Differential expression of interleukin-15, a pro-inflammatory cytokine and T-cell growth factor, and its receptor in human prostate.

BACKGROUND: Pro-inflammatory interleukin (IL)-15 plays a major role in host defense and chronic inflammation by stimulating T-lymphocyte recruitment and growth. Expression of IL-15 and IL-15 receptor (IL-15R) in human prostate was examined. METHODS: Normal and benign hyperplastic (BPH) prostate specimens (n = 23) were analyzed for IL-15 and IL-15Ralpha-chain expression by immunohistochemistry and Real-Time-PCR/RT-PCR. Regulation of prostatic stromal cell (PSC) IL-15 mRNA and effect of IL-15 on prostatic cell growth were analysed in vitro. RESULTS: In normal prostate, anti-IL-15 and anti-IL-15Ralpha-chain reactivity were restricted to smooth muscle and stromal cells. However, in BPH, in addition epithelial cells frequently exhibited discrete anti-IL-15R and often intense, membranous anti-IL-15 reactivity. IL-15/IL-15R mRNA were detected in all prostatic cells types. In BPH tissues, IL-15 mRNA content was variable (15-fold). IL-15 mRNA synthesis of PSC was significantly up-regulated by IFN-gamma. Furthermore IL-15 strongly stimulated the growth of BPH-T-lymphocytes and weakly that of carcinoma cell lines, but not of stromal cells. CONCLUSIONS: Overexpression of IL-15 and IL-15Ralpha-chain in BPH and massive proliferation of BPH-T-lymphocytes induced by IL-15 suggest a role for IL-15 in prostatic inflammation. Since IFN-gamma, a T-lymphocyte product, stimulates prostatic IL-15 production; chronic inflammation might be triggered by this paracrine loop.