Tumor necrosis factor-alpha and interleukin-17 differently affects Langerhans cell distribution and activation in an innovative three-dimensional model of normal human skin

• We evaluated the effect of psoriasic cytokines on epidermal Langerhans cells (LCs).
• An innovative three-dimensional model of organotypic human skin cultures was used.
• Tumor necrosis factor-alpha and interleukin-17 were added to the culture medium.
• Interleukin-17 significantly affects the LC immunophenotype.
• The combination of both cytokines was chemo-attractant for epidermal LCs.

Among the several cytokines involved in the psoriasis pathogenesis, tumor necrosis factor (TNF)-alpha and interleukin (IL)-17 play a central role. Many biomolecular steps remain unknown due to difficulty to obtain psoriatic models. To investigate the effect of TNF-alpha and IL-17 on the ultrastructure, immunophenotype, and number of epidermal Langerhans cells (LCs), human skin explants (n = 7) were cultured air–liquid interface in a Transwell system. Four different conditions were used: medium alone (control), medium added with 100 ng/ml TNF-alpha or 50 ng/ml IL-17 or a combination of both cytokines. Samples were harvested 24 and 48 h after cytokine addition and were frozen. Samples harvested at 24 h were also processed for transmission electron microscopy (TEM). By immunofluorescence analysis with anti-human Langerin antibody (three experiments/sample) we calculated the percentage of LCs/mm2 of living epidermis after 24 and 48 h of incubation (considering control as 100%). At 24 h LC number was significantly higher in samples treated with both cytokines (216.71 + 15.10%; p < 0.001) and in TNF-alpha (125.74 + 26.24%; p < 0.05). No differences were observed in IL-17-treated samples (100.14 + 38.42%). After 48 h, the number of epidermal Langerin-positive cells in IL-17- and TNF-alpha treated samples slightly decreased (94.99 + 36.79% and 101.37 + 23% vs. their controls, respectively). With the combination of both cytokines epidermal LCs strongly decreased (120 + 13.36%).By TEM, upon TNF-alpha stimulus LCs appeared with few organelles, mostly mitochondria, lysosomes, and scattered peripherical BGs. Upon IL-17 stimulus, LCs showed a cytoplasm with many mitochondria and numerous BGs close to the perinuclear space and Golgi apparatus, but also at the periphery, at the beginning of the dendrites. The addition of both cytokines did not affect LC ultrastructure.Our study showed that IL-17 induced significant changes in LC ultrastructure, while the combination of both cytokines seems to have a strong chemo-attractant effect on epidermal LCs, supporting the relevance of investigating the interplay between LCs and pro-inflammatory cytokines in the ongoing of the disease.