Regulation of mast cell-mediated innate immunity during early response to bacterial infection

Angiogenic Host Defense Peptide AG-30/5C and Bradykinin B2 Receptor Antagonist Icatibant Are G Protein Biased Agonists for MRGPRX2 in Mast Cells

AG-30/5C is an angiogenic host defense peptide that activates human mast cells (MC) via an unknown mechanism. Using short hairpin RNA-silenced human MC line LAD2 and stably transfected RBL-2H3 cells, we demonstrate that AG-30/5C induces MC degranulation via Mas-related G protein-coupled receptor X2 (MRGPRX2). Most G protein-coupled receptors signal via parallel and independent pathways mediated by G proteins and β-arrestins. AG-30/5C and compound 48/80 induced similar maximal MC degranulation via MRGPRX2, which was abolished by pertussis toxin. However, compound 48/80 induced a robust β-arrestin activation as determined by transcriptional activation following arrestin translocation (Tango), but AG-30/5C did not. Overnight culture of MC with compound 48/80 resulted in reduced cell surface MRGPRX2 expression, and this was associated with a significant decrease in subsequent MC degranulation in response to compound 48/80 or AG-30/5C. However, AG-30/5C pretreatment had no effect on cell surface MRGPRX2 expression or degranulation in response to compound 48/80 or AG-30/5C. Icatibant, a bradykinin B₂ receptor antagonist, promotes MC degranulation via MRGPRX2 and causes pseudoallergic drug reaction. Icatibant caused MC degranulation via a pertussis toxin-sensitive G protein but did not activate β-arrestin. A screen of the National Institutes of Health Clinical Collection library led to the identification of resveratrol as an inhibitor of MRGPRX2. Resveratrol inhibited compound 48/80-induced Tango and MC degranulation in response to compound 48/80, AG-30/5C, and Icatibant. This study demonstrates the novel finding that AG-30/5C and Icatibant serve as G protein-biased agonists for MRGPRX2, but compound 48/80 signals via both G protein and β-arrestin with distinct differences in receptor regulation.

Mast cells and histamine are triggering the NF-κB-mediated reactions of adult and aged perilymphatic mesenteric tissues to acute inflammation

This study aimed to establish mechanistic links between the aging-associated changes in the functional status of mast cells and the altered responses of mesenteric tissue and mesenteric lymphatic vessels (MLVs) to acute inflammation. We used an in vivo model of acute peritoneal inflammation induced by lipopolysaccharide treatment of adult (9-month) and aged (24-month) F-344 rats. We analyzed contractility of isolated MLVs, mast cell activation, activation of nuclear factor-κB (NF-κB) without and with stabilization of mast cells by cromolyn or blockade of all types of histamine receptors and production of 27 major pro-inflammatory cytokines in adult and aged perilymphatic mesenteric tissues and blood. We found that the reactivity of aged contracting lymphatic vessels to LPS-induced acute inflammation was abolished and that activated mast cells trigger NF-κB signaling in the mesentery through release of histamine. The aging-associated basal activation of mesenteric mast cells limits acute inflammatory NF-κB activation in aged mesentery. We conclude that proper functioning of the mast cell/histamine/NF-κB axis is necessary for reactions of the lymphatic vessels to acute inflammatory stimuli as well as for interaction and trafficking of immune cells near and within the collecting lymphatics.

Aged Lymphatic Vessels and Mast Cells in Perilymphatic Tissues

This review provides a comprehensive summary of research on aging-associated alterations in lymphatic vessels and mast cells in perilymphatic tissues. Aging alters structure (by increasing the size of zones with low muscle cell investiture), ultrastructure (through loss of the glycocalyx), and proteome composition with a concomitant increase in permeability of aged lymphatic vessels. The contractile function of aged lymphatic vessels is depleted with the abolished role of nitric oxide and an increased role of lymphatic-born histamine in flow-dependent regulation of lymphatic phasic contractions and tone. In addition, aging induces oxidative stress in lymphatic vessels and facilitates the spread of pathogens from these vessels into perilymphatic tissues. Aging causes the basal activation of perilymphatic mast cells, which, in turn, restricts recruitment/activation of immune cells in perilymphatic tissues. This aging-associated basal activation of mast cells limits proper functioning of the mast cell/histamine/NF-κB axis that is essential for the regulation of lymphatic vessel transport and barrier functions as well as for both the interaction and trafficking of immune cells near and within lymphatic collecting vessels. Cumulatively, these changes play important roles in the pathogenesis of alterations in inflammation and immunity associated with aging.

Emerging concepts: mast cell involvement in allergic diseases

In a process known as overt degranulation, mast cells can release all at once a diverse array of products that are preformed and present within cytoplasmic granules. This occurs typically within seconds of stimulation by environmental factors and allergens. These potent, preformed mediators (ie, histamine, heparin, serotonin, and serine proteases) are responsible for the acute symptoms experienced in allergic conditions such as allergic conjunctivitis, allergic rhinitis, allergy-induced asthma, urticaria, and anaphylaxis. Yet, there is reason to believe that the actions of mast cells are important when they are not degranulating. Mast cells release preformed mediators and inflammatory cytokines for periods after degranulation and even without degranulating at all. Mast cells are consistently seen at sites of chronic inflammation, including nonallergic inflammation, where they have the ability to temper inflammatory processes and shape tissue morphology. Mast cells can trigger actions and chemotaxis in other important immune cells (eg, eosinophils and the newly discovered type 2 innate lymphocytes) that then make their own contributions to inflammation and disease. In this review, we will discuss the many known and theorized contributions of mast cells to allergic diseases, focusing on several prototypical allergic respiratory and skin conditions: asthma, chronic rhinosinusitis, aspirin-exacerbated respiratory disease, allergic conjunctivitis, atopic dermatitis, and some of the more common medication hypersensitivity reactions. We discuss traditionally accepted roles that mast cells play in the pathogenesis of each of these conditions, but we also delve into new areas of discovery and research that challenge traditionally accepted paradigms.

