Interleukin-6-mediated growth enhancement of cell lines derived from pyothorax-associated lymphoma

Malignant lymphomas frequently develop 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 PAL are diffuse large cell lymphoma of B cell type that contain Epstein-Barr virus DNA. We have established two lymphoma cell lines from the biopsy specimens of PAL cases, OPL-1 and OPL-2. Because PAL develop in the sites of chronic inflammation, inflammatory cytokines might be involved in the lymphomagenesis. To address this point, we examined the regulation of the growth of OPL by human IL-6. Human recombinant IL-6 enhanced the growth rate of OPL. OPL-1 responded to recombinant IL-6 by growing faster even at concentrations of less than 0.1 ng/ml, whereas OPL-2 required higher concentrations of recombinant IL-6. OPL expressed IL-6 receptor mRNA detectable by reverse transcriptase PCR analysis and IL-6 receptor on cell surface by flow cytometric analysis, using anti-IL-6 receptor antibodies. On the other hand, only OPL-1 showed expression of IL-6 mRNA, which was detectable only by reverse transcriptase PCR, and secreted IL-6 protein into the culture media. The culture supernatant of OPL-1 exhibited growth-enhancing effects on OPL-1 and OPL-2. The addition of anti-IL-6 antibodies to the cultures inhibited the growth of OPL-1 but not OPL-2. OPL-2 did not secrete IL-6 protein into the media, and the culture supernatant from OPL-2 did not enhance growth of OPL-2. These findings suggest the involvement of IL-6 in the growth regulation of OPL, i.e., an autocrine mechanism of IL-6-related proliferation in OPL-1 and a paracrine mechanism in OPL-2. IL-6 locally produced in chronic pyothorax might also promote the development of PAL.