Mast cell density and subtypes in the skin of dogs with atopic dermatitis

A review of cutaneous hypersensitivity reactions in dogs: A diagnostician's guide to allergy

Allergic dermatoses are common in people and domestic animals. Resultant lesions are routinely biopsied and submitted for histological examination to confirm a diagnosis or rule out diseases with overlapping or atypical clinical features. Diagnostic pathologists and clinicians are often faced with the difficult task of determining whether an allergic reaction pattern is present on both the microscopic and macroscopic levels and correlating histopathologic findings with clinical and historical data to achieve a precise clinical diagnosis. The bulk of the current veterinary literature on allergic dermatoses focuses on atopic dermatitis in dogs, distantly followed by cats, horses, and other animals. The objectives of this review are to demonstrate the key histopathologic and clinical diagnostic features of the various allergy-mediated reaction patterns, and to provide diagnosticians with a practical guide for clinicopathological correlations. Current concepts in the pathophysiology of immediate hypersensitivity reactions, with a focus on atopic dermatitis, are discussed. Points of potential histopathologic overlap between the "classic" allergic reaction pattern and less common inflammatory, predominately eosinophilic, conditions that may mimic this pattern will be discussed with the goal of highlighting the critical need for collaboration between pathologists and clinicians in furthering patient care.

Carboxypeptidase A3 expression in canine mast cell tumors and tissue-resident mast cells

Mast cell tumors (MCTs) are one of the most common cutaneous malignancies in dogs. Previous studies have reported expression of mast cell–specific proteases chymase and tryptase in canine cutaneous MCTs and in connective tissue and mucosal mast cells. In humans and rodents, mast cells express an additional specific protease, carboxypeptidase A3 (CPA3). In this article, we describe CPA3 immunoreactivity in connective tissue, visceral, mucosal, and neoplastic mast cells in dogs. Positive immunolabeling for CPA3 was observed in nonneoplastic mast cells in 20/20 formalin-fixed paraffin-embedded normal tissues (skin, liver, spleen, intestine), and in 63/63 MCTs irrespective of their histological grade. CPA3 protein expression was comparable to that of c-kit in both the nonneoplastic and neoplastic mast cells. Three distinct labeling patterns (membranous, diffuse, and focal cytoplasmic) were observed for CPA3 in MCTs. The focal cytoplasmic labeling pattern was associated with high-grade MCTs staged with the Kiupel 2-tier grading criteria. We propose CPA3 as a novel immunohistochemical marker for canine mast cells in health and disease.

Increased levels of palmitoylethanolamide and other bioactive lipid mediators and enhanced local mast cell proliferation in canine atopic dermatitis

BACKGROUND

Despite the precise pathogenesis of atopic dermatitis (AD) is unknown, an immune dysregulation that causes Th2-predominant inflammation and an intrinsic defect in skin barrier function are currently the two major hypotheses, according to the so-called outside-inside-outside model. Mast cells (MCs) are involved in AD both by releasing Th2 polarizing cytokines and generating pruritus symptoms through release of histamine and tryptase. A link between MCs and skin barrier defects was recently uncovered, with histamine being found to profoundly contribute to the skin barrier defects.Palmitoylethanolamide and related lipid mediators are endogenous bioactive compounds, considered to play a protective homeostatic role in many tissues: evidence collected so far shows that the anti-inflammatory effect of palmitoylethanolamide depends on the down-modulation of MC degranulation.Based on this background, the purpose of the present study was twofold: (a) to determine if the endogenous levels of palmitoylethanolamide and other bioactive lipid mediators are changed in the skin of AD dogs compared to healthy animals; (b) to examine if MC number is increased in the skin of AD dogs and, if so, whether it depends on MC in-situ proliferation.

RESULTS

The amount of lipid extract expressed as percent of biopsy tissue weight was significantly reduced in AD skin while the levels of all analyzed bioactive lipid mediators were significantly elevated, with palmitoylethanolamide showing the highest increase.In dogs with AD, the number of MCs was significantly increased in both the subepidermal and the perifollicular compartments and their granule content was significantly decreased in the latter. Also, in situ proliferation of MCs was documented.

