Interleukin-32 promotes detachment and activation of human Langerhans cells in a human skin explant model
British Journal of Dermatology
Cross-talk between skin keratinocytes (KCs) and Langerhans cells (LCs) plays a fundamental role in the body's first line of immunological defences. However, the mechanism behind the interaction between these two major epidermal cells is unknown. Interleukin (IL)-32 is produced in inflammatory skin disorders. We questioned the role of IL-32 in the epidermis. Objectives We aimed to determine the role of IL-32 produced by KCs on surrounding LCs. Methods We used an ex vivo human explant model from
... ealthy donors and investigated the role of IL-32 on LC activation using imaging, flow cytometry, reverse transcriptase quantitative polymerase chain reaction and small interfering (si)RNA treatment. Results Modified vaccinia virus ankara (MVA) infection induced KC death alongside the early production of the proinflammatory cytokine IL-32. We demonstrated that IL-32 produced by MVA-infected KCs induced modest but significant morphological changes in LCs and downregulation of adhesion molecules, such as epithelial cell adhesion molecule and very late antigen-4, and CXCL10 production. The treatment of KCs with IL-32-specific siRNA, and anti-IL-32 blocking antibody significantly inhibited LC activation, demonstrating the role of IL-32 in LC activation. We also found that some Toll-like receptor ligands induced a very high level of IL-32 production by KCs, which initiated LC activation. Conclusions We propose, for the first time, that IL-32 is a molecular link between KCs and LCs in healthy skin, provoking LC migration from the epidermis to the dermis prior to their migration to the draining lymph nodes. What's already known about this topic? • The shortening of dendrites in Langerhans cells (LCs), morphological changes and migration to the draining lymph nodes is a major step allowing for the initiation of adaptive immunity. • LC and keratinocyte interactions involve the regulation of adhesion molecule expression. • Keratinocytes produce interleukin (IL)-32 in pathological inflammatory disorders such as atopic dermatitis. 179, pp145-153 Pam3CSK4 and medium. Cells were washed prior to coculture with LCs. CXCL10 + producing LCs (ViViD À CD45 + CD1c + cells) were analysed at 24 h by flow cytometry. All data are represented using a box and whisker plot with median (min/max) for n = 6 donors. For comparisons of more than two groups, Friedman test was applied before one-tailed Wilcoxon matched paired signed-rank test. *P < 0Á05. PBS, phosphatebuffered saline (PBS).