Characterization of the inflammatory infiltrate during IgE-mediated late phase reactions in the skin of normal and atopic dogs

Phenotypic Shift of an Inflammatory Eosinophil Subset into a Steady-State Resident Phenotype after 2 Years of Vaccination against IL-5 in Equine Insect Bite Hypersensitivity

Eosinophils play a key role in allergic diseases such as insect bite hypersensitivity (IBH). Together with Th2 cells, they shape the course of inflammation in associated type I/IVb allergies. Therefore, a virus-like particle (VLP)-based vaccine targeting equine interleukin-5 (eIL-5), eIL-5-CuMV-TT, was developed to interfere with the IL-5 dependency of eosinophils by inducing the production of anti-self-IL-5 antibodies and alleviating clinical signs in IBH-affected horses. A previous study highlighted the presence of two eosinophil subsets, steady-state resident eosinophils (rEos) and inflammatory eosinophils (iEos), circulating in the blood of healthy and IBH-affected horses, distinguishable by the expression of integrin CD49f. Furthermore, eIL-5-CuMV-TT 1st year vaccination showed a significant decrease of total eosinophils and, in particular, iEos. Nevertheless, the very few remaining eosinophils still shared an iEos phenotype, reflected by bigger size and higher granularity. The aim of this study was to follow up on the phenotype of eosinophils in the 2nd year of vaccination of IBH-affected horses with eIL-5-CuMV-TT. Using flow cytometry analysis of the blood of healthy, IBH, IBH-placebo, and IBH-vaccinated horses, the percentage and count of cells were compared between groups with a focus on pair analysis of eosinophils in 1st and 2nd year vaccinated horses. Our data showed comparably low levels of iEos and a significant increase of rEos in 2nd year compared to 1st year vaccinated horses, suggesting a phenotypic shift toward a resident-like eosinophil population, primarily associated with the phenotype of healthy horses. The reduction of size, granularity, and expression of integrin CD49f in the 2nd year suggests a benefit of long-term treatment with the eIL-5-CuMV-TT vaccine.

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.

Immunomodulatory effects of canine mesenchymal stem cells in an experimental atopic dermatitis model

Mesenchymal stem cells (MSCs) have the potential to differentiate into multi-lineage cells, suggesting their future applicability in regenerative medicine and biotechnology. The immunomodulatory properties of MSCs make them a promising replacement therapy in various fields of animal research including in canine atopic dermatitis (AD), a skin disease with 10-15% prevalence. We investigated the immunomodulatory effects of MSCs in an experimental canine AD model induced by Dermatophagoides farinae extract ointment. Canine adipose tissue-derived MSCs (cAT-MSCs) were differentiated into mesodermal cell lineages at the third passage. Alterations in immunomodulatory factors in control, AD, and MSC-treated AD groups were evaluated using flow cytometric analysis, enzyme-linked immunosorbent assay, and quantitative reverse transcription PCR. In the MSC-treated AD group, the number of eosinophils decreased, and the number of regulatory T cells (Tregs) increased compared to those in the AD group. In addition, the immunoglobulin E (IgE) and prostaglandin E₂ levels were reduced in the MSC-treated AD group compared to those in the AD group. Furthermore, the filaggrin, vascular endothelial growth factor, and interleukin-5 gene expression levels were relatively higher in the MSC-treated AD group than in the AD group, however, not significantly. cAT-MSCs exerted immunomodulatory effects in an AD canine model via a rebalancing of type-1 and -2 T helper cells that correlated with increased levels of Tregs, IgE, and various cytokines.

Lack of Interference of Oclacitinib with the results of intradermal testing or allergen-specific IgE serology in Dermatophagoides farinae-sensitized beagle dogs

Canine atopic dermatitis (AD) is associated with increased levels of allergen-specific IgE due to hyper-sensitization to environmental allergens. Intradermal testing (IDT) and allergen-specific IgE serology testing are often used to determine the allergens which elicit an IgE response in animals with a diagnosis of AD. The objective of this study was to determine the effects of oclacitinib on IDT and allergen-specific IgE serology testing using a laboratory model of house-dust mite sensitized Beagle dogs. Twenty-four (24) normal, healthy purpose-bred Beagle dogs were sensitized to house dust mites (HDM, Dermatophagoides farinae) and randomly assigned to placebo-, oclacitinib- (0.4 mg/kg/dose PO), or prednisolone-treated (0.5 mg/kg/dose PO) groups. After 14 days of twice daily dosing, the effects of prednisolone and oclacitinib were compared to placebo using baseline and post-dose IDT and allergen-specific IgE serum measurements. Sensitized dogs had increased circulating HDM-specific IgE for at least two weeks post-sensitization. Prednisolone significantly inhibited the measurable sensitivity of IDT, while oclacitinib did not. Neither prednisolone nor oclacitinib imposed significant effects on allergen-specific IgE serum levels, suggesting oclacitinib may have potential to be used in dogs concurrently undergoing intradermal skin testing and/or allergen-specific IgE serology testing without interference with test results.

