Complement resistance is distal to C1q binding.

DHL-4 and NCEB-1 are sensitive and resistant, respectively, to rituximab-induced complement. This figure demonstrates flow cytometry following staining with C1q-FITC on the x-axis and PI on the y-axis in cells treated with rituximab alone (A and C), or rituximab and human serum (B and D). (A) DHL-4 control cells: 0.1% bind C1q and 2.1% undergo lysis. (B) DHL-4 cells treated with rituximab and human serum: 84% bind C1q and 44% undergo lysis. (C) NCEB-1 control cells: 0.1% bind C1q and 4.4% undergo lysis. (D) NCEB-1 cells treated with rituximab and human serum: 73% bind C1q and 8% undergo lysis. In contrast to DHL-4 cells, the resistant NCEB-1 cell line binds C1q, but cells do not undergo lysis.