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Peripheral blood mononuclear cell responses to Dermatophagoides farinae in canine atopic dermatitis

https://doi.org/10.1016/S0165-2427(01)00361-0Get rights and content

Abstract

Atopic dermatitis is a chronic inflammatory and pruritic skin disease commonly seen in dogs and humans that is characterised by the presence of allergen-specific IgE. Data from skin tests and serological analysis suggest that the house dust mite Dermatophagoides farinae is the most important allergen in dogs with atopic dermatitis. The aim of this study was to determine if D. farinae specific peripheral blood mononuclear cell (PBMC) responses could be detected in dogs with atopic dermatitis. PBMCs were isolated by the density centrifugation from dogs with atopic dermatitis that were skin test positive for D. farinae, dogs with atopic dermatitis that were skin test negative for D. farinae, and healthy dogs. Cells were cultured with increasing concentrations of the D. farinae extract, no antigen, vaccine antigens or concanavalin A (ConA). There was significantly greater responsiveness of PBMCs from the D. farinae positive dogs than from either the D. farinae negative or healthy dogs (ANOVA, P<0.05). In contrast, no significant differences were observed in the control responses between the three groups. This is the first study to demonstrate that D. farinae specific circulating memory cells are involved in the pathogenesis of canine house dust mite hypersensitivity.

Introduction

Atopic dermatitis is a well-recognised chronic inflammatory skin disease of humans (Rothe and Grant-Kels, 1996) and dogs (Scott et al., 1995). The relative risk of atopic dermatitis is strongly correlated to the house dust mite exposure (Cooper, 1994). Between 40 and 80% of human patients have house dust mite specific serum IgE and positive skin tests (Halbert et al., 1995), and approximately 60% of atopic dogs have positive skin tests to the house dust mite allergens (Sture et al., 1995). The major house dust mite species in temperate areas are Dermatophagoides farinae and Dermatophagoides pteronyssinus. D. pteronyssinus prefers more humid conditions than D. farinae and is the most common species in the UK (Thomas et al., 1998). Despite this, skin test reactions to D. farinae are more frequent than to D. pteronyssinus in atopic dogs in the UK (Sture et al., 1995).

Canine atopic dermatitis has been viewed as an IgE/mast cell-mediated disease (Scott et al., 1995). However, IgE production is dependent on the allergen-specific CD4+ TH-cells (Lydyard and Grossi, 1998) and infiltration of CD4+ and CD8+ lymphocytes is observed in lesional atopic skin in both dogs (Olivry et al., 1997) and humans (Leung, 2000). Several studies in humans have demonstrated PBMC proliferation to the crude Dermatophagoides extracts and purified allergens (reviewed in Leung, 2000). Despite this, investigation of PBMC responses in atopic dogs has been limited. One unpublished report suggested that PBMCs from atopic dogs had a proliferative response to the crude D. pteronyssinus extract and major allergens identified on Western blots (Shaw, 2000), but responses to D. farinae were not investigated.

The aim of this study, therefore, was to determine if allergen-specific T-cells were involved in the pathogenesis of canine atopic dermatitis by investigating PBMC responses to D. farinae in dogs with atopic dermatitis that were skin test positive to D. farinae, skin test negative to D. farinae and healthy dogs.

Section snippets

Study population

Dogs with atopic dermatitis were recruited from the Dermatology Clinic at the University of Edinburgh Hospital for Small Animals. Diagnosis was based on compatible history and clinical signs, and exclusion of other causes of pruritus (Willemse, 1986, Nuttall et al., 1998). Coat brushings, skin scrapings and trial therapy were used to eliminate the possibility of ectoparasite infestation. All dogs underwent a 6 weeks, home cooked diet trial to eliminate the food intolerance. Seborrhoea,

Results and discussion

To our knowledge, this study documents for the first time the presence of circulating Dermatophagoides farinae specific T-cells in canine atopic dermatitis. PBMCs from D. farinae positive atopic dogs showed greater proliferation to all concentrations of the D. farinae extract than PBMCs from either D. farinae negative atopic dogs or healthy dogs (Fig. 1). Optimum proliferation was seen with 50 micrograms/ml D. farinae. At this concentration, there was significantly greater proliferation of

Acknowledgements

The authors are grateful for the help and assistance shown by Dr. K.L. Thoday, Mr. A.W. Carter and Mr. P. Fosythe of the Dermatology Service at the University of Edinburgh Hospital for Small Animals, Prof. H.R.P. Miller and Mrs. E. Thornton of the Department of Veterinary Clinical Studies and Dr. G.F. Hoyne, Dr. S.E.M. Howie, Dr. N. Savage and Ms. G. Hall of the Respiratory Medicine Unit, Immunobiology Group, MRC Centre for Inflammation Research. This study was funded by The Wellcome Trust.

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