Evaluation of Skin Prick-Test Reactions for Allergic Sensitization in Dogs With Clinical Symptoms Compatible With Atopic Dermatitis. A Pilot Study

Skin prick-test is the first choice for the detection of type I hypersensitivity in human atopic dermatitis. Canine atopic dermatitis resembles several symptoms of the disease in the human counterpart. In canine atopic dermatitis, intradermal testing is the test of choice, and there are few reports on the use of skin prick test (SPT) in dogs. The purpose of this study was to evaluate SPT reactions in atopic dogs and a healthy control group to 11 environmental allergens. Eleven glycerinated allergens were applied on the left lateral thorax of nine atopic dogs and nine healthy dogs. The skin was pricked with a feather lancet and evaluated for the positive percutaneous reaction at 5, 10, 15, and 20 min after the application of the allergens. Data were analyzed by the Shapiro-Wilk test to test for normal distribution. Data that did not meet normality were analyzed by a one-sided Wilcoxon ranked sum test with a p-value of 0.05. Six out of 9 atopic dogs tested positive for at least one of the allergens tested. None of the dogs in the control group showed a positive reaction to the allergens included in the test. Blomia tropicalis, Dermatophagoides farine, and Dermatophagoides pteronyssinus exhibited the highest reaction rate among the group of atopic dogs. There was not a statistical difference in the histamine reaction (positive control) between both groups. In this set of dogs, the test exhibited a 100% specificity and a sensitivity of 66%. The use of skin prick-test in the detection of causative allergens of human atopic dermatitis has proved to be a sensitive and specific tool frequently used by human allergists. Due to the number of similarities in canine and human atopic dermatitis, this could be a valuable tool that needs intensive research in veterinary medicine. The published research so far correlates to the results obtained in this investigation. However, future studies evaluating the concordance between in vitro specific IgE antibody assays and SPT must be carried out simultaneously to validate the test.

The anti-inflammatory effect of topical tofacitinib on immediate and late-phase cutaneous allergic reactions in dogs: a placebo-controlled pilot study

BACKGROUND

Topical Janus kinase (JAK) inhibition is a promising therapeutic target for several inflammatory skin diseases of humans.

OBJECTIVES

To evaluate the anti-inflammatory effect of tofacitinib, a JAK 1/3 inhibitor, on immediate and late-phase skin reactions in dogs.

ANIMALS

Five healthy laboratory beagle dogs.

METHODS

Topical tofacitinib (total daily dosage: 0.5 mg/cm² ) or its gel vehicle were applied on either the left or right lateral thorax of each dog for eight days. Three days before application and after eight days of topical treatment, intradermal injections of histamine and anticanine-IgE antibodies were performed on both sides; they were evaluated by an investigator blinded to the interventions.

RESULTS

The tofacitinib gel was well-tolerated; one dog developed mild erythema at Day 5 that resolved by the next application. Treatment with tofacitinib reduced histamine and anticanine-IgE global wheal scores (one-way ANOVA, P ≤ 0.005 for both) compared to baseline; there was no significant difference for the vehicle placebo (histamine; P = 0.163; IgE, P = 0.223). Late-phase reactions (LPRs) were markedly, but not significantly reduced after tofacitinib treatment (P = 0.071). A blinded histological evaluation of 6 h-anti-IgE-associated LPRs revealed a significant reduction in the total leucocyte superficial dermal cellularity (P = 0.022), as well as eosinophil (P = 0.022) and mast cell (P = 0.022) counts at tofacitinib-treated sides compared with pretreatment values. Post-treatment complete blood counts and serum chemistry profiles did not show relevant tofacitinib-induced changes.

CONCLUSIONS

Our observations suggest that topical tofacitinib exerts an inhibitory effect on activated canine skin-emigrating immune cells; this drug should be investigated further as a topical immunosuppressive drug in dogs.

Characterization of IgE-mediated cutaneous immediate and late-phase reactions in nonallergic horses

OBJECTIVE

To characterize the response of skin of nonallergic horses following ID injection of polyclonal rabbit anti-canine IgE (anti-IgE) and rabbit IgG.

ANIMALS

6 healthy horses.

PROCEDURES

Skin in the cervical area was injected ID with anti-IgE and IgG. Wheal measurements and skin biopsy specimens were obtained before and 20 minutes and 6, 24, and 48 hours after injection. Tissue sections were evaluated for inflammatory cells at 4 dermal depths. Immunohistochemical analysis for CD3, CD4, and CD8 was performed, and cell counts were evaluated.

RESULTS

Anti-IgE wheals were significantly larger than IgG wheals at 20 minutes and 6 and 24 hours after injection. There were significantly more degranulated mast cells after anti-IgE injection than after IgG injection. There were significantly more eosinophils at 6, 24, and 48 hours and neutrophils at 6 hours after anti-IgE injection, compared with cell numbers at those same times after IgG injection. There were significantly more eosinophils in the deeper dermis of anti-IgE samples, compared with results for IgG samples. No significant differences between treatments were detected for CD3(+), CD4(+), or CD8(+) cells.

CONCLUSIONS AND CLINICAL RELEVANCE

Injection of anti-IgE antibodies was associated with the development of gross and microscopic inflammation characterized by mast cell degranulation and accumulation of inflammatory cells, particularly eosinophils and neutrophils. This pattern appeared to be similar to that of horses with naturally developing allergic skin disease, although lymphocytes were not increased; thus, ID injection of anti-IgE in horses may be of use for evaluating allergic skin diseases of horses.

