGROUND

The fetal time period is a critical window of immune system development and resulting heightened susceptibility to the adverse effects of environmental exposures. Epidemiologists and toxicologists have hypothesized that persistent organic pollutants, pesticides and metals have immunotoxic properties. Immunotoxic effects may manifest as an altered immune system profile at birth. Immunoglobulin E, thymic stromal lymphopoietin (TSLP), and interleukin-33 (IL-33) may be implicated in the etiology of childhood allergy and are detectable at birth. The objective of this study was to examine the potential relationship between maternal concentrations of metals, persistent organic pollutants, and pesticides and elevated umbilical cord blood concentrations of IgE, TSLP, and IL-33 in a Canadian birth cohort.

METHODS

This study utilized data collected in the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a trans-Canada cohort study of 2,001 pregnant women. Of these women, 1258 had a singleton, term birth and cord blood sample. Logistic regression was used to determine associations between log-transformed continuous variables and immune system biomarkers.

RESULTS

Inverse relationships were observed between lead, DDE, PCB-118, and a summary index of organophosphorous metabolites and jointly elevated concentrations of IL-33 and TSLP. None of the environmental contaminants were associated with increased odds of a high cord blood immune system biomarker concentration.

CONCLUSIONS

In this primarily urban Canadian population of pregnant women and their newborns, maternal blood or urine concentrations of persistent organic pollutants, pesticides, and metals were not associated with immunotoxic effects that manifest as increased odds of elevated concentrations of IgE, TSLP or IL-33.

Prospective study of infantile haemangiomas: incidence, clinical characteristics and association with placental anomalies

BACKGROUND

The aetiology and exact incidence of infantile haemangiomas (IHs) are unknown. Prior studies have noted immunohistochemical and biological characteristics shared by IHs and placental tissue.

OBJECTIVES

We investigated the possible association between placental anomalies and the development of IHs, as well as the demographic characteristics and other risk factors for IHs.

PATIENTS AND METHODS

Pregnant women (n = 578) were prospectively enrolled and their offspring followed for 9 months. Placental evaluations were performed and demographic data collected on all mother-infant pairs.

RESULTS

We evaluated 594 infants: 34 haemangiomas [either IH or congenital (CH)] were identified in 29 infants, yielding an incidence of 4·5% for IH (27 infants) and 0·3% for CH (two infants). Placental anomalies were noted in almost 35% of haemangioma-related pregnancies, approximately twice the incidence noted in pregnancies with unaffected infants (P = 0·025). Other risk factors for IH included prematurity (P = 0·016) and low birth weight (P = 0·028). All IHs were present by 3 months of age, and cessation of growth had occurred in all by 9 months of age. Most occurred on the trunk. Of note, 20% of identified IHs were abortive or telangiectatic in nature, small focal lesions that did not proliferate beyond 3 months of age. Only one IH required intervention.

CONCLUSIONS

This is the first prospective American study to document the incidence of IHs in infants followed from birth to early infancy. The association with placental anomalies was statistically significant. The overall incidence mirrors prior estimates, but the need for treatment was lower than previously reported.

Predictors of interleukin-33 and thymic stromal lymphopoietin levels in cord blood

BACKGROUND

The fetal immune system is a critical window of development. The epithelial cell-derived cytokines, thymic stromal lymphopoietin (TSLP), and interleukin-33 (IL-33) have received attention for their role in allergic responses but not been studied during this critical window. The objectives were to assess correlations among IL-33, TSLP, and IgE in umbilical cord blood samples and identify prenatal predictors of these biomarkers.

METHODS

This study utilized data and banked cord blood collected in the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a trans-Canada cohort study of 2001 pregnant women. Our analytic sample comprised the 1254 women with a singleton, term birth with a cord blood sample. Spearman correlation coefficients (SCC) and logistic regression models were used to examine associations between biomarkers and identify potential predictors of elevated biomarker levels.

RESULTS

Thymic stromal lymphopoietin and IL-33 were more strongly correlated with each other (SCC = 0.75, p < 0.0001) than with IgE (IL-33 SCC = 0.14, TSLP SCC = 0.21). Maternal allergy, heavy street traffic, and elevated birth weight were significantly associated with jointly elevated TSLP and IL-33 levels, whereas maternal age and female infant sex were inversely associated with elevated IgE.

CONCLUSIONS

In this population of Canadian women and infants, TSLP and IL-33 were detectable in cord blood, more strongly correlated with each other than with IgE, and associated with maternal characteristics indicative of inflammatory responses. This study motivates investigation into the value of cord blood IL-33 and TSLP levels as childhood allergy predictors and raises interesting questions regarding in utero coordinated regulation of these cytokines.

