Selective and site-specific mobilization of dermal dendritic cells and Langerhans cells by Th1- and Th2-polarizing adjuvants.

Dendritic cells (DCs) initiate and polarize adaptive immune responses toward varying functional outcomes. By means of intravital two-photon microscopy, we report that dermal dendritic cells (DDCs) and Langerhans cells (LCs) are differentially mobilized during contact sensitization and by adjuvants such as unmethylated CpG oligonucleotide (CpG) and LPS that induce T helper type 1 (Th1) responses, or papain that induces T helper type 2 (Th2) responses. In ear pinna, contact sensitization, CpG, LPS, and papain all mobilized DDCs in three distinct phases: increased motility and dendritic probing, directed migration, and entry into lymphatic vessels. During the same treatments, the adjacent LCs in ear pinna remained immotile over a 48-hr period of observation. In contrast, footpads lacked DDCs and Th1-polarizing adjuvants selectively induced a delayed mobilization of LCs after 48 hr. Th1 polarization of CD4(+) T cells was independent of the immunization site, whereas ear immunization favored Th2 polarization, correlating with site-specific DC distribution and dynamics. Our results provide an initial description of peripheral DC dynamics in response to adjuvants and imply that LC mobilization enhances a Th1 response and is not sufficient to trigger a Th2 response, whereas mobilization of DDCs alone is sufficient to trigger T-cell proliferation and to polarize initial T-cell activation toward a Th2 response.