A study for characterization of IgE-mediated cutaneous immediate and late-phase reactions in non-allergic domestic cats

Immunoglobulin-E (IgE) mediated reactions can be induced by intradermal injection of anti-IgE antibodies in both humans and dogs. These reactions grossly and histologically mimic changes seen in naturally occurring allergic dermatitis in these species. Similar studies have not been conducted in the cat. Purified polyclonal rabbit-origin IgG specific for canine IgE (anti-IgE) and rabbit immunoglobulin G (IgG) were injected intradermally in 7 non-allergic laboratory colony cats. Wheal measurements were obtained and biopsies collected before injection and at injection sites after 20 min, 6, 24, and 48 h. Injection of anti-IgE induced an immediate wheal response which was significantly larger than that seen after injection of rabbit IgG. Anti-IgE injected skin was also significantly thicker than IgG-injected skin. This corresponded with a significant increase in number of visibly degranulated mast cells in anti-IgE samples when compared to IgG samples. Injection of anti-IgE was associated with the rapid recruitment of inflammatory cells to the injected dermis. The number of inflammatory cells and mononuclear cells were significantly elevated after the injection of anti-IgE when compared to IgG-injected skin. Both eosinophils and neutrophils were significantly increased in anti-IgE samples relative to IgG, although neutrophils were only transiently increased. The high eosinophil and relatively low neutrophil cell counts in these samples were consistent with previously documented histologic features of naturally occurring feline allergic skin disease. Immunohistochemistry identified a significantly overall increased CD1a(+) cells after the intradermal injection of anti-IgE when compared to IgG and non-injected skin. CD3(+), CD8(+) and CD4(+) were also significantly increased overall in anti-IgE injected skin relative to IgG injected skin. These data document the gross and cellular response to injection of anti-IgE in the skin of healthy, non-allergic cats and support a possible role for IgE in the development of feline allergic dermatitis.

Effects of pentoxifylline on immediate and late-phase cutaneous reactions in response to anti-immunoglobulin E antibodies in clinically normal dogs

OBJECTIVE

To characterize the effects of pentoxifylline on the gross and microscopic variables associated with immediate and late-phase inflammation following injection of IgE-specific antibodies in the skin of clinically normal dogs.

ANIMALS

6 healthy adult mixed-breed dogs.

PROCEDURES

Intradermal injections (0.1 mL each) of PBS solution, histamine phosphate, and cross-linking rabbit-origin anti-canine IgE antibodies (3 injections/dog) were administered at 0 hours on day 0; wheal sizes were evaluated at 20 minutes, 6 hours, and 24 hours. Biopsy specimens of injected and noninjected skin were collected 24 hours after injection. On day 2, treatment with pentoxifylline (20 mg/kg, PO, q 8 h) was initiated and continued until day 30. For each dog, injection, measurement, and biopsy procedures were repeated on days 30 to 31 and on days 37 to 38 (ie, after discontinuation of pentoxifylline administration).

RESULTS

Pentoxifylline administration was associated with a significant decrease in wheal size at 6 and 24 hours (but not at 20 minutes) after injection of anti-canine IgE. Repeated injections performed 1 week after drug discontinuation revealed partial recovery of the 6-hour cutaneous reaction and complete recovery of the 24-hour cutaneous reaction. Pentoxifylline administration was also associated with inhibition of mast cell degranulation and significant decreases in the total numbers of cutaneous inflammatory cells and eosinophils, compared with pretreatment findings.

CONCLUSIONS AND CLINICAL RELEVANCE

In clinically normal dogs, pentoxifylline effectively impaired late-phase reactions but not immediate reactions at sites of intradermal injection of IgE-specific antibodies by inhibiting mast cell degranulation and recruitment of cutaneous inflammatory cells, especially eosinophils.

Cowhage can induce itch in the atopic dog

Itch is a cardinal symptom of atopic dermatitis in humans and dogs. Until now, experimental induction of itch in dogs has proven difficult. The objectives of this study were to determine whether protease-rich spicules, protein extracts and the protease mucunain of the tropical legume cowhage provoked itch and inflammation when rubbed onto canine skin. Native spicules variably induced itch manifestations in about half of the dogs, while challenges with protease-deactivated spicules remained negative. The epicutaneous application of cowhage extract and mucunain after microneedle roller usage also induced pruritus and inflammation. Importantly, there was an interindividual inconsistency in pruritus and inflammation induction and also marked differences in pruritus intensity after challenge. In conclusion, cowhage spicules, protein-rich extracts and mucunain can all induce pruritus and inflammation in dogs as in other species, but the inconsistency of provocation is currently a limitation of this challenge type for future studies of pruritus in dogs.

Inhibitory effect of topical adelmidrol on antigen-induced skin wheal and mast cell behavior in a canine model of allergic dermatitis

BACKGROUND

Adelmidrol is a semisynthetic derivative of azelaic acid and analogue of the anti-inflammatory compound palmitoylethanolamide (PEA). Based upon its physicochemical properties, adelmidrol is suitable for topical application. The main objective of the present study was to evaluate the efficacy of a topical adelmidrol emulsion on early and late inflammatory responses in hypersensitive dogs. Repeated intradermal injections of Ascaris suum extract were performed in both lateral thoracic areas of six conscious hypersensitive Beagle dogs, topically treated during 8 consecutive days. Adelmidrol (2%) was applied to one side and vehicle to the other. 24 hours after the last antigen challenge, two biopsies (adelmidrol- and vehicle-treated side) were obtained for each dog at the antigen injection site.

RESULTS

A significant reduction in the antigen-induced wheal areas was observed on the 4th and 7th day of adelmidrol treatment. Moreover, cutaneous mast cell numbers were significantly decreased in biopsies obtained after 8 consecutive days of topical adelmidrol treatment.

