Dose response curves for IFN-β-1b (Betaseron), IFN-β-1b prepared by us (BBT IFN-β-1b), and representative IFN-β-1b cysteine analogs and PEGylated cysteine analogs for inhibiting in vitro proliferation of human Daudi B cells. Daudi cells were incubated with serial dilutions of the indicated test proteins and incubated for 4 days at 37°C in a tissue culture incubator. On day 4, cell number was quantified using Cell-Titer AqueousOne solution. Absorbance on the Y-axis is proportional to cell number. (A) Compares in vitro bioactivities of IFN-β-1b (Betaseron), BBT IFN-β-1b, and the T112C protein. (B) Compares IFN-β-1b (Betaseron), N25C, and 5 kDa-PEG-N25C. (C) Compares F111C and F111C modified with 20 kDa-, 30 kDa-, and 40 kDa-PEGs. Data are means±SD of triplicate wells for each protein dilution. SD generally were <10% of the means.