Activation of human mast cells by retrocyclin and protegrin highlight their immunomodulatory and antimicrobial properties

Preclinical evaluation of Retrocyclins (RC-100, RC-101) and Protegrin-1 (PG-1) antimicrobial peptides (AMPs) is important because of their therapeutic potential against bacterial, fungal and viral infections. Human mast cells (HMCs) play important roles in host defense and wound healing but the abilities of retrocyclins and protegrin-1 to harness these functions have not been investigated. Here, we report that chemically synthesized RC-100 and PG-1 caused calcium mobilization and degranulation in HMCs but these responses were not blocked by an inhibitor of formyl peptide receptor-like 1 (FPRL1), a known receptor for AMPs. However, RC-100 and PG-1 induced degranulation in rat basophilic leukemia (RBL-2H3) cells stably expressing Mas related G protein coupled receptor X2 (MrgX2). Chemical synthesis of these AMPs is prohibitively expensive and post-synthesis modifications (cyclization, disulfide bonds, folding) are inadequate for optimal antimicrobial activity. Indeed, we found that synthetic RC-100, which caused mast cell degranulation via MrgX2, did not display any antimicrobial activity. Green-fluorescent protein (GFP)-tagged RC-101 (analog of RC-100) and GFP-tagged PG-1 purified from transgenic plant chloroplasts killed bacteria and induced mast cell degranulation. Furthermore, GFP-PG1 bound specifically to RBL-2H3 cells expressing MrgX2. These findings suggest that retrocyclins and protegrins activate HMCs independently of FPRL1 but via MrgX2. Harnessing this novel feature of AMPs to activate mast cell's host defense/wound healing properties in addition to their antimicrobial activities expands their clinical potential. Low cost production of AMPs in plants should facilitate their advancement to the clinic overcoming major hurdles in current production systems.

Roles of Mas-related G protein-coupled receptor X2 on mast cell-mediated host defense, pseudoallergic drug reactions, and chronic inflammatory diseases

Mast cells (MCs), which are granulated tissue-resident cells of hematopoietic lineage, contribute to vascular homeostasis, innate/adaptive immunity, and wound healing. However, MCs are best known for their roles in allergic and inflammatory diseases, such as anaphylaxis, food allergy, rhinitis, itch, urticaria, atopic dermatitis, and asthma. In addition to the high-affinity IgE receptor (FcεRI), MCs express numerous G protein-coupled receptors (GPCRs), which are the largest group of membrane receptor proteins and the most common targets of drug therapy. Antimicrobial host defense peptides, neuropeptides, major basic protein, eosinophil peroxidase, and many US Food and Drug Administration-approved peptidergic drugs activate human MCs through a novel GPCR known as Mas-related G protein-coupled receptor X2 (MRGPRX2; formerly known as MrgX2). Unique features of MRGPRX2 that distinguish it from other GPCRs include their presence both on the plasma membrane and intracellular sites and their selective expression in MCs. In this article we review the possible roles of MRGPRX2 on host defense, drug-induced anaphylactoid reactions, neurogenic inflammation, pain, itch, and chronic inflammatory diseases, such as urticaria and asthma. We propose that host defense peptides that kill microbes directly and activate MCs through MRGPRX2 could serve as novel GPCR targets to modulate host defense against microbial infection. Furthermore, mAbs or small-molecule inhibitors of MRGPRX2 could be developed for the treatment of MC-dependent allergic and inflammatory disorders.

Human umbilical cord blood mesenchymal stem cell-derived PGE2 and TGF-β1 alleviate atopic dermatitis by reducing mast cell degranulation

Mesenchymal stem cell (MSC) is a promising tool for the therapy of immune disorders. However, their efficacy and mechanisms in treating allergic skin disorders are less verified. We sought to investigate the therapeutic efficacy of human umbilical cord blood-derived MSCs (hUCB-MSCs) against murine atopic dermatitis (AD) and to explore distinct mechanisms that regulate their efficacy. AD was induced in mice by the topical application of Dermatophagoides farinae. Naïve or activated-hUCB-MSCs were administered to mice, and clinical severity was determined. The subcutaneous administration of nucleotide-binding oligomerization domain 2 (NOD2)-activated hUCB-MSCs exhibited prominent protective effects against AD, and suppressed the infiltration and degranulation of mast cells (MCs). A β-hexosaminidase assay was performed to evaluate the effect of hUCB-MSCs on MC degranulation. NOD2-activated MSCs reduced the MC degranulation via NOD2-cyclooxygenase-2 signaling. In contrast to bone marrow-derived MSCs, hUCB-MSCs exerted a cell-to-cell contact-independent suppressive effect on MC degranulation through the higher production of prostaglandin E2 (PGE2 ). Additionally, transforming growth factor (TGF)-β1 production from hUCB-MSCs in response to interleukin-4 contributed to the attenuation of MC degranulation by downregulating FcεRI expression in MCs. In conclusion, the subcutaneous application of NOD2-activated hUCB-MSCs can efficiently ameliorate AD, and MSC-derived PGE2 and TGF-β1 are required for the inhibition of MC degranulation.

