Expression of thymic stromal lymphopoietin in canine atopic dermatitis

Background – In humans, thymic stromal lymphopoietin (TSLP) plays a central role in the development of allergic inflammation, such as atopic dermatitis (AD), but it is unknown whether it is involved in the pathogenesis of canine AD (CAD). Hypothesis/Objectives – Our aim was to characterize canine TSLP and to assess its expression in CAD. Methods – Canine TSLP was identified based on sequence homology with human TSLP and the complementary DNA (cDNA) cloned by RT‐PCR. Real‐time quantitative RT‐PCR was established to assess the expression of canine TSLP in cultured canine keratinocytes and in skin biopsy specimens from lesional and nonlesional skin of 12 dogs with CAD and eight healthy control dogs. Results – Partial canine TSLP cDNA was cloned and characterized. It contained four exons that shared 70 and 73% nucleotide identity with human and equine TSLP, respectively, encoding the signal peptide and full‐length secreted protein. We found significantly increased TSLP expression in lesional and nonlesional skin of dogs with CAD compared with healthy control dogs (P < 0.05), whereas no difference was measured between lesional and nonlesional samples. In cultured primary canine keratinocytes, we found increased TSLP expression after stimulation with house dust mite allergen extract or Toll‐like receptor ligands lipopolysaccharide and poly I:C. Conclusions and clinical importance – Increased TSLP expression in the skin of dogs with CAD supports an involvement of TSLP in the pathogenesis of CAD similar to that in humans. Further studies should elucidate the function and therapeutic potential of TSLP in CAD.     

Interleukin 4-producing CD4+ T cells in the skin of cats with allergic dermatitis

Lesional skin of cats with allergic dermatitis has a cellular infiltrate and a CD4/CD8 ratio comparable to that in humans with atopic dermatitis. CD4+ helper T cells and in particular cells belonging to the Th2 subset play an important role in disease pathogenesis in humans. We investigated the cytokine pattern of CD4+ T cells in situ, with special emphasis on the putative presence of cells producing interleukin 4 (IL4), in cats with allergic dermatitis. Immunohistochemical procedures were used to determine that CD4+ T cells in lesional and nonlesional skin of cats with allergic dermatitis can produce IL4, as occurs in humans. Lesional and nonlesional skin of cats with allergic dermatitis had significantly more IL4+ T cells (P = 0.001) than did skin of healthy control cats. Double staining indicated that all IL4+ cells were positive for pan-T or CD4 markers. Double labeling for mast cell chymase and IL4 stained primarily different cells. Western blotting demonstrated cross-reactivity between the antibody against human IL4 and a feline recombinant IL4. These results indicate that IL4 is primarily produced by CD4+ T cells and is also present in clinically uninvolved skin, indicating a role in the pathogenesis of allergic dermatitis in cats.     

Characterization of cytokines associated with Th17 cells in the eyes of horses with recurrent uveitis

Objective Equine recurrent uveitis (ERU) is a spontaneous disease that is the most common cause of blindness in horses, affecting up to 15% of the horse population. Th17 cells are a major cell population driving the pathogenesis in several mouse models of autoimmune inflammation, including experimental autoimmune uveitis. The purpose of this study is to investigate the role a Th17 cell‐mediated response plays in the pathogenesis of ERU. Procedure Banked, Davidson’s‐fixed equine globes histopathologically diagnosed with ERU (n = 7) were compared immunohistochemically with healthy control globes (n = 7). Immunohistochemical staining was performed using a pan‐Leptospira antibody and antibodies against IL‐6, IL‐17, and IL‐23. Additionally, immunostaining was performed for T‐cell (CD3) and B‐cell (CD79α) markers. Specificity of immunoreactivity was confirmed by western blot analysis. Results Immunohistochemical staining was positive for IL‐6, IL‐17, and IL‐23 within the cytoplasm of nonpigmented ciliary epithelial cells and mononuclear inflammatory cells infiltrating the iris, and ciliary body of ERU horses (n = 7) but negative in controls (n = 7). ERU‐affected eyes were CD3 positive (n = 7) and CD79α negative (n = 7). Staining for Leptospira was negative in all ERU and control globes. Conclusions Strong immunoreactivity for IL‐6, IL‐17, and IL‐23, in conjunction with the fact that T lymphocytes are the predominating inflammatory cells present in ERU, suggests that IL‐17‐secreting helper T‐cells play a role in the pathogenesis of ERU. These findings suggest that horses with ERU may serve as a naturally occurring animal model for autoimmune uveitis.     

