IL-6 Signalling to Responding T Cells Is Key to Calcitonin Gene-Related Peptide-Exposed Endothelial Cell Enhancement of Th17 Immunity During Langerhans Cell Antigen Presentation

Calcitonin gene-related peptide (CGRP) biases Langerhans cell (LC) Ag presentation to CD4⁺ T cells towards Th17-type immunity through actions on endothelial cells (ECs). We now report further evidence that IL-6 signalling at responding T cells mediates this effect. This CGRP effect was absent with ECs from IL-6 KO mice. Exposure of LCs, but not T cells, to IL-6 enhanced IL-6 and IL-17A production and reduced IFN-γ in the T-cell response. Pretreatment of LCs with IL-6 receptor α-chain (IL-6Rα) antibodies prior to IL-6 exposure significantly inhibited these responses. However, T-cell pretreatment with an IL-6/IL-6Rα chimera mimicked the effect of IL-6 pretreatment of LCs on T-cell responses. When this experiment was performed in the presence of the ADAM17 and ADAM10 inhibitor TAPI-1 during LC pretreatment of LCs and during the Ag presentation culture, release of soluble IL-6Rα chains into the medium was very significantly reduced, but this did not affect levels of T-cell cytokine release. Interestingly, LC exposure to IL-6 significantly increased LC IL-6 expression. Furthermore, pretreatment of T cells with antibodies against the IL-6 receptor β-chain significantly inhibited the IL-6 effect. CGRP may stimulate ECs in lymphatics and/or lymph nodes to produce IL-6 which likely results in migrating LCs nonclassically presenting IL-6. Furthermore, we found that IL-6 induces IL-6 production by LCs, suggesting an autocrine amplification pathway for this effect.