Establishment and characterization of a new human mesothelioma cell line (T‐85) from malignant peritoneal mesothelioma with remarkable thrombocytosis

A mesothelioma cell line, termed T‐85, was established from a patient with malignant peritoneal mesothelioma and remarkable thrombocytosis (1.4 × 106/mm3). Electron microscopically, two types of mesothelioma cells have been characterized; the major type of cells with dense‐cored granules in the cytoplasm and the minor one with evenly dense granules. Immunologically, the cells showed staining for inter‐leukin‐6 (IL‐6), cytokeratin, collagen type IV, vimentin, laminin, fibronectin and Factor VIII‐related antigen. Quanti‐tation by ELISA revealed a high concentration of IL‐6 in T‐85 cell culture supernatants. RT‐polymerase chain reaction of T‐85 cells showed two positive bands of cDNA at 628 and 251 base pairs indicating the constitutive expression of IL‐6 and IL‐6 receptor mRNA. Moreover, prominent pro‐platelet process formation activity in T‐85 cell culture supernatants indicated the presence of a thrombopoietic activity due mainly to IL‐6 but not the c‐MpI ligand or erythropoietin. However, the fact that 15% of PPF activity remained in the supernatants treated with anti‐IL‐6 antibody indicated the presence of another thrombopoietic substance. T‐85 is so far the first mesothelioma cell line derived from a case with remarkable thrombocytosis.