Investigation of neutrophil infiltration in the acute canine atopic dermatitis model.

Atopic dermatitis (AD) is an inflammatory skin condition associated with chronic itch and inflammation in both humans and animals. While this disease depends upon various immune cell types, the precise role and kinetics of neutrophils remain elusive, particularly in relevant large-animal models. Given a recent report suggesting the involvement of neutrophils in a mouse model, we aimed to characterize the temporal presence and infiltration of these cells in a canine model of house dust mite (HDM)-induced AD. AD was induced in canines via HDM exposure, and skin biopsies were analyzed over a time course (0-96 h) using standard H&E staining and specific immunofluorescent (IF) staining for canine neutrophils. Our results showed general cellular infiltration with the H&E method, while IF further confirmed detectable neutrophil immunoreactivity starting between 24 and 96 h post-challenge in atopic skin. Quantitation demonstrated a significant increase in neutrophil infiltration (cells/mm2) in atopic skin at 48 h following HDM exposure compared to baseline (p = 0.041). Collectively, our data confirms time-dependent infiltration of neutrophils into the skin of the canine AD model following allergen challenge, supporting the hypothesis that this previously overlooked immune cell may play a role in the acute phase of AD pathogenesis and sensitization.