Antigen binding of chimeric antibodies.

Saturating concentrations of chimeric IgA1, IgA2, and IgG1 isotypes of HLA class II antibody F3.3 demonstrated similar binding to HLA class II–transfected L66 cells, as measured by indirect immunofluorescence (panel A; 1 of 2 experiments with similar results is shown). In order to estimate antibody affinity, dilutions of chimeric antibodies were investigated for antigen binding, and antibody concentrations at half-maximal binding were determined (panel B; mean ± SEM for each of 3 experiments is displayed). Thus, IgG1, IgA2, and IgA1 demonstrated half-maximal binding at 1.8 μg/mL (X, Y) and 3.5 μg/mL (Z), respectively. FITC-labeled antihuman kappa–light chain antibody was used for staining.