Figure 2. Fab-mediated effector functions were not impaired by the d471 mutation. (A) Binding of 225-IgA2-wt and –d471 to EGFR-expressing A431 cells was analyzed by indirect immunofluorescence analyses using anti-human kappa light chain directed secondary antibody. (B) Blocking of EGF binding was detected by FACS analyses treating A431 cells simultaneously with FITC-labeled EGF and excess of specific or nonspecific antibodies. (C) DiFi colon carcinoma cells were incubated with IgA