Updated project metadata. The functions of human testicular peritubular cells (HTPCs), which form a small compartment located between the seminiferous epithelium and the interstitials areas of the testis, go beyond intratesticular sperm transport and include immunological roles. The expression of the glucocorticoid receptor (GR/NR3C1) by these cells indicates that they are a target of glucocorticoids (GCs), yet detailed insights into consequences of GC actions are unknown. To address this point, we studied cultured HTPCs, which serve as a window into the human testis. We used a cytokine profiler assay to screen for changes in secreted cytokines upon dexamethasone (Dex) treatment and employed qPCR and ELISA studies to verify the results. Dex, used in a therapeutic concentration, decreased proinflammatory factors, including IL6, IL8, MCP1 and CXCL1 within 24 - 48 h. An siRNA-mediated knockdown of GR reduced these actions. Exposure to Dex resulted in reduced GR levels, implying that exposure to Dex could also reduce anti-inflammatory actions of Dex. To evaluate the influence of Dex on HTPCs further, we performed a proteomic analysis of cellular components and secreted proteins. Strong responses were detectable after 24 h (31 significantly altered cellular proteins) and more pronounced ones after 72 h (30 less abundant and 42 more abundant cellular proteins). Dex also altered the composition of the secretome (33 proteins decreased, 13 increased) after 72 h. Among the regulated proteins were ECM- and basement membrane components (e.g. FBLN2, COL1A2, COL3A1), as well as PTX3 and StAR. These results reveal that Dex via GR exerts profound actions in HTPCs. If transferrable to the human testis, changes specifically in ECM and the immunological state of the testis may result in men upon treatment with Dex for medical reasons. -Proteome Data Subset 72 h-