Canine Model Of Atopic Dermatitis Research Articles

Investigation on the Effect of Dose, Frequency and Duration of Allergen Exposure on Development of Staphylococcal Infections in a Chronic Model of Canine Atopic Dermatitis.

Canine atopic dermatitis (CAD) is chronic and frequently complicated by Staphylococcal infections. Understanding the role of allergen dose, frequency and duration of exposure in triggering infections requires a model. Most models elicit acute inflammation and do not mimic real-life disease. Here we describe the effects of allergen exposures on development of infections in a model of chronic CAD. Diagnosis of pyoderma was based on clinical signs and consistent cytology. Study 1 evaluated the role of duration of exposure keeping the daily dose constant (25 mg/day). The one-week protocol involved three exposures, 3 days in a row. The one-month protocol involved twice-weekly challenges for 4 weeks. The three-month protocol involved twice-weekly challenges for 12 weeks. Study 2 evaluated different daily doses while keeping constant the total weekly dose (25 mg) and duration (3 weeks). Low-dose used 5 mg/day for 5 days, each week. High-dose used 12.5 mg/day twice-weekly. In Study 1, the longer the exposure, the more dogs developed pyoderma (6/9 in the three-month study, 2/9 in the one-month and 0 in the one-week). In Study 2, low-dose daily exposure caused more infections (5/8) than high-dose infrequent exposure (0/8). It is concluded that low-grade, daily exposure for a long time is most relevant for development of staphylococcal infections.

Topical κ‐opioid receptor agonist asimadoline improves dermatitis in a canine model of atopic dermatitis

This prospective, 4-week, placebo-controlled, cross-over study aimed to investigate the efficacy of 1% topical κ-opioid agonist, asimadoline, in a model of canine atopic dermatitis (AD). Fourteen beagles were challenged with house dust mites every 3-4days for a total of 9 challenges. Severity of dermatitis was assessed, and pruritus was monitored using GoPro HERO cameras. Pruritus scoring was evaluated at 10 time periods; baseline, 4h post allergen challenge and the last day of the study on Day 28. Scoring was done blindly by personnel using BORIS software. A global subjective score was also given using a visual analogue scale (VAS). A 4-week washout period occurred and dogs were crossed-over, the study was repeated, and the results were analysed using combined data. Gel was applied once daily on inguinal area (0.6ml/dog). ANOVA showed significant effect of time (p<0.0001) and group (p=0.0001) on dermatitis scores. Overall, no statistically significant effect on pruritus was found due to a crossing of scores on Day 17. Overtime the placebo scores increased while the active ingredient showed decrease after first 3weeks. It is concluded that this approach is promising in dogs with AD and longer studies with more frequent application may be beneficial.

Double blinded, vehicle controlled, crossover study on the efficacy of a topical endocannabinoid membrane transporter inhibitor in atopic Beagles.

The endocannabinoid system is important for skin homeostasis and alterations are linked to inflammatory diseases like atopic dermatitis (AD). Importantly, activation of cannabinoid receptor CB2 decreases pruritus and inflammation in mouse models. Reduction of inactivation of endogenous cannabinoids could, therefore, be a therapeutic option for AD. Dogs spontaneously develop AD, which closely mimics the human disease making them suitable to test new therapies. Our study aimed to test the effects of a topical endocannabinoid membrane transporter inhibitor (WOL067-531, 1% gel) on pruritus and dermatitis in a canine model of AD. Nineteen Beagles allergic to dust mites (DM) were randomized to receive either active ingredient or vehicle on inguinal area while challenged epicutaneously with DM twice weekly for 28days. Treatment was administered twice daily and started after three challenges (day 8). Dermatitis and pruritus were scored weekly by personnel blinded to treatment allocation. Dermatitis was scored using a validated scoring system and pruritus was scored using camera recordings. After a 4-week washout, dogs were crossed over and the study was repeated. On days 15 and 22, dermatitis scores were significantly increased after DM challenge in the vehicle group (16.34, p = 0.0089 and 7.42, p = 0.04845, respectively) but not in the active ingredient group (p = 0.3177 and p = 0.3190, respectively). Significant decrease on pruritus both on inguinal area and overall (p = 0.048 and p = 0.032, respectively) occurred in the active ingredient group. No adverse effects were noted. In conclusion, the newly developed topical endocannabinoid membrane transporter inhibitor (WOL067-531) minimized allergic flares and pruritus in a canine model of AD.

