Unequivocal delayed hypersensitivity in mast cell-deficient and beige mice

Exosome Carrier Effects; Resistance to Digestion in Phagolysosomes May Assist Transfers to Targeted Cells; II Transfers of miRNAs Are Better Analyzed via Systems Approach as They Do Not Fit Conventional Reductionist Stoichiometric Concepts

Carrier effects of extracellular vesicles (EV) like exosomes refer to properties of the vesicles that contribute to the transferred biologic effects of their contents to targeted cells. This can pertain to ingested small amounts of xenogeneic plant miRNAs and oral administration of immunosuppressive exosomes. The exosomes contribute carrier effects on transfers of miRNAs by contributing both to the delivery and the subsequent functional intracellular outcomes. This is in contrast to current quantitative canonical rules that dictate just the minimum copies of a miRNA for functional effects, and thus successful transfers, independent of the EV carrier effects. Thus, we argue here that transfers by non-canonical minute quantities of miRNAs must consider the EV carrier effects of functional low levels of exosome transferred miRNA that may not fit conventional reductionist stoichiometric concepts. Accordingly, we have examined traditional stoichiometry vs. systems biology that may be more appropriate for delivered exosome functional responses. Exosome carrier properties discussed include; their required surface activating interactions with targeted cells, potential alternate targets beyond mRNAs, like reaching a threshold, three dimensional aspects of the RNAs, added EV kinetic dynamic aspects making transfers four dimensional, and unique intracellular release from EV that resist intracellular digestion in phagolysosomes. Together these EV carrier considerations might allow systems analysis. This can then result in a more appropriate understanding of transferred exosome carrier-assisted functional transfers. A plea is made that the miRNA expert community, in collaboration with exosome experts, perform new experiments on molecular and quantitative miRNA functional effects in systems that include EVs, like variation in EV type and surface constituents, delivery, dose and time to hopefully create more appropriate and truly current canonical concepts of the consequent miRNA functional transfers by EVs like exosomes.

Mast Cells in Inflammation and Disease: Recent Progress and Ongoing Concerns

Mast cells have existed long before the development of adaptive immunity, although they have been given different names. Thus, in the marine urochordate Styela plicata, they have been designated as test cells. However, based on their morphological characteristics (including prominent cytoplasmic granules) and mediator content (including heparin, histamine, and neutral proteases), test cells are thought to represent members of the lineage known in vertebrates as mast cells. So this lineage presumably had important functions that preceded the development of antibodies, including IgE. Yet mast cells are best known, in humans, as key sources of mediators responsible for acute allergic reactions, notably including anaphylaxis, a severe and potentially fatal IgE-dependent immediate hypersensitivity reaction to apparently harmless antigens, including many found in foods and medicines. In this review, we briefly describe the origins of tissue mast cells and outline evidence that these cells can have beneficial as well as detrimental functions, both innately and as participants in adaptive immune responses. We also discuss aspects of mast cell heterogeneity and comment on how the plasticity of this lineage may provide insight into its roles in health and disease. Finally, we consider some currently open questions that are yet unresolved.

Mast Cell-Specific Deletion of Group III Secreted Phospholipase A2 Impairs Mast Cell Maturation and Functions

Tissue-resident mast cells (MCs) have important roles in IgE-associated and -independent allergic reactions. Although microenvironmental alterations in MC phenotypes affect the susceptibility to allergy, understanding of the regulation of MC maturation is still incomplete. We previously reported that group III secreted phospholipase A2 (sPLA2-III) released from immature MCs is functionally coupled with lipocalin-type prostaglandin D2 (PGD2) synthase in neighboring fibroblasts to supply a microenvironmental pool of PGD2, which in turn acts on the PGD2 receptor DP1 on MCs to promote their proper maturation. In the present study, we reevaluated the role of sPLA2-III in MCs using a newly generated MC-specific Pla2g3-deficient mouse strain. Mice lacking sPLA2-III specifically in MCs, like those lacking the enzyme in all tissues, had immature MCs and displayed reduced local and systemic anaphylactic responses. Furthermore, MC-specific Pla2g3-deficient mice, as well as MC-deficient KitW-sh mice reconstituted with MCs prepared from global Pla2g3-null mice, displayed a significant reduction in irritant contact dermatitis (ICD) and an aggravation of contact hypersensitivity (CHS). The increased CHS response by Pla2g3 deficiency depended at least partly on the reduced expression of hematopoietic PGD2 synthase and thereby reduced production of PGD2 due to immaturity of MCs. Overall, our present study has confirmed that MC-secreted sPLA2-III promotes MC maturation, thereby facilitating acute anaphylactic and ICD reactions and limiting delayed CHS response.

Integrative transcriptome analysis deciphers mechanisms of nickel contact dermatitis

Background

Nickel‐induced allergic contact dermatitis (nACD) remains a major occupational skin disorder, significantly impacting the quality of life of suffering patients. Complex cellular compositional changes and associated immunological pathways are partly resolved in humans; thus, the impact of nACD on human skin needs to be further elucidated.

Methods

To decipher involved immunological players and pathways, human skin biopsies were taken at 0, 2, 48, and 96 hours after nickel patch test in six nickel‐allergic patients. Gene expression profiles were analyzed via microarray.

Results

Leukocyte deconvolution of nACD‐affected skin identified major leukocyte compositional changes at 48 and 96 hours, including natural killer (NK) cells, macrophage polarization, and T‐cell immunity. Gene set enrichment analysis mirrored cellular‐linked functional pathways enriched over time. NK cell infiltration and cytotoxic pathways were uniquely found in nACD‐affected skin compared to sodium lauryl sulfate–induced irritant skin reactions.

Conclusion

These results highlight key immunological leukocyte subsets as well as associated pathways in nACD, providing insights into pathophysiology with the potential to unravel novel therapeutic targets.

Novel cutaneous mediators of chemical allergy

Chemical allergy can manifest into allergic contact dermatitis and asthma and the importance of skin sensitization in both of these diseases is increasingly being recognized. Given the unique characteristics of chemical allergy, coupled with the distinct immunological microenvironment of the skin research is still unraveling the mechanisms through which sensitization and elicitation occur. This review first describes the features of chemical sensitization and the known steps that must occur to develop a chemical allergy. Next, the unique immunological properties of the skin - which may influence chemical sensitization - are highlighted. Additionally, mediators involved with the development of allergy are reviewed, starting with early ones - including the properties of haptens, skin integrity, the microbiome, the inflammasome, and toll-like receptors (TLR). Novel cellular mediators of chemical sensitization are highlighted, including innate lymphoid cells, mast cells, T-helper (T_H) cell subsets, and skin intrinsic populations including γδ T-cells and resident memory T-cells. Finally, this review discusses two epigenetic mechanisms that can influence chemical sensitization, microRNAs and DNA methylation. Overall, this review highlights recent research investigating novel mediators of chemical allergy that are present in the skin. It also emphasizes the need to further explore these mediators to gain a better understanding of what makes a chemical an allergen, and how best to prevent the development of chemical-induced allergic diseases.