α-Hemolysin enhances Staphylococcus aureus internalization and survival within mast cells by modulating the expression of β1 integrin

Mast cells (MCs) are important sentinels of the host defence against invading pathogens. We previously reported that Staphylococcus aureus evaded the extracellular antimicrobial activities of MCs by promoting its internalization within these cells via β1 integrins. Here, we investigated the molecular mechanisms governing this process. We found that S. aureus responded to the antimicrobial mediators released by MCs by up-regulating the expression of α-hemolysin (Hla), fibronectin-binding protein A and several regulatory systems. We also found that S. aureus induced the up-regulation of β1 integrin expression on MCs and that this effect was mediated by Hla-ADAM10 (a disintegrin and metalloproteinase 10) interaction. Thus, deletion of Hla or inhibition of Hla-ADAM10 interaction significantly impaired S. aureus internalization within MCs. Furthermore, purified Hla but not the inactive HlaH35L induced up-regulation of β1 integrin expression in MCs in a dose-dependent manner. Our data support a model in which S. aureus counter-reacts the extracellular microbicidal mechanisms of MCs by increasing expression of fibronectin-binding proteins and by inducing Hla-ADAM10-mediated up-regulation of β1 integrin in MCs. The up-regulation of bacterial fibronectin-binding proteins, concomitantly with the increased expression of its receptor β1 integrin on the MCs, resulted in enhanced S. aureus internalization through the binding of fibronectin-binding proteins to integrin β1 via fibronectin.

Mast cells' integrated actions with eosinophils and fibroblasts in allergic inflammation: implications for therapy

Mast cells (MCs) and eosinophils (Eos) are the key players in the development of allergic inflammation (AI). Their cross-talk, named the Allergic Effector Unit (AEU), takes place through an array of soluble mediators and ligands/receptors interactions that enhance the functions of both the cells. One of the salient features of the AEU is the CD48/2B4 receptor/ligand binding complex. Furthermore, MCs and Eos have been demonstrated to play a role not only in AI but also in the modulation of its consequence, i.e., fibrosis/tissue remodeling, by directly influencing fibroblasts (FBs), the main target cells of these processes. In turn, FBs can regulate the survival, activity, and phenotype of both MCs and Eos. Therefore, a complex three players, MCs/Eos/FBs interaction, can take place in various stages of AI. The characterization of the soluble and physical mediated cross talk among these three cells might lead to the identification of both better and novel targets for the treatment of allergy and its tissue remodeling consequences.

Aged lymphatic contractility: recent answers and new questions

Abstract An overview is presented of recent findings related to biology of aging of the lymph transport system. The authors discuss recently obtained data on the aging-associated alterations of lymphatic contractility in thoracic duct and mesenteric lymphatic vessels; on comparisons of function of aged mesenteric lymphatic vessels in situ versus isolated specimens and important conclusions which arose from these studies; on aging-associated changes in functional status of mast cells located close to aged mesenteric lymphatic vessels; on evidence of presence of oxidative stress in aged lymphatic vessels and changes in arrangement of muscle cells in their walls. The authors conclude that future continuation of the research efforts in this area is necessary and will be able to provide not only novel fundamental knowledge on the biology of lymphatic aging, but also will create solid foundation for the subsequent developments of lymphatic-oriented therapeutic interventions in many diseases of the elderly.

Effects of Lactoferrin on IL-6 Production by Peritoneal and Alveolar Cells in Cyclophosphamide-Treated Mice

Previous studies have shown that oral treatment with lactoferrin (LF) restores the immune response in cyclophosphamide (CP) immunocompromised mice. The aim of the present investigation was to determine the regulatory ability of LF on the production of interleukin 6 (IL-6) in peritoneal and alveolar cells, derived from CP-treated mice. CBA mice were injected with a single, intraperitoneal (i.p.) dose of CP (350 mg/kg body weight) followed by LF administered in drinking water (0.5% solution) for 21 days. The control counterparts were given water. Peritoneal and alveolar cells were isolated from mice and the production of IL-6, both spontaneous and lipopolysaccharide (LPS) induced, was determined in 24h cell cultures using a bioassay. The results showed increased production of IL-6 in both CP-treated mice and in mice given, in addition, LF. The administration of LF alone led also to an increase in IL-6 production by the cell cultures. Intravenous (i.v.) administration of LPS resulted in a significant increase in IL-6 serum levels in CP and CP/LF but not in LF-treated mice. Analysis of cell type composition in the peritoneal cavity revealed a strong increase in mastocyte and neutrophil content in CP and CP/LF-treated groups. Our findings suggest that enhanced IL-6 production in CP and CP/LF-treated mice may contribute to reconstitution of immune system function in immunocompromised mice.

Aging-associated shifts in functional status of mast cells located by adult and aged mesenteric lymphatic vessels

We had previously proposed the presence of permanent stimulatory influences in the tissue microenvironment surrounding the aged mesenteric lymphatic vessels (MLV), which influence aged lymphatic function. In this study, we performed immunohistochemical labeling of proteins known to be present in mast cells (mast cell tryptase, c-kit, prostaglandin D(2) synthase, histidine decarboxylase, histamine, transmembrane protein 16A, and TNF-α) with double verification of mast cells in the same segment of rat mesentery containing MLV by labeling with Alexa Fluor 488-conjugated avidin followed by toluidine blue staining. Additionally, we evaluated the aging-associated changes in the number of mast cells located by MLV and in their functional status by inducing mast cell activation by various activators (substance P; anti-rat DNP Immunoglobulin E; peptidoglycan from Staphyloccus aureus and compound 48/80) in the presence of ruthenium red followed by subsequent staining by toluidine blue. We found that there was a 27% aging-associated increase in the total number of mast cells, with an ∼400% increase in the number of activated mast cells in aged mesenteric tissue in resting conditions with diminished ability of mast cells to be newly activated in the presence of inflammatory or chemical stimuli. We conclude that higher degree of preactivation of mast cells in aged mesenteric tissue is important for development of aging-associated impairment of function of mesenteric lymphatic vessels. The limited number of intact aged mast cells located close to the mesenteric lymphatic compartments to react to the presence of acute stimuli may be considered contributory to the aging-associated deteriorations in immune response.

