Differential expression of interleukins IL-13 and IL-15 in normal ovarian tissue and ovarian carcinomas

Abstract

Objective. To determine the temporal and spatial expression of interleukins (IL)-13 and IL-15 in ovarian carcinoma compared to normal ovarian tissue.

Methods. Quantitative RT-PCR, ELISA and immunohistochemistry.

Results. Q-RT-PCR, ELISA and immunohistochemical analysis indicates that IL-13 and IL-15 mRNA and protein are expressed in normal ovary at various phases of the menstrual cycle with immunoreactive proteins detected in granulosa/theca and luteal cells and to a lesser extent in stromal cells and surface epithelial cells. Compared to normal ovary, ovarian carcinoma expresses elevated levels of IL-13 and IL-15 mRNA, with higher IL-13 expression in primary vs. metastatic tumors. IL-13 and IL-15 protein expression was also higher in the tumor tissues compared to ascites. In normal ovary, ovarian tumors and ascites, the ratio of IL-13/IL-15 favored IL-13. Immunoreactive IL-13 and IL-15 proteins were localized primarily in the tumor cells and infiltrated inflammatory cells with increased intensity with disease stage.

Conclusion. Normal ovary and ovarian tumors express IL-13 and IL-15 and pattern of their expression in carcinomas suggests that these cytokines may function in various ovarian cellular activities including inflammatory/immune responses that are integrated cellular events taking place in normal ovary and ovarian tumors.

Introduction

It is estimated that 80–90% of ovarian cancers are initiated by transformation of ovarian surface epithelial cells. During the early stage of the disease, the tumor's growth is confined to the ovaries, while in the advanced stages, tumor cells metastasize within the abdominal cavity (peritoneal lining, diaphragm and omentum), and through hematogenous and lymphatic routes to distant sites [1], [2], [3], [4], [5]. Advanced ovarian cancer is also associated with development of ascites. Molecular mechanisms responsible for initiation of ovarian epithelial cellular transformation, and their subsequent growth and metastasis are unknown. However, hormonal environment and repeated injury to the ovarian surface during ovulation are considered to increase the risk of developing epithelial ovarian cancer [1], [2], [3], [4], [5], [6], [7], [8], [9]. It is also well established that a coordinated inflammatory/immune reaction initiated as a result of natural host response to cancer, and following normal tissue injury, plays a key role in the development and progression of cancer and normal wound healing processes [6], [10], [11]. These processes are highly regulated by a network of growth factors, cytokines and chemokines, and their autocrine/paracrine actions can influence the outcome of tumor growth and metastasis, as well as tissue repair [10], [11], [12], [13], [14], [15].

The expression profile of many of these growth factors, cytokines and chemokines in several ovarian cell types, including surface epithelial cells, ovarian tumors, and resident tissue and peritoneal inflammatory/immune related cells are well documented [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. In the ovary, these cytokines regulate folliculogenesis, ovulation and steroid biosynthesis [16], [19]. Tumor-derived cytokines are considered to act as chemotactic factors for recruitment and activation of inflammatory/immune-related cells, and to regulate tumor cell growth, invasion and metastasis [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. Selective accumulation of inflammatory/immune cells and their secretory products in the peritoneal cavity of patients with ovarian cancer is also reported to influence the outcome of the disease.

Among the cytokines involved in the above processes are interleukins (IL), with pro- and anti-inflammatory/immune properties. The balance of IL production is critical to the outcome and maintenance of inflammatory and immune responses [12], [13]. IL-13 and IL-15 are novel members of the interleukin family with key regulatory functions in various normal cellular activities and many pathological disorders [20], [21]. IL-13 is expressed by various cells and tissues, with mast cells, T cells and activated basophils as its major sources. IL-13 and IL-13 receptor expression has been reported in head and neck cancer cells, glioblastoma, Hodgkin's lymphoma and other hematological malignancies, renal cell carcinoma, lung tumors, breast carcinoma, Kaposi's sarcoma and colon carcinoma [22], [23], [24], [25], [26], [27], [28], [29], [30], [31]. Specific biological functions associated with IL-13 include regulation of B-cell proliferation, IgG, IgE and MHC class II antigen expression, and inhibition of cytokine production by Th1 cells [20], [32]. IL-13 also acts as an anti-inflammatory cytokine, in part through differential regulation of pro-inflammatory cytokines such as IL-1β and TNF-α, and IL-1 receptor antagonist and IL-1 type II receptor expression [20], [33]. In addition, IL-13 has been shown to regulate steroid hormone production by normal mammary and prostatic epithelial cells in primary cultures and cancer cell lines [34], [35].

IL-15 is produced by a wide variety of cells and tissues and is considered a key regulator of local innate tissue inflammatory infiltrate and adaptive immunity [21], [36], [37], [38]. IL-15 promotes proliferation and survival of T and B lymphocytes, natural killer cells and neutrophils, and by regulating NK cell cytotoxic killing, IFN-γ and TNF-α production control local inflammatory and immune reactions [21], [36], [37], [38]. Altered expression of IL-15 is reported in several inflammatory and autoimmune disorders as well as in tumor cell lines which include lung and ovarian carcinomas, melanoma, leukemia, osteosarcoma and rhabdomyosarcoma cells [39], [40], [41], [42], [43].

Since IL-13 and IL-15 act as key regulators of inflammatory/immune responses, which are part of normal ovarian function and occur in ovarian cancer, we sought to assess their temporal and spatial expression in normal ovarian tissues at various stages of the menstrual cycle. In addition, we compared the profile of their expression in normal ovaries with that of ovarian cancer tissues from primary ovarian tumors and metastatic lesions and associated ascites.