Phenotypical and functional characterization of human skin dermal dendritic cells and Langerhans cells.

Cutaneous antigen presenting cells (APCs) are critical for the induction and regulation of skin immune responses. The human skin contains phenotypically and functionally distinct APCs subsets that are present at two separated locations. While CD1ahigh LCs form a dense network in the epidermis, the CD14+ and CD1a+ APCs reside in the dermal compartment. A better understanding of the biology of human skin APC subsets is necessary for the improvement of vaccine strategies that use the skin as administration route. In particular, progress in the characterization of uptake and activatory receptors will certainly improve APC-targeting strategies in vaccination. Here we performed a detailed analysis of the expression and function of glycan-binding and pattern-recognition receptors in skin APC subsets. Detailed analysis of the differentially expressed genes amongst both populations confirmed the exclusive expression of langerin in LCs and DC-SIGN in dermal APCs. Although several genes, such as galectin-1, -3 and -9, MGL and dectin-1 were highly abundant on both APC subpopulations, a number of glycan-binding receptors defined a cell-specific expression signature . Thus, next to langerin, Siglec-5 and L-SIGN were specific to LCs, whereas dermal APCs expressed higher levels of CLEC4A (also known as DCIR), Macrophage mannose receptor, AGR2, CLEC1A, COLEC12, MDL1, Galectin 2 and Siglec 7. Most of these glycan-binding proteins have been involved in antigen uptake, illustrating that dDC have a more specialized function in recognizing a broad repertoire of antigens for internalization than LCs. Based on these data, we can conclude that the APC subsets found in the epidermis and dermis of human skin share a significant amount of glycan-binding receptor genes, but have also unique CLRs on LC and dermal APCs illustrating that these cells may differ in their antigen recognition and uptake function. Human dermal APCs and LCs were purified using MACS beads after 3 days of in vitro cell migration using CD19 and HLA-DR beads for the dermal APC sample and CD1a for the LC samples. CD19+ B cells were depleted from the dDC samples prior to RNA isolation. RNA was extracted using the Qiagen RNeasy Mini kit and used to probe the GLYCOv4 oligonucleotide array.