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Background: The most intriguing function attributed to interleukin-31 (IL-31) isits ability to induce pruritus in pathologic conditions, such as atopic dermatitis(AD). As of today, this feature of IL-31 was testedin vivoonly in animal models.

Methods: Ten patients with AD and 10 healthy controls were challenged withIL-31 and NaCl (negative control) by skin prick testing. Twenty additionalhealthy controls were subjected to skin prick testing with histamine. Itch andlocal inflammatory responses of the skin were assessed for up to 72 h.

Results: All of the histamine-challenged subjects developed immediate pruritus(i.e. within the first 5 min). In contrast, only one IL-31- and two of the NaCl-challenged subjects reported immediate itch at the provocation site (short lasting,for 2–6 min). Nine subjects (five patients with AD) reported late itch responses toIL-31 challenges with a mean delay of 143 min. No subject reported late itchresponses to histamine or NaCl testing. There was no significant difference inIL-31-induced itch start time, duration and intensity between patients with AD and healthy volunteers.

Conclusion: IL-31 does not induce immediate itch responses in humans. The lateonset of IL-31-induced itch supports the notion that IL-31 exerts its pruritic effectindirectly via keratinocytes and secondary mediators, rather than through itsreceptors on cutaneous nerves.