CONCLUSIONS

The levels of palmitoylethanolamide and other bioactive lipid mediators were shown to increase in AD skin compared to healthy samples, leading to the hypothesis that they may be part of the body's innate mechanisms to maintain cellular homeostasis when faced with AD-related inflammation. In particular, the increase may be considered a temptative response to down-regulating the observed elevation in the number, functionality and proliferative state of MCs in the skin of AD dogs. Further studies are warranted to confirm the hypothesis.

The effect of wasabi rhizome extract on atopic dermatitis-like symptoms in HR-1 hairless mice

We investigated the effect of wasabi rhizome extract on atopic dermatitis (AD) model mice. The wasabi extract was fed to the HR-1 hairless mice, which develop AD-like symptoms with a special diet (HR-AD diet). The extract was expected to reduce the symptoms induced. Wasabi rhizome-containing HR-AD diet (5% and 10%) reduced the scratching behavior, and the 10% wasabi rhizome HR-AD diet significantly reduced scratching behavior on days 28, 35 and 42. Plasma components (histamine, eotaxin, IgE and thymus and activation-regulated chemokine (TARC)) were decreased in the 10% wasabi rhizome HR-AD diet. In histopathological examinations (toluidine blue (T.B.), major basic protein (MBP), CD4, IL-4, IL-5, eotaxin, TARC and IgE), the wasabi rhizome-containing HR-AD diet (5% and 10%) significantly reduced the number of positive stained cells. These results suggested that the wasabi rhizome extract improved the AD-like symptoms of HR-1 hairless mice.

The role of mast cells in atopy: what can we learn from canine models? A thorough review of the biology of mast cells in canine and human systems

Mast cell research has largely focused on the role of these cells in the early phase of allergic reactions. However, their involvement may well extend beyond this stage, and even reach across nonallergic conditions. Mast cells from different sources have helped advance our knowledge of their biology. Although in vitro and in vivo research in this area has mainly focused on humans, such studies are limited by the extent to which cells from certain human tissues and/or human patients can be collected or studied. While rodents also provide valuable models with which to further our understanding of the behaviour of mast cells and their contribution to allergy, reported differences between human and murine mast cells, and, in some instances, the limitations of in vivo rodent models of mast cell-mediated allergic conditions, preclude their use. In this review, we introduce a relatively unknown mast cell population, that of the dog. Canine mast cells display many phenotypic and functional similarities with their human counterparts, and dogs develop spontaneous and induced allergic diseases that share clinical and pathophysiological features with the human condition. Therefore, the use of canine cells can shed light on the general role of mast cells, particularly in relation to allergic diseases given the potential of in vivo dog models within this field. Here we provide a detailed review of the data reported from in vitro and in vivo studies of canine mast cells, and compare them with results obtained in human systems. We also highlight direct evidence of the mast cell contribution to canine atopy. We conclude that the dog offers useful in vitro and in vivo models in which to investigate mast cell behaviour, and that its use should be considered when undertaking studies aimed either at elucidating the role of mast cells in health and disease, or at prescreening novel therapies prior to entry into man.

Immune dysregulation in flea allergy dermatitis—A model for the immunopathogenesis of allergic dermatitis

BACKGROUND

Flea allergy dermatitis (FAD) is a common skin disease in dogs and can be induced experimentally. It often coexists with other allergic conditions. So far no studies have investigated the quantitative production of cytokine mRNA in skin biopsies and peripheral blood mononuclear cells (PBMC) in flea allergic dogs.

OBJECTIVE

The aim of our study was to improve the understanding of the immunopathogenesis of allergic dermatitis as a response to fleabites.

MATERIAL AND METHODS

Allergic and non-allergic dogs were exposed to fleas. Before and after 4 days of flea exposure mRNA was isolated from biopsies and PBMC. Production of chymase, tryptase, IL-4, IL-5, IL-13, TNF-alpha and IFN-gamma mRNA was measured by real-time RT-PCR. The inflammatory infiltrate in the skin was scored semi-quantitatively. The number of eosinophils, mast cells (MC) and IgE+ cells/mm2 was evaluated to complete the picture.

