Optimization of an Immunohistochemical Method to Assess Distribution of Tight Junction Proteins in Canine Epidermis and Adnexae

Epidermal tight junctions (TJs) have been well characterized in human medicine. Abnormality of these structures is involved in skin diseases such as atopic dermatitis. There is little information about the expression and distribution of TJ proteins in the canine skin. The aim of this study was to develop an optimal immunohistochemical method for assessment of the expression of TJ proteins in the skin of healthy dogs. Formalin-fixed and paraffin wax-embedded skin biopsy samples from healthy human and canine patients were used. Canine skin samples were from the inguinal region and the nasal planum. Immunohistochemistry was used to study the expression of zonula occludens-1 (ZO-1), occludin and claudin-1, -4 and -7. Heat-induced antigen retrieval with EDTA (pH 9.0) yielded the best labelling of TJ proteins. ZO-1 and occludin were expressed in the cytoplasm and along the keratinocyte membrane, while claudin-1 and -4 were mainly membrane in distribution. ZO-1, occludin and claudin-1 were detected in all epidermal layers with the exception of the stratum corneum, while claudin-4 expression was restricted to the stratum granulosum. Expression of claudin-7 was difficult to evaluate. There was no difference in labelling pattern between inguinal and nasal planum skin. [Display omitted] Tight junction proteins ZO-1, occludin, claudin-1 and claudin-4 are expressed in the cytoplasm (C) or on the membrane (M) of epidermal keratinocytes in canine skin. •An immunohistochemical method was proposed to stain tight junctions in canine skin.•ZO-1 and occludin were expressed both in the cytoplasm and along the membranes.•Claudin-1 and claudin-4 were mainly localized along the membranes.•ZO-1, occludin and claudin-1 were detected in all layers except the stratum corneum.•Claudin-4 staining was restricted to the stratum granulosum.