Humanized Mice Are Instrumental to the Study of Plasmodium falciparum Infection

Research using humanized mice has advanced our knowledge and understanding of human haematopoiesis, non-adaptive and adaptive immunity, autoimmunity, infectious disease, cancer biology, and regenerative medicine. Challenges posed by the human-malaria parasite Plasmodium falciparum include its complex life cycle, the evolution of drug resistance against anti-malarials, poor diagnosis, and a lack of effective vaccines. Advancements in genetically engineered and immunodeficient mouse strains, have allowed for studies of the asexual blood stage, exoerythrocytic stage and the transition from liver-to-blood stage infection, in a single vertebrate host. This review discusses the process of "humanization" of various immunodeficient/transgenic strains and their contribution to translational biomedical research. Our work reviews the strategies employed to overcome the remaining-limitations of the developed human-mouse chimera(s).

Genetic and Imaging Approaches Reveal Pro-Inflammatory and Immunoregulatory Roles of Mast Cells in Contact Hypersensitivity

Contact hypersensitivity (CHS) is a common T cell-mediated skin disease induced by epicutaneous sensitization to haptens. Mast cells (MCs) are widely deployed in the skin and can be activated during CHS responses to secrete diverse products, including some with pro-inflammatory and anti-inflammatory functions. Conflicting results have been obtained regarding pathogenic versus protective roles of MCs in CHS, and this has been attributed in part to the limitations of certain models for studying MC functions in vivo. This review discusses recent advances in the development and analysis of mouse models to investigate the roles of MCs and MC-associated products in vivo. Notably, fluorescent avidin-based two-photon imaging approaches enable in vivo selective labeling and simultaneous tracking of MC secretory granules (e.g., during MC degranulation) and MC gene activation by real-time longitudinal intravital microscopy in living mice. The combination of such genetic and imaging tools has shed new light on the controversial role played by MCs in mouse models of CHS. On the one hand, they can amplify CHS responses of mild severity while, on the other hand, can limit the inflammation and tissue injury associated with more severe or chronic models, in part by representing an initial source of the anti-inflammatory cytokine IL-10.

Roles of basophils and mast cells in cutaneous inflammation

Mast cells and basophils are associated with T helper 2 (Th2) immune responses. Newly developed mast cell-deficient mice have provided evidence that mast cells initiate contact hypersensitivity via activating dendritic cells. Studies using basophil-deficient mice have also revealed that basophils are responsible for cutaneous Th2 skewing to haptens and peptide antigens but not to protein antigens. Recently, several studies reported the existence of innate lymphoid cells (ILCs), which differ from classic T cells in that they lack the T cell receptor. Mast cells and basophils can interact with ILCs and play some roles in the pathogenesis of Th2 responses. Basophil-derived interleukin (IL)-4 enhances the expression of the chemokine CCL11, as well as IL-5, IL-9, and IL-13 in ILC2s, leading to the accumulation of eosinophils in allergic reactions. IL-33-stimulated mast cells can play a regulatory role in the development of ILC2-mediated non-antigen-specific protease-induced acute inflammation. In this review, we discuss the recent advances in our understanding of mast cells and basophils in immunity and inflammation.

Regulatory roles of mast cells in immune responses

Mast cells are important immune cells for host defense through activation of innate immunity (via toll-like receptors or complement receptors) and acquired immunity (via FcεRI). Conversely, mast cells also act as effector cells that exacerbate development of allergic or autoimmune disorders. Yet, several lines of evidence show that mast cells act as regulatory cells to suppress certain inflammatory diseases. Here, we review the mechanisms by which mast cells suppress diseases.

Mast Cells Contribute to Radiation-Induced Vascular Hyperpermeability

Induction of vascular hyperpermeability is one of the early vascular responses to radiation exposure and is considered to contribute to subsequent fibrosis and tissue injuries. However, the mechanism underlying radiation-induced hyperpermeability has not yet been clearly elucidated. Here, we provide experimental evidence indicating that mast cells contribute to the increase in vascular permeability for albumin in normal mouse skin after irradiation. Vascular permeability in the skin of C3H mice increased after 2, 15 and 50 Gy irradiation, peaked at 24 h after irradiation and gradually decreased thereafter to the baseline level within 3-10 days. Both the extent and duration of hyperpermeability were dose dependent. We found significant degranulation of mast cells in the skin after 15 Gy irradiation. To further investigate the role of mast cells in the radiation-induced increase in vascular permeability, we measured vascular permeability in the skin of mast cell-deficient mice (WW(v)) and their wild-type littermates at 24 h after irradiation. Vascular permeability in WW(v) mice did not change, whereas that in wild-type mice significantly increased after irradiation. There were no appreciable changes in the total tissue levels of vascular endothelial growth factor or endothelial nitric oxide synthase after 15 Gy irradiation and there was no detectable expression of inducible nitric oxide synthase. Collectively, these results show that exposure to radiation induces vascular hyperpermeability in a dose-dependent manner and that mast cells contribute to this process.

Role of mast cell in the late phase of contact hypersensitivity induced by trimellitic anhydride

Mast cells are known as effector cells of IgE-mediated allergic responses, but role of mast cells in contact hypersensitivity (CHS) has been considered controversial. In this study, we investigated role of mast cell in trimellitic anhydride (TMA)-induced CHS. The mice were sensitized to TMA on the back and repeatedly challenged with TMA on the left ear at 1-week intervals. The ear after challenge showed biphasic responses. The repetition of TMA challenge shifted in time course of ear response and enlarged the extent of early and late phase reactions in proportion to the frequency of TMA challenges in C57BL/6 mice. In late phase reaction, peak of ear response by single challenge showed at 24 hours after challenge, but the peak by repeat challenges at 8 hours after the last challenge. Number of mast cells and eosinophils per unit area increased in proportion to frequency of TMA challenges. However, mast cell-deficient WBB6F1/J-Kit^W/Kit^W-v mice developed the late phase reaction without the early phase reaction. The repetition of TMA challenge shifted in time course of ear response and enlarged the extent of ear response and the infiltration of eosinophils. The magnitude of these responses observed according to the frequency of the TMA challenge in mast cell-deficient WBB6F1/J-Kit^W/Kit^W-v mice was significantly lower than that in C57BL/6 mice. Also TMA elicited mast cell degranulation and histamine release from rat peritoneal mast cells in a concentration-dependent manner. Conclusively, TMA induces the early and late phase reactions in CHS, and mast cells may be required for TMA-induced CHS.

Protective effect of small molecule analogues of the Acanthocheilonema viteae secreted product ES-62 on oxazolone-induced ear inflammation

•

Small molecule analogues (SMAs) of the immunomodulator, ES-62, have been produced.

