Expression of IL-18, IL-18 binding protein, and IL-18 receptor by normal and cancerous human ovarian tissues: possible implication of IL-18 in the pathogenesis of ovarian carcinoma

Abstract

Proinflammatory cytokine IL-18 has been shown to be elevated in the sera of ovarian carcinoma patients. The aim of the study was to examine the levels and cellular origin of IL-18, IL-18 binding protein, and IL-18 receptor in normal and cancerous ovarian tissues. Ovarian tissue samples were examined by immunohistochemical staining for IL-18, IL-18BP, and IL-18R and mRNA of these cytokines was analyzed with semiquantitative PT-PCR. IL-18 levels were significantly higher in cancerous ovarian tissues (P = 0.0007), IL-18BP levels were significantly higher in normal ovarian tissues (P = 0.04), and the ratio of IL-18/IL-18BP was significantly higher in cancerous ovarian tissues (P = 0.036). Cancerous ovarian tissues expressed significantly higher IL-18 mRNA levels (P = 0.025), while there was no difference in the expression of IL-18BP mRNA and IL-18R mRNA between cancerous and normal ovarian tissues. IL-18 and IL-18BP were expressed dominantly in the epithelial cells of both cancerous and normal ovarian tissues, while IL-18R was expressed dominantly in the epithelial cells of cancerous ovarian tissues but expressed similarly in the epithelial and stromal cells of normal cancerous tissues. This study indicates a possible role of IL-18, IL-18BP, and IL-18R in the pathogenesis of epithelial ovarian carcinoma.

Figure 1

IL-18 and IL-18BP protein levels in normal and cancerous ovarian tissue homogenates. Normal and cancerous ovarian samples were homogenized. IL-18 (a) and IL-18BP (b) protein levels were evaluated by specific ELISA kits. Levels are expressed as pg/μg protein; each point represents one of the positive samples; n = 28 (normal) and 24 (carcinoma) in (a) and 18 (normal) and 10 (carcinoma) in (b). Horizontal lines indicate MEAN ± SEM. ∗/∗∗∗ indicates statistical significance according to t-test: *P = 0.04; ***P = 0.0007.

Figure 2

IL-18, IL-18BP, and IL-18R mRNA levels in normal and cancerous ovarian homogenates. Normal and cancerous ovarian samples were homogenized. The expression levels of IL-18 (a), IL-18BP (b), and IL-18R (c) mRNA were evaluated by semiquantitative RT-PCR. Quantitative evaluation of the positive PCR products was performed by densitometry. Each point represents the ratio between IL-18, IL-18BP, or IL-18R bands and β-actin bands of the same sample; n = 13 and 10 in (a), 12 and 10 in (b), and 10 and 7 in (c), for the normal and carcinoma samples, respectively. Horizontal lines indicate MEAN ± SEM. (d) Representative samples of normal (1–4) and cancerous (5–8) ovarian tissues are presented. ∗ indicates statistical significance according to t-test: *P = 0.025.

Figure 3

Immunohistochemical staining of normal and cancerous ovarian tissues for IL-18, IL-18R, and IL-18BP. Immunohistochemical staining of normal ((a), (f), (k)) and different types of cancerous ovarian tissues: serous papillary ((b), (g), (l)), mucinous ((c), (h), (m)), and endometrioid ((d), (i), (n)) with mouse anti-human IL-18 ((a)–(d)), mouse anti-human IL-18R ((f)–(i)), and goat anti-human IL-18BP ((k)–(n)) antibodies. Both normal (j) and cancerous ((e), (o)) tissues were used as negative control. EP: epithelial cells and S: stroma. Magnification: ×600.