Anaplasma phagocytophilum infects mast cells via alpha1,3-fucosylated but not sialylated glycans and inhibits IgE-mediated cytokine production and histamine release

Mast cells are sentinels for infection. Upon exposure to pathogens, they release their stores of proinflammatory cytokines, chemokines, and histamine. Mast cells are also important for the control of certain tick-borne infections. Anaplasma phagocytophilum is an obligate intracellular tick-transmitted bacterium that infects neutrophils to cause the emerging disease granulocytic anaplasmosis. A. phagocytophilum adhesion to and infection of neutrophils depend on sialylated and α1,3-fucosylated glycans. We investigated the hypotheses that A. phagocytophilum invades mast cells and inhibits mast cell activation. We demonstrate that A. phagocytophilum binds and/or infects murine bone marrow-derived mast cells (BMMCs), murine peritoneal mast cells, and human skin-derived mast cells. A. phagocytophilum infection of BMMCs depends on α1,3-fucosylated, but not sialylated, glycans. A. phagocytophilum binding to and invasion of BMMCs do not elicit proinflammatory cytokine secretion. Moreover, A. phagocytophilum-infected cells are inhibited in the release of tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), IL-13, and histamine following stimulation with IgE or antigen. Thus, A. phagocytophilum mitigates mast cell activation. These findings potentially represent a novel means by which A. phagocytophilum usurps host defense mechanisms and shed light on the interplay between mast cells and vector-borne bacterial pathogens.

Mast cell/IL-4 control of Francisella tularensis replication and host cell death is associated with increased ATP production and phagosomal acidification

Mast cells are now recognized as effective modulators of innate immunity. We recently reported that mast cells and secreted interleukin-4 (IL-4) effectively control intramacrophage replication of Francisella tularensis Live Vaccine Strain (LVS), and that mice deficient in mast cells or IL-4 receptor (IL-4R(-/-)) exhibit greater susceptibility to pulmonary challenge. In this study, we further evaluated the mechanism(s) by which mast cells/IL-4 control intramacrophage bacterial replication and host cell death, and found that IL-4R(-/-) mice exhibited significantly greater induction of active caspase-3 within lung macrophages than wild-type animals following intranasal challenge with either LVS or the human virulent type A strain SCHU S4. Treatment of LVS-infected bone-marrow-derived macrophages with a pancaspase inhibitor (zVAD) did not alter bacterial replication, but minimized active caspase-3 and other markers (Annexin V and propidium iodide) of cell death, whereas treatment with both rIL-4 and zVAD resulted in concomitant reduction of both parameters, suggesting that inhibition of bacterial replication by IL-4 was independent of caspase activation. Interestingly, IL-4-treated infected macrophages exhibited significantly increased ATP production and phagolysosomal acidification, as well as enhanced mannose receptor upregulation and increased internalization with acidification, which correlated with observations in mast cell-macrophage co-cultures, with resultant decreases in F. tularensis replication.

Janus kinase-3 dependent inflammatory responses in allergic asthma

Allergic asthma is a chronic inflammatory condition of the lung characterized by reversible airway obstruction, high serum immunoglobulin (Ig) E levels, and chronic airway inflammation. A number of cells including mast cells, T cells, macrophages and dendritic cells play a role in the pathogenesis of the disease. Janus kinase (JAK)-3, a non-receptor protein tyrosine kinase, traditionally known to mediate cytokine signaling, also regulates functional responses of these cells. In this review the role of JAK-3 in regulating various pathogenic processes in allergic asthma is discussed. We propose that targeting JAK-3 is a rationale approach to control the inflammatory responses of multiple cell types responsible for the pathogenesis of allergic asthma.

Stable overexpression of miRNAs in bone marrow-derived murine mast cells using lentiviral expression vectors

MicroRNAs (miRNAs) constitute a class of molecules regulating gene expression in many different cell types, including cells of the mammalian immune system. Indeed, changes in miRNA expression patterns have been implicated in various physiological and pathological processes. Mast cells (MCs) are hematopoietic cells that originate in the bone marrow and migrate into the tissues, where they mature and reside. They have an important immunoregulatory and effector role in IgE-associated allergic disorders, as well as in certain innate and adaptive immune responses. An effective way to explore the functions of miRNAs in murine MCs includes the modification of miRNA expression in primary bone marrow-derived mast cells (BMMCs), followed by the analysis of the phenotypic consequences of such perturbation. In this chapter, we describe how to differentiate BMMCs and transduce them with lentiviruses. As an example, we expressed miR-221 and miR-222, which showed stable expression in BMMCs and acted as post-transcriptional regulators of c-Kit expression.