RESULTS

FAD was associated with a higher number of MC before flea exposure and with a significant increase of eosinophils after flea exposure as compared to non-allergic dogs. The number of IgE+ cells was higher in allergic dogs before and after flea exposure. In allergic dogs mRNA for most cytokines and proteases tested was higher before flea exposure than after flea exposure. After exposure to fleas an increased mRNA production was only observed in non-allergic dogs. In vitro stimulation with flea antigen resulted in a decreased expression of most cytokines in allergic dogs before flea exposure. In contrast, in PBMC, only increased levels of IL-4 and IL-5 mRNA were observed in allergic dogs before flea exposure. However, after flea exposure and additional stimulation with flea antigen the production of mRNA for all cytokines tested was significantly increased in allergic dogs.

CONCLUSION

We demonstrated that the response in biopsies and PBMC is different and that FAD is associated with a TH2 response.

Immunohistochemical and histochemical stains for differentiating canine cutaneous round cell tumors

Immunohistochemical and histochemical stains are useful adjunct techniques in the diagnosis of canine cutaneous round cell tumors, which can appear histologically similar. We applied a panel of monoclonal antibodies (recognizing tryptase, chymase, serotonin for mast cells; CD1a, CD18, MHC class II for histiocytes; CD3 for T lymphocytes; CD79a for B lymphocytes and plasma cells) and one histochemical stain (naphthol AS-D chloroacetate for chymase activity) to formalin-fixed, paraffin-embedded sections of canine cutaneous mast cell tumors, histiocytomas, lymphosarcomas, plasmacytomas, and unidentified round cell tumors. Of 21 tumors with a histologic diagnosis of mast cell tumor, 7/7 (100%) grade I, 6/7 (85.7%) grade II, and 3/7 (42.9%) grade III tumors were diagnosed as mast cell tumors based on positive staining for tryptase antigen and chymase activity. Mast cells were positive for both tryptase antigen and chymase activity, indicating equal efficacy of tryptase immunohistochemistry and chymase histochemistry. Chymase was detected immunohistochemically in both tumor and nontumor cells, while serotonin was not detected in most mast cell tumors, and thus, neither was useful in the diagnosis of mast cell tumors. Immunohistochemistry to detect CD18 and MHC class II was equally effective in staining histiocytomas, although lymphosarcoma must be ruled out through the use of CD3 and CD79a immunohistochemistry. Immunohistochemistry using three different monoclonal antibodies to human CD1a showed no cross-reactivity in canine histiocytomas and was not useful. A final diagnosis was obtained for 4/5 (80%) of the unidentified tumors, indicating the usefulness of multiple stains in poorly differentiated round cell tumors.

Optimization of an Acridine Orange-bisbenzimide procedure for the detection of apoptosis-associated fluorescence colour changes in etoposide-treated cell cultures

This study was initiated in order to investigate the possibility of improving fluorescence microscopy as a method for evaluating apoptosis in cells by combining two fluorescent dyes with different staining characteristics. Cells were vitally stained with bisbenzimide (1.3 microM) and Acridine Orange (6.6 microM) and observed using the following filter configuration: excitation 380 nm, beamsplitter 395 nm and longpass filter 397 nm. Control cells exhibited clear blue fluorescent nuclei and red fluorescing lysosomes. In cells treated with etoposide to induce apoptosis, two distinct occurrences were observed: a change in the spectrum of emitted light from bisbenzimide bound to the nuclear region and an increase in lysosomal Acridine Orange fluorescence. The two occurrences together permit a more unbiased detection of apoptosis than most assays. Only one filter set is required for evaluation and the resulting images can be easily evaluated visually or processed further by image analysis.

Mast Cells and Eosinophils in Feline Allergic Dermatitis: A Qualitative and Quantitative Analysis

Mast cells (MCs) and eosinophils are prominent in the perivascular infiltrate of cats with allergic dermatitis. In the skin of allergic cats MCs were mainly observed diffusely in the superficial dermis, while eosinophils were found mainly in the deep dermis in a perivascular pattern. MC counts were significantly higher in cats with allergic dermatitis (P < 0.05) than in healthy control cats, but the number varied widely. Moreover, the numbers of eosinophils in the skin of allergic and control cats differed significantly (P < 0.05) none being found in the latter. There was no significant correlation between numbers of mast cells and eosinophils in the same biopsy sample. In the allergic cats, a significantly lower number of MCs was detected by staining for tryptase than by staining for chymase or by Astra blue staining. Additionally, the chymase: tryptase ratio in healthy cats was reversed in cats with allergic dermatitis. These changes were observed in lesional and nonlesional skin of cats with allergic dermatitis. The findings indicate a generalized effect on MCs in allergic dermatitis. In addition, eosinophils are an important indicator of allergic dermatitis.

