Evidence of Programmed Death-Ligand 1 Expression in a Highly Inflammatory Prostate: A Literature Review and Our...

Chronic inflammation (CI), a common finding in the human prostate, is associated with the most frequent socially important prostate diseases: prostatitis, benign prostatic hyperplasia, and prostate adenocarcinoma. Programmed cell death protein 1 (PD-1) and its ligand (PD-L1) expression are induced on the surface of immune and epithelial cells of healthy and tumor tissues in response to various cytokines. Here, we provide a comprehensive review of the PD-1/PD-L1 pathway in the non- and peri-tumoral inflammatory prostate, focusing on the structure and expression of PD-L1 and the diverse biological functions of PD-L1 signaling in health, high-grade CI (National Institutes of Health, category IV prostatitis or histologic prostatitis), and immune-related diseases, including autoimmunity, tumor microenvironmental immunity, and immune privilege. This review explores the possible pathophysiological interpretations of clearly visible, selective, and strong PD-L1 expression in the immuno-inflammatory-induced and related, histologically distinct sites of this expression: the ductal lymphoepithelial lesions and prostatic granulomas.