Immunoblot analysis of cytoplasmic extracts from PLC/PRF/5 cells cultured with different concentrations of polyclonal anti-HBs IgG (HBIG). The cells were cultured in medium without human IgG (lanes 1), with 0.2 mg of HBIG/ml (lanes 2), with 1.0 mg of HBIG/ml (lanes 3), or with 2.0 mg of HBIG/ml (lanes 4). (a) Amido black staining of proteins. (b) Detection of human IgG. (c) Detection of HBsAg. INT, intensity of the chemiluminescence signal measured by FluorS MultiImager in arbitrary units. The arrows indicate the signals for the γ chain of IgG (50 kDa) and for both forms of HBsAg (24 and 27 kDA). LM, protein length marker.