Immunohistochemical evaluation of filaggrin polyclonal antibody in atopic and normal beagles

In human atopic dermatitis (AD), impairments in skin barrier function are emphasized and hypothesized to increase risk of allergic sensitization. Filaggrins, crucial proteins for keratinization, are decreased in lesional and nonlesional human atopic skin. As canine AD shares numerous similarities with the human counterpart, this study aimed to evaluate a polyclonal antibody against human filaggrin in atopic beagles sensitized to house dust mites (HDM) and normal healthy dogs. The effects of HDM exposure on immunostaining and clinical signs were evaluated in both groups. Positive immunohistochemical staining with anti-filaggrin antibody was evaluated both objectively and subjectively by two blinded investigators. Pearson correlation test showed significant correlation between objective and subjective scores, both at baseline and after allergen exposure (r = 0.80; P = 0.0017 and r = 0.75; P = 0.013 respectively). Analysis of variance showed significant effect of time (P = 0.01) with immunostaining being higher in baseline samples than after HDM exposure. It also showed a significant group x time interaction (P = 0.02) with immunostaining not changing significantly over time in atopic dogs, while decreasing in normal dogs after HDM exposure. An independent t-test showed that, at baseline, atopic beagles had significantly less positive immunostaining than controls (P = 0.009) and that, after HDM exposure, there was no significant difference between groups. No correlation existed between clinical scores and immunostaining. In atopic dogs immunostaining was characterized by faint granular staining, while normal samples showed discrete intense staining. Moreover, immunostaining was present in all epidermal layers in many samples, suggesting cross-reactivity of the antibody used with other epidermal proteins besides filaggrin.