Epidermal langerhans cell movement in situ: a model for understanding immunologic function in the skin.

E PIDERMAL LANGERHANS CELLS (LCS) REPREsent an immature dendritic cell subset at the environmental interface. They undergo maturational changes and migrate to draining lymph nodes in response to danger signals, eg, the presence of proinflammatory cytokines and microbial products (Figure 1). Our research group has recently developed a system to visualize dynamic behaviors of epidermal LCs by combining time-lapse, intravital, confocal imaging technology and I-A –enhanced green fluorescent protein (EGFP) knock-in mice in which LCs can be identified by EGFP-associated fluorescence. Under the steady state, some LCs exhibited a unique motion, called the dendrite surveillance extension and retraction cycling habitude (dSEARCH), characterized by rhythmic extension and retraction of dendritic processes through intercellular spaces (Figure 2) (supplemental video S1). Topical application of dinitrofluorobenzene (DNFB) not only provoked dSEARCH motion but also triggered direct cell-to-cell contact formation among adjacent LCs (Figure 3) (supplemental video S2). Although functional outcomes of such motile behaviors remain unclear, it is tempting to speculate that dSEARCH motion may facilitate more efficient and broader antigen sampling by epidermal LCs and that adjacent LCs may exchange the antigens under pathologic conditions.