The role of interleukin 6 in plasmacytomagenesis.

Interleukin 6 (IL-6) is a polyfunctional cytokine which regulates the immune response, the acute-phase reaction and haemopoiesis. IL-6 plays a critical role in differentiation of B cells into plasma cells, and is a potent growth factor for plasmacytomas and myelomas. A relationship between IL-6 and polyclonal plasma cell abnormalities has been demonstrated. Abnormal production of IL-6 was first suggested to be related to hypergammaglobulinaemia with autoantibody production in patients with cardiac myxoma. A role of IL-6 in the generation of plasmacytoma has also been indicated. In support of these clinical and experimental observations, we demonstrated that transgenic C57BL/6 mice carrying the human IL-6 gene showed a massive polyclonal plasmacytosis with production of autoantibodies. However, the tumour was not transplantable to syngeneic animals. Susceptibility to pristane-induced plasmacytomagenesis is genetically determined--pristane can induce plasmacytomas in BALB/c but not in C57BL/6 mice. IL-6 transgenic C57BL/6 mice were backcrossed to BALB/c mice to elucidate the genetic influence on plasmacytomagenesis. Transplantable monoclonal plasmacytoma with a t(12;15) chromosomal translocation was generated in some of the backcrossed mice, indicating that IL-6 plays a key role in the multistep oncogenesis of plasma cell neoplasia.