Background Infiltration of the skin by pathogenic T cells is regarded as a key factor in the development of inflammatory skin diseases such as atopic dermatitis (AD) and psoriasis.

Objectives To investigate whether T cells containing cytotoxic proteins may contribute to the generation of skin inflammation in these skin diseases.

Methods Skin biopsy specimens were obtained from non‐lesional and lesional skin of patients with chronic AD (n = 8) and psoriasis (n = 6), and from non‐atopic controls with normal skin (n = 6). Expression of perforin and granzyme B was investigated by immunohistochemistry.

Results A significant enhancement of perforin and granzyme B expression was observed in lesional AD skin as compared with normal skin, non‐lesional AD skin and psoriasis. Expression of these cytotoxic proteins was also increased in psoriasis as compared with normal skin and non‐lesional psoriatic skin. Immunoreactivity for perforin and granzyme B was mainly found in the cytoplasm of lymphocytic cells located in the perivascular infiltrate. In AD increased numbers of positive cells were also observed focally at sites of spongiosis in the epidermis. Double immunostaining revealed that both CD4+ and CD8+ T cells are capable of expressing perforin and granzyme B.

Conclusions Our data suggest that cytotoxic CD4+ and CD8+ T cells containing perforin and granzyme B may play an integral part in eliciting cutaneous inflammation in AD.