Quantitative analysis of tryptase- and chymase-containing mast cells in eosinophilic conditions of cats

The presence and density of tryptase-positive/chymase-positive mast cells (MCs) (MC(TC)), chymase-positive/tryptase-negative MCs (MCC), and tryptase-positive/chymase-negative MCs (MC(T)) in lesional skin from cats with eosinophilic conditions were investigated. Skin biopsy specimens from eight cats with eosinophilic plaque (three cats), eosinophilic granuloma (two cats), and eosinophilic dermatitis (three cats) were studied. Toluidine blue staining and a double-enzyme-immunohistochemical staining technique were performed to determine MC density and MC subtypes, respectively. MC density varied from 170.3 to 503 cells/mm2 (mean value of 314.9 cells/mm2). In the superficial dermis, 5.9% of the MC belonged to the MC(T), 12.8% to the MC(C), and 81.2% to the MC(TC) subtype. In the deep dermis, 12.8% belonged to the MC(T), 12.8% to the MC(C), and 73.8% to the MC(TC) subtype. It is the first time that MC(C) have been identified. The double-labeling procedure proved to be a reliable tool for identifying simultaneously the presence of MC subtypes in feline skin.

Flea bite hypersensitivity: new aspects on the involvement of mast cells

A study was performed to test the effect of sensitization to flea antigen, followed by exposure to fleas on mast cells (MCs), their subtypes, and IgE+ cells. Biopsies were taken from flea-sensitized dogs (n=28) and non-sensitized dogs (n=5) that had been exposed to fleas. Control groups consisted of flea-sensitized (n=12) and non-sensitized dogs (n=9) that were not exposed to fleas. Biopsies, taken before, 24 and 72 h after local flea exposure, were stained with haematoxylin and eosin (H&E), toluidine blue, a double labelling technique for MC chymase and tryptase and anti-IgE. An intradermal test for flea antigen was performed and serum titres of allergen-specific IgE and IgG were measured. Significantly higher numbers (P<0.001) of double labelled MCs compared to toluidine blue stained MCs were detectable in flea-sensitized dogs independent of flea exposure. In contrast, in non-sensitized dogs, the number of toluidine blue stained MCs and the number of double labelled MCs did not differ. In flea-sensitized dogs after flea exposure the percentage of C-MC was significantly increased at day 1 (P<0.001) and day 3 (P<0.001), whereas the percentage of TC-MCs decreased significantly at day 1 (P<0.001) and day 3 (P<0.05). The percentage of T-MCs decreased (P<0.05 day 0 versus day 1; P<0.05 day 0 versus day 3). No significant difference was detectable after toluidine blue staining and staining for IgE+ cells between the groups nor between the MC density and the number of IgE+ cells. All flea-sensitized dogs had positive skin tests to flea antigen and high serum titres of flea-specific serum IgE and IgG antibodies. In non-sensitized dogs, these results were negative. Our data provide strong evidence for an upregulation of MC proteases during the process of sensitization and a generalized selective release of mast cell tryptase after exposure to the antigen.

Evaluation of the usefulness of sensitization to aeroallergens as a model for canine atopic dermatitis in genetically predisposed Beagles

OBJECTIVE

To evaluate a model for atopic dermatitis (AD) and to measure the effect of sensitization in Beagles genetically predisposed to produce high serum concentrations of allergen specific IgE.

ANIMALS

22 laboratory Beagles.

PROCEDURE

Seventeen dogs were sensitized from birth to 3 allergens (recombinant birch pollen, Dermatophagoides pteronyssinus, and D farinae). Five nonsensitized dogs from the same litters served as controls. Clinical scoring, regular intradermal testing, measurement of serum concentrations of allergen-specific IgE, and collection of biopsy specimens of skin at 23, 32, and 43 weeks of age were performed. Serial tissue sections were stained for identification of IgE+ cells, mast cells and their subtypes, T-cells, Langerhans cells, and major histocompatibility complex class-II+ cells. At the age of 15 months, dogs were continuously exposed to 2 microg of mite allergen/g of dust.

