Healthy skin of humans, mice, cattle, sheep, and alpacas contains resident dermal T-lymphocytes. Studies in horses looking at the resident lymphocyte population in skin have yielded conflicting results, with some describing small numbers of lymphocytes in the epidermis and superficial dermis, and others describing the absence of resident lymphocytes. The objective of this study was to determine the prevalence of CD20+ and CD3+ lymphocytes in the epidermis, adnexal epithelium, and dermis of biopsy samples from 29 horses with normal skin. Skin-biopsy specimens from the normal dorsolateral thorax from 29 horses were examined histologically and immunohistochemically for the presence of CD3+ (T-lymphocytes) and CD20+ (B-lymphocytes) cells in the dermis, epidermis, and adnexal epithelia. CD3+ lymphocytes were found in the dermis of 27/29 samples, primarily in a perivascular location, and in the epidermis of 9/29 samples and adnexal epithelia in 16/29 samples. CD20+ dermal lymphocytes were seen in 11/29 samples and not in the epidermis or adnexal epithelia. T- and rare B-lymphocytes appear to be a component of normal equine skin.

A 17-year-old, castrated male domestic shorthaired cat was presented with a more than 10-year history of plaques, and a pruritic dark brown crust along with a nodule on the neck for two years. Bowenoid in situ carcinoma (BISC) was suspected and the nodule was excised. Histopathological examination revealed proliferation of atypical keratinocytes in the epidermis and partial infiltration of atypical cells into the dermis. Mohs’paste was applied to the remaining plaques three times. The cat died on the 896th day and a necropsy was performed. Respiratory failure due to pulmonary squamous cell adenocarcinoma was considered as the cause of death. No metastatic lesion associated with BISC was observed.