CD3+ lymphocytes predominate in the dermis, epidermis, and adnexal epithelia of the normal dorsolateral thorax of horses

Abstract

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.