T Matsuda

Interleukin 6 (IL-6) has been suggested to be involved in the pathogenesis of polyclonal and monoclonal plasma cell abnormalities. To address this possibility, transgenic mice carrying the human IL-6 genomic gene fused with a human immunoglobulin heavy chain enhancer were generated. High concentrations of human IL-6 and polyclonal increase in IgG1 (120- to 400-fold) in sera of all transgenic mice were observed. A massive plasmacytosis in thymus, lymph node, and spleen and an infiltration of plasma cells in lung, liver, and kidney were observed. However, the plasma cells were not transplantable to syngeneic mice and were found not to contain chromosomal aberrations including c-myc gene rearrangements. The evidence indicates that deregulated gene expression of IL-6 can trigger polyclonal plasmacytosis but cannot induce plasmacytoma. It is suggested that additional genetic changes may be required for the generation of plasma cell neoplasia. Other interesting findings in these transgenic mice were the development of mesangio-proliferative glomerulonephritis and an increase in megakaryocytes in bone marrow.

Abstract Murine hybridomas producing monoclonal antibodies (mAb) specific to human interleukin 6 (IL6/BSF‐2) were established. One of these hybridomas (MH60.BSF2) was found to be dependent on IL6 for its in vitro growth. None of the known biological factors tested, such as recombinant (r) human (Hu) Illα, rHuILlα, rHuIL2, rHuIL3, rHuIL4, rHu interferon (1FN)‐γ, HuIFN‐β, rHuG‐CSF, or recombinant murine (Mu) IL3, MuIL4, rMuIL5, could induce the in vitro growth of MH60.BSF2 cells. The half‐maximum tritiated thymidine uptake by MH60.BSF2 cells could be achieved by picogram amounts of rIL 6, making this hybridoma clone an indicator cell for specific and sensitive detection of the IL6 activity in test samples. The MH166.BSF2 clone was found to produce IgG l ,χ type mAb (αBSF2‐166) capable of neutralizing IL6 activity. The other clone, MH60.BSF2, produced IgM,x type mAb (aBSF2‐60) unable to neutralize IL6 activity. Both mAb specifically reacted with IL6 as demonstrated by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and Western blotting analysis. An enzyme‐linked immunosorbent assay (ELISA) utilizing αBSF2‐166 and rabbit anti‐IL 6 antibodies was established which could detect as low as 50 pg/ml of IL6. Since both the ELISA and MH60.BSF2 hybridoma could detect small amounts of IL6 in biological fluids, they constitute powerful tools in exploring the presence or the role of IL6 in various immunological disorders.

The mechanisms through which pristane or mineral oil can induce plasmacytomas in BALB/c or NZB mice are not fully understood, but involvement of interleukin 6 (IL-6), a growth factor for plasmacytomas and myelomas, has been strongly suggested. To clarify the role of IL-6 in plasmacytomagenesis, a human IL-6 cDNA was introduced into mouse germ lines under the transcriptional control of the murine major histocompatibility complex class I (H-2Ld) promoter. IL-6 transgenic mice of C57BL/6 origin developed a massive plasmacytosis but not plasmacytomas. However, introduction of BALB/c genetic background into IL-6 transgenic mice could generate monoclonal transplantable plasmacytomas with the chromosomal translocation t(12;15). These results provide firm evidence of the critical role of IL-6 in the plasmacytoma development.