Differential responsiveness of Langerhans cell subsets of varying phenotypic states in normal human epidermis

Epidermal Langerhans cell heterogeneity is poorly understood with regard to phenotypic characteristics, such as the expression of human leukocyte antigen (HLA)-DR, integrin, and Fc receptor molecules, as well as functional characteristics, such as the ability to process and present antigens or produce cytokines during various phases of immigration and maturation. Technical limitations of Langerhans cell number have limited functional assays on putative Langerhans cell subsets in in vivo epidermis. Therefore, we used flow cytometry for simultaneous phenotypic and functional assessment at the single-cell level within the Langerhans cell population. Freshly isolated human epidermal cell suspensions were stained with a battery of monoclonal antibodies, including anti-HLA-DR, -CD1a, -CD1c, -CD11c, -Fc gamma RII, and -Fc epsilon RI. Two distinct Langerhans cell subsets were identified by their different levels of HLA-DR expression. The DRHi subset expressed higher amounts of CD11c and exhibited greater cytoplasmic complexity and higher baseline calcium than the DRLo subset (p < or = 0.03 for each). Some subjects also expressed high levels of Fc epsilon RI in the DRHi, CD11cHi subset. To determine whether these phenotypic subsets may exhibit differential signal-transduction functional properties, Langerhans cells were partially enriched over Ficoll-Hypaque and their cytosolic mobilization after the addition of ionomycin was analyzed using the calcium indicator, indo-1, in conjunction with quantitative analysis of HLA-DR expression. By this real-time flow cytometric analysis, a new subpopulation was revealed within the DRLo Langerhans cell subset. This subset increased its cytosolic calcium concentration much more than the other two subsets (change in indo-1 blue:violet emission ratio of 37.33 +/- 2.34 in the Hi Flux DRLo subset versus 13.23 +/- 0.29 in the Lo Flux DRLo subset, and versus 7.6 +/- 2.99 in the Lo Flux DRHi subset). These data indicate that functional, as well as phenotypic, subsets of Langerhans cells exist within normal human epidermis. Their responses to physiologic stimuli may relate to maturational stage or the level of in vivo activation.