CONCLUSIONS

The results obtained in the present study show that topical treatment with adelmidrol might represent a new therapeutic tool in controlling the early and late allergic inflammatory skin responses in companion animals.

Cells of the skin immune system in dogs with atopy

Twenty-five dogs with signs of atopic dermatitis were included in this study. Additionally, 10 healthy dogs were chosen as healthy skin controls. Skin biopsy specimens were taken from these dogs and evaluated for the following cells: basal cell layer including the number of mitotic figures in this layer, spinous cell layer, macrophages, melanocytes, mast cells and dendritic cells. Identification of mast cells and dendritic cells was performed by means of immunohistochemistry. Histological and statistical investigations showed that the number of mitotic figures in the basal cell layer as well as the number of mast cells, melanocytes, dendritic cells and macrophages was significantly higher in the skin of dogs with atopic dermatitis compared to the healthy dogs (p< 0.01). This finding indicates multilateral quantitative activation within the cellular elements of the skin immune system. Furthermore, marked morphological heterogeneity and distinct degranulation patterns observed among mast cells in atopic skin points to their significant functional activation and confirms that canine atopic dermatitis is still notably a mast cell-dependent disease.

Cutaneous infiltrates and peripheral blood immune responses in dogs with immunomodulatory-responsive lymphocytic-plasmacytic pododermatitis

This study characterizes T- and B-lymphocyte responses in the peripheral blood and lesional skin of dogs with immunomodulatory-responsive lymphocytic-plasmacytic pododermatitis (ImR-LPP), a term previously proposed to denote a subpopulation of dogs with idiopathic pododermatitis. T-cell (CD3+, CD4+ and CD8+ ) and B-cell (CD21+) counts were significantly increased in both the epidermis and dermis of lesional ImR-LPP skin compared with that in pedal skin from healthy controls. CD3+ , CD4+, CD8+ and CD21+ cells were commonly observed in perivascular sites in the superficial dermis, periadnexally, beneath the dermal-epidermal (DE) junction and in the epidermis of lesional ImR-LPP skin. The CD8+ /CD3+ T-cell ratio in peripheral blood was significantly increased in the ImR-LPP group (0.42 versus 0.35 in controls). Serum IgA, IgG and IgM concentrations were all significantly elevated in affected dogs. Lymphocyte stimulation indices in ImR-LPP dogs were comparable with control levels except for a lower response to ionomycin (6.0 versus 11.1). Dogs with ImR-LPP had a higher incidence and mean (semi-quantitative) score for IgA, IgG and IgM deposits in the epidermis, and a significantly increased incidence of dermal IgA+, IgG+ and IgM+ mononuclear inflammatory cells. The results indicate that upregulated T- and B-lymphocyte responses may contribute to the pathogenesis of the skin lesions observed in dogs with ImR-LPP.

Canine immunoglobulin E

Canine IgE discovery and characterization historically closely paralleled that of human IgE. The reason for this would seem to be the early recognition of the spontaneous manifestation of allergic diseases in dogs that are nearly identical to human allergic diseases. The discovery and characterization of human IgE being dependent upon its biological activity in sensitizing mast cells and basophils was matched early on by analogous approaches readily applied to dogs. Following the early work on IgE, cloning and sequencing of the IgE heavy chain, epsilon, lagged well behind the human and rodent for want of IgE producing canine myelomas. As with human allergic diseases, measurement of allergen-specific and total IgE in canine tissues and body fluids revealed the same associations with various disease manifestations that some times defied discovery of straight-forward cause and effect relationships because of the complexity of pathogenesis in spontaneous allergic disease. However it is clear that research on IgE in spontaneously allergic dogs offers many opportunities to explore novel immunotherapeutic approaches to the control of allergic disease that will benefit both dogs and humans.

A study of dendritic cell and MHC class II expression in dogs with immunomodulatory-responsive lymphocytic-plasmacytic pododermatitis

The term immunomodulatory-responsive lymphocytic-plasmacytic pododermatitis (ImR-LPP) has previously been proposed to denote a sub-population of dogs with idiopathic pododermatitis. The objective of this study was to investigate dendritic cell (DC) and MHC class II antigen expression in lesional skin of dogs with ImR-LPP (n=47). Median epidermal CD1c(+) cell counts were 37.8 and 12.5 mm(-1) in ImR-LPP dogs and healthy controls (n=27), respectively (P<0.01), while the corresponding dermal cell counts were 180.9 and 45.0 mm(-2), respectively (P<0.01). Intra-epidermal clusters of DCs were observed in 18/47 dogs with ImR-LPP. Median epidermal MHC class II(+) cell counts were 32.5 and 10.5 mm(-1) in ImR-LPP dogs and healthy controls, respectively (P<0.01), while the corresponding dermal cell counts were 216.9 and 46.9 mm(-2), respectively (P<0.01). Dermal MHC class II(+) staining was primarily associated with DCs (47/47 dogs), mononuclear inflammatory cells (45/47), fibroblast-like cells (19/47) and vascular endothelium (14/47). The DC hyperplasia and increased MHC class II expression in lesional ImR-LPP skin are consistent with enhanced antigen presentation, and suggest that both parameters may contribute to the pathogenesis of ImR-LPP through the priming and activation of CD4(+) T cells. Equally, it is possible that the enhanced DC numbers observed in this study may contribute to the immunoregulation of steady-state pathology in lesional ImR-LPP skin through additional expanded, although as yet unresolved, mechanisms.

