965 The importance of CD206+ macrophages in squaric acid dibutylester-induced hair cycle activation

Squaric acid dibutylester (SADBE) is a topical sensitizer useful for contact immunotherapy of alopecia areata (AA). However, the mechanism of action is not fully understood. Macrophages activated by cytokines such as IL-1β or IL-4 are reported to promote hair growth. M2 macrophages induced by IL-4, IL-10 or IL-13 exhibit anti-inflammatory function and produce several growth factors that induce tissue repair, and are proposed to contribute hair regrowth. C3H/HeJ mice spontaneously develop AA and the AA mice that were applied with SADBE showed hair regrowth on day 28. To evaluate the effect of SADBE in a simpler experimental system, young mice without AA were shaved and applied with SADBE. In this setting, hair growth was observed on day 14, and histologically, anagen hairs were induced at least on day 5. Immunohistochemical examinations revealed the intense infiltration of macrophages expressing CD206, a typical marker of M2 macrophages, in the dermal tissues. Quantitative image analysis showed that the infiltrating cells were divided into three subsets: CD206+F4/80–, CD206+F4/80+, and CD206–F4/80+. These subsets formed three-layered structure, and CD206+/F4/80+ cells were localized around the dermal papilla. Likewise, repeated application of SADBE in AA mice induced hair regrowth in correlation with the increase of CD206+ macrophages. Our observations suggest that SADBE induces M2-like macrophages around the dermal papilla on day 3 and triggers hair cycle progression as early as on day 5. In shaved mice without AA, macrophage depletion by intradermal injection of clodronate liposomes inhibited SADBE-induced hair growth suggesting that macrophages are indispensable. Therefore, CD206+macrophages play important role in hair growth promotion via SADBE-induced contact dermatitis and have the potential to be a novel therapeutic target for AA.