•

Two SMAs protect against oxazolone-induced skin inflammation in mouse ears.

•

Protection is associated with reduced cellular infiltration and collagen deposition.

•

Protection is associated with decreased IFNγ mRNA in the ears.

ES-62 is the major secreted protein of the rodent filarial nematode Acanthocheilonema viteae. The molecule contains covalently attached phosphorylcholine (PC) residues, which confer anti-inflammatory properties on ES-62, underpinning the idea that drugs based on this active moiety may have therapeutic potential in human diseases associated with aberrant inflammation. Here we demonstrate that two synthetic small molecule analogues (SMAs) of ES-62 termed SMA 11a and SMA 12b are protective in the oxazolone-induced acute allergic contact dermatitis mouse model of skin inflammation, as measured by a significant reduction in ear inflammation following their administration before oxazolone sensitisation and before oxazolone challenge. Furthermore, it was found that when tested, 12b was effective at reducing ear swelling even when first administered before challenge. Histological analysis of the ears showed elevated cellular infiltration and collagen deposition in oxazolone-treated mice both of which were reduced by treatment with the two SMAs. Likewise, the oxazolone-induced increase in IFNγ mRNA in the ears was reduced but no effect on other cytokines investigated was observed. Finally, no influence on the mast cell populations in the ear was observed.

Approaches for analyzing the roles of mast cells and their proteases in vivo

The roles of mast cells in health and disease remain incompletely understood. While the evidence that mast cells are critical effector cells in IgE-dependent anaphylaxis and other acute IgE-mediated allergic reactions seems unassailable, studies employing various mice deficient in mast cells or mast cell-associated proteases have yielded divergent conclusions about the roles of mast cells or their proteases in certain other immunological responses. Such "controversial" results call into question the relative utility of various older versus newer approaches to ascertain the roles of mast cells and mast cell proteases in vivo. This review discusses how both older and more recent mouse models have been used to investigate the functions of mast cells and their proteases in health and disease. We particularly focus on settings in which divergent conclusions about the importance of mast cells and their proteases have been supported by studies that employed different models of mast cell or mast cell protease deficiency. We think that two major conclusions can be drawn from such findings: (1) no matter which models of mast cell or mast cell protease deficiency one employs, the conclusions drawn from the experiments always should take into account the potential limitations of the models (particularly abnormalities affecting cell types other than mast cells) and (2) even when analyzing a biological response using a single model of mast cell or mast cell protease deficiency, details of experimental design are critical in efforts to define those conditions under which important contributions of mast cells or their proteases can be identified.

Mast cells and basophils in cutaneous immune responses

Mast cells and basophils share some functions in common and are generally associated with T helper 2 (Th2) immune responses, but taking basophils as surrogate cells for mast cell research or vice versa for several decades is problematic. Thus far, their in vitro functions have been well studied, but their in vivo functions remained poorly understood. New research tools for their functional analysis in vivo have revealed previously unrecognized roles for mast cells and basophils in several skin disorders. Newly developed mast cell-deficient mice provided evidence that mast cells initiate contact hypersensitivity via activating dendritic cells. In addition, studies using basophil-deficient mice have revealed that basophils were responsible for cutaneous Th2 skewing to haptens and peptide antigens but not to protein antigens. Moreover, human basophils infiltrate different skin lesions and have been implicated in the pathogenesis of skin diseases ranging from atopic dermatitis to autoimmune diseases. In this review, we will discuss the recent advances related to mast cells and basophils in human and murine cutaneous immune responses.

Targeting interleukin-2-inducible T-cell kinase (ITK) and resting lymphocyte kinase (RLK) using a novel covalent inhibitor PRN694

Interleukin-2-inducible T-cell kinase (ITK) and resting lymphocyte kinase (RLK or TXK) are essential mediators of intracellular signaling in both normal and neoplastic T-cells and natural killer (NK) cells. Thus, ITK and RLK inhibitors have therapeutic potential in a number of human autoimmune, inflammatory, and malignant diseases. Here we describe a novel ITK/RLK inhibitor, PRN694, which covalently binds to cysteine residues 442 of ITK and 350 of RLK and blocks kinase activity. Molecular modeling was utilized to design molecules that interact with cysteine while binding to the ATP binding site in the kinase domain. PRN694 exhibits extended target residence time on ITK and RLK and is highly selective for a subset of the TEC kinase family. In vitro cellular assays confirm that PRN694 prevents T-cell receptor- and Fc receptor-induced cellular and molecular activation, inhibits T-cell receptor-induced T-cell proliferation, and blocks proinflammatory cytokine release as well as activation of Th17 cells. Ex vivo assays demonstrate inhibitory activity against T-cell prolymphocytic leukemia cells, and in vivo assays demonstrate durable pharmacodynamic effects on ITK, which reduces an oxazolone-induced delayed type hypersensitivity reaction. These data indicate that PRN694 is a highly selective and potent covalent inhibitor of ITK and RLK, and its extended target residence time enables durable attenuation of effector cells in vitro and in vivo. The results from this study highlight potential applications of this dual inhibitor for the treatment of T-cell- or NK cell-mediated inflammatory, autoimmune, and malignant diseases.

New models for analyzing mast cell functions in vivo

In addition to their well-accepted role as critical effector cells in anaphylaxis and other acute IgE-mediated allergic reactions, mast cells (MCs) have been implicated in a wide variety of processes that contribute to disease or help to maintain health. Although some of these roles were first suggested by analyses of MC products or functions in vitro, it is critical to determine whether, and under which circumstances, such potential roles actually can be performed by MCs in vivo. This review discusses recent advances in the development and analysis of mouse models to investigate the roles of MCs and MC-associated products during biological responses in vivo, and comments on some of the similarities and differences in the results obtained with these newer versus older models of MC deficiency.

New helping friends for B cells

Over the past decade, a growing recognition of the importance of neutralizing antibodies in host defense combined with the success of B-cell depletion therapies in treating auto-immune disorders has led to an increased focus on better understanding the pathways underpinning B-cell antibody production. In general, B cells require cognate interaction with T helper cells in the germinal center of lymphoid follicles to generate protective antibodies. However, recent evidence shows that B cells receive additional help from invariant natural killer T cells, dendritic cells, and various granulocytes, including neutrophils, eosinophils, and basophils. These innate immune cells enhance T-cell-dependent antibody responses by delivering B-cell helper signals both in the germinal center and at postgerminal center lymphoid sites such as the bone marrow. In addition to enhancing and complementing the B-cell helper activity of canonical T cells, invariant natural killer T cells, dendritic cells, and granulocytes can deliver T cell-independent B-cell helper signals at the mucosal interface and in the marginal zone of the spleen to initiate rapid innate-like antibody responses. Here, we discuss recent advances in the role of adaptive and innate B-cell helper signals in antibody diversification and production.