Investigation on the association between atopic dermatitis and the development of mycosis fungoides in dogs: a retrospective case-control study

In human medicine, the relationship between the immunodysregulation observed in atopic dermatitis (AD) and the development of mycosis fungoides (MF) has triggered considerable interest due to the increasing number of patients with MF who have a previous history of AD. The purpose of this retrospective case-control study was to investigate whether dogs diagnosed with MF were more likely to have AD. The records of 96 000 canine patients at the University of Florida were searched. Inclusion criteria were a clinical and histological diagnosis of MF. Dogs admitted to the University of Florida, Veterinary Medical Center during the same time period (1991-2004) without a diagnosis of MF were included as controls. Four controls for each study dog were randomly selected (matched by year of admission). Frequency of AD and other exposure variables were compared among case and control dogs by using conditional logistic regression. Records of 19 dogs with a diagnosis of MF were identified. Five of them (5/19, 26.3%) had previous diagnosis of AD. The odds of having MF was 12 times (OR = 12.54; 95% CI = 1.95-80.39; P < 0.01) higher in dogs with AD than in dogs without AD. In conclusion, this study suggests an association between AD and MF in dogs. Future studies are necessary to confirm this finding and to investigate the pathogenic mechanisms involved in this association.

Changes in Morphology and Key Cytokine Gene Expression after Intradermal Injection of Louse (Bovicola ovis) Antigen in Sheep with Naturally Occurring Atopic Dermatitis

Groups of louse-infested and louse-naïve lambs (n=6 or 7) were used in two experiments to determine the sequential tissue response (macroscopical, microscopical and key cytokine mRNA) to intradermal injection of crude louse (Bovicola ovis) antigen over a period of 72 or 96 h. Histamine diphosphate and phosphate-buffered saline/glycerol (antigen vehicle control) solutions were also injected intradermally in each lamb for comparison. In both experiments, louse-infested lambs showed immediate and late-phase responses (LPRs) to louse antigen that differed significantly from the responses in the louse-naïve lambs. In experiment 1, biopsy samples taken at 7, 24, 48 and 96 h after injections showed more extensive dermal inflammation and leucocyte infiltration in response to louse antigen in louse-infested than in louse-naïve lambs. Eosinophils were significantly more numerous in the dermis of louse-infested lambs after all treatments and increased substantially in these lambs after antigen injection. Additionally, the louse-infested lambs differed from the naïve lambs in showing significantly higher mononuclear leucocyte and basophil infiltration and significantly lower neutrophil infiltration after antigen injection. In experiment 2, biopsy samples taken 4, 24, 48 and 72 h after injections showed trends in eosinophil infiltration of the dermis similar to those observed in experiment 1. Peak IL-4 mRNA expression was detected 4 h after antigen injection in the louse-infested lambs and remained significantly elevated at 24 h as compared with the results in the louse-naïve lambs. No significant difference in IFN-gamma mRNA expression between the louse-infested and the louse-naïve lambs was observed. These results indicated that louse-infested lambs show a cutaneous LPR analogous to that observed in atopic human beings and dogs. However, some differences were observed, including the longer duration of the LPR, the profuse eosinophil infiltration, and an absence of increased IFN-gamma mRNA expression.

The Intradermal Leishmanin Reaction Induces Antigen-specific Maturation of Canine Dendritic Cells with Up-regulation of MHCII Synthesis and Expression

Dendritic cells (DCs) are professional antigen-presenting cells that reside in many tissues, including the skin. This study showed that intradermal injection of leishmanin in Leishmania infantum-infected dogs induced the "up-regulation" of surface MHCII expression, associated with progressive ultrastrucutural changes characteristic of DC maturation, including the formation of multilaminar MHC class II-containing compartments and arrays of tubulo-vesicular structures. These changes were not observed in control dogs from L. infantum non-endemic areas. The results indicated that canine DCs were effector cells in delayed-type hypersensitivity, that the leishmanin reaction was specific for a cell-mediated reaction to L. infantum in infected dogs, and that canine DCs possessed ultrastructural organelles reminiscent of those in activated human DCs.

Cellular and cytokine kinetics after epicutaneous allergen challenge (atopy patch testing) with house dust mites in high-IgE beagles

The cellular and cytokine dynamics of reactions triggered by atopy patch testing with house dust mites were studied in six high-IgE beagles. Sites were scored and biopsied at 6, 24, 48, and 96 h, and samples were processed for histopathology, immunohistochemistry, and polymerase chain reaction (PCR). All dogs developed positive reactions at some point in time. Mean clinical scores were significantly higher than baseline at 24, 48, and 96 h. Clinically, one of six dogs had a positive reaction at 6 h; two of six reacted at 24 and 48 h, and five of six at 96 h. Histologically, superficial perivascular mononuclear and granulocytic dermatitis developed (5/6) after 6 h, and progressed in severity at 24 h (6/6). Additionally, at 48 h epidermal spongiosis, hyperplasia and pustules developed (5/6), and were marked at 96 h (6/6). At and beyond 6 h, progressive CD1c-positive epidermal Langerhans cell hyperplasia with cluster formation and dermal dendritic cell infiltration was noted. Cutaneous infiltration of CD3-positive T lymphocytes with epidermal clusters developed over time. mRNA expression for the cytokines gamma-interferon (gamma-IFN), interleukin-6 (IL-6), IL-12p35, IL-13, IL-18, and thymus and activation regulated chemokine (TARC) exhibited significant increases during the challenge compared to baseline, but there was no appreciable alteration in expression for tumour necrosis factor-alpha (TNF-alpha), IL-12p40, IL-10, regulated on activation normal T-cell expressed and secreted (RANTES), IL-5, IL-2, IL-4, and IL-8. No correlation was detected between clinical scores and cytokines. It is concluded that IL-6 plays a role in early reactions followed by an increase of TARC and IL-13, while IL-18 progressively increases in later reactions.

