Cover photograph: Functional interleukin-17 receptors (IL-17RS) are expressed on various cell types. Upon interaction with the host microbiota, T helper lymphocytes release IL-17, which affects healthy and neoplastic epithelial cells, eosinophils (Eos), dendritic cells (DC), endothelial cells, stromal cells, macrophages (MØ), healthy and neoplastic plasma cells (PC), osteoclasts (OC), and neutrophils or myeloid-derived suppressor cells (CD11b), eventually propelling immune-mediated inflammatory diseases (IMID) and cancer. Therefore, Th17 cells represent the missing link between host microbiota and IMIDs and cancer. (See related article in June 2020, vol. 84, no. 2, e00064-19.) (Copyright © 2020 American Society for Microbiology. All Rights Reserved.)