RESULTS

Sensitized dogs had positive intradermal test reactions and significantly higher serum concentrations of allergen specific IgE, compared with nonsensitized dogs. In sensitized and nonsensitized dogs, a significantly higher number of mast cells was found at predilection sites, compared with the control biopsy site. The number of mast cells at predilection sites increased with age. Sensitization significantly increased the number of epidermal Langerhans cells by 23 weeks of age. The number of epidermal Langerhans cells significantly increased in nonsensitized dogs by 32 weeks of age. Clinical scoring only revealed mild transient erythema in some dogs.

CONCLUSIONS

increases in concentrations of serum allergen-specific IgE and exposure to allergens is not sufficient to induce clinical signs of AD in genetically predisposed dogs.

Non-specific labelling of mast cells in feline oral mucosa--a potential problem in immunohistochemical studies

Non-specific labelling of mast cells was found to occur in formalin-fixed sections of feline oral mucosa during immunohistochemical procedures. The phenomenon occurred when normal goat, rabbit or mouse serum was applied as a negative control in place of primary antibodies. In addition, with murine isotype-specific negative control reagents, non-specific labelling of mast cells was intense when IgG2b was applied as the primary reagent, but absent or mild when IgGl or IgG2a isotypes were utilized. The non-specific labelling could be eliminated or diminished by reducing the pH of the washing and dilution buffers from 7.4 to 6.0, or by preincubating sections with heparin. The non-specific binding could also be abolished by preincubating sections with heparinase-I. The results suggest that the non-specific binding was mediated by heparin present within feline oral mucosal mast cells. These findings illustrate the importance of the inclusion of adequate control sections in immunohistochemical studies.

Assessment of proliferative activity of canine dermal mast cells by bromodeoxyuridine and proliferating cell nuclear antigen labelling

Cutaneous mast cells from skin biopsies of three healthy dogs and three dogs with atopic dermatitis were assessed for their proliferative potential using bromodeoxyuridine and proliferating cell nuclear antigen labelling. Mast cells isolated from the skin of two healthy dogs were also studied using bromodeoxyuridine labelling. Mast cells in skin biopsy specimens and mast cells isolated from the skin of healthy dogs did not incorporate bromodeoxyuridine. Two mast cells expressing proliferating cell nuclear antigen were seen around two superficial vessels in the dermis of one atopic dog. Epidermal cells, glandular epithelial cells, fibroblasts and endothelial cells incorporated bromodeoxyuridine and showed positive staining for proliferating cell nuclear antigen. These results suggest that canine mature mast cells do not proliferate in the dermis.

The mast cell in wound healing

This review describes the role of the mast cell in the pathobiology of skin healing. After illustrating its main morphofunctional characteristics, with special reference to the dog and cat, we consider the involvement of the mast cell in the various phases of skin repair. With the aid of a wide array of newly formed or preformed mediators released by degranulation, the activated mast cell controls the key events of the healing phases: triggering and modulation of the inflammatory stage, proliferation of connective cellular elements and final remodelling of the newly formed connective tissue matrix. The importance of the mast cell in regulating healing processes is also demonstrated by the fact that a surplus or deficit of degranulated biological mediators causes impaired repair, with the formation of exuberant granulation tissue (e.g. keloids and hypertrophic scars), delayed closure (dehiscence) and chronicity of the inflammatory stage.

Distribution and enzyme histochemical characterisation of mast cells in cats

Mast cells from 15 different cat organs were examined in terms of distribution and protease activity. The number of mast cells in each site was found to vary when visualised by metachromatic staining using Alcian Blue. Enzyme histochemical analysis revealed the existence of two subtypes of mast cells. These were categorised based on protease content, i.e. whether the mast cells contained chymase or tryptase. Tryptase-positive mast cells were clearly identifiable in every organ examined, whereas chymase-containing mast cells were predominantly observed in the ear (skin), tongue, spleen, and submucosa of the stomach and rectum. The chymase-reactive cells were not detected in the heart, or in the muscularis or serosa of the duodenum, jejunum, ileum or rectum. In addition, we suggest the existence of another subtype of mast cell containing both chymase and tryptase and localised within the ear (skin), tongue, spleen and submucosa of the rectum.