Metabolic patterns (NAD(P)H) in rat basophilic leukemia (RBL-2H3) cells and human hepatocellular carcinoma (Hep G2) cells with autofluorescence imaging

Although the spatial and temporal distributions of cellular NAD(P)H concentrations have been theoretically predicted as typical patterns of the metabolism in living cells, so far such a pattern was observed only in neutrophils. In this work, the dynamic NAD(P)H distributions in rat basophilic leukemia (RBL-2H3) and human hepatocellular carcinoma (Hep G2) cells were studied by imaging the autofluorescence of cellular NAD(P)H with a sensitive CCD detector in a confocal microscope. The typical pattern of the cytoplasmic NAD(P)H wave traveling along the long axis of the elongated cell with a velocity of 2.2+/-0.6 mircom/s was detected in RBL-2H3 cells. While in the case of Hep G2 cells, only the oscillation of the mitochondrial NAD(P)H was observed because the NAD(P)H mainly localized in mitochondria of Hep G2 cells. These results confirm the metabolic pattern of NAD(P)H in living cells and suggest that the expression of the metabolic pattern probably differs in different cell lines.

Human natural killer cells exposed to IL-2, IL-12, IL-18, or IL-4 differently modulate priming of naive T cells by monocyte-derived dendritic cells

Dendritic cells (DCs) play a crucial role in naive T-cell priming. Recent data suggested that natural killer (NK) cells can influence the capability of DCs to promote Th1 polarization. This regulatory function is primarily mediated by cytokines released in the microenvironment during inflammatory responses involving NK cells. In this study, we show that human NK cells exposed for short time to interleukin (IL)-12, IL-2, or IL-18, promote distinct pathways of Th1 priming. IL-12- or IL-2-conditioned NK cells induce maturation of DCs capable of priming IFN-gamma-producing Th1 cells. On the other hand, IL-18-conditioned NK cells induce Th1 polarization only when cocultured with both DCs and T cells. In this case, IL-2 released by T cells and IL-12 derived from DCs during the priming process promote interferon (IFN)-gamma production. In contrast, when NK cells are exposed to IL-4, nonpolarized T cells releasing only low levels of IL-2 are generated. Thus, the prevalence of IL-12, IL-2, IL-18, or IL-4 at inflammatory sites may differentially modulate the NK-cell interaction with DCs, leading to different outcomes in naive T-cell polarization.

Effects of low power laser irradiation on intracellular calcium and histamine release in RBL-2H3 mast cells

Although laser irradiation has been reported to promote skin wound healing, the mechanism is still unclear. As mast cells are found to accumulate at the site of skin wounds we hypothesized that mast cells might be involved in the biological effects of laser irradiation. In this work the mast cells, RBL-2H3, were used in vitro to investigate the effects of laser irradiation on cellular responses. After laser irradiation, the amount of intracellular calcium ([Ca2+]i) was increased, followed by histamine release, as measured by confocal fluorescence microscopy with Fluo-3/AM staining and a fluorescence spectrometer with o-phthalaldehyde staining, respectively. The histamine release was mediated by the increment of [Ca2+]i from the influx of the extracellular buffer solution through the cation channel protein, transient receptor potential vanilloid 4 (TRPV4). The TRPV4 inhibitor, Ruthenium Red (RR) can effectively block such histamine release, indicating that TRPV4 was the key factor responding to laser irradiation. These induced responses of mast cells may provide an explanation for the biological effects of laser irradiation on promoting wound healing, as histamine is known to have multi-functions on accelerating wound healing.

Mast cells initiate early anti-Listeria host defences

The Gram-positive bacterium Listeria monocytogenes (L. m.) is the aetiological agent of listeriosis. The early phase listeriosis is characterized by strong innate host responses that play a major role in bacterial clearance. This is emphasized by the fact that mice deficient in T and B cells have a remarkable ability to control infection. Mast cells, among the principal effectors of innate immunity, have largely been studied in the context of hyper-reactive conditions such as allergy and autoimmune diseases. In the present study, we evaluated the significance of mast cells during the early phase of listeriosis. Compared with controls, mice depleted of mast cells showed hundred-fold higher bacterial burden in spleen and liver and were significantly impaired in neutrophil mobilization. Although L. m. interacts with and triggers mast cell degranulation, bacteria were hardly found within such cells. Mainly neutrophils and macrophages phagozytosed L. m. Thus, mast cells control infection not via direct bacterial uptake, but by initiating neutrophils influx to the site of infection. We show that this is initiated by pre-synthesized TNF-alpha, rapidly secreted by mast cell upon activation by L. m. We also show that upon recruitment, neutrophils also become activated and additionally secrete TNF-alpha thus amplifying the anti-L. m. inflammatory response.

Mast cells play a crucial role in Staphylococcus aureus peptidoglycan-induced diarrhea

Bacterium-induced diarrhea results in 2 to 2.5 million deaths in the world each year. The mechanism needs to be further understood. Staphylococcus aureus infection has a close relation with diarrhea; its cell wall component peptidoglycan (PGN) has strong biological activity on immune cells and possibly plays a role in S. aureus-induced diarrhea. The present study showed that oral PGN-induced diarrhea in mice in a dose-dependent manner. Intestinal epithelial cells absorbed PGN via the intracellular pathway. Intestinal mast cells were activated after PGN gavage. Toll-like receptor (TLR)2 expression was detected in mast cells in the intestine as well as in the murine mast cell line p815 cells. Blocking TLR2 or nucleotide-binding oligomerization domain (NOD)1 with related antibodies or RNA interference abolished PGN-induced p815 cell activation. The mast cell mediator histamine and serotonin had synergistic effects in PGN-induced diarrhea. In summary, oral PGN can induce diarrhea in mice, and TLR2 and NOD1 mediate the PGN-induced mast cell activation that plays a critical role in diarrhea induction. Blockade of TLR2 or NOD1 or treating mice with a mast cell stabilizer can efficiently inhibit PGN-induced-diarrhea, providing potential therapeutic significance.

