Functional Langerinhigh-Expressing Langerhans-like Cells Can Arise from CD14highCD16− Human Blood Monocytes in Serum-Free Condition

Abstract

Langerhans cells (LCs) are epithelial APCs that sense danger signals and in turn trigger specific immune responses. In steady-state, they participate in the maintenance of peripheral tolerance to self-antigens whereas under inflammation LCs efficiently trigger immune responses in secondary lymphoid organs. It has been demonstrated in mice that LC-deprived epithelia are rapidly replenished by short half-life langerin-expressing monocyte-derived LCs (MDLCs). These surrogate LCs are thought to be progressively replaced by langerinhigh LCs arising from self-renewing epithelial precursors of hematopoietic origin. How LCs arise from blood monocytes is not fully understood. Hence, we sought to characterize key factors that induce differentiation of langerinhigh-expressing monocyte-derived Langerhans-like cells. We identified GM-CSF and TGF-β1 as key cytokines to generate langerinhigh-expressing cells but only in serum-free conditions. These cells were shown to express the LC-specific TROP-2 and Axl surface markers and contained Birbeck granules. Surprisingly, E-cadherin was not spontaneously expressed by these cells but required a direct contact with keratinocytes to be stably induced. MDLCs induced stronger allogeneic T cell proliferations but released low amounts of inflammatory cytokines upon TLR stimulation compared with donor-paired monocyte-derived dendritic cells. Immature langerinhigh MDLCs were responsive to MIP-3β/CCL20 and CTAC/CCL27 chemokine stimulations. Finally, we demonstrated that those cells behaved as bona fide LCs when inserted in a three-dimensional rebuilt epithelium by becoming activated upon TLR or UV light stimulations. Collectively, these results prompt us to propose these langerinhigh MDLCs as a relevant model to address LC biology–related questions.

Differentiation of Langerhans Cells from Monocytes and Their Specific Function in Inducing IL-22–Specific Th Cells

“…In this study, we observed that moLCs were more potent to induce proliferation of allogeneic T cells to secrete IL-22. These findings are compatible to a recent report indicating that moLCs induce a stronger allogeneic T cell proliferation but release low amounts of inflammatory cytokines upon TLR stimulation (26). Thus, even though moLCs displayed a lower ability to respond to external foreign Ags by stimulation of CD1a molecules with lipid Ags than moDCs, they established a local defense and skin homeostasis through induction of IL-22-specific T cells.…”

Differentiation of human dendritic cell subsets for immune tolerance induction

“…1A and B). When cultured in the presence of GM-CSF and TGF-ß1, monocytes generated large number (60%) of dendritic cells as moLCs that expressed Langerin (CD207) as referred to the literature [15] (Fig. 1A and B) but not CD209 compared to moDCs or CD14 and in minor levels compared to monocyte (Fig.…”

“…Langerhans cells form a stable self-renewing population that does not require CD34 + progenitors in the absence of inflammation [24]. It can be differentiated from monocytes [15,17], dermal resident CD14 + cells [25] and CD1c + DC [26]. It has become clear that LCs were not only capable of triggering adaptive immune responses but also of mediating immune tolerance to self-antigens in non-inflammatory conditions [27,28].…”

Altered Monocyte and Langerhans Cell Innate Immunity in Patients With Recurrent Respiratory Papillomatosis (RRP)

“…We have shown alterations in both monocyte-and tissuederived iLCs from patients with RRP and postulate that these alterations could contribute to the anti-inflammatory immune response these patients make to persistent HPV6/11 infection (8,9). Monocytes can be subdivided into three main subgroups, based on their surface markers (41). The classical monocyte subpopulation is the major source of monocyte-derived iLCs (41), although we have now found that the intermediate and alternate subpopulations can also generate small numbers of iLCs.…”

“…The iLCs in normal, non-inflamed epithelia are not bone marrow derived (37,46), although to our knowledge, no one has identified the source of laryngeal iLCs. Immature LC precursors migrate to epithelial surfaces early in embryogenesis (35,36,38,46), becoming long-lived iLCs that exist in direct contact with keratinocytes through tight junctions, and they show some differences from monocyte-derived iLCs (41,47,48). Monocytes can enter inflamed/damaged tissues, or tumors, and differentiate into iLCs (48), but there is no evidence of inflammation in respiratory papillomas (8,12,49).…”