Topical pimecrolimus 1% reverses long-term suberythemal ultraviolet B-induced epidermal Langerhans cell reduction and...

Some literature reported that topical calcineurin inhibitors (TCIs) did not accelerate photocarcinogenesis in hairless mice after long-term simulated solar radiation. In this work, we investigate the effects of topical pimecrolimus 1% on long-term suberythemal ultraviolet B (UVB) irradiated epidermal Langerhans cells (LCs) in mice.

Thirty female mice were randomly divided into two groups, including four subgroups: (1A) control, (1B) pimecrolimus 1% only, (2A) 25 mJ/cm2 UVB only, (2B) UVB plus pimecrolimus. After being treated for 60 days, the dorsal skin was collected and given immunohistochemical staining of active caspase 3, and immunofluorescence staining for cluster of differentiation 1a (CD1a).

Our results show that, compared with the control subgroup, the CD1a+ LC number in the epidermal sheet of the UVB-only subgroup decreased substantially from 578.6 per mm2 to 227 per mm2 (P<.001). Compared with the UVB-only subgroup, the UVB plus pimecrolimus subgroup significantly restored the LC number from 227 per mm2 to 475.7 per mm2 (P<.001). Compared with other subgroups, the LC morphology of the UVB-only subgroup became rounder, and the LC dendrites became shorter. There were no significant active caspase 3-positive cells in the epidermis in any of the four subgroups.

Our results show that topical pimecrolimus 1% reverses long-term UVB-induced epidermal LC reduction and morphologic changes in mice, where the exact mechanism is likely not related to apoptosis.