Isolation of Human Skin Dendritic Cell Subsets. 
Dendritic cells (DCs) are specialized leukocytes with antigen-processing and antigen-presenting functions.  DCs can be divided into distinct subsets by anatomical location, phenotype and function.  In human, the two most accessible tissues to study leukocytes are peripheral blood and skin.  DCs are rare in human peripheral blood (<1 % of mononuclear cells) and have a less mature phenotype than their tissue counterparts (MacDonald et al.,  Blood.  100:4512-4520, 2002; Haniffa et al.,  Immunity 37:60-73, 2012).  In contrast, the skin covering an average total surface area of 1.8 m(2) has approximately tenfold more DCs than the average 5 L of total blood volume (Wang et al.,  J Invest Dermatol 134:965-974, 2014).  DCs migrate spontaneously from skin explants cultured ex vivo, which provide an easy method of cell isolation (Larsen et al.,  J Exp Med 172:1483-1493, 1990; Lenz et al.,  J Clin Invest 92:2587-2596, 1993; Nestle et al.,  J Immunol 151:6535-6545, 1993).  These factors led to the extensive use of skin DCs as the "prototype" migratory DCs in human studies.  In this chapter, we detail the protocols to isolate DCs and resident macrophages from human skin.  We also provide a multiparameter flow cytometry gating strategy to identify human skin DCs and to distinguish them from macrophages.