60 h after injection, single-cell suspension from pooled CLNs were stained with PE-labeled H-2Kb-OVA257-264tetramers and V2, CD8, and CD5 antibodies to detect the OT-I transferred cells. the absence Chrysin of I-E . Knowledge of this extra reactivity is important because it could be, and already has been, mistakenly interpreted to support the view that Chrysin antigen transfer can occur between LCs and DDCs. Chrysin Collectively, these data revisit the transfer of antigen that occurs between keratinocytes and the five distinguishable skin DC subsets and stress the high degree of functional specialization that exists among them. Langerhans cells (LCs) constitute a subset of DCs. In their immature state, they reside in the stratified squamous epidermal layer of the skin and in the mucosal epithelia lining the ocular, oral, and vaginal surfaces (Iwasaki, 2007). LCs have long been regarded as the exclusive APCs of the skin, detecting pathogens that penetrate the skin barrier and, after undergoing a phase of maturation, conveying this information via lymphatic vessels to T cells present in cutaneous LNs (CLNs;Steinman and Nussenzweig, 2002;Larregina and Falo, 2005). Recent studies have shown, however, that LCs do not constitute the exclusive APCs of the skin. In addition to LCs, the skin contains a second type of DCs known as dermal DCs (DDCs). Epidermal LCs and DDCs migrate to CLNs under both steady-state and inflammatory conditions and constitute the direct precursors of the migratory LCs (mLCs) and migratory DDCs (mDDCs) found in CLNs, respectively. Some studies also suggested that migratory skin DCs play an indirect role in T cell priming, possibly by ferrying skin-derived Chrysin antigens to those DCs that reside throughout their life cycle in CLNs and are denoted as lymphoid tissueresident DCs to distinguish them from tissue-derived migratory DCs (Allan et al., 2003;Carbone et al., 2004;Allenspach et al., 2008). Langerin (CD207) is a C-type lectin originally thought to be specifically expressed in LCs (Valladeau et al., 2000;Kissenpfennig et al., 2005a). The use ofLang-EGFPmice that express an enhanced GFP (EGFP) under the control of thelangeringene showed that CD207 alone is not a reliable marker for the identification of LCs once they have migrated outside the epidermis (Kissenpfennig et al., 2005b) and led to the identification of three subsets of CD207+DCs in steady-state CLNs (Bursch et al., 2007;Ginhoux et al., 2007;Poulin et al., 2007;Shklovskaya et al., 2008). A minor subset corresponds to lymphoid tissueresident CD207lowCD8+DCs and represents 10% of the CD207+DCs found in CLNs. The two other subsets account for 90% of the CD207+cells present in CLNs and, consistent with their CD11cinter-to-highMHCIIhighphenotype, originate from the skin. They result from two independent developmental pathways that coexist in steady-state conditions. The first pathway gives rise to epidermal LCs and to their migratory derivatives found in CLNs, whereas the second pathway generates the CD207+DCs that reside in the dermis and their CD207+mDDC progeny (Bursch et al., 2007;Ginhoux et al., 2007;Poulin et al., 2007;Shklovskaya et al., 2008). LCs are radio resistant, and their numbers are maintained through continuous in situ proliferation (Merad et al., 2002;Tripp et al., 2004;Poulin et al., 2007). In contrast, the continuous renewal of DDCs and of lymphoid tissue-resident DCs depends on blood-borne radiosensitive BM precursors (Liu et al., 2009). As a consequence, in lethally Rabbit polyclonal to RBBP6 irradiated mice reconstituted with BM transplants, LCs in the epidermis and their migratory counterparts in the dermis and CLNs remain of host origin, whereas other DC subsets are primarily repopulated by donor BMderived cells (Merad et al., 2002). The role played by LCs and DDCs during Chrysin skin immune responses remains controversial (Kaplan et al., 2008;Lee et al., 2009). Therefore, the present study intends to further analyze the phenotypic and functional complexity of the DC network present in the skin and of their migratory derivatives present in CLNs. Based on the expression of CD207, CD11b, and CD103, we identified five distinct skin DC subsets and evaluated whether some functional specialization exists among them. We examined the contribution of each of them to the presentation of keratinocyte- or LC-expressed antigens. We demonstrated that CD207+CD103+DDCs are endowed with the unique capability of cross-presenting a model antigen expressed by keratinocytes and showed that such a task can be accomplished irrespective of the presence of LCs. In contrast to a previous study (Ginhoux et al., 2007), we also demonstrated that DDCs do not have the capacity to capture a model antigen carried by mLCs en route to the CLNs. == RESULTS == == Five distinct DC subsets coexist in steady-state dermis == We previously characterized the DCs that migrate out of whole skin explants in response to the CCL21 chemokine (Poulin et al., 2007). However, this approach does.