The effects of skin disease on the penetration kinetics of hydrocortisone through canine skin in vitro

This study investigated the effects of allergic skin disease on the penetration kinetics of hydrocortisone through canine skin in vitro. Full-thickness lesional and nonlesional (normal) skin was removed from the dorsal lumbosacral and dorsocaudal thoracic regions, respectively, of five canine cadavers. The dogs were suspected of having flea allergy dermatitis based on their distribution and types of skin lesions. Nonlesional skin was confirmed to be histologically normal, and the histopathology of the lesional skin was consistent with allergic dermatitis. Excised skin was clipped, mounted in Franz-type diffusion cells, and the transdermal penetration of a saturated, radiolabelled hydrocortisone solution was measured over 30 h. When the penetration data for all five dogs were pooled, a restricted (or residual) maximal likelihood mixed model predicted that the permeability coefficient and pseudosteady-state flux of hydrocortisone was more than twice as great (95% confidence interval 1.55-2.71 times as great; P < 0.0001) through lesional compared with nonlesional skin. There was no significant difference in the lag time for hydrocortisone penetration through lesional compared with nonlesional skin of the dogs. This study has confirmed that the transdermal penetration of hydrocortisone may be altered, typically increased twofold, but could be as high as 10-fold, through lesional compared with nonlesional skin of dogs with suspected flea allergy dermatitis. This is likely to be affected by variables such as disease severity, concurrent infections and interindividual differences in skin characteristics.     

FC‐54 Evaluation of IgE‐mediated late‐phase reactions in the skin of normal placebo‐ and prednisolone‐treated dogs: cellular,cytokine and chemokine responses

IgE‐mediated late‐phase reactions can be induced in the skin of normal and atopic dogs by intradermal injections of anti‐IgE antibody. The histology of these reactions is very similar to that of naturally occurring atopic dermatitis. To characterize the cellular, cytokine and chemokine responses in the skin of placebo‐ and prednisolone‐treated dogs, normal beagles received either placebo or 0.5 mg/kg prednisolone twice daily for three days prior to intradermal injection of polyclonal rabbit anti‐canine IgE. Eight‐millimetre punch biopsy skin samples were taken before injection and at the injection sites after 6, 24 and 48 h. Histological and immunohistochemical examination revealed a rapid cellular influx. Eosinophil and neutrophil numbers increased from <1 to 61.4 ± 14.1, and from 7 to 62.2 ± 10.8 cells/mm², respectively, within 6 h after injection, and remained moderately elevated 48 h later. The numbers of CD1c+, CD3+ and CD4+ mononuclear cells were also increased by 6 h. Taqman analysis demonstrated 2.5‐ to 72‐fold increases in mRNA expression for IL‐13, IL‐5, MCP (CCL2), RANTES (CCL5) and TARC (CCL17). Levels of mRNA for IL‐2, IL‐4, IL‐6, and IFNγ remained negligible. Prednisolone administration suppressed the influx of neutrophils and eosinophils, and the expression of IL‐13, CCL2, CCL5 and CCL17 (33, 97, 58, 86, 73 and 90%, respectively), as well as the influx of CD1c+ and CD3+ cells. These data document the cytokine and chemokine response to anti‐IgE injection and demonstrate the anti‐inflammatory effect of prednisolone. Funding: Schering‐Plough Animal Health.     

Skin mast cell histamine release following stem cell factor and high-affinity immunoglobulin E receptor cross-linking in dogs with atopic dermatitis

