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

In canine and human atopic patients, the intracutaneous injection of offending allergens is followed by the development of both immediate and late‐phase reactions. The present study was performed to expand on the characterization and dynamics of inflammatory cell subsets during IgE‐mediated late‐phase reactions in canine skin. Three normal dogs and three Dermatophagoides farinae‐allergic dogs were selected for this experiment. All dogs were challenged intradermally with mite allergen, purified anticanine IgE antibodies (positive control) or phosphate‐buffered saline (negative control). Skin biopsies were obtained before and 6, 12 and 24 h post‐injection. Sections were stained with metachromatic and eosinophil‐specific histological stains. Additionally, we used an immunohistochemical method with antibodies specific for canine leukocyte antigens. This study confirmed the occurrence of a late‐phase reaction in atopic skin following allergen challenge, and in normal and atopic canine skin after intradermal injection of IgE‐specific antibodies. Whereas early emigrating dermal cells were composed chiefly of neutrophil and activated eosinophil granulocytes, there was an influx of αβ T‐lymphocytes and dermal dendritic cells in later stages of the late‐phase reactions. Because IgE‐mediated late‐phase reactions resemble spontaneous atopic canine skin lesions, both at macroscopic and microscopic levels, we propose the use of similar challenges to study the anti‐inflammatory effects of anti‐allergic drugs in a pre‐clinical setting.