Migratory Langerhans cells (LCs) are the most efficient skin dendritic cells (DCs) at polarizing Th22 cell subset.

<p>Purified migratory skin DCs were cultured with allogeneic CD4⁺ (A, C, D) or CD8⁺ (B) naïve T cells for 6 days and restimulated with phorbol myristate acetate (PMA) and ionomycin. (A, B) Cell supernatants were harvested after 24 hours and IL-22 secretion was measured by ELISA. Each marker illustrates experiments performed with different donors. (A) ** p<0.001, *p<0.002, as compared with LC values. (C, D) Intracytoplasmic cytokines were analyzed after 6 hours. (D) Results are the mean±SD percentage of stained cells from 4 experiments carried out with different donors.</p

TGF-β down-regulates both IL-22 and IL-21 production by naïve CD4⁺T cells.

<p>Purified migratory skin DCs were cultured with allogeneic naïve CD4⁺T cells in the presence of exogeneous human TGF-β (50 ng/ml) or anti-human TGF-β mAb (10 µg/ml). Culture medium was RPMI 1640 supplemented with 10% human AB serum or (B, left panel) serum free medium. After 6 days cells were restimulated with phorbol myristate acetate (PMA) and ionomycin. Cell supernatants were harvested after 24 hours and (A) IL-22 or (B) IL-21 secretion was measured by ELISA. Each marker illustrates experiments carried out with different donors.</p

Migratory Langerhans cells can induce IL-21 production by naïve CD4⁺T cells in serum-free conditions.

<p>Purified migratory skin DCs were cultured with allogeneic CD4⁺ naïve T cells for 6 days and restimulated with phorbol myristate acetate (PMA) and ionomycin. Culture medium was (A) RPMI-1640 supplemented with 10% human AB serum or (B, C, E, F) X-vivo 15 serum free medium. (A, B) Cell supernatants were harvested after 24 hours and IL-21 secretion was measured by ELISA. Results were from (A) five or (B) seven experiments performed with different donors. (C, D, E, F) Intracytoplasmic cytokines were analyzed after 6 hours. (D) Results are from the same experiment carried out in either serum-supplemented or depleted medium.</p

Langerhans cells are stronger stimulators of allogeneic naïve CD4⁺T cell proliferation than dermal DCs.

<p>A. Phenotypic analysis of co-stimulatory molecules on migratory skin DC. CD80, CD86, ICOS-L and PD-L1 expression were measured by Flow Cytometry method B. Il-6 and TNF-α secretion after LPS stimulation of migratory skin DC. Migratory skin DC were stimulated with LPS. After 48 hours of stimulation IL-6 and TNF-α were measured by ELISA methods. Results are express in pg/ml ±SD of triplicate cultures and representative of three experiments C Allogeneic proliferation capacity. Purified migratory human skin DCs were added in graded numbers to allogeneic naïve CD4⁺T cells. Proliferation was measured after 5 days by ³H-thymidine incorporation. Results are the mean counts per minute (cpm) ±SD of triplicate cultures and representative of three experiments. T cells alone gave less than 100 cpm.</p

Differential Capacity of Human Skin Dendritic Cells to Polarize CD4⁺T Cells into IL-17, IL-21 and IL-22 Producing Cells

<div><p>Accumulating evidence suggests a contribution of T cell-derived IL-17, IL-21 and IL-22 cytokines in skin immune homeostasis as well as inflammatory disorders. Here, we analyzed whether the cytokine-producing T lymphocytes could be induced by the different subsets of human skin dendritic cells (DCs), i.e., epidermal Langerhans cells (LCs), dermal CD1c⁺CD14⁻ and CD14⁺ DCs (DDCs). DCs were purified following a 2-day migration from separated epidermal and dermal sheets and co-cultured with allogeneic T cells before cytokine secretion was explored. Results showed that no skin DCs could induce substantial IL-17 production by naïve CD4⁺ or CD8⁺T lymphocytes whereas all of them could induce IL-17 production by memory T cells. In contrast, LCs and CD1c⁺CD14⁻DDCs were able to differentiate naïve CD4⁺T lymphocytes into IL-22 and IL-21-secreting cells, LCs being the most efficient in this process. Intracellular cytokine staining showed that the majority of IL-21 or IL-22 secreting CD4⁺T lymphocytes did not co-synthesized IFN-γ, IL-4 or IL-17. IL-21 and IL-22 production were dependent on the B7/CD28 co-stimulatory pathway and ICOS-L expression on skin LCs significantly reduced IL-21 level. Finally, we found that TGF-β strongly down-regulates both IL-21 and IL-22 secretion by allogeneic CD4⁺ T cells. These results add new knowledge on the functional specialization of human skin DCs and might suggest new targets in the treatment of inflammatory skin disorders.</p> </div