Update of immune events in the murine contact hypersensitivity model: toward the understanding of allergic contact dermatitis

Allergic contact dermatitis (ACD) is one of the most common skin diseases, consisting of sensitization and elicitation phases. With the advancement of technology and the discovery of new types of immune cells, our knowledge of the immunological mechanisms of contact hypersensitivity (CHS) as a murine model of ACD has expanded significantly in the past decade. For example, by introducing regulatory T cells, CD4(+) T-helper 17 cells, and Langerin-positive dermal dendritic cells, the initiation and termination mechanism of CHS has been revealed. In addition, the role of mast cells in CHS, long a matter of debate, has become apparent by developing conditional mast cell-deficient mice. Moreover, the role of the innate immunity system, such as that of Toll-like receptor signaling, has made a breakthrough in this field. In this review, we will integrate the recent advancement of immunological mechanisms of both the sensitization and elicitation phases of CHS into the classic view, and we will discuss updated mechanisms on its development and future directions.

Mast cells and company

Classically, allergy depends on IgE antibodies and on high-affinity IgE receptors expressed by mast cells and basophils. This long accepted IgE/FcεRI/mast cell paradigm, on which the definition of immediate hypersensitivity was based in the Gell and Coomb's classification, appears too reductionist. Recently accumulated evidence indeed requires that not only IgE but also IgG antibodies, that not only FcεRI but also FcγR of the different types, that not only mast cells and basophils but also neutrophils, monocytes, macrophages, eosinophils, and other myeloid cells be considered as important players in allergy. This view markedly changes our understanding of allergic diseases and, possibly, their treatment.

Early immune events in the induction of allergic contact dermatitis

The skin is a barrier site that is exposed to a wide variety of potential pathogens. As in other organs, pathogens that invade the skin are recognized by pattern-recognition receptors (PRRs). Recently, it has been recognized that PRRs are also engaged by chemical contact allergens and, in susceptible individuals, this elicits an inappropriate immune response that results in allergic contact dermatitis. In this Review, we focus on how contact allergens promote inflammation by activating the innate immune system. We also examine how innate immune cells in the skin, including mast cells and dendritic cells, cooperate with each other and with T cells and keratinocytes to initiate and drive early responses to contact allergens.

Reduced mast cell and basophil numbers and function in Cpa3-Cre; Mcl-1fl/fl mice

It has been reported that the intracellular antiapoptotic factor myeloid cell leukemia sequence 1 (Mcl-1) is required for mast cell survival in vitro, and that genetic manipulation of Mcl-1 can be used to delete individual hematopoietic cell populations in vivo. In the present study, we report the generation of C57BL/6 mice in which Cre recombinase is expressed under the control of a segment of the carboxypeptidase A3 (Cpa3) promoter. C57BL/6-Cpa3-Cre; Mcl-1(fl/fl) mice are severely deficient in mast cells (92%-100% reduced in various tissues analyzed) and also have a marked deficiency in basophils (58%-78% reduced in the compartments analyzed), whereas the numbers of other hematopoietic cell populations exhibit little or no changes. Moreover, Cpa3-Cre; Mcl-1(fl/fl) mice exhibited marked reductions in the tissue swelling and leukocyte infiltration that are associated with both mast cell- and IgE-dependent passive cutaneous anaphylaxis (except at sites engrafted with in vitro-derived mast cells) and a basophil- and IgE-dependent model of chronic allergic inflammation, and do not develop IgE-dependent passive systemic anaphylaxis. Our findings support the conclusion that Mcl-1 is required for normal mast cell and basophil development/survival in vivo in mice, and also suggest that Cpa3-Cre; Mcl-1(fl/fl) mice may be useful in analyzing the roles of mast cells and basophils in health and disease.

Requirement of interaction between mast cells and skin dendritic cells to establish contact hypersensitivity

The role of mast cells (MCs) in contact hypersensitivity (CHS) remains controversial. This is due in part to the use of the MC-deficient Kit ^W/Wv mouse model, since Kit ^W/Wv mice congenitally lack other types of cells as a result of a point mutation in c-kit. A recent study indicated that the intronic enhancer (IE) for Il4 gene transcription is essential for MCs but not in other cell types. The aim of this study is to re-evaluate the roles of MCs in CHS using mice in which MCs can be conditionally and specifically depleted. Transgenic Mas-TRECK mice in which MCs are depleted conditionally were newly generated using cell-type specific gene regulation by IE. Using this mouse, CHS and FITC-induced cutaneous DC migration were analyzed. Chemotaxis assay and cytoplasmic Ca²⁺ imaging were performed by co-culture of bone marrow-derived MCs (BMMCs) and bone marrow-derived dendritic cells (BMDCs). In Mas-TRECK mice, CHS was attenuated when MCs were depleted during the sensitization phase. In addition, both maturation and migration of skin DCs were abrogated by MC depletion. Consistently, BMMCs enhanced maturation and chemotaxis of BMDC in ICAM-1 and TNF-α dependent manners Furthermore, stimulated BMDCs increased intracellular Ca²⁺ of MC upon direct interaction and up-regulated membrane-bound TNF-α on BMMCs. These results suggest that MCs enhance DC functions by interacting with DCs in the skin to establish the sensitization phase of CHS.

Phenylbutyrate suppresses distinct skin reactions that are enhanced by blockade of epidermal growth factor receptor signaling

BACKGROUND

Epidermal growth factor receptor inhibitors (EGFRIs) cause skin inflammation, and understanding the factors that mediate this reaction is fundamental for designing therapies for EGFRI-related cutaneous side effects.

OBJECTIVE

We characterized EGFRI-enhanced skin reactions and evaluated the therapeutic efficacy of phenylbutyrate, a histone deacetylase inhibitor.

METHODS

PD168393, an EGFRI, was applied topically to the ear skin of mice with or without mast cell deficiency. The skin was then irritated once or pre-sensitized and repeatedly challenged with 2,4-dinitrofluorobenzene (DNFB). The reaction pattern, the type and number of infiltrating cells, changes in protein, cytokine (TNF-α) and chemokine (CCL2) expression, and the immune response were analyzed. Phenylbutyrate, formulated as a gel for topical treatment or dissolved in water for intraperitoneal administration, was tested as a treatment.

RESULTS

EGFRI rapidly upregulated the mast cell chemotactic factor, stem cell factor (SCF) and augmented DNFB-induced immediate contact dermatitis within hours of treatment in the presence of mast cells. Topical phenylbutyrate treatment suppressed EGFRI-induced SCF expression in the epithelium, inhibited DNFB-induced mast cell recruitment in the dermis, and ameliorated the EGFRI-enhanced acute skin reaction. EGFRI also enhanced the delayed-type DNFB-induced hypersensitive reaction that was mast-cell independent but was associated with T lymphocytes. Systemic phenylbutyrate administration suppressed EGFRI-enhanced delayed-type skin hypersensitivity by increasing the number and function of Foxp3(+) T regulatory suppressor cells, which inhibited T helper cell proliferation.

