Characterization of stable vIL-6 transfectants. (A) Western blotting with anti–vIL-6 peptide Ab of cell lysates from BCP-1 (lane 1); parental NIH3T3 (lane 2); NIH3T3 transfected with BCMGSneo-vIL-6 (lane 3); NIH3T3 transfected with BCMGSneo (lane 4); and conditioned media from NIH3T3 cells transfected with BCMGSneo-vIL-6 (lane 5) and with control BCMGSneo (lane 6). The conditioned media were concentrated 10-fold using Centriprep-10 (Amicon). (B) Representative vIL-6 staining by indirect immunofluorescence of vIL-6 (upper) and vector control (lower) transfectants. (C) B9 cell proliferative responses to serial dilutions of conditioned media from parental line NIH3T3 (x); vector controls BN5 (○); BN7 (•); and vIL-6 transfectant v6C (□); and v6H (▪), v6I (▵), and v6O (▴) clones. Each data point is the average (±SD) of six determinations. (D) Spontaneous proliferation of parental NIH3T3, vector control transfected BN7 clone, and vIL-6 transfected clones v6H and v6O. Cells (2,000 cells/well) were cultured for 72 hours in complete culture medium. The results reflect mean proliferation (±SD) of triplicate cultures.