Patch testing of experimentally sensitized beagle dogs: development of a model for skin lesions of atopic dermatitis

In humans with atopic dermatitis (AD), the epicutaneous application of allergens (atopy patch tests or APT) to which the patients are sensitized often results in the development of inflammation resembling that of spontaneous skin lesions. Dogs are affected with a natural homologue of human AD, but information on the induction of positive patch testing reactions is limited. The objectives of this pilot study were to determine the nature and cellular dynamics of inflammation occurring after APT in dogs hypersensitive to house dust mite and flea allergens. Laboratory Beagles were sensitized experimentally to Dermatophagoides farinae house dust mites (two dogs), Ctenocephalides felis flea saliva (one dog) or both (two dogs). Two other dogs served as nonsensitized controls. Both allergens and saline were applied epicutaneously. Macroscopic evaluations and skin biopsies were performed at 4, 24, 48 and 96 h after starting allergenic challenge. Biopsies were evaluated histologically and immunohistochemically with a panel of monoclonal antibodies specific for canine leucocyte antigens. Positive macroscopic reactions consisted of erythema, oedema and induration, and they occurred between 24 and 96 h after allergen application. Macroscopic and microscopic APT reactions developed only whenever serum IgE was present against tested allergens. Microscopically, positive APT was associated with epidermal hyperplasia, Langerhans' cell hyperplasia, and eosinophil and lymphocyte epidermotropism. Dermal inflammation was mixed and arranged in a superficial perivascular to interstitial pattern. Numerous IgE+-CD1+ dendritic cells and gamma-delta T-lymphocytes were observed. Macroscopically and microscopically, APT reactions in these experimentally sensitized animals resembled those seen in lesional biopsy specimens of dogs and humans with spontaneous AD. Therefore, APT in hypersensitive dogs provides a relevant experimental model to investigate the pathogenesis and treatment of both canine and human AD skin lesions.

Serological, intradermal and live flea challenge tests in the assessment of hypersensitivity to flea antigens in cats (Felis domesticus)

The results of intradermal testing with three commercial flea antigens and a serological test for IgE antibodies to flea antigens were compared with live flea challenge in cats. Eight control cats with no prior flea exposure had negative serological test and flea challenge results. By contrast, 17 out of 27 cats with previous flea exposure showed immediate reactivity to flea challenge; reactivity at 6, 24 and 48 h after flea exposure was noted in 12, 16 and 21 cats, respectively. Seventeen of these cats had positive serological test results. Seven cats showed immediate intradermal test reactions to the ARTU allergen, six reacted to the Biophady allergen, and six reacted to the Greer allergen. Intradermal test reactivity was less frequent at the other time points. Using the results of the flea challenge as the 'gold standard' for the presence or absence of sensitisation to fleas, the sensitivity and specificity of the serological test was 0.88 and 0.77, respectively. Sensitivities of the intradermal tests at the four time points ranged from 0 to 0.33, whereas the specificities ranged from 0.78 to 1.0. Live flea challenge is better able to detect cats with hypersensitivity to fleas than either intradermal or serological testing.

A canine model of cutaneous late-phase reactions: prednisolone inhibition of cellular and cytokine responses

Immunoglobulin E (IgE)-mediated late-phase reactions can be induced in atopic humans by intradermal injection of relevant allergens or anti-IgE antibodies. The histology of these reactions resembles that of naturally occurring atopic dermatitis. Strikingly similar responses can be induced in dogs, suggesting that a canine model could prove valuable for preclinical investigation of drugs targeting late-phase reactions. This study was designed to characterize the cellular, cytokine and chemokine responses after intradermal anti-IgE injection in untreated and prednisolone-treated dogs. Normal beagles were untreated or treated with prednisolone before intradermal injection of polyclonal rabbit anti-canine IgE or normal rabbit IgG. Biopsies were taken before injection and 6, 24 and 48 hr after injection. Samples were evaluated by histological and immunohistochemical staining, as well as by real-time quantitative polymerase chain reaction analysis. Dermal eosinophil and neutrophil numbers increased dramatically within 6 hr after injection of rabbit anti-canine IgE, and remained moderately elevated at 48 hr. The numbers of CD1c(+) and CD3(+) mononuclear cells were also increased at 6 hr. The real-time quantitative polymerase chain reaction demonstrated marked increases in mRNA expression for interleukin-13 (IL-13), CCL2, CCL5 and CCL17. Levels of mRNA for IL-2, IL-4, IL-6 and IFN-gamma did not change within the limits of detection. Prednisolone administration suppressed the influx of neutrophils, eosinophils, CD1c(+) and CD3(+) cells, as well as expression of IL-13, CCL2, CCL5 and CCL17. These data document the cytokine and chemokine responses to anti-IgE injection in canine skin, and they demonstrate the ability of the model to characterize the anti-inflammatory effects of a known therapeutic agent.

