Does filaggrin expression correlate with severity of clinical signs in dogs with atopic dermatitis?

Background - Filaggrin expression is decreased in subsets of humans and dogs with atopic dermatitis (AD). Filaggrin expression is modulated by inflammation, but it is unknown whether expression is inversely correlated with clinical signs. Hypothesis/Objectives - To investigate the correlation between filaggrin expression and the severity of clinical signs in an experimental model of canine AD. Animals - Eighteen atopic research beagle dogs sensitized to house dust mite allergens. Methods - Dogs were challenged with house dust mites for 3 days consecutively (days 1-3) and skin biopsies collected on days 1 (before allergen challenge), 3 (peak of challenge) and 10 (at resolution of lesions). Clinical signs were scored using a modified version of CADESI-03, the Canine Atopic Dermatitis Extent and Severity Index. Immunohistochemical staining was measured subjectively by three investigators who graded filaggrin staining for continuity, granularity and intensity. For objective evaluation of staining, the stratum granulosum and epidermis were traced, and the percentage of filaggrin per unit stratum granulosum and epidermal area were calculated. Correlations were investigated using Pearson's product-moment correlation (for linear correlations) and Spearman's rank correlation (for nonlinear correlations), pooling all days together and then separately on each day, using total clinical scores and either subjective or objective filaggrin scores. Results - The only significant correlation was found between the subjective filaggrin scores and total clinical scores on day 1. Conclusions and clinical importance - No inverse correlation exists between the severity of clinical signs and filaggrin expression; the clinical relevance of filaggrin in canine AD is unknown.