Human and viral IL-6–induced DNA synthesis of INA-6 cells in the absence or presence of antibodies specific for hIL-6, hIL-6R (gp80), and gp130. A polyclonal antiserum was used for neutralization of IL-6 protein. Monoclonal antibodies 17506.1 and 28126.111 were used as IL-6R– and gp130-specific reagents. All antibodies were added at initiation of cultures at a final concentration of 10 μg/mL.