Generation of therapeutic antibody responses against IgE in dogs, an animal species with exceptionally high plasma IgE levels

Allergic diseases are common in dogs and the involvement of IgE in the pathogenesis of canine atopic dermatitis (CAD) and flea allergy dermatitis (FAD) is documented. However, many dogs do not achieve sufficient control of their allergic disease, and there is a great need for new treatment strategies. In order to address this issue we first needed to obtain a better picture of IgE-levels in dogs and how plasma IgE-levels are affected by breed, age and health status. IgE is normally present at diminutive concentrations in sera and detection by diagnostic methods has been a technical challenge. Here, we present a new in vitro assay for determining absolute levels of total IgE in sera from dogs. In a panel of 76 adult dogs diagnosed either as healthy or suffering from atopic dermatitis, autoimmunity or infection by skin parasites, we show that levels of IgE range from 1 to 41 microg/ml. This is almost 100 times the level observed in non-atopic humans. However, these exceptionally high IgE-levels in the dogs could not be correlated to either breed or health status. To address the issue of novel treatment strategies, the possibility of reducing the IgE-levels in nine Beagle dogs by immunization with a new therapeutic vaccine was investigated. High levels of anti-IgE antibodies were induced in all dogs, and the IgE-levels were subsequently decreased by a mean of 65%. This shows that the allergy vaccine is potent enough to break the tolerance against IgE, even when the initial IgE-levels are as high as those observed in dogs. Thus, the vaccination treatment may have the potential to serve as a future therapy for dogs with atopic diseases.

Increase of CC chemokine receptor 4-positive cells in the peripheral CD4+ cells in dogs with atopic dermatitis or experimentally sensitized to Japanese cedar pollen

BACKGROUND

Since dogs frequently develop allergic diseases, similar to those in humans, dogs represent a possible animal model for allergy in humans. In human atopic dermatitis (AD), CC chemokine receptor 4 (CCR4) has been shown to play an important role in the development of allergic inflammation of AD; however, the association between allergic reaction and CCR4 is not well understood in dogs.

OBJECTIVE

To examine CCR4 expression in peripheral blood CD4+ cells in dogs that had AD and were experimentally sensitized with Japanese cedar pollen.

MATERIALS AND METHODS

Peripheral blood mononuclear cells (PBMCs) were isolated from 17 dogs with AD. The proportion of CCR4+ cells in peripheral blood CD4+ cells (CCR4/CD4) was evaluated by flow cytometry and compared with that in 10 healthy dogs. Similarly, in dogs that were experimentally sensitized to Japanese cedar pollen antigen, the proportion of CCR4/CD4 was examined pre- and post-sensitization.

RESULTS

The proportion of CCR4/CD4 in dogs with AD was 40.3+/-3.3%, which was significantly higher than that in normal dogs (23.6+/-4.3%) (P<0.01). In the experimentally sensitized dogs, the proportion of CCR4/CD4 was 25.4+/-2.6% at pre-sensitization and it was significantly increased (29.8+/-2.9%) at post-sensitization (P<0.01).

CONCLUSION

The proportion of CCR4+ cells in peripheral blood CD4+ cells was measured in dogs with allergic conditions. The present findings indicate that CCR4+ cells may be involved in the pathogenesis of allergy in dogs as in humans.

Investigation on the effects of topical therapy with 0.1% tacrolimus ointment (ProtopicR) on intradermal skin test reactivity in atopic dogs

Tacrolimus ointment (TAC) is an effective treatment for atopic dermatitis in humans and dogs. The purposes of the present study were to evaluate the effect of 4 weeks of TAC on intradermal skin testing (IST), and in case of suppression, to investigate if reactivity returned to baseline by 2 or 4 weeks post treatment. Intradermal skin test was performed using saline, histamine, lipopolysaccharide (LPS, 0.4 mg mL(-1)), house dust (25 PNU mL(-1)) and house dust mite (1 : 40 000 w/v) at weeks 0, 4, 6 and 8 on nine dogs enrolled in a blinded, crossover, clinical trial, using 0.1% TAC or placebo once daily for 4 weeks. Reactions were evaluated at 15 min, and at 4 and 6 h. Ointment was applied after the 15-min evaluation on weeks 0 and 4. Data were analysed using the statistical software SAS System for Windows. At week 4, TAC did not affect 15-min IST, but some reactions in the TAC group were suppressed at 6 h compared to baseline. In the TAC group, 4-h IST reactivity was reduced 2 weeks after discontinuation but returned to baseline by 4 weeks. In conclusion, TAC has no effect on immediate reactions but decreased some late-phase reactions. Therefore, no withdrawal is recommended to evaluate only immediate reactions, but a 4-week withdrawal may be necessary for evaluation of late-phase reactions.

Canine atopic dermatitis: new targets, new therapies

Atopic dermatitis is a common allergic skin disease of complex etiopathogenesis in both humans and dogs. Immediate-type hypersensitivity to environmental allergens that arises as a result of environmental and genetic factors is a major part of the pathogenesis in most but not all patients. Alterations in epidermal barrier function, priming of cutaneous antigen-presenting cells with IgE, intrinsic keratinocyte defects, and even development of autoimmunity are also factors that contribute to the primary disease. Secondary factors, especially infections with Staphylococcus and yeast organisms, strongly influence the course of this skin disease. The relatively recent understanding of the complexities of atopic dermatitis has resulted in changes in diagnostic and therapeutic strategies for the disease. We now know that the best therapeutic approach is to use combinations of multiple modalities individualized for each patient over the course of his or her lifetime.

