Background.  The immune system of the skin has a network of resident dendritic cells (DCs) consisting of epidermal Langerhans cells and various subsets of dermal DCs. We recently reported on a new population of dermal DCs, called slan (6-sulfoLacNAc+) DCs, which have a potent capacity to stimulate Th17/Th1 T-cell responses.

Aim.  To understand the characteristics of slanDCs as a new population of dermal DCs in the context of other DC populations in healthy and psoriatic skin.

Methods.  We immunofluorescently stained skin samples from healthy controls and from patients with psoriasis.

Results.  Staining healthy skin for DCs showed that slanDCs (CD1a− CD1c− CD11c− CD14− CD163−) were present at a similar frequency to that of CD1c+ CD11c+ CD1a+ CD14− CD163− dermal DCs, which have previously been regarded as the major population of resident DCs. In psoriatic skin, the frequency of slanDCs and CD1c+ DCs was doubled, and the slanDCs expressed CD11c. In-depth analysis of DCs in psoriatic skin by four-colour immunofluorescence analysis showed that the pool of CD11c+ cells could be further subdivided into CD11c+ CD14+ CD163− DCs and CD11c+ CD163+ CD14+ macrophages.

Conclusion.  SlanDCs, initially described as large population of proinflammatory DCs in blood, are a novel and major part of the resident dermal myeloid DC system in both healthy and inflamed skin.