Human mast cell activation with viruses and pathogen products

Mast cells have been demonstrated to have critical roles in host defense against a number of types of pathogens. In order to better understand how mast cells participate in effective immune responses, it is important to evaluate their ability to respond directly to pathogens and their products. In the current chapter we provide a methodology to evaluate human mast cell responses to a number of bacterial and fungal pathogen products and to mammalian reovirus as a model of acute viral infection. These methods should provide key information necessary to aid in the effective design of experiments to evaluate human mast cell responses to a number of other organisms. However, it is important to carefully consider the biology of the mast cell subsets and pathogens involved and the optimal experimental conditions necessary to evaluate mediators of interest.

Toll-like receptor 2 as a regulator of oral tolerance in the gastrointestinal tract

Food allergy, other adverse immune responses to foods, inflammatory bowel disease, and eosinophilic esophagitis have become increasingly common in the last 30 years. It has been proposed in the "hygiene hypothesis" that dysregulated immune responses to environmental microbial stimuli may modify the balance between tolerance and sensitization in some patients. Of the pattern recognition receptors that respond to microbial signals, toll-like receptors (TLRs) represent the most investigated group. The relationship between allergy and TLR activation is currently at the frontier of immunology research. Although TLR2 is abundant in the mucosal environment, little is known about the complex relationship between bystander TLR2 activation by the commensal microflora and the processing of oral antigens. This review focuses on recent advances in our understanding of the relationship between TLR2 and oral tolerance, with an emphasis on regulatory T cells, eosinophils, B cells, IgA, intestinal regulation, and commensal microbes.

Mast cells as targets for immunotherapy of solid tumors

Mast cells have historically been studied mainly in the context of allergic disease. In recent years, we have come to understand the critical importance of mast cells in tissue remodeling events and their role as sentinel cells in the induction and development of effective immune responses to infection. Studies of the role of mast cells in tumor immunity are more limited. The pro-tumorigenic role of mast cells has been widely reported. However, mast cell infiltration predicts improved prognosis in some cancers, suggesting that their prognostic value may be dependent on other variables. Such factors may include the nature of local mast cell subsets and the various activation stimuli present within the tumor microenvironment. Experimental models have highlighted the importance of mast cells in orchestrating the anti-tumor events that follow immunotherapies that target innate immunity. Mast cells are long-lived tissue resident cells that are abundant around many solid tumors and are radiation resistant making them unique candidates for combined treatment modalities. This review will examine some of the key roles of mast cells in tumor immunity, with a focus on potential immunotherapeutic interventions that harness the sentinel role of mast cells.

MAPK kinase 3 is a tumor suppressor with reduced copy number in breast cancer

Cancers are initiated as a result of changes that occur in the genome. Identification of gains and losses in the structure and expression of tumor-suppressor genes and oncogenes lies at the root of the understanding of cancer cell biology. Here, we show that the mitogen-activated protein kinase (MAPK) MKK3 suppresses the growth of breast cancer, in which it varies in copy number. A pervasive loss of MKK3 gene copy number in patients with breast cancer is associated with an impairment of MKK3 expression and protein level in malignant tissues. To assess the functional role of MKK3 in breast cancer, we showed in an animal model that MKK3 activity is required for suppression of tumor growth. Active MKK3 enhanced expression of the cyclin-dependent kinase inhibitors p21(Cip1/Waf1) and p27(Kip1), leading to increased cell-cycle arrest in G1 phase of the cell cycle. Our results reveal the functional significance of MKK3 as a tumor suppressor and improve understanding of the dynamic role of the MAPK pathway in tumor progression.

Local and systemic immunological parameters associated with remission of asthma symptoms in children

The immunological and clinical parameters that are associated with asthma remission are poorly understood. The cytokine and local mediator changes associated with the resolution of asthma symptoms were examined in three groups of subjects 12-18 years of age (n = 15 in each group): (a) continuing asthma group (CA) who had persistent symptoms since early childhood, (b) an age, sex and atopic status-matched group who had persistent symptoms in early childhood but in whom these had resolved (RA), and (c) a non-atopic, non-asthmatic control group. Clinical parameters, sputum cell counts, peripheral blood mononuclear cell (PBMC) cytokine production and activation marker expression were determined. All of the CA had methacholine airway hyperresponsiveness compared with only half of the RA subjects. The CA showed elevated numbers of eosinophils and increased ECP and IL-5 in sputum, which were not observed in the RA. PBMC cytokine studies revealed increased production of the type 1 cytokines IL-12, IFN-γ and TNF-α in the CA group compared with the RA group, under a range of activation conditions, however, the production of IL-4 and IL-5 were unchanged. These findings suggest that decreased type 1 cytokine expression as well as decreased eosinophilic inflammation is associated with the resolution of asthma symptoms.

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.

Mast cells and IgE activation do not alter the development of oral tolerance in a murine model

BACKGROUND

In addition to their well-known role as potent effector cells in patients with allergic disease, mast cells have important immunomodulatory roles regulating tolerance in allograft rejection models. The roles of mast cells in oral tolerance development have not previously been examined.

