Design and expression of mbaIL6. (A) Schema of the mbaIL6 construct. (B) mbaIL6 and GFP expression in Jurkat cells transduced with either GFP alone (“Control”) or GFP plus mbaIL6, labeled with biotin-conjugated goat anti-human F(ab′)2 and streptavidin-APC. (C) IL-6 binding of control or mbaIL6-transduced Jurkat cells, labeled with IL-6 biotin and streptavidin-APC. Soybean trypsin inhibitor (STI)–biotin was used as a labeling control. (D) Control or mbaIL6-transduced Jurkat cells were labeled with IL-6 biotin and streptavidin-APC; confocal images were captured with a 60× objective lens. (E) Log10 molecules of equivalent APC (MEAPC) and log10 mean fluorescence intensity (MFI) were plotted on a standard curve constructed using allophycocyanin calibration particles (ACP-30-5K). Using the MFI of IL-6–biotin bound to mbaIL6 in the transduced Jurkat cells, the average number of receptors per cell was estimated as follows: log MFI of mbaIL6, 5.27956; log molecules of equivalent APC, 4.321 by intrapolation; yielding 10^4.321 = 20 941 mbaIL6 receptors per cell. VH, variable heavy chain; VL, variable light chain.