The ACVD task force on canine atopic dermatitis (XVIII): histopathology of skin lesions

For years, the histopathology of skin lesions of canine atopic dermatitis was deemed non-specific for this diagnosis. However, more recent studies have established that canine atopic skin lesions exhibit an inflammatory pattern characterized as a chronic, hyperplastic and spongiotic, mixed perivascular dermatitis. The nature of epidermal and dermal inflammatory cell infiltrates has now been characterized using modern immunological techniques. Epitheliotropic cells include Langerhans' cells, T-lymphocytes and rare eosinophils. Dermal cells are composed of mast cells, dermal antigen-presenting cells, T-lymphocytes and occasional intact and degranulated eosinophils. This paper provides an historical review of the landmark papers that have elucidated the pathology of canine atopic dermatitis.

The ACVD task force on canine atopic dermatitis (V): biology and role of inflammatory cells in cutaneous allergic reactions

Numerous inflammatory cells are thought to play a role in the pathogenesis of canine atopic dermatitis (AD) although, in the past, mast cells were considered the most important. However, evidence for this assumption is lacking. In this paper, we review the literature concerning the role of inflammatory cells in allergic reactions and conclude that a complex interplay exists between a wide variety of cell types. Thus, on the basis of the available evidence, the cells that appear to be the most important in the pathogenesis of canine AD are Langerhans' cells and dermal dendritic cells (both responsible for antigen processing and presentation), B-lymphocytes (responsible for reaginic antibody production), allergen-specific helper T-lymphocytes (responsible for cytokine production leading to activation of B-cells and other inflammatory cells) and mast cells (production of inflammatory mediators leading to inflammation).

The ACVD task force on canine atopic dermatitis (VI): IgE-induced immediate and late-phase reactions, two inflammatory sequences at sites of intradermal allergen injections

Intradermal testing is a common diagnostic procedure used in the evaluation of dogs with suspected atopic dermatitis (AD). To do this, most investigators assess the appearance of wheals that develop at the sites of intradermal allergen injections. However, wheals are rarely seen in dogs with naturally occurring AD. Furthermore, infiltration of inflammatory cells into the injection sites can occur 6-24h later, a phenomenon known as the late-phase reaction. The histological appearance of these late-phase reactions closely approximates that seen in the natural disease, suggesting that they might be more relevant than the immediate reactions. In this paper, we review the literature on immediate and late-phase reactions and re-assess the evidence for using current intradermal testing procedures as a diagnostic test in dogs.

The ACVD task force on canine atopic dermatitis (VII): mediators of cutaneous inflammation

Controversy still exists on the role of various inflammatory mediators in the pathogenesis of canine atopic dermatitis. The objective of this article is to review the most recent information available on the inflammatory mediators that have been implicated in the pathogenesis of this disease. Studies on the role of histamine, serotonin, leukotrienes and various cytokines are presented in a comparative manner reviewing the experimental evidence for a role in the pathogenesis and the arguments against it.

Intradermal skin test reactivity to histamine and substance P is blunted in dogs with atopic dermatitis

Skin reactivity to intradermal injections (0.1, 0.5 and 1 nM) of substance P (SP) was evaluated in 20 clinically normal dogs and 20 dogs with atopic dermatitis (AD). Saline and histamine were used as negative and positive controls, respectively. Wheal diameters were measured. Reactions were evaluated for erythema and induration and a subjective score, on a scale from 0 to 4+, was given. Evaluations were performed at 3, 5, 10, 15 and 30 min after the injections. Wheal diameters for histamine and SP injections were significantly smaller in dogs with AD compared with clinically normal dogs. In both groups, reactions to the various concentrations of SP were not significantly different from each other and were always smaller than histamine reactions. Erythema was not seen with SP injections. In addition, subjective scores for SP injections were significantly lower in dogs with AD compared with controls. The results of this study are similar to those reported in human medicine, where a role for SP in AD is proposed and desensitization of receptors to both SP and histamine is hypothesized. Further studies are needed to investigate the role of SP in the pathogenesis of canine AD.