Stem cell factor (SCF) influences mast cell activation and inflammatory mediator release, and is elevated in tissues undergoing allergic inflammation. Wheal formation in response to the injection of SCF or anti-immunoglobulin (Ig)E antibody injection was compared between normal (n = 10) and nonlesional atopic (n = 10) canine skin. In situ SCF secretion was compared between lesional and nonlesional skin using immunohistochemistry. Histamine release by skin cell suspensions after stimulation with SCF, concanavalin A (ConA) or rabbit anticanine IgE antibodies was compared between normal and atopic dogs. All dogs exhibited strong responses to intradermal SCF injection at 10 and 50 ng mL(-1). Atopic dogs had significantly (P = 0.002) larger wheal responses to anti-IgE than normal dogs; but there was no difference in numbers of skin mast cells bearing IgE as detected by immunohistochemistry. Only atopic dogs exhibited interstitial deposition of SCF in both lesional and nonlesional skin specimens. Median histamine release stimulated by SCF in the absence of IgE from lesional skin cells was higher in atopic than normal dogs (P = 0.04). These experiments suggest that dermal SCF secretion could potentiate histamine release following IgE receptor cross-linking and thus, could be one of the explanations for the inherent mast cell hyperexcitability observed in canine atopic dermatitis.     

Herpesvirus dermatitis in two cats without facial lesions

Background – Cats with feline herpesvirus (FeHV‐1)‐associated dermatitis typically present with ulcerative lesions on the rostral muzzle and nasal planum. This report describes FeHV‐1 dermatitis in the flank region, in the absence of facial lesions. Hypothesis/Objectives – Clinicians should be aware of this unusual manifestation of FeHV‐1 dermatitis to prevent potential misdiagnosis. Animals – A 12‐year‐old male castrated Bengal cat and a 3‐year‐old male castrated Siamese cat with plaques and ulcers in the flank region are described. Methods – Formalin‐fixed biopsy samples were obtained from lesional skin. Histopathology and FeHV‐1 immunohistochemistry were performed. Results – Each sample had epidermal and follicular necrosis with a dense dermal infiltrate of eosinophils. Few to moderate numbers of intranuclear inclusion bodies were present in keratinocytes. The presence of FeHV‐1 in the lesions was confirmed with immunohistochemistry. Conclusions and clinical importance – Feline herpesvirus‐associated dermatitis should not be ruled out based on the location of the lesion, because a correct diagnosis is imperative for proper treatment. Future studies to assess the cause of lesions at this unusual site are warranted.     

Thromboelastography in healthy horses and horses with inflammatory gastrointestinal disorders and suspected coagulopathies

Objectives – To evaluate the use of citrated recalcified (nonactivated) thromboelastography (TEG) in healthy horses and horses with colitis and suspected coagulopathies. Design – Prospective, observational study conducted between October 2007 and June 2009. Setting – Veterinary Teaching Hospital. Animals – Forty‐five healthy adult horses and 12 sick adult horses with colitis and prolonged prothrombin time (PT) or activated partial thromboplastin time (aPTT). Interventions – None. Measurements and Main Results – Whole blood was collected on admission. Coagulation profile (PT, aPTT, platelet count, and fibrinogen concentration) and citrated recalcified whole blood TEG analysis (R‐time [R], K‐time [K], angle [α], maximum amplitude [MA], G value [G], lysis at 60 min [LY60]) were evaluated. Mean values (SD) for TEG parameters in healthy horses were: R=10.4 (3.1) minutes; K=3.5 (1.2) minutes; α=46.3 (11.0)°; MA=55.6 (5.1) mm; G=6,429 (1,341) dyn/cm², and LY60=5.1 (2.4)%. Mean coefficients of variation for intra‐assay/interindividual variability in healthy horses were: R=4.7%/30.7%, K=4.8%/35.3%, α=4.4%/23.8%, MA=1.4%/9.3%, G=3.4%/20.8%, and LY60=13.1%/47.7%, respectively. Horses with colitis and prolonged PT and/or aPTT had longer mean values for R (P<0.001) and K (P<0.001), narrower mean α (P<0.001), decreased mean MA (P=0.001), and smaller mean G (P=0.02); changes consistent with hypocoagulability. Conclusions – Citrated recalcified (nonactivated) TEG demonstrated changes consistent with hypocoagulability in horses with colitis that had preidentified coagulation abnormalities. This technique has high interindividual variability and low intra‐assay variability. TEG may be useful for detecting hypocoagulable states in horses with colitis and suspected coagulopathies.     

