title: Expression of interleukin-18 by nasopharyngeal carcinoma cells: a factor that possibly initiates the massive leukocyte infiltration.
abstract: Interleukin-18 (IL-18) is a single-chain cytokine that is produced by various cells. With interleukin-12 (IL-12), it synergistically stimulates activated T cells and natural killer (NK) cells to produce interferon-gamma (IFN-gamma). Nasopharyngeal carcinoma (NPC) is the most common form of nasal and nasopharyngeal malignancy, and in NPC tumor tissues there is an intense leukocyte infiltration comprising predominantly T cells and macrophages. We previously showed an increased expression of IFN-gamma in the infiltrating T cells. To identify the cells that provide IL-12 and IL-18 for stimulating the expression of IFN-gamma in activated T cells, NPC cell lines CNE-2 and HK-1, as well as biopsies obtained from NPC and control individuals, were examined. CNE-2 and HK-1 cells were found to express messenger RNA encoding IL-18, but not IL-12. Secreted IL-18 was detected in the culture supernatant. Addition of a caspase-1 inhibitor decreased the secretion level, indicating that this IL-18 secretion was caspase-1 dependent. Moreover, the in vitro IL-18 production in NPC cell lines correlated with the NPC tumor cells in situ. NPC tumor cells in the biopsies produced IL-18, as detected by immunohistochemistry and immunofluorescent double staining. In contrast, IL-18 expression was not observed in the control biopsies. We suggest that IL-18 secreted by NPC tumor cells plays a role in initiating the leukocyte infiltration process. IL-18 stimulates T cells and NK cells to produce IFN-gamma, which consequently activates macrophages and other immune cells to secrete chemokines to start a leukocyte recruitment cascade.
authors.affiliation: Department of Microbiology, Faculty of Medicine, National University Medical Institute, National University of Singapore, Singapore, Singapore.
authors.forename: Huaizhong
authors.initials: H
authors.lastname: Hu
authors.forename: Kin Fai
authors.initials: KF
authors.lastname: Tang
authors.forename: Yen Ni
authors.initials: YN
authors.lastname: Chua
authors.forename: Jinhua
authors.initials: J
authors.lastname: Lu
authors.forename: Ping
authors.initials: P
authors.lastname: Feng
authors.forename: Chuan Tieh
authors.initials: CT
authors.lastname: Chew
authors.forename: Soh Ha
authors.initials: SH
authors.lastname: Chan
mesh_terms: D020170:Caspase 1 / Q000378:metabolism; D045744:Cell Line, Tumor; D002465:Cell Movement; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007150:Immunohistochemistry; D020382:Interleukin-18 / Q000096:biosynthesis*; D007962:Leukocytes / Q000378:metabolism*; D009303:Nasopharyngeal Neoplasms / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D004791:Enzyme Inhibitors; D020382:Interleukin-18; D020170:Caspase 1