CONCLUSIONS

Our data suggest that phenylbutyrate has dual beneficial therapeutic effects on EGFRI-enhanced acute (local inflammatory) and late (systemic immune) skin reactions.

Mast cells are key promoters of contact allergy that mediate the adjuvant effects of haptens

A prominent feature of sensitizing environmental compounds that cause allergic contact dermatitis is the rapid induction of an innate inflammatory response that seems to provide danger signals for efficient T cell priming. We generated mouse models of mast cell deficiency, mast cell-specific gene inactivation, and mast cell reporter mice for intravital imaging and showed that these adjuvant effects of contact allergens are mediated by mast cells and histamine. Mast cell deficiency resulted in impaired emigration of skin DCs to the lymph node and contact hypersensitivity was dramatically reduced in the absence of mast cells. In addition, mast cell-specific inactivation of the Il10 gene did not reveal any role for mast cell-derived IL-10 in the regulation of contact allergy. Collectively, we demonstrate that mast cells are essential promoters of contact hypersensitivity, thereby highlighting their potential to promote immune responses to antigens entering via the skin.

The mast cell in innate and adaptive immunity

Mast cells (MCs) were once considered only as effector cells in pathogenic IgE- and IgG-mediated responses such as allergy. However, developments over the last 15 years have suggested that MCs have evolved in vertebrates as beneficial effector cells that are involved in the very first inflammatory responses generated during infection. This pro-inflammatory environment has been demonstrated to be important for initiating innate responses in many different models of infection and more recently, in the development of adaptive immunity as well. Interestingly this latter finding has led to the discovery that small MC-activating compounds can behave as adjuvants in vaccine formulations. Thus, our continued understanding of the MC in the context of infectious disease is likely to not only expand our scope of the MC in the normal processes of immunity, but provide new therapeutic targets to combat disease.

Mast cells: novel clinical perspectives from recent insights

Mast cells are still generally viewed as mediators of type I allergic or pseudoallergic reactions. Research over the past 10 years revealed that our view was too small and that mast cells are of key importance in innate immunity and also types II, III and IV adaptive immune reactions. Understanding their role in modulating and amplifying of inflammatory responses provides important insights into the pathogenesis of skin diseases such as psoriasis, atopic dermatitis, bullous pemphigoid or the control of infections. This helps us to understand the course of these diseases, their trigger mechanisms, and, the new role of agents, which can modulate the function of mast cells. These insights will help to develop new therapeutic approaches.

New developments in mast cell biology

Mast cells can function as effector and immunoregulatory cells in immunoglobulin E-associated allergic disorders, as well as in certain innate and adaptive immune responses. This review focuses on exciting new developments in the field of mast cell biology published in the past year. We highlight advances in the understanding of FcvarepsilonRI-mediated signaling and mast cell-activation events, as well as in the use of genetic models to study mast cell function in vivo. Finally, we discuss newly identified functions for mast cells or individual mast cell products, such as proteases and interleukin 10, in host defense, cardiovascular disease and tumor biology and in settings in which mast cells have anti-inflammatory or immunosuppressive functions.

Mast cells regulate the magnitude and the cytokine microenvironment of the contact hypersensitivity response

The role that mast cells play during contact hypersensitivity (CS) response is unclear because some studies have shown that mast cell-deficient mice have relatively intact CS responses whereas others have shown opposing results. Mast cells secrete a wide range of immunomodulatory mediators and can potentially influence the type of immune response generated in the skin during CS. Therefore, we examined the type of microenvironment generated during CS in both W/Wv mast cell-deficient and wild-type mice in response to different immunizing doses of hapten (oxazolone). The CS response elicited after low-dose oxazolone was significantly diminished in W/Wv mice compared with wild-type mice. Unexpectedly, the CS response elicited in W/Wv mice immunized with high-dose oxazolone was more severe compared with wild-type mice. In addition, after immunization with high-dose oxazolone, the granulocyte infiltrate in W/Wv mice was increased by twofold compared with wild-type mice. A shift in the cytokine milieu toward the expression of type-1 cytokines as well as a significant increase in the local adhesion of neutrophils and CD4 T cells in the microvasculature of the skin was observed after hapten challenge in W/Wv mice immunized with high-dose oxazolone compared with wild-type mice. These results suggest that mast cells can act as regulators and inducers of the inflammatory response depending on immunizing stimulus strength.

Stressor-specific alterations in corticosterone and immune responses in mice

Different stressors likely elicit different physiological and behavioral responses. Previously reported differences in the effects of stressors on immune function may reflect qualitatively different physiological responses to stressors; alternatively, both large and subtle differences in testing protocols and methods among laboratories may make direct comparisons among studies difficult. Here we examine the effects of chronic stressors on plasma corticosterone concentrations, leukocyte redistribution, and skin delayed-type hypersensitivity (DTH), and the effects of acute stressors on plasma corticosterone and leukocyte redistribution. The effects of several commonly used laboratory stressors including restraint, forced swim, isolation, and low ambient temperatures (4 degrees C) were examined. Exposure to each stressor elevated corticosterone concentrations, with restraint (a putative psychological stressor) evoking a significantly higher glucocorticoid response than other stressors. Chronic restraint and forced swim enhanced the DTH response compared to the handled, low temperature, or isolation conditions. Restraint, low temperature, and isolation significantly increased trafficking of lymphocytes and monocytes compared to forced swim or handling. Generally, acute restraint, low temperature, isolation, and handling increased trafficking of lymphocytes and monocytes. Considered together, our results suggest that the different stressors commonly used in psychoneuroimmunology research may not activate the physiological stress response to the same extent. The variation observed in the measured immune responses may reflect differential glucocorticoid activation, differential metabolic adjustments, or both processes in response to specific stressors.

Mast cells: versatile regulators of inflammation, tissue remodeling, host defense and homeostasis

The possible roles of mast cells in heath and disease have been a topic of interest for over 125 years. Many adaptive or pathological processes affecting the skin or other anatomical sites have been associated with morphological evidence of mast cell activation, and/or with changes in mast cell numbers or phenotype. Such observations, taken together with the known functions of the diverse mediators, cytokines and growth factors which can be secreted by mast cells, have suggested many potential functions for mast cells in health and disease. Definitively identifying the importance of mast cells in biological responses in humans is difficult. However, mutant mice which are profoundly mast cell-deficient, especially those which can undergo engraftment with wild-type or genetically altered mast cells, provide an opportunity to investigate the importance of mast cells, and specific mast cell functions or products, in various adaptive or pathological responses in mice. Such work has shown that mast cells can significantly influence multiple features of inflammatory or immune responses, through diverse effects that can either promote or, surprisingly, suppress, aspects of these responses. Through such functions, mast cells can significantly influence inflammation, tissue remodeling, host defense and homeostasis.