Expression of toll‐like receptor 2 mRNA in bronchial epithelial cells is not induced in RAO‐affected horses

Reasons for performing study: Airway inflammation in recurrent airway obstruction (RAO) is triggered by housing affected horses in stables. It has been suggested that RAO is an allergic condition, but innate immune mechanisms are also involved. Fungal products activate innate immune mechanisms through toll‐like receptor 2 (TLR2). In human airway epithelium, TLR2 activation leads to interleukin (IL)‐8 production. This pathway is negatively regulated by the zinc finger protein A20. This study was performed to enhance understanding of innate immune mechanisms in RAO. Hypothesis: TLR2 and IL‐8 mRNA are elevated in RAO during stabling compared with controls. A20 mRNA is negatively associated with the numbers of airway inflammatory cells. Objectives: To determine TLR 2 , IL‐8 and A20 mRNA expression in lungs of stabled and pastured RAO‐affected and control horses. Methods: Airway obstruction and inflammatory cell counts in bronchoalveolar lavage were measured, and TLR 2 , IL‐8 and A20 mRNA expression quantified by qRT‐PCR in 6 RAO‐affected and 6 control horses, during and after exposure to hay and straw. Results: Airway obstruction and neutrophils were increased in RAO‐affected horses during stabling. While stabling increased IL‐ 8 , TLR2 and A20 mRNA were unaffected. TLR2 and A20 were significantly correlated (r = 0.83) and A20 mRNA was negatively associated with inflammatory cells. Potential relevance: Stabling does not lead to an increase in TLR2 expression. Other molecules or processes in the TLR2 cascade might be important in fungal‐induced airway inflammation. Equine epithelial‐derived A20 may be involved in modulation of airway inflammation.     

Dermatophagoides farinae house dust mite allergen challenges reduce stratum corneum ceramides in an experimental dog model of acute atopic dermatitis

Background – Ceramides are essential stratum corneum (SC) lipids and they play a pivotal role in maintaining effective cutaneous barrier function. Objectives – The present study aimed at determining the effect of a Dermatophagoides farinae house dust mite (Df‐HDM) allergen challenge on SC ceramides of atopic dogs experimentally sensitized to these allergens. Animals – Six Df‐HDM‐sensitized atopic Maltese–beagle dogs were used. Methods – Prechallenge SC was obtained by cyanoacrylate stripping. One week later, the dogs were challenged topically with Df‐HDM allergens, which resulted in mild to moderate inflammation 24 h later. Two weeks after challenge, SC of lesional and nonlesional skin was obtained. Finally, SC was collected from challenge sites 2 months after lesion resolution. The different SC lipids were quantified blindly by thin‐layer chromatography. Results – Significantly lower amounts of ceramides [AH], [AP], [AS], [NP], [EOP], [NS] and [EOS] were observed in lesional SC compared with prechallenge samples, while no significant effect was found on the amount of other lipids, including cholesterol and free fatty acids. The ceramide profile of nonlesional skin generally showed the same postchallenge reduction pattern. Ceramide amounts returned to normal within 2 months after lesion remission. Conclusion and clinical importance – These findings suggest that the allergic reactions caused by Df‐HDM allergens lead to a selective reduction of SC ceramides, not only at sites of inflammation but also at sites away from those of allergen application. There is normalization of ceramide amounts after inflammation subsides. These observations suggest that the deficiency of ceramides observed in canine atopic skin occurs, at least in part, secondary to inflammation.     

Interleukin‐31: its role in canine pruritus and naturally occurring canine atopic dermatitis

Background – Interleukin‐31 (IL‐31) is a member of the gp130/interleukin‐6 cytokine family that is produced by cell types such as T helper 2 lymphocytes and cutaneous lymphocyte antigen positive skin homing T cells. When overexpressed in transgenic mice, IL‐31 induces severe pruritus, alopecia and skin lesions. In humans, IL‐31 serum levels correlate with the severity of atopic dermatitis in adults and children. Hypothesis/Objective – To determine the role of IL‐31 in canine pruritus and naturally occurring canine atopic dermatitis (AD). Animals – Purpose‐bred beagle dogs were used for laboratory studies. Serum samples were obtained from laboratory animals, nondiseased client‐owned dogs and client‐owned dogs diagnosed with naturally occurring AD. Methods – Purpose‐bred beagle dogs were administered canine interleukin‐31 (cIL‐31) via several routes (intravenous, subcutaneous or intradermal), and pruritic behaviour was observed/quantified via video monitoring. Quantitative immunoassay techniques were employed to measure serum levels of cIL‐31 in dogs. Results – Injection of cIL‐31 into laboratory beagle dogs caused transient episodes of pruritic behaviour regardless of the route of administration. When evaluated over a 2 h period, dogs receiving cIL‐31 exhibited a significant increase in pruritic behaviour compared with dogs that received placebo. In addition, cIL‐31 levels were detectable in 57% of dogs with naturally occurring AD (≥13 pg/mL) but were below limits of quantification (<13 pg/mL) in normal, nondiseased laboratory or client‐owned animals. Conclusions – Canine IL‐31 induced pruritic behaviours in dogs. Canine IL‐31 was detected in the majority of dogs with naturally occurring AD, suggesting that this cytokine may play an important role in pruritic allergic skin conditions, such as atopic dermatitis, in this species.     

