IL-18 expression in clinical human pituitary adenoma

Background: IL-18 is known as an interferon-inducing factor that belongs to the IL-1 family, and is synthesized as an inactive precursor protein.

Objective: The present study aims to investigate the expression of IL-18, IL-18R, R and IL-18 binding protein (BP) mRNA in various types of human pituitary tumors, such as adrenocorticotropic hormone (ACTH), growth hormone (GH), prolactin (PRL), thyroid stimulating hormone (TSH)-producing adenomas and non-function adenomas.

Methods: Pituitary adenoma tissues were obtained during the surgery of 41 patients: nine patients had ACTH-producing pituitary adenomas, nine patients had GH-producing pituitary adenomas, five patients had TSH-producing pituitary adenomas, seven patients had PRL-producing pituitary adenomas, and 11 patients had non-functioning adenomas. The mRNA expression levels of IL-18, IL-18BP, IL-18R and IL-18R were quantified using real-time quantitative PCR.

Results: The mRNA expression of IL-18 was significantly higher in ACTH-, GH- and PRL-producing adenomas, when compared to non-function tumors. Similarly, a significantly higher mRNA expression of IL-18BP and IL-18R was observed in ACTH-, GH- and PRL-producing adenomas, when compared with non-functional adenomas. In contrast, no upregulation of IL-18R mRNA was observed in any of the pituitary adenomas.

Conclusions: The mRNA levels of IL-18, IL-18BP and IL-18R are significantly elevated in clinical pituitary tumors, such as ACTH-, GH- and PRL-producing adenomas, when compared to non-functional adenomas. These present results suggest the possibility that IL-18 may be involved in the pathogenesis of pituitary adenoma.