Conventional and new approaches to hyposensitization

Hyposensitization in IgE-mediated allergic diseases has traditionally been induced by immunotherapy in which increasing amounts of allergens have been injected until a maximal tolerated dose has been achieved. Among the most obvious immunological effects of immunotherapy have been the production of allergen-specific IgG and some impairment in the synthesis of allergen-specific IgE. In addition to allergen-specific IgG (sometimes described as blocking antibodies) anti-idiotypic and anti-isotypic (IgG anti-IgE) have recently attracted attention as possibly being involved in hyposensitization. The effects of immunotherapy at the cellular level (either as T cell control of IgE synthesis or as modulation of mediator release by effector cells) also deserve further investigation.

Mast cell-derived interleukin 10 limits skin pathology in contact dermatitis and chronic irradiation with ultraviolet B

Allergic contact dermatitis, such as in response to poison ivy or poison oak, and chronic low-dose ultraviolet B irradiation can damage the skin. Mast cells produce proinflammatory mediators that are thought to exacerbate these prevalent acquired immune or innate responses. Here we found that, unexpectedly, mast cells substantially limited the pathology associated with these responses, including infiltrates of leukocytes, epidermal hyperplasia and epidermal necrosis. Production of interleukin 10 by mast cells contributed to the anti-inflammatory or immunosuppressive effects of mast cells in these conditions. Our findings identify a previously unrecognized function for mast cells and mast cell-derived interleukin 10 in limiting leukocyte infiltration, inflammation and tissue damage associated with immunological or innate responses that can injure the skin.

Mast cells in the promotion and limitation of chronic inflammation

Observations of increased numbers of mast cells at sites of chronic inflammation have been reported for over a hundred years. Light and electron microscopic evidence of mast cell activation at such sites, taken together with the known functions of the diverse mediators, cytokines, and growth factors that can be secreted by appropriately activated mast cells, have suggested a wide range of possible functions for mast cells in promoting (or suppressing) many features of chronic inflammation. Similarly, these and other lines of evidence have implicated mast cells in a variety of adaptive or pathological responses that are associated with persistent inflammation at the affected sites. Definitively characterizing the importance of mast cells in chronic inflammation in humans is difficult. However, mice that genetically lack mast cells, especially those which can undergo engraftment with wildtype or genetically altered mast cells, provide a means to investigate the importance of mast cells and specific mast cell functions or products in diverse models of chronic inflammation. Such work has confirmed that mast cells can significantly influence multiple features of chronic inflammatory responses, through diverse effects that can either promote or, perhaps more surprisingly, suppress aspects of these responses.

Vascular endothelial growth factor receptor tyrosine kinase inhibitor PTK787/ZK 222584 inhibits both the induction and elicitation phases of contact hypersensitivity

Vascular endothelial growth factor (VEGF) and its endothelial cell receptors (VEGFR) have been shown to be involved in the pathogenesis of the contact hypersensitivity (CHS) reaction. Previous studies have demonstrated that anti-VEGFR-2 antibody significantly suppresses the elicitation phase of CHS but does not affect the induction phase. PTK787/ZK 222584 (1-[4-chloroanilino]-4-[4-pyridylmethyl] phthalazine succinate; PTK/ZK) is a potent inhibitor of VEGFR tyrosine kinases. To test the effect of PTK/ZK on the induction and elicitation phases of CHS separately, we used an established method of CHS assay-sensitization and challenge in BALB/c mice. Either 50 mg/kg/day PTK/ZK or vehicle serving as a control was administered orally in the induction or elicitation phases separately. In the afferent phase, flow cytometry of skin-draining lymph node cells revealed that the migration of Langerhans cells was suppressed in the mice treated with PTK/ZK at sensitization. The degrees of ear swelling at 24 and 48 h were significantly diminished in mice treated with PTK/ZK at sensitization (P < 0.05). In the efferent phase, the degrees of ear swelling at 24 h (P < 0.01) and 48 h (P < 0.05), ear blood flow at 24 and 48 h (P < 0.01), and production of VEGF in the epidermis at 24 h (P < 0.05) were significantly suppressed in mice treated with PTK/ZK at elicitation. These findings and previous demonstrations suggest that both VEGF R-1 and VEGF R-2 are needed during the induction phase, and that VEGFR-2 has a pivotal role in the elicitation phase of the CHS reaction.

Histamine in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by a persistent inflammation of the synovium, leading to the erosion of articular cartilage and bone. Synovial mast cells and their effector molecule, histamine, receive increased attention as mediators of joint inflammation. The aim of our study was to analyse levels of free histamine in serum and joint fluid of RA patients and to evaluate the potential inflammatogenic properties of histamine in vivo and in vitro. Histamine levels were measured by an ELISA in synovial fluid and sera of RA patients and of healthy controls. Histamine levels were also assessed in plasma of RA patients undergoing anti-TNF-alpha treatment. In the murine part of the study, histamine was injected intra-articularly in the knee joint of mice and the joints were subsequently analysed with respect to induction of inflammation. RA patients displayed significantly lower levels of histamine in circulation (0.93 +/- 0.16 ng/ml) compared with the healthy controls (1.89 +/- 0.45 ng/ml, P < 0.001). Locally, in synovial fluid the levels of histamine were even lower (0.37 +/- 0.16 ng/ml, P < 0.0006). Long-term anti-TNF-alpha treatment significantly increased circulating levels of histamine in RA patients. Our experiments on animals show that histamine on its own neither induces inflammation in the joint cavity nor influences the course of HMGB1 and peptidoglycan-induced joint inflammation. Based on our experimental and clinical studies we suggest that histamine lacks harmful properties in RA.

Topical application of F991, an immunoglobulin free light chain antagonist, prevents development of contact sensitivity in mice

BACKGROUND

Exposure to reactive chemicals or environmental allergens can lead to hypersensitivity reactions in the skin of predisposed people. Most of these reactions are of atopic origin, but a subgroup of patients exhibits skin hypersensitivity reactions without features of atopy.

OBJECTIVE

This study was undertaken to examine the effect of inhibiting the action of Ig-free light chains in a murine model for non-atopic skin hypersensitivity by dermal application of the free light chain antagonist F991.

METHODS

To study the efficacy of F991, BALB/c mice were either passively immunized with trinitrophenyl (TNP)-specific immunoglobulin light chains (IgLC) and challenged with the hapten picryl chloride (PCl) or actively skin-sensitized and challenged with dinitrofluorobenzene (DNFB). The effect of F991 or control treatment was investigated by measuring local edema formation and the production of pro-inflammatory cytokines.

RESULTS

Passive immunization with TNP-specific IgLC resulted in an increase in ear swelling 2 h after PCl challenge. F991 inhibited this enhanced ear swelling in a dose-dependent manner when applied 4 h before the sensitization with IgLC. F991 also inhibited DNFB-induced contact hypersensitivity reaction in the mouse skin 2 and 24 h after challenge when applied before challenge. Besides the prophylactic action, F991 when applied 2 h after DNFB-challenge, it was also able to attenuate symptoms of the DNFB-induced hypersensitivity reaction at 24 h after challenge. We showed that the beneficial effects of F991 are restricted to the side of application.