Role of mast cells in allergic and non-allergic immune responses: comparison of human and murine data

The versatile role of mast cells in allergy, in innate immune responses and in the regulation of tissue homeostasis is well recognized. However, it is often not made clear that most mast-cell data derive solely from experiments in mice or rats, species that obviously never suffer from allergic and most other mast-cell-associated human diseases. Data on human mast cells are limited, and the mast-cell source and species from which findings derive are frequently not indicated in the titles and summaries of research publications. This Review summarizes recent data on human mast cells, discusses differences with murine mast cells, and describes new tools to study this increasingly meaningful cell type in humans.

Fc gamma RIIa, not Fc gamma RIIb, is constitutively and functionally expressed on skin-derived human mast cells

The expression of FcgammaR by human skin-derived mast cells of the MC(TC) type was determined in the current study. Expression of mRNA was analyzed with microarray gene chips and RT-PCR; protein by Western blotting and flow cytometry; function by release of beta-hexosaminidase, PGD(2), leukotriene C(4) (LTC(4)), IL-5, IL-6, IL-13, GM-CSF, and TNF-alpha. FcgammaRIIa was consistently detected along with FcepsilonRI at the mRNA and protein levels; FcgammaRIIc was sometimes detected only by RT-PCR; but FcgammaRIIb, FcgammaRI, and FcgammaRIII mRNA and protein were not detected. FcgammaRIIa-specific mAb caused skin MC(TC) cells to degranulate and secrete PGD(2), LTC(4), GM-CSF, IL-5, IL-6, IL-13, and TNF-alpha in a dose-dependent fashion. FcepsilonRI-specific mAb caused similar amounts of each mediator to be released with the exception of LTC(4), which was not released by this agonist. Simultaneous but independent cross-linking of FcepsilonRI and FcgammaRIIa did not substantially alter mediator release above or below levels observed with each agent alone. Skin MC(TC) cells sensitized with dust-mite-specific IgE and IgG, when coaggregated by Der p2, exhibited enhanced degranulation compared with sensitization with either IgE or IgG alone. These results extend the known capabilities of human skin mast cells to respond to IgG as well as IgE-mediated signals.

Evidence for a restricted rather than generalized stimulatory response of skin-derived human mast cells to substance P

To resolve the controversy regarding substance P (SP) mediated stimulation of mast cells (MC), we demonstrate that SP triggers histamine release from purified human skin MC (sMC), but contrast to stimulation via FcepsilonRI, does not effect the production of TNF-alpha or IL-8. Conversely, both anti-IgE and SP are suppressive in terms of IL-6. By quantitative RT-PCR, the amount of templates at baseline (per 25 ng total RNA) is 2178 (IL-6), 2,665 (IL-8) and 94 (TNF-alpha), and remains unaltered by SP. Contrast to sMC, LAD2 MC respond to SP with stronger histamine release and robust TNF-alpha production in an only partially neurokinin-1R mediated manner, while histamine release of sMC is chiefly mediated by this receptor. We conclude that human sMC are responsive to SP in a selective manner by eliciting degranulation without the induction of cytokines and that SP-triggered cytokine production varies among MC subtypes, likely through differences in signaling mechanisms.

Cytokines, PGE2 and endotoxic fever: a re-assessment

The innate immune system serves as the first line of host defense against the deleterious effects of invading infectious pathogens. Fever is the hallmark among the defense mechanisms evoked by the entry into the body of such pathogens. The conventional view of the steps that lead to fever production is that they begin with the biosynthesis of pyrogenic cytokines by mononuclear phagocytes stimulated by the pathogens, their release into the circulation and transport to the thermoregulatory center in the preoptic area (POA) of the anterior hypothalamus, and their induction there of cyclooxygenase (COX)-2-dependent prostaglandin (PG)E(2), the putative final mediator of the febrile response. But data accumulated over the past 5 years have gradually challenged this classical concept, due mostly to the temporal incompatibility of the newer findings with this concatenation of events. Thus, the former studies generally overlooked that the production of cytokines and the transduction of their pyrogenic signals into fever-mediating PGE(2) proceed at relatively slow rates, significantly slower certainly than the onset latency of fever produced by the i.v. injection of bacterial endotoxic lipopolysaccharides (LPS). Here, we review the conflicts between the earlier and the more recent findings and summarize new data that reconcile many of the contradictions. A unified model based on these data explicating the generation and maintenance of the febrile response is presented. It postulates that the steps in the production of LPS fever occur in the following sequence: the immediate activation by LPS of the complement (C) cascade, the stimulation by the anaphylatoxic C component C5a of Kupffer cells, their consequent, virtually instantaneous release of PGE(2), its excitation of hepatic vagal afferents, their transmission of the induced signals to the POA via the ventral noradrenergic bundle, and the activation by the thus, locally released norepinephrine (NE) of neural alpha(1)- and glial alpha(2)-adrenoceptors. The activation of the first causes an immediate, PGE(2)-independent rise in core temperature (T(c)) [the early phase of fever; an antioxidant-sensitive PGE(2) rise, however, accompanies this first phase], and of the second a delayed, PGE(2)-dependent T(c) rise [the late phase of fever]. Meanwhile-generated pyrogenic cytokines and their consequent upregulation of blood-brain barrier cells COX-2 also contribute to the latter rise. The consecutive steps that initiate the febrile response to LPS would now appear, therefore, to occur in an order different than conceived originally.