Grey eosinophils in a Miniature Schnauzer with a poorly differentiated mast cell tumor

A 10‐year‐old female spayed Miniature Schnauzer was presented for investigation of an intra‐nasal mass. The mass was diagnosed by histopathologic examination as an undifferentiated round cell neoplasm with an infiltrate of segmented leukocytes, interpreted as neutrophilic inflammation. The mass was treated with palliative radiation and systemic chemotherapy due to the presence of regional lymph node metastasis. During subsequent monitoring over several months, the peripheral leukocyte concentration was repeatedly within reference intervals to slightly increased with low numbers of toxic neutrophils. Four months after the initial diagnosis, there was a significant leukocytosis of 66 100 cells/μL, and 39 700 cells/μL of the leukocytes had variably mature, lobulated, and hypolobulated nuclei, and grey cytoplasm with clear vacuoles, resembling grey eosinophils. To further characterize these cells, peripheral blood smears from the patient and a canine control with eosinophilia were stained for alkaline phosphatase (AP), peroxidase, and esterase activities, and with Luxol fast blue (LFB). Histopathologic sections of the nasal mass were stained with LFB and immunohistochemically for tryptase. On blood smears, the cytoplasm of the suspected grey eosinophils stained for AP and granules stained with LFB confirmed that there was an eosinophilic lineage. Peroxidase staining was weak, and esterase staining was absent. On histopathologic sections from the nasal mass, the segmented leukocytes contained LFB‐staining granules, indicating an eosinophilic infiltrate was present. Neoplastic cells expressed tryptase, which confirms a mast cell lineage. Our findings suggest that grey eosinophils might be under‐recognized and interpreted incorrectly as toxic neutrophils. This report expands the canine breeds in which these eosinophils have been identified.     

Evaluation of canine antimicrobial peptides in infected and noninfected chronic atopic skin

Background – Antimicrobial peptides (AMPs) are small immunomodulatory peptides produced by epithelial and immune cells. β‐Defensins (BDs) and cathelicidins (Caths) are the most studied AMPs. Recently, increased cutaneous expression of AMPs was reported in atopic humans and in beagles with experimentally induced atopy. Hypothesis/Objectives – Our goal was to analyse mRNA expression and protein levels of canine (c)BD1‐like, cBD2‐like/122, cBD3‐like, cBD103 and cCath in healthy and naturally affected atopic dogs, with and without active skin infection, along with their distribution in the epidermis using indirect immunofluorescence. Animals – Skin biopsies were taken from 14 healthy and 11 atopic privately owned dogs. Methods – The mRNA levels of cBD1‐like, cBD2‐like/122, cBD3‐like, cBD103 and cCath were quantified using quantitative real‐time PCR. The protein levels of cBD3‐like and cCath were analysed by relative competitive inhibition enzyme‐linked immunosorbent assay, while the distributions of cBD2‐like/122, cBD3‐like and cCath were detected by indirect immunofluorescence. Results – Dogs with atopic dermatitis had significantly greater mRNA expression of cBD103 (P = 0.04) than control dogs. Furthermore, atopic skin with active infection had a higher cBD103 mRNA expression (P = 0.01) and a lower cBD1‐like mRNA expression (P = 0.04) than atopic skin without infection. No significant differences in protein levels (cBD3‐like and cCath) or epidermal distribution of AMPs (cBD2‐like/122, cBD3‐like and cCath) were seen between healthy and atopic dogs. Conclusions and clinical importance – Expression of cBD103 mRNA was greater, while expression of cBD1‐like mRNA was lower in dogs with atopic dermatitis that had active infections. Work is needed to clarify the biological mechanisms and possible therapeutic options to maintain a healthy canine skin.