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. 2023 Jan 26;14:1087532. doi: 10.3389/fimmu.2023.1087532

Figure 2.

Figure 2

IgG4 activates complement at high antigen densities and antibody concentrations. (A) C3b deposition induced by anti-biotin IgG1 and IgG4 antibodies on biotinylated human serum albumin (HSA; 30, 60, 120 and 240 μM biotin; corresponding to approximately 2, 4, 8 and 50 biotins per HSA molecule respectively), in the presence of 2.5% human serum. All antibodies were tested in a two-fold serial dilution starting from 10 µg/mL for IgG4 and 2 µg/mL for IgG1 antibodies in four independent assays. (B) The capacity of biotin-specific IgG1 and IgG4 antibodies to induce complement-mediated lysis (as percentage) of biotinylated human red blood cells at various antigen densities (0.25, 0.5, 1, and 2.5 mM biotin) in the presence of 10% human serum. All antibodies were tested in a two-fold serial dilution starting from 20 µg/mL for IgG4 and 10 µg/mL for IgG1 antibodies in triplicates. The data was normalized to a 100% lysis control (RBCs with saponin).