CONCLUSION

F991 is able to effectively alleviate symptoms of contact sensitivity in mice. Our study suggests that local interference with IgLC-induced allergic symptoms may be attractive in the treatment of hypersensitivity responses.

Effector and potential immunoregulatory roles of mast cells in IgE-associated acquired immune responses

Mast cells are best known as critical effector cells in anaphylaxis and other examples of IgE-associated immediate hypersensitivity reactions. However, mast cells also can contribute to the development of the late-phase responses that occur in some sensitized subjects hours after initial exposure to specific antigen, and can promote many of the features of chronic allergic inflammation, including tissue remodeling and functional changes in the affected organs. In addition to such effector cell functions in IgE-associated immune responses, recent evidence indicates that mast cells can importantly influence the sensitization phase of at least some acquired immune responses, and can contribute to the pathology of autoimmune disorders and to the expression of peripheral tolerance.

Novel anti-inflammatory properties of the angiogenesis inhibitor vasostatin

Endothelial cells are critically involved in the pathogenesis of inflammation, which is characterized by vasopermeability, plasma leakage, leukocyte recruitment, and neovascularization. Therefore, inhibitors of endothelial cell function could reduce inflammation. In this study, we evaluated the effects of the angiogenesis inhibitor vasostatin on inflammations induced by contact hypersensitivity reactions in mouse ears. Vasostatin-treated mice revealed significantly reduced edema formation, resulting from lower plasma leakage and inhibition of inflammation-associated vascular remodeling. Intravital microscopy studies of inflamed ears showed a decrease in the fraction of rolling leukocytes in vasostatin-treated mice, and Lycopersicon esculentum lectin-perfused ears revealed fewer leukocytes adherent to the vessel wall. The inflammatory infiltrate from vasostatin-treated mice was characterized by fewer CD8+ T cells, neutrophils, and macrophages compared to the saline-treated animals. In a modified Miles assay, vasostatin inhibited vascular endothelial growth factor-A-induced permeability, and inflamed ear tissues from vasostatin-treated mice expressed significantly reduced levels of the vascular destabilizer angiopoietin-2. These results reveal a previously unrecognized anti-inflammatory property of the angiogenesis inhibitor vasostatin, and suggest that vasostatin is a potential candidate drug for the treatment of inflammation.

Mast cell-associated TNF promotes dendritic cell migration

Mast cells represent a potential source of TNF, a mediator which can enhance dendritic cell (DC) migration. Although the importance of mast cell-associated TNF in regulating DC migration in vivo is not clear, mast cells and mast cell-derived TNF can contribute to the expression of certain models of contact hypersensitivity (CHS). We found that CHS to FITC was significantly impaired in mast cell-deficient Kit(W-sh/W-sh) or TNF(-/)(-) mice. The reduced expression of CHS in Kit(W-sh/W-sh) mice was fully repaired by local transfer of wild-type bone marrow-derived cultured mast cells (BMCMCs), but was only partially repaired by transfer of TNF(-/)(-) BMCMCs. Thus, mast cells, and mast cell-derived TNF, were required for optimal expression of CHS to FITC. We found that the migration of FITC-bearing skin DCs into draining lymph nodes (LNs) 24 h after epicutaneous administration of FITC in naive mice was significantly reduced in mast cell-deficient or TNF(-/)(-) mice, but levels of DC migration in these mutant mice increased to greater than wild-type levels by 48 h after FITC sensitization. Mast cell-deficient or TNF(-/)(-) mice also exhibited significantly reduced migration of airway DCs to local LNs at 24 h after intranasal challenge with FITC-OVA. Migration of FITC-bearing DCs to LNs draining the skin or airways 24 h after sensitization was repaired in Kit(W-sh/W-sh) mice which had been engrafted with wild-type but not TNF(-/)(-) BMCMCs. Our findings indicate that mast cell-associated TNF can contribute significantly to the initial stages of FITC-induced migration of cutaneous or airway DCs.

T cell- and B cell-independent adaptive immunity mediated by natural killer cells

It is commonly believed that only T lymphocytes and B lymphocytes expressing recombination-dependent antigen-specific receptors mediate contact hypersensitivity responses to haptens. Here we found that mice devoid of T cells and B cells demonstrated substantial contact hypersensitivity responses to 2,4-dinitrofluorobenzene and oxazolone. Those responses were adaptive in nature, as they persisted for at least 4 weeks and were elicited only by haptens to which mice were previously sensitized. No contact hypersensitivity was induced in mice lacking all lymphocytes, including natural killer cells. Contact hypersensitivity responses were acquired by such mice after adoptive transfer of natural killer cells from sensitized donors. Transferable hapten-specific memory resided in a Ly49C-I(+) natural killer subpopulation localized specifically in donor livers. These observations indicate that natural killer cells can mediate long-lived, antigen-specific adaptive recall responses independent of B cells and T cells.

Mast cells as "tunable" effector and immunoregulatory cells: recent advances

This review focuses on recent progress in our understanding of how mast cells can contribute to the initiation, development, expression, and regulation of acquired immune responses, both those associated with IgE and those that are apparently expressed independently of this class of Ig. We emphasize findings derived from in vivo studies in mice, particularly those employing genetic approaches to influence mast cell numbers and/or to alter or delete components of pathways that can regulate mast cell development, signaling, or function. We advance the hypothesis that mast cells not only can function as proinflammatory effector cells and drivers of tissue remodeling in established acquired immune responses, but also may contribute to the initiation and regulation of such responses. That is, we propose that mast cells can also function as immunoregulatory cells. Finally, we show that the notion that mast cells have primarily two functional configurations, off (or resting) or on (or activated for extensive mediator release), markedly oversimplifies reality. Instead, we propose that mast cells are "tunable," by both genetic and environmental factors, such that, depending on the circumstances, the cell can be positioned phenotypically to express a wide spectrum of variation in the types, kinetics, and/or magnitude of its secretory functions.

Mast cells in the development of adaptive immune responses

Mast cells are so widely recognized as critical effector cells in allergic disorders and other immunoglobulin E-associated acquired immune responses that it can be difficult to think of them in any other context. However, mast cells also can be important as initiators and effectors of innate immunity. In addition, mast cells that are activated during innate immune responses to pathogens, or in other contexts, can secrete products and have cellular functions with the potential to facilitate the development, amplify the magnitude or regulate the kinetics of adaptive immune responses. Thus, mast cells may influence the development, intensity and duration of adaptive immune responses that contribute to host defense, allergy and autoimmunity, rather than simply functioning as effector cells in these settings.