Enhanced clearance of Escherichia coli and Staphylococcus aureus in mice treated with cyclophosphamide and lactoferrin

Previous studies on cyclophosphamide (CP)-immunocompromised mice showed accelerated reconstitution of immune system function following oral treatment with lactoferrin (LF). The aim of this investigation was to evaluate the ability of mice, treated with a sublethal dose of CP and given LF, to combat bacterial infections. Mice were injected with a single, intraperitoneal dose of CP (350 mg/kg body weight). One group of CP-treated mice was also given LF in drinking water (0.5% solution) for 14 days. Untreated and LF-treated mice served as controls. On day 15 following CP administration, mice were infected intravenously with 10(8) Escherichia coli or 5 x 10(7) Staphylococcus aureus. Twenty-four hours later, the number of colony-forming units (CFU) in spleens and livers were determined. Phenotypic analysis of blood leukocytes was determined, as well as the ability of splenic and peritoneal cells to produce IL-6 spontaneously and in the presence of lipopolysaccharide (LPS). Treatment with CP, or with CP and LF, led to profound reduction of E. coli CFU in the liver and the spleen; treatment with LF alone had significant inhibitory effects on organ enumerated CFU. S. aureus CFUs were also significantly reduced in spleens of mice treated with CP or CP/LF and, to a lesser degree, after LF alone. These effects were also significantly reduced in the livers. Analysis of blood cellular phenotype revealed total number of peripheral leukocytes was lower in the CP-treated group (52.6%) but not significantly different from control values in CP/LF and LF-treated groups (90.7% and 104.6%, respectively). Conversely, percentage of blood neutrophils was markedly elevated in CP and CP/LF groups--62% and 42.5% vs. 18.4% in controls. These findings were accompanied by production of IL-6 by splenic and peritoneal cells which was significantly increased in CP- and CP/LF-treated groups. It was concluded that the increased clearance of bacteria in the organs of mice treated with CP and CP/LF may result from a rise in the number of neutrophils infiltrating the organs and contributing to accelerated clearance of bacteria. The study also suggests that the ability of cells from CP- and CP/LF-treated mice to produce significantly more IL-6 may also contribute to increased resistance to infections. Lastly, together with our previous data, this study indicates that LF used to reconstitute the antigen-specific immune response in CP-treated mice does not impair their resistance to infection.

Contribution of mast cells to bacterial clearance and their proliferation during experimental cystitis induced by type 1 fimbriated E. coli

Bacterial infections of the urinary bladder are very common, and the role of mast cells in these infections is invariably thought of as a detrimental one. However, recent studies have shown that mast cells play a key role in host defense against various enterobacterial infections. In this manuscript, using mast cell-deficient (WBB6F1 - W/Wv) and mast cell-sufficient (WBB6F1 - +/+) mice we have investigated the protective role of mast cells in urinary bladder infections in vivo. Our findings show that (i) the mast cells are activated by FimH-expressing E. coli, and release large amount of histamine in the urinary bladder; (ii) the number of surviving bacteria in the urine is dependent on the presence of mast cells, and (iii) mast cell number in the bladder increases following uropathogenic infection in mice which is likely due to an increase in the mast cell growth-promoting cytokine IL-3 in bacteria-activated mast cells. Taken together, these observations suggest a beneficial role of mast cells in urinary bladder infections in mice.

LPS-induced upregulation of SHIP is essential for endotoxin tolerance

An initial exposure to lipopolysaccharide (LPS) induces a transient state of hyporesponsiveness to a subsequent challenge with LPS. The mechanism underlying this phenomenon, termed endotoxin tolerance, remains poorly understood despite a recent resurgence of interest in this area. We demonstrate herein that SHIP(-/-) bone marrow-derived macrophages (BMmphis) and mast cells (BMMCs) do not display endotoxin tolerance. Moreover, an initial LPS treatment of wild-type BMmphis or BMMCs increases the level of SHIP, but not SHIP2 or PTEN, and this increase is critical for the hyporesponsiveness to subsequent LPS stimulation. Interestingly, this increase in SHIP protein is mediated by the LPS-induced production of autocrine-acting TGFbeta and neutralizing antibodies to TGFbeta block LPS-induced endotoxin tolerance. In vivo studies with SHIP(+/+) and SHIP(-/-) mice confirm these in vitro findings and show a correlation between the duration of endotoxin tolerance and elevated SHIP levels.

Signaling through Toll-like receptors triggers HIV-1 replication in latently infected mast cells

Evidence that human progenitor mast cells are susceptible to infection with CCR5-tropic strains of HIV-1 and that circulating HIV-1-infected FcepsilonRIalpha(+) cells with a similar progenitor phenotype have been isolated from AIDS patients has led to speculation that mast cells may serve as a potential reservoir for infectious HIV-1. In this study, progenitor mast cells, developed in vitro from CD34(+) cord blood stem cells, were experimentally infected with the CCR5-tropic strain HIV-1Bal after 28 days in culture as they reached their HIV-1-susceptible progenitor stage. HIV-1 p24 Ag levels were readily detectable by day 7 postinfection (PI), peaked at 2-3 wk PI as mature (tryptase/chymase-positive) HIV-1 infection-resistant mast cells emerged, and then steadily declined to below detectable limits by 10 wk PI, at which point integrated HIV-1 proviral DNA was confirmed by PCR quantitation in ( approximately 34% of) latently infected mast cells. Stimulation by ligands for Toll-like receptor (TLR) 2, TLR4, or TLR9 significantly enhanced viral replication in a dose- and time-dependent manner in both HIV-1-infected progenitor and latently infected mature mast cells, without promoting degranulation, apoptosis, cellular proliferation, or dysregulation of TLR agonist-induced cytokine production in infected mast cells. Limiting dilution analysis of TLR activated, latently infected mature mast cells indicated that one in four was capable of establishing productive infections in A301 sentinel cells. Taken together, these results indicate that mast cells may serve both as a viral reservoir and as a model for studying mechanisms of postintegration latency in HIV infection.

