Distribution of interleukin 1 receptor antagonist protein (IRAP), interleukin 1 receptor, and interleukin 1 alpha in normal and psoriatic skin. Decreased expression of IRAP in psoriatic lesional epidermis.

The distribution of interleukin 1 alpha (IL-1 alpha), type 1 interleukin 1 receptor (IL-1R), and the interleukin 1 receptor antagonist protein (IRAP), was investigated in biopsies of normal skin, and in uninvolved and lesional skin of patients with psoriasis, using specific monoclonal antibodies. We report the novel finding that IRAP is distributed throughout the living layers of the epidermis in normal skin, and is also associated with sebaceous glands and eccrine sweat glands. Our finding that the inhibitor protein IRAP is present in areas where the pro-inflammatory cytokine IL-1 alpha is distributed provides strong evidence in favour of a cytokine regulatory system in normal skin. We further document for the first time that IL-1R in normal skin is localized to the living layers of the epidermis, sebaceous and eccrine glands, as well as to a prominent network of dermal dendritic cells, and upper dermal blood vessels. There was a consistent reduction in the level of IRAP expression in lesional compared with uninvolved skin in biopsies from six out of seven psoriasis patients. Decreased IRAP expression in lesions of psoriasis indicates that alterations in the level of this inhibitor protein may be important in the pathogenesis of inflammatory skin conditions.