OBJECTIVE

We sought to evaluate the importance of mast cells, IgE-mediated mast cell activation, and histamine receptor 1 or 2 blockade on oral tolerance development in mice.

METHODS

Oral tolerance was assessed in 2 mast cell-deficient murine strains (Kit(W-sh/W-sh) and Kit(W/W-v) mice) and control mice. Mice were fed ovalbumin (OVA) or peanut butter for 1 week and then immunized and boosted with relevant protein antigens. Antibody responses were assessed by using ELISA. The oral antihistamines pyrilamine and ranitidine were administered during tolerance induction to OVA. IgE-mediated mast cell activation was initiated during oral tolerance induction or OVA immunization. OVA-specific regulatory T cells were assessed in the Peyer patches, mesenteric lymph nodes, and spleens by using flow cytometry after adoptive transfer.

RESULTS

Oral tolerance was successfully induced to OVA and peanut butter in mast cell-deficient mice. Kit(W-sh/W-sh) mice had higher proportions of antigen-specific regulatory T cells in the mesenteric lymph nodes than mast cell-containing control mice. However, mast cell reconstitution studies suggested this effect was mast cell independent. Oral antihistamine treatments with pyrilamine or ranitidine did not impair tolerance and neither did IgE-mediated activation.

CONCLUSIONS

Mast cells are not necessary for the induction of oral tolerance, and allergic activation of mast cells does not impair tolerance to OVA. Oral antihistamine treatments do not disrupt the development of oral tolerance.

RNA sensors enable human mast cell anti-viral chemokine production and IFN-mediated protection in response to antibody-enhanced dengue virus infection

Dengue hemorrhagic fever and/or dengue shock syndrome represent the most serious pathophysiological manifestations of human dengue virus infection. Despite intensive research, the mechanisms and important cellular players that contribute to dengue disease are unclear. Mast cells are tissue-resident innate immune cells that play a sentinel cell role in host protection against infectious agents via pathogen-recognition receptors by producing potent mediators that modulate inflammation, cell recruitment and normal vascular homeostasis. Most importantly, mast cells are susceptible to antibody-enhanced dengue virus infection and respond with selective cytokine and chemokine responses. In order to obtain a global view of dengue virus-induced gene regulation in mast cells, primary human cord blood-derived mast cells (CBMCs) and the KU812 and HMC-1 mast cell lines were infected with dengue virus in the presence of dengue-immune sera and their responses were evaluated at the mRNA and protein levels. Mast cells responded to antibody-enhanced dengue virus infection or polyinosiniċpolycytidylic acid treatment with the production of type I interferons and the rapid and potent production of chemokines including CCL4, CCL5 and CXCL10. Multiple interferon-stimulated genes were also upregulated as well as mRNA and protein for the RNA sensors PKR, RIG-I and MDA5. Dengue virus-induced chemokine production by KU812 cells was significantly modulated by siRNA knockdown of RIG-I and PKR, in a negative and positive manner, respectively. Pretreatment of fresh KU812 cells with supernatants from dengue virus-infected mast cells provided protection from subsequent infection with dengue virus in a type I interferon-dependent manner. These findings support a role for tissue-resident mast cells in the early detection of antibody-enhanced dengue virus infection via RNA sensors, the protection of neighbouring cells through interferon production and the potential recruitment of leukocytes via chemokine production.

Virus stimulation of human mast cells results in the recruitment of CD56⁺ T cells by a mechanism dependent on CCR5 ligands

The trafficking of effector cells to sites of infection is crucial for antiviral responses. However, the mechanisms of recruitment of the interferon-γ-producing and cytotoxic CD56(+) T cells are poorly understood. Human mast cells are sentinel cells found in the skin and airway and produce selected proinflammatory mediators in response to multiple pathogen-associated signals. The role of human mast cell-derived chemokines in T-cell recruitment to virus infection was examined. Supernatants from primary human cord blood-derived mast cells (CBMCs) infected with mammalian reovirus were examined for chemokine production and utilized in chemotaxis assays. Virus-infected CBMCs produced several chemokines, including CCL3, CCL4, and CCL5. Supernatants from reovirus-infected CBMCs selectively induced the chemotaxis of CD8(+) T cells (10±1%) and CD3(+)CD56(+) T cells (19±5%). CD56(+) T-cell migration was inhibited by pertussis toxin (65±9%) and met-RANTES (56±7%), a CCR1/CCR5 antagonist. CD56(+) T cells expressed CCR5, but little CCR1. The depletion of CCL3, CCL4, and CCL5 from reovirus-infected CBMC supernatants significantly (41±10%) inhibited CD56(+) T-cell chemotaxis. This study demonstrates a novel role for mast cells and CCR5 in CD56(+) T-cell trafficking and suggests that human mast cells enhance immunity to viruses through the selective recruitment of cytotoxic effector cells to virus infection sites. These findings could be exploited to enhance local T-cell responses in chronic viral infection and malignancies at mast cell-rich sites.

