Production and regulation of interleukin 6 in human B lymphoid cells

Abstract

Human B cell lines were screened for production of interleukin 6 (IL 6) by the B9 hybridoma cell bioassay. Some long‐established lines such as RPMI 1788, CESS and recently established early‐passage Epstein‐Barr virus (EBV)‐transformed lymphoblastoid lines were constitutive IL 6 producers. Other long‐established lymphoblastoid lines such as RPMI 8866 and SKW6.4 and all Burkitt lymphomalines tested were nonproducers of IL 6. Constitutive production of IL 6 in early passage lines could be enhanced by the phorbol ester phorbol 12‐myristate 13‐acetate (PMA) and recombinant (r)IL 4 but not by rIL 1α or rIL 1β. Nonproducing EBV‐transformed lymphoblastoid cell lines could be induced to IL 6 production by PMA, rIL 1α, IL 1β and IL 4. Amongthe nonproducing lines SKW6.4 was induced to IL 6 production by PMA, rIL 1α, rIL 1β and rIL 4, whereas RPMI 8866 was induced only by PMA, to a limited extent by rIL 1α and rIL 1β but not at all by rIL 4. There was no induction of IL 6 by any recombinant cytokine in the two Burkitt lymphoma lines but measurable production of IL 6 was induced by PMA in one of them (EB4). Cytokines which wereneither enhancers nor inducers of cell lines on their own included rIL 2, rIL 5, interferon (rIFN)‐γ, native purified IFN‐α, tumor necrosis factor (rTNF)‐α, rTNF‐β and purified platelet‐derived transforming growth factor‐β. rIL 4 synergized with either rIL 1α or rIL 1β in the induction of IL 6 in the nonproducing line SKW6.4. Similar effects were also seen in this line with combinations of (a) rIFN‐γ and rIL 4 and (b) IFN‐α and both rIL 1α and rIL 1β. rIL 4, with or without rIL 1, was more effective than rIL 6 in the induction of IgM synthesis in SKW6.4 and the effect was only partially inhibited by anti‐IL 6antiserum at a dose which totally inhibited IL 6‐induced IgM production. Normal peripheral blood lymphocyte populations pre‐activated by anti‐immunoglobulin rosetting exhibited enhanced production of IL 6 in the presence of rIL 4 and PMA but not in the presence of rIL 1, in contrast to the behavior of adherent mononuclear blood cells which showed IL 4‐induced down‐regulation of IL 6 production. Human B lymphoblastoid cell‐derived IL 6 was shown by Western blotting (using a polyvalent goat antiserum) to be composed of at least three distinct bands between 21 and 30 kDa, andboth constitutively produced and induced activities were neutralized by the same antiserum. The finding that human B cell lines differ in their constitutive and inducible productionof IL 6, a cytokine implicated in both the growth and differentiation of these cells, is discussed with respect to its possible role as an autocrine factor.