SKIN TESTING OF THE PRURITOGENIC ACTIVITY OF HISTAMINE AND CYTOKINES (INTERLEUKIN-2 AND TUMOR-NECROSIS-FACTOR-ALPHA) AT THE DERMAL-EPIDERMAL JUNCTION

Cytokines have been proposed as histamine-independent itch mediators, To investigate this hypothesis, single doses of interleukin-2 (IL-2, 1 0 MU/mL) and tumour necrosis factor alpha (TNF-alpha, 10 mu g/mL) were delivered to the epidermis of 10 healthy volunteers with a controlled skin-prick model; 1% histamine and solvent controls were included in a double-blind, randomized crossover design, Itch ratings (computerize d visual analogue scale) were obtained every 20s for 15 mill and cutan eous reactions (weal, flare and temperature) were measured, Reactions were also recorded after 2, 24 and 48 h, The mean itch ratings were: h istamine 35.5, IL-2 3.3 (both P<0.01 compared with control), TNF-alpha 1.6 and solvent control 1.75 (not significant), Weal and flare occurr ed only with histamine. In two volunteers, an inflammatory papule with transient pruritus developed 12-18 h after applying IL-2. In conclusi on, IL-2 showed a rapid, low pruritogenic effect, which may be followe d by an inflammatory response, TNF-alpha induced no itching in this se tting, Skin-prick testing with appropriate doses of potential pruritog ens provides a safe and sensitive model for further chemoreceptor stud ies.