Zebrafish mast cells possess an FcɛRI-like receptor and participate in innate and adaptive immune responses

We previously identified a zebrafish mast cell (MC) lineage and now aim to determine if these cells function analogously in innate and adaptive immunity like their mammalian counterparts. Intraperitoneal (IP) injection of compound 48/80 or live Aeromonas salmonicida resulted in significant MC degranulation evident histologically and by increased plasma tryptase compared with saline-injected controls (p=0.0006, 0.005, respectively). Pre-treatment with ketotifen abrogated these responses (p=0.0004, 0.005, respectively). Cross-reactivity was observed in zebrafish to anti-human high-affinity IgE receptor gamma (FcɛRIγ) and IgE heavy chain-directed antibodies. Whole mount in situ hybridization on 7-day embryos demonstrated co-localization of cpa5, a MC-specific marker, with myd88, a toll-like receptor adaptor, and zebrafish FcɛRI subunit homologs. Zebrafish injected IP with matched dinitrophenyl-sensitized mouse (anti-DNP) IgE and DNP-BSA or trinitrophenyl-sensitized mouse (anti-TNP) IgE and TNP-BSA demonstrated increased plasma tryptase compared with mismatched controls (p=0.03, 0.010, respectively). These results confirm functional conservation and validate the zebrafish model as an in vivo screening tool for novel MC modulating agents.

Tissue eosinophilia in a mouse model of colitis is highly dependent on TLR2 and independent of mast cells

The mechanisms initiating eosinophil influx into sites of inflammation have been well studied in allergic disease but are poorly understood in other settings. This study examined the roles of TLR2 and mast cells in eosinophil accumulation during a nonallergic model of eosinophilia-associated colitis. TLR2-deficient mice (TLR2(-/-)) developed a more severe colitis than wild-type mice in the dextran sodium sulfate (DSS) model. However, they had significantly fewer eosinophils in the submucosa of the cecum (P < 0.01) and mid-colon (P < 0.01) than did wild-type mice after DSS treatment. Decreased eosinophilia in TLR2(-/-) mice was associated with lower levels of cecal CCL11 (P < 0.01). Peritoneal eosinophils did not express TLR2 protein, but TLR2 ligand injection into the peritoneal cavity induced local eosinophil recruitment, indicating that TLR2 activation of other cell types can mediate eosinophil recruitment. After DSS treatment, mast cell-deficient (Kit(W-sh/W-sh)) mice had similar levels of intestinal tissue eosinophilia were observed as those in wild-type mice. However, mast cell-deficient mice were partially protected from DSS-induced weight loss, an effect that was reversed by mast cell reconstitution. Overall, this study indicates a critical role for indirect TLR2-dependent pathways, but not mast cells, in the generation of eosinophilia in the large intestine during experimental colitis and has important implications for the regulation of eosinophils at mucosal inflammatory sites.

A critical role for mast cells and mast cell-derived IL-6 in TLR2-mediated inhibition of tumor growth

Several TLR agonists are effective in tumor immunotherapy, but their early innate mechanisms of action, particularly those of TLR2 agonists, are unclear. Mast cells are abundant surrounding solid tumors where they are often protumorigenic and enhance tumor angiogenesis. However, antitumor roles for mast cells have also been documented. The impact of mast cells may be dependent on their activation status and mediator release in different tumors. Using an orthotopic melanoma model in wild-type C57BL/6 and mast cell-deficient Kit(W-sh/W-sh) mice and a complementary Matrigel-tumor model in C57BL/6 mice, mast cells were shown to be crucial for TLR2 agonist (Pam(3)CSK(4))-induced tumor inhibition. Activation of TLR2 on mast cells reversed their well-documented protumorigenic role. Tumor growth inhibition after peritumoral administration of Pam(3)CSK(4) was restored in Kit(W-sh/W-sh) mice by local reconstitution with wild-type, but not TLR2-deficient, mast cells. Mast cells secrete multiple mediators after Pam(3)CSK(4) activation, and in vivo mast cell reconstitution studies also revealed that tumor growth inhibition required mast cell-derived IL-6, but not TNF. Mast cell-mediated anticancer properties were multifaceted. Direct antitumor effects in vitro and decreased angiogenesis and recruitment of NK and T cells in vivo were observed. TLR2-activated mast cells also inhibited the growth of lung cancer cells in vivo. Unlike other immune cells, mast cells are relatively radioresistant making them attractive candidates for combined treatment modalities. This study has important implications for the design of immunotherapeutic strategies and reveals, to our knowledge, a novel mechanism of action for TLR2 agonists in vivo.