A sensitive, specific immunobioassay for quantitation of human interleukin 6.

Picogram quantities of human interleukin 6 (h-IL-6) were detected by a two-step method. A microtiter plate coated with anti-h IL-6 monoclonal antibody was used to capture the IL-6 present in biological samples. An IL-6- dependent B cell line (7TD1) that proliferates in response to IL-6 was added to the captured IL-6. The lower limit of detection for this immunobioassay with serum or cell culture supernatants was 5 pg/ml. The specificity of the assay was achieved by the antibody used in the first step. The sensitivity was provided by the IL-6-dependent cell line. The method also allows for the removal of inhibitors, metabolites, antagonists or activating agents used to induce IL-6. This immunobioassay has the advantage over other current methods in that it measures immunoactive as well as biologically active IL-6.