Role of an immunosuppressive cytokine, interleukin-10, in the development of pyothorax-associated lymphoma.

Malignant lymphoma frequently develops in the pleural cavity of the patients with long-standing pyothorax. Thus, the term pyothorax-associated lymphoma (PAL) has been proposed for this type of tumor. Most of PALs are diffuse lymphoma of B cell type and contain Epstein-Barr virus (EBV) DNA. We have established two lymphoma cell lines from the biopsy specimens of PAL cases, OPL-1 and OPL-2. Both cell lines contain EBV DNA, but only OPL-1 expresses Epstein-Barr virus nuclear antigen 2 (EBNA2) that works as a target molecule for cell-mediated immune response. In this study, we examined the expression of immunosuppressive factors in OPLs. Only OPL-1, not OPL-2, expressed interleukin-10 (IL-10) mRNA and secreted IL-10 into culture supernatant. Both OPL-1 and OPL-2 expressed transforming growth factor (TGF) beta 1 mRNA, however, neither expressed latent TGF beta binding protein (LTBP) mRNA at detectable level by Northern blot analysis. Because TGF beta expresses its functions in cooperation with LTBP, the biological functions of TGF beta 1 could be negligible. Neither cell lines expressed EBV BCRF1 mRNA at detectable level, a viral gene product which is partly homologous to human IL-10 and shares biological activities of IL-10. Since OPL-1 shows weaker proliferative activity than OPL-2 and expresses viral antigens, the production of an immunosuppressive cytokine, IL-10, might contribute to the development of overt lymphoma. The present study suggested that immunosuppressive cytokine plays a role in lymphomagenesis of immunocompetent patients.