A randomized controlled trial of misoprostol monotherapy for canine atopic dermatitis: effects on dermal cellularity and cutaneous tumour necrosis factor-alpha

In this blinded randomized placebo-controlled trial, 20 dogs with atopic dermatitis (AD) were given placebo (8 dogs) or misoprostol (12 dogs) at 5 micro g kg-1, orally, three times daily for 3 weeks. Administration of the active drug, but not of placebo, led to a significant decrease in lesional and pruritus scores. The median reduction from baseline of both scores was approximately 30%. Misoprostol therapy did not lead to decreases of dermal cell counts or skin tumour necrosis factor (TNF)alpha mRNA copy numbers that were significantly different from those of placebo. Skin TNFalpha protein production, assessed using indirect immunofluorescence, decreased or remained unchanged in dogs receiving misoprostol. In contrast, post treatment TNFalpha fluorescence scores were higher in all but two dogs given placebo. The changes from baseline of TNFalpha fluorescence scores did not correlate significantly with those of lesional or pruritus indices. These observations confirm the modest efficacy of misoprostol for treatment of canine AD and suggest that its mild anti-allergic effects are not associated with either inhibition of inflammatory cell emigration or TNFalpha production.

Intradermal test reactivity to Malassezia pachydermatis in healthy basset hounds and basset hounds with Malassezia dermatitis

Nineteen healthy beagles, eight healthy basset hounds and 17 basset hounds with Malassezia dermatitis were tested intradermally with two extracts of M pachydermatis. One healthy beagle and two affected basset hounds showed wheal and flare reactions 15 minutes after the injection. Delayed reactions, consisting of erythematous macules and plaques, were commonly observed 24 hours after the injection in both the healthy and affected basset hounds, but occurred infrequently in the beagles. At 24 hours the diameters of the lesions in the healthy and affected basset hounds were significantly (P<0.01) greater than those in the healthy beagles, but the diameters in the healthy and affected basset hounds did not vary significantly. Delayed reactions in six of the basset hounds with Malassezia dermatitis were characterised histologically by superficial perivascular and periadnexal infiltrates of neutrophils and lymphocytes.

Late-phase reactions to intradermal testing with Dermatophagoides farinae in healthy dogs and dogs with house dust mite-induced atopic dermatitis

OBJECTIVE

To determine the prevalence of late-phase reactions to intradermal testing with Dermatophagoides farinae in healthy dogs and dogs with atopic dermatitis and an immediate reaction to D farinae.

ANIMALS

6 healthy dogs and 20 dogs with atopic dermatitis and immediate reactions to D farinae.

PROCEDURE

ntradermal tests were performed with D farinae at 1:1,000 wt/vol and 1:50,000 wt/vol concentrations, and skin reactivity was evaluated after 0.25, 6, and 24 hours. Serum D farinae-specific IgE antibodies were assayed. Extent of lesions (atopy index) and pruritus (visual analogue scale) were evaluated in dogs with atopic dermatitis.

RESULTS

Late-phase reactions were observed in healthy dogs at 6 hours (n = 2 dogs) and 24 hours (1) with the 1:1,000 wt/vol concentration, and at 6 hours (1) and 24 hours (1) with the 1:50,000 wt/vol concentration of allergen. Late-phase reactions in healthy dogs were only observed in dogs with an immediate reaction to D farinae. Late-phase reactions were observed in 11 of 20 dogs with atopic dermatitis at 6 and 24 hours with the 1:1,000 wt/vol concentration and in 10 of 20 at 6 and 24 hours with the 1:50,000 wt/vol concentration of allergen. There was no difference in mean atopy index, mean visual analogue scale of pruritus, or mean serum D farinae-specific IgE concentration of dogs with a late-phase reaction, compared to dogs without a late-phase reaction.

CONCLUSIONS AND CLINICAL RELEVANCE

Late-phase reactions may be observed after an immediate reaction to intradermal skin testing in healthy and allergic dogs but are more commonly observed in dogs with atopic dermatitis.

The ACVD task force on canine atopic dermatitis (XVII): intradermal testing

Intradermal testing has been practiced for decades in human and veterinary medicine. The primary utility of intradermal testing is in the demonstration of IgE-mediated allergen hypersensitivity. The presence of a positive reaction on an intradermal test is not always indicative of allergy, as it may sometimes be an indication of sub-clinical hypersensitivity. Despite its widespread use by veterinary dermatologists, the usefulness of the intradermal test would be greatly enhanced by the use of standardized allergen extracts and homogeneous criteria for the interpretation of results. Irrespective of these shortcomings, intradermal testing is regarded as a valuable tool in the demonstration of allergen-specific hypersensitivity when performed according to accepted guidelines.

The ACVD task force on canine atopic dermatitis (III): the role of antibodies in canine atopic dermatitis

Although an important pathogenic role for IgE is established in the case of allergic asthma and rhinitis in man, its role in atopic dermatitis is less clear. There are many studies where allergists and immunologists have provided evidence in favour of such a role, whereas dermatologists are less than convinced. In dogs, however, there is an abundance of clinical evidence implying that atopic dermatitis is antigen driven, and recent studies suggest that there may be a role for IgE, not only in the effector pathway, but also in antigen capture. Although an IgG response often accompanies an IgE response in dogs with atopic dermatitis, there is little evidence in support of a pathogenic role in respect of the former isotype.

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.