Comparative cytokine profile of human skin mast cells from two compartments--strong resemblance with monocytes at baseline but induction of IL-5 by IL-4 priming

Although known as heterogenous, mast cells (MC) are believed to induce allergic inflammation, partially by secretion of T helper cell type 2 (Th2) cytokines. We show here that MC purified from two human skin compartments produce cytokines that are primarily associated with inflammation and innate immunity [interleukin (IL)-1beta, IL-6, IL-8, tumor necrosis factor alpha (TNF-alpha)]. Although these are detectable even without stimulation, immunoglobulin (Ig)E receptor cross-linking is able to enhance only TNF-alpha production, but phorbol 12-myristate 13-acetate additionally promotes IL-1beta and IL-8. With the exception of TNF-alpha, the presence of serum has a positive impact on cytokine production. Although IL-13 transcripts (but not those for IL-4 and -5) are produced by skin MC, all Th2 cytokines remain undetectable in the supernatants or lysates of MC from foreskin and breast skin by all treatments. Therefore, rather than sharing similarity with Th2 cells, the cytokine profile of skin MC at baseline resembles that of monocytes. Of note, MC precultured in the presence of IL-4 [alone or plus stem cell factor (SCF)] before anti-IgE stimulation, acquired the ability to produce IL-5, and IL-1beta was concomitantly suppressed. Additionally, strong up-regulation of IL-6 by SCF was observed, which was inhibited by IL-4. In summary, we present a detailed analysis of the cytokine array of human skin MC immediately upon isolation; demonstrate that MC from different skin compartments, although producing the same pattern of cytokines, display quantitative differences in several aspects; and provide further evidence that MC possess a proinflammatory capacity, which can, however, be altered by microenvironmental stimuli, substantiating the marked plasticity of the cells.

Identification of specific gene expression profiles in human mast cells mediated by Toll-like receptor 4 and FcepsilonRI

Rodent mast cells (MCs) are reported to play a pivotal role in both innate and adaptive immunity. However, there is so far no evidence that human MCs are involved in innate immunity. We found that a functional Toll-like receptor 4 (TLR4) was expressed on human MCs when it was up-regulated by interferon gamma (IFN-gamma). To systematically explore how human MCs modulate the immune system following TLR4-mediated activation and FcepsilonRI aggregation, we used high-density oligonucleotide probe arrays (GeneChip) to compare the lipopolysaccharide (LPS)-induced gene expression profile with the IgE/anti-IgE-mediated profile in MCs. Both a shared core response, and LPS- or anti-IgE-specific programs of gene expression were observed in MCs. Furthermore, MCs exhibited an antiviral response gene program in response to IFN-gamma, and LPS sustained that expression. Compared with the LPS-stimulated gene expression profile of human peripheral blood mononuclear cells, LPS-stimulated MCs specifically induced a subset of genes that included a Th2 cytokine and chemokines that recruit Th2 cells and eosinophils. These results reveal that human MCs express tailored pathogen- and antigen-specific immune responses and that human MCs may play important roles in innate and adaptive immunity.

T-cell proliferation induced by local application of LPS in the nasal mucosa of nonatopic children

BACKGROUND

Recently, there has been a great deal of interest in the role of bacterial products in altering the allergic immune response in early life.

OBJECTIVE

We sought to develop a model of bacterial inflammation in human subjects to characterize the ex vivo response to LPS in the nasal mucosa of young nonatopic children.

METHODS

Using the explant technique, we cultured nasal mucosa in the presence or absence of increasing concentrations of LPS (0.001-1 microg LPS/mL) for 24 hours. Immunocytochemistry and in situ hybridization were used to phenotype the cells and cytokines in the explant, and immunofluorescence was used to study proliferation of T cells in explants cultured with LPS and 5-bromo-2'-deoxyuridine (BrdU).

RESULTS

CD68, CD3, tryptase, elastase, IFN- gamma IL-12, and IL-10 immunoreactivity was detected in unstimulated tissue. LPS stimulation caused a dose-dependent increase in the number of CD3(+) (n = 7, P <.05), CD68(+) (n = 7, P <.01), elastase-positive (n = 7, P <.01), tryptase-positive (n = 7, P <.05), IL-2 -positive (n = 6, P <.05), IL-12 -positive (n = 6, P <.05), and IFN- gamma-positive (n = 6, P <.05) cells compared with media alone. LPS had no effect on major basic protein, IL-4, IL-5, or IL-13 immunoreactivity. LPS (0.1 microg/mL) caused an increase in the number of BrdU-positive cells as early as 2 hours after incubation (n = 8, P <.001). The maximal BrdU immunoreactivity was seen 24 hours after incubation with LPS, at which time approximately 70% of BrdU- positive cells were CD3(+) T cells.

CONCLUSIONS

Our results suggest that LPS is capable of inducing local inflammation, T(H)1 cytokine immunoreactivity, and proliferation of CD3(+) activated T cells in the absence of de novo cell recruitment. This model holds promise for future studies investigating the importance of bacterial products in regulating local immune function in young atopic children.