IgE-mediated mast cell activation induces Langerhans cell migration in vivo

Langerhans cells and mast cells are both resident in large numbers in the skin and act as sentinel cells in host defense. The ability of mast cells to induce Langerhans cell migration from the skin to the draining lymph node in vivo was examined. Genetically mast cell-deficient (W/Wv) mice and control mice were sensitized with IgE Ab in the ear pinna. Seven to 14 days later, mice were challenged with Ag i.v. After a further 18-24 h, epidermal sheets and draining auricular lymph nodes were examined using Langerin/CD207 immunostaining. In mast cell-containing mice, a significant decrease in the number of Langerhans cells was observed at epidermal sites of mast cell activation. A significant increase in total cellularity and accumulation of Langerin-positive dendritic cells was observed in the auricular lymph nodes, draining the sites of IgE-mediated mast cell activation. These changes were not observed in W/Wv mice, but were restored by local mast cell reconstitution. Treatment of mast cell-containing mice with the H2 receptor antagonist cimetidine significantly inhibited the observed IgE/Ag-induced changes in Langerhans cell location. In contrast, Langerhans cell migration in response to LPS challenge was not mast cell dependent. These data directly demonstrate the ability of mast cells to induce dendritic cell migration to lymph nodes following IgE-mediated activation in vivo by a histamine-dependent mechanism.

Anti-vascular endothelial growth factor receptor-2 (Flk-1/KDR) antibody suppresses contact hypersensitivity

The angiogenic mediator vascular endothelial growth factor (VEGF) and its receptors (VEGFRs) have been studied extensively in neoplastic disease and some inflammatory conditions. Contact hypersensitivity (CHS) is a prototypic Langerhans' cell-dependent, T-helper (Th) 1 cell-mediated inflammatory skin disease that is now also thought to involve angiogenic mediators. The purpose of our study was to examine the role of angiogenesis and VEGF in CHS. We demonstrated that VEGF production is up-regulated in murine skin after challenge with dinitrofluorobenzene. Administration of a monoclonal antibody directed against the VEGFR-2 (DC101) resulted in a 28.8% decrease in CHS response (P < 0.001). Examination of the DC101-treated mouse skin 24 h after challenge revealed decreases in dermal inflammatory cellular infiltrates and total vessel area. Furthermore, mRNA and protein of the Th1-type cytokine interferon (IFN)-gamma was significantly down-regulated in skin of DC101-treated animals 24 h after challenge. The results of the study demonstrate that VEGFR-2 blockade significantly reduces vascular enlargement and edema formation and effects IFN-gamma expression in the skin during challenge in CHS. Our findings suggest that DC101 could function by reducing inflammatory cell migration and hence IFN-gamma expression during the CHS response.

Induction of cutaneous delayed-type hypersensitivity reactions in VEGF-A transgenic mice results in chronic skin inflammation associated with persistent lymphatic hyperplasia

Vascular endothelial growth factor-A (VEGF-A) expression is up-regulated in several inflammatory diseases including psoriasis, delayed-type hypersensitivity (DTH) reactions, and rheumatoid arthritis. To directly characterize the biologic function of VEGF-A in inflammation, we evaluated experimental DTH reactions induced in the ear skin of transgenic mice that overexpress VEGF-A specifically in the epidermis. VEGF-A transgenic mice underwent a significantly increased inflammatory response that persisted for more than 1 month, whereas inflammation returned to baseline levels within 7 days in wild-type mice. Inflammatory lesions in VEGF-A transgenic mice closely resembled human psoriasis and were characterized by epidermal hyperplasia, impaired epidermal differentiation, and accumulation of dermal CD4+ T-lymphocytes and epidermal CD8+ lymphocytes. Surprisingly, VEGF-A also promoted lymphatic vessel proliferation and enlargement, which might contribute to the increased inflammatory response, as lymphatic vessel enlargement was also detected in human psoriatic skin lesions. Combined systemic treatment with blocking antibodies against VEGF receptor-1 (VEGFR-1) and VEGFR-2 potently inhibited inflammation and also decreased lymphatic vessel size. Together, these findings reveal a central role of VEGF-A in promoting lymphatic enlargement, vascular hyperpermeability, and leukocyte recruitment, thereby leading to persistent chronic inflammation. They also indicate that inhibition of VEGF-A bioactivity might be a new approach to anti-inflammatory therapy.

Immune Sensitization in the Skin Is Enhanced by Antigen-Independent Effects of IgE

Contact sensitivity responses require both effective immune sensitization following cutaneous exposure to chemical haptens and antigen-specific elicitation of inflammation upon subsequent hapten challenge. We report that antigen-independent effects of IgE antibodies can promote immune sensitization to haptens in the skin. Contact sensitivity was markedly impaired in IgE(-/-) mice but was restored by either transfer of sensitized cells from wild-type mice or administration of hapten-irrelevant IgE before sensitization. Moreover, IgE(-/-) mice exhibited impairment in the reduction of dendritic cell numbers in the epidermis after hapten exposure. Monomeric IgE has been reported to influence mast cell function. We observed diminished contact sensitivity in mice lacking FcepsilonRI or mast cells, and mRNA for several mast cell-associated genes was reduced in IgE(-/-) versus wild-type skin after hapten exposure. We speculate that levels of IgE normally present in mice favor immune sensitization via antigen-independent but FcepsilonRI-dependent effects on mast cells.

Th2 cytokines, IgE and mast cells play a crucial role in the induction of para-phenylenediamine-induced contact hypersensitivity in mice

We previously reported the establishment of a mouse model system of contact hypersensitivity (CHS) to paraphenylemediamine (PPD). In order to analyse the functional contribution of Th2 cytokines, IL-4 and IL-5, in PPD induced CHS, STAT6 deficient (STAT6-/-) and wild-type control (WT) mice (C57BL/6) were immunized by the topical application of a PPD solution, and then the subsequent skin reactions were examined. Ear swelling was significantly reduced with a delayed peak response in STAT6-/- mice as compared with that of WT mice. A histological analysis showed the infiltration of both eosinophils and neutrophils in the skin of STAT6-/- mice challenged 24 h previously to significantly decrease in comparison with that in the WT mice. The expression of Th2 cytokines (IL-4, IL-5) by ELISA in the PPD-challenged skin tissue specimens as well as the IgE and IgG1 response after challenge were also profoundly reduced in the STAT6-/- mice. The adoptive transfer of the serum obtained from sensitized WT mice for the putative IgE transfer induced a peak response at 3 h and 24 h after challenge. To further investigate the role of mast cells in the induction of PPD-CHS, mast cell deficient W/Wv mice were sensitized with PPD and then were challenged. Maximal ear swelling was detected from 12 to 24 h and another small peak response was observed at 1 h in+/+mice, whereas only a small peak response at 24 h was detected in W/Wv mice. These data indicate that not only Th2 cytokines and IgE but also mast cells play an essential role in the induction of PPD-CHS.