Investigation of the correlation of serum IL-31 with severity of dermatitis in an experimental model of canine atopic dermatitis using beagle dogs.

IL-31 is a cytokine that is believed to play an important role in atopic dermatitis (AD). IL-31 levels positively correlate with disease severity in children with AD. Currently, there is no study that has investigated such a correlation in atopic dogs. The purpose of this study was to evaluate the correlation between IL-31 serum levels and severity of dermatitis. It was hypothesized that a positive correlation exists between severity of AD and circulating levels of IL-31. Sixteen atopic beagles experimentally sensitized to house dust mites. Atopic beagles were exposed to dust mites epicutaneously twice weekly for four weeks. Severity of dermatitis was scored by the Canine Atopic Dermatitis and Extent Severity Index, 3rd iteration (CADESI-03) on days 0 and 28. Blood samples were taken on days 0 and 28 to measure serum IL-31 using a commercially available ELISA. Correlation between CADESI-03 scores and serum IL-31 levels was not detected on day 0 (Pearson, r = -0.2609, P = 0.3291). After flare-up of dermatitis was induced with allergen exposure, a significant positive correlation was detected between serum IL-31 and CADESI-03 on Day 28 (r = 0.6738, P = 0.004). Positive correlation was detected in active disease between severity of dermatitis and circulating levels of IL-31. Additional studies are needed to investigate this correlation in other breeds of dogs and to test whether circulating levels of IL-31 may predict clinical response to biological agents aimed at IL-31.

Increased filaggrin-metabolizing enzyme activity in atopic skin: a pilot study using a canine model of atopic dermatitis.

Filaggrin (FLG) and its metabolites are essential for skin barrier function and hydration of the stratum corneum. Alteration of the FLG metabolism could be the basis for an abnormal skin barrier in allergic dogs. To investigate the expression and distribution of calpain-1, caspase-14, furin and matriptase, four enzymes involved in FLG metabolism, in the skin of atopic and healthy beagles. Skin biopsies were collected from four healthy and four atopic beagles before and after allergen exposure. The dogs were challenged for three consecutive days to mimic an acute exposure, or once weekly to mimic a chronic exposure to allergens. Skin biopsies were taken on days 0 (nonlesional), 3 and 10 in the "acute" model and on days 0 (nonlesional), 14 and 28 in the "chronic" model. Four healthy dogs were used as controls. Indirect immunofluorescence was used to analyse the distribution and the expression of FLG enzymes in a semi-quantitative manner. Five consecutive pictures/section were taken and the intensity analysed tracing the epidermis and using ImageJ on the traced areas. The enzymes' expression was compared between healthy and atopic nonlesional skin (Day 0) and over time in each group. All enzymes were expressed in all layers of the epidermis. A significantly higher expression of calpain-1 (P = 0.028), caspase 14 (P = 0.028) and matriptase (P=0.028) was evident in atopic compared to control dogs on Day 0. No differences over time were seen for any enzyme analysed. This preliminary study suggests an abnormal catabolism of FLG in canine atopic skin.

Longitudinal Evaluation of the Skin Microbiome and Association with Microenvironment and Treatment in Canine Atopic Dermatitis

Host-microbe interactions may play a fundamental role in the pathogenesis of atopic dermatitis, a chronic relapsing inflammatory skin disorder characterized by universal colonization with Staphylococcus species. Toexamine the relationship between epidermal barrier function and the cutaneous microbiota in atopic dermatitis, this study used a spontaneous model of canine atopic dermatitis. In a cohort of 14 dogs with canineatopic dermatitis, the skin microbiota were longitudinally evaluated with parallel assessment of skin barrier function at disease flare, during antimicrobial therapy, and post-therapy. Sequencing of the bacterial 16S ribosomal RNA gene showed decreased bacterial diversity and increased proportions of Staphylococcus (S.pseudintermedius in particular) and Corynebacterium species compared with a cohort of healthy control dogs (n= 16). Treatment restored bacterial diversity with decreased proportions of Staphylococcus species, concurrent with decreased canine atopic dermatitis severity. Skin barrier function, as measured by corneometry, pH, and transepidermal water loss also normalized with treatment. Bacterial diversity correlated with transepidermal water loss and pH level but not with corneometry results. These findings provide insights intothe relationship between the cutaneous microbiome and skin barrier function in atopic dermatitis, show the impact of antimicrobial therapy on the skin microbiome, and highlight the utility of canine atopic dermatitis as a spontaneous nonrodent model of atopic dermatitis.

Decreased expression of caspase-14 in an experimental model of canine atopic dermatitis

Alterations in skin barrier function and filaggrin expression have been reported in atopic dermatitis (AD). Caspase-14, a protease important for filaggrin processing, is decreased in human AD. Atopic Beagle dogs with skin barrier alterations have been validated as model for AD. This study aimed to investigate caspase-14 in normal and atopic Beagle dogs. Skin biopsies from non-lesional and control skin were analyzed for caspase-14 by immunofluorescence. Six images/sections were blindly scored for intensity. Data were tested with unpaired Student's t test. A P value of <0.05 was considered significant. Caspase-14 was decreased in atopic compared to normal skin both quantitatively (P < 0.001) and qualitatively (P = 0.006; agreement = 0.93; consistency = 0.94). In conclusion, caspase-14 is decreased in this model similarly to reports in humans, highlighting the relevance of filaggrin metabolic defects in AD.

Use of a Canine Model of Atopic Dermatitis to Investigate the Efficacy of a CCR4 Antagonist in Allergen-Induced Skin Inflammation in a Randomized Study

Atopic dermatitis (AD) is an inflammatory skin disease characterized by infiltration of skin homing lymphocytes into the dermis. Most of these lymphocytes express the chemokine receptor CCR4, and the frequency of blood CCR4(+) lymphocytes correlates with AD disease severity. Canine AD is a pruritic inflammatory condition that shows many features of the human disease, including CCR4 overexpression. Therefore, we tested a potent selective CCR4 antagonist in an allergen challenge model of canine AD, both clinically and histologically, to investigate whether this chemokine pathway plays a role in the inflammatory response. Using a four-period randomized cross-over study design, 14 beagles were challenged with allergen and clinically monitored. Biopsy samples were taken before and after allergen challenge. A clear reduction of clinical scores was observed with oral prednisolone (P < 0.0001) but not for the CCR4 inhibitor. A subset of the dogs (5/13) showed partial inhibition (30-49%) of the clinical signs with CCR4 inhibitor treatment, and this finding was supported by the results of histopathologic analysis of skin biopsy samples. This partial response is consistent with redundancy in chemokine pathways and highlights the need for therapies blocking multiple pathways. This study shows the utility of this canine model of AD for testing new therapeutic agents.

Use of activity monitors for assessment of pruritus in an acute model of canine atopic dermatitis.

We developed a canine model of acute atopic dermatitis to evaluate the potential of compounds to treat pruritus and skin lesions induced in Dermatophagoides farinae (Df)-sensitized dogs. The aim was to investigate the effectiveness of long-term recording activity monitors to assess pruritus induced by allergen challenges. Thirty-two Df-sensitized laboratory dogs. In two blinded crossover studies, 28 Df-sensitized dogs were challenged on 3days with a Df slurry applied to clipped abdominal skin. Dogs were treated with a positive control (prednisolone 1mg/kg once daily for 5days, starting 1day before challenge) or left untreated; all were fitted with activity monitors. To confirm pruritus, a parallel study with four dogs was conducted, filming the dogs before and during challenge and assessing the film for pruritic behaviour. The activity of dogs treated with prednisolone was significantly lower between 00.00 and 03.00h and between 03.00 and 06.00h compared with untreated dogs (repeated-measures ANCOVA; P<0.0001). To determine whether the recorded night-time activity corresponded to pruritic manifestations, we compared activity monitor and video recordings of four dogs for two periods (16.30-20.30 and 24.00-03.00h) before and during a Df challenge. The correlation between night-time activity monitor activity and observed pruritic behaviour was highly significant (test of correlation coefficient versus zero: r=0.57, P<0.0001). Determination of night-time activity with activity monitors after allergen challenge appears to be an objective and practical way to assess pruritus in this experimental model of canine atopic dermatitis.

Investigation of the effect of probiotic exposure on filaggrin expression in an experimental model of canine atopic dermatitis

Atopic dermatitis (AD) results from complex interactions between an impaired skin barrier and immunological stimulation. Filaggrin is a key protein for the skin barrier, and its expression is decreased in subsets of atopic dogs and can be modified by inflammation; thus, immunomodulatory approaches may alter its expression. Probiotics have been explored for the prevention and treatment of allergies, owing to their immunomodulatory properties; however, it is currently unknown whether they can modulate filaggrin expression. The purpose of this study was to evaluate whether probiotics can modulate filaggrin expression in an experimental model of canine AD. Eighteen atopic (11 probiotic exposed and seven control) and five normal beagles were challenged for three consecutive days with Dermatophagoides farinae. Skin biopsies were taken before (day0), at the peak (day3) and after the end of the allergen challenge (day10). Immunohistochemistry for filaggrin was done using a polyclonal antibody specific for canine filaggrin, and staining was scored both subjectively (for intensity, granularity and continuity) and objectively, by tracing the stratum granulosum and calculating the percentage of filaggrin per unit traced area. Analysis of variance of the percentage of filaggrin in the stratum granulosum showed a significant effect of group (P=0.0414, AD<normal), time (P=0.0066, days3 and 10>day0) and marginal group×time interaction (P=0.0606). Within the atopic group, exposure to probiotics did not change filaggrin expression. No significant differences were found in the subjective scores among groups. It is concluded that probiotic exposure early in life does not alter filaggrin expression in this AD model.

Clinical and Immunologic Effects of Allergen-Specific Sublingual Immunotherapy in a Canine Model of Atopic Dermatitis: A Double Blind, Randomized, Controlled Study

Sublingual Allergen Specific Immunotherapy (SLIT) has been advocated for the treatment for allergies. Controlled studies are difficult to perform in humans due to the variety of allergies, diet, and allergenic exposure. This prospective, randomized, controlled study evaluated clinical and immunological effects of one year of SLIT using an experimental model of atopic dermatitis in dogs. Eighteen Beagles, sensitized to dust mites, timothy grass and ragweed were divided into control (n=6, vehicle) and active (n=12, 3 allergens) groups. Allergen challenge and scoring of clinical signs was done before and at the end of one year of SLIT. Blood was drawn at baseline, 4,8, and 12 months of SLIT and 2 months after stopping SLIT to measure allergen-specific IgE, IL-10, and TGF-beta. After 12 months of SLIT, ANOVA showed significant decrease of clinical scores for both groups (p<.0001) but no significant differences between groups. T tests within each group comparing pre vs. post treatment scores showed statistically significant decrease in the control (p=0.042) and in the SLIT group (p=0.00027). Effect size using Cohen’s d was 1.182 for control and 2.1 for allergen group. Thus, decrease from baseline to post-treatment was nearly twice as large in the allergen as in the control group. Mixed results were found for allergen-specific IgE with significant decrease for dust mites (p=0.0242) and increase for ragweed (p=0.0074) at the end of the study. SLIT induced significant increase of TGF-beta (p=0.03) and IL-10 (p=0.0009) after ragweed stimulation compared to baseline and to the control group. TGF-beta increase abated after SLIT discontinuation results consistent with SLIT induced T regulatory response. Interestingly a significant increase for IL-10 after timothy stimulation was seen for both groups at the end of study (p<.0001).It is concluded that this experimental model is useful to investigate treatments for atopic dermatitis and their immunologic effects.

Early exposure to probiotics in a canine model of atopic dermatitis has long-term clinical and immunological effects

Probiotics modulate the immune response and may have protective effects against atopic dermatitis (AD). Clinical trials using dogs with spontaneous disease are limited by confounding factors such as different diets, environments and sensitizations while a more controlled evaluation is possible using experimental models. A validated model of canine AD showed that early exposure to Lactobacillus rhamnosus GG (LGG) significantly decreases allergen-specific IgE and partially prevents AD in the first 6 months of life. This study is a follow-up three years after discontinuation of LGG. Clinical signs were evaluated after allergen challenge with ragweed, timothy, Dermatophagoides farinae. Allergen-specific IgE, IL-10 and TGF-β were measured on the 1st day of challenge, before allergen exposure. Normal dogs were included as controls. Analyses included seven dogs in the non-probiotic and nine in the probiotic litter. For clinical scores, a 2-Group×9-Time Analysis of Variance showed significant effects of group (p=0.0003, probiotic<controls), time (p<0.0001) and group×time interaction (p<0.0001). IL-10 for all allergens was significantly higher in the control group than probiotics-exposed dogs. Allergen-specific IgE and TGF-β did not differ between litters. Early exposure to probiotics has long-term clinical and immunological effects in this model and larger studies using dogs with spontaneous disease are needed.

Expression and distribution of canine antimicrobial peptides in the skin of healthy and atopic beagles

Antimicrobial peptides (AMPs) are small immuno-modulatory proteins important in defense against pathogenic organisms. Defensins and cathelicidin are the most frequently studied human AMPs. An increase in AMPs in atopic humans has been reported recently. Our goals were to determine the distribution of AMPs and evaluate their mRNA and protein expression in non-lesional (Day 0), acute lesional skin (Day 3) and post-challenged skin after resolution of skin lesions (Day 10) using a canine model of atopic dermatitis (AD). All dogs were environmentally challenged for three consecutive days with house dust mite. Clinical evaluation of atopic beagles was performed using a CADESI score at each time point before and after environmental challenge. Skin biopsies were taken from six healthy and seven atopic beagles before and after allergen challenge (Day 0, Day 3 and Day 10). The transcription of canine cathelicidin (cCath) and beta-defensins (cBD)-1, -2 and -3 mRNA was quantified using quantitative-RT-PCR while the protein distribution of cBD2, cBD3 and cCath was detected by indirect immunofluorescence. A significant effect, over-time, was seen in CADESI score in AD beagles with an increase score after challenge (Day 3). Quantitative analysis showed a significant difference in mRNA transcript levels between groups (with atopic dogs having more than controls) for all AMPs but cBD2. No effect over time was evident for either group. No significant differences were seen for the AMP protein patterns of distribution (homogenous distribution). Although, these results showed no differences in AMP's localization after allergen exposure in each group; atopic dogs had a higher mRNA expression of AMPs when compared with healthy dogs, a similar finding to humans.

Tolerability and clinical efficacy of oral immunotherapy with house dust mites in a model of canine atopic dermatitis: a pilot study

Atopic dermatitis (AD) is a chronic, life-long disease. In humans, immunotherapy (IT) is the only treatment that can alter the course of AD. Oral IT is appealing owing to the ease of administration and the potential for increased compliance. The purposes of this study were to investigate the tolerability, clinical efficacy and effects on allergen-specific IgE of oral IT using a canine AD model. Thirteen atopic beagles sensitized to house dust mites (HDMs) were randomly divided into two groups. One group received daily oral doses of HDMs while the other group received vehicle only for 7 months. The investigator evaluating the dogs was blinded to the allocation of treatments. Prior to and after 2 and 7 months of IT, dogs were challenged daily with HDMs for 3 days concurrently, and clinical signs were scored using a modified Canine Atopic Dermatitis Extent and Severity Index (CADESI). Prior to and at completion of oral IT, serum was collected for measurement of allergen-specific IgE. Oral IT was well tolerated, and no adverse effects were noted. Analysis of variance showed no significant effect of time, group and group × time interaction for CADESI scores. In addition, there were no significant differences in allergen-specific IgE levels. In conclusion, it appears that oral administration of HDMs is well tolerated in these atopic beagles but that this protocol was not sufficient to induce clinical improvement. Further, longer-term studies will be necessary to explore the potential of oral IT in veterinary medicine.

Transmission electron microscopy studies in an experimental model of canine atopic dermatitis

Impairment of skin barrier function has been hypothesized in canine atopic dermatitis (AD). In this prospective, controlled study, the ultrastructure of the upper epidermal layers was investigated using an experimental model of canine AD. Seven atopic Beagles sensitized to Dermatophagoides farinae and four healthy Beagles were used as controls. Both normal and atopic dogs were challenged with D. farinae for 3 days. Clinical signs were scored and skin biopsies were taken from the inguinal area before and 3 days after allergen exposure. Samples were processed to enhance lipid visibility and evaluated by Transmission Electron Microscopy. Emphasis was placed on evaluation of the lipid lamellae (LL), and lamellar bodies (LB) of the stratum corneum.After allergen challenge, atopic Beagles developed severe pruritic dermatitis while no skin lesions were noted in the controls. Ultrastructurally, before allergen challenge, atopic Beagles displayed focally severe abnormalities in LL organization and wider intercellular spaces containing abnormal lipid material. In atopic Beagles, LBs were frequently found inside corneocytes while this finding was not observed in the controls. After allergen challenge, further increase of intercellular spaces was observed in the stratum corneum of atopic Beagles while no appreciable changes were observed in the normal dogs. Intercellular spaces in atopic Beagles were filled with abundant amounts of abnormal lipid material and highly disorganized LL. It is concluded that baseline differences in the ultrastructure of the skin exist between normal and experimentally sensitized atopic Beagles and that these changes are aggravated by allergen challenge and the resulting flare-up of dermatitis.

Temporal Dynamic Changes of Phenotypic Expression of Peripheral CD4 Cells during Environmental Allergen Challenge in an Experimental Model of Canine Atopic Dermatitis: A Pilot Study

The immunopathology behind atopic dermatitis (AD) involves a myriad of inflammatory cells and their mediators. Thymus and activation-regulated chemokine (TARC) plays a significant role in the inflammatory phase by recruiting CCR4(+) T(H)2 cells. In addition, CD25(+) activated T cells further propagate the allergic response after sensitization by producing cytokines. The purpose of this pilot study was to evaluate how exposure to a common allergen (house dust mite, HDM) would affect the proportions of circulating CD4(+)CCR4(+) T(H)2 cells and CD4(+)CD25(+)activated T cells in an experimental model of AD using high-IgE Beagles. In this experimental model, previously sensitized Beagles develop lesions and pruritus upon allergen challenge consisting of 3-day environmental exposure, 3 hours/day. Blood samples were obtained before, during, and after the end of challenge (days 0, 2, 4, and 17). Clinical signs were evaluated and scored at the same time points. Peripheral blood mononuclear cells (PBMCs) were isolated and used for flow cytometry to identify proportions of CD4(+)cells positive for either CCR4 or CD25 receptors. Both CD4(+)cell types (CD25(+) and CCR4(+)) peaked at day 17, when clinical signs had resolved. It is proposed that the increase of circulating CD4(+)CCR4(+) and CD4(+)CD25(+)cells most likely demonstrates the sensitization status of atopic individuals after environmental allergen challenge. Understanding of these two cell types could prompt additional research concerning therapeutic drugs for AD.

Epicutaneous sensitization with Dermatophagoides farinae induces generalized allergic dermatitis and elevated mite‐specific immunoglobulin E levels in a canine model of atopic dermatitis

Atopic dermatitis (AD) is a cutaneous hypersensitivity associated with elevated levels of antigen-specific IgE, commonly to house dust mites (HDMs). It remains controversial as to whether sensitization and clinical disease are induced by cutaneous exposure to HDM. The objectives of this study were to determine whether repeated applications of Dermatophagoides farinae slurry to intact skin of Maltese-Beagle atopic (MAB) dogs would result in the development of clinical signs or lesions resembling spontaneous canine AD, to determine whether repeated slurry applications would induce elevations in mite-specific IgE and/or IgG, and to determine whether mite antigens could be demonstrated within the dermis of application sites. Dogs received weekly slurry applications to the axilla and groin, and were patch tested at 120 days, or were patch tested at days 1, 60 and 120, but did not receive further slurry applications. Skin biopsies and serum samples were obtained on days 1, 60 and 120. Pruritic dermatitis was seen in all dogs by day 60. D. farinae-specific IgE was elevated by day 60. Histologic examination of early application sites revealed mild, mononuclear perivascular dermatitis. Later application sites were characterized by a dense inflammatory infiltrate and oedema in both the dermis and the epidermis. Immunofluorescent staining confirmed the presence of D. farinae antigens in the dermis. This study demonstrated that epicutaneous application of HDM slurry to MAB dogs results in elevations of HDM-specific IgE, localized and generalized pruritic dermatitis resembling spontaneous canine AD, and histologic changes typical of IgE-driven inflammation. We feel that these results suggest that epicutaneous exposure to allergen may play an important role during both the sensitization and the perpetuation of AD, and provide support for the use of a canine model in the investigation of the pathogenesis of AD.

Toward a canine model of atopic dermatitis: amplification of cytokine-gene transcripts in the skin of atopic dogs.

The objectives of the present study were to characterize and compare the repertoire of cytokine-genes transcribed in skin homogenates obtained from normal dogs and dogs with atopic dermatitis (AD) using a reverse-transcriptase polymerase chain reaction and canine-specific cytokine-gene primers. Whereas IL-4 and IL-5 cytokine-gene transcripts were detected more commonly in atopic skin biopsy homogenates, IL-2 mRNA was amplified more often from normal control specimens. IFN-gamma mRNA was detected in 5/29 atopic specimens, 4 of them obtained from the only dog with chronic skin lesions. One-fourth of atopic samples exhibited clear type-2 cytokine profiles; the remainder did not demonstrate polarized repertoires. Conversely, type-1 cytokine profiles were characterized in one-fourth of normal control specimens. The present study establishes, for the first time, the transcription of type-2 cytokine-genes in the skin of dogs with AD. Future experiments investigating the cellular origin and dynamics of allergic cytokine-gene transcription are needed to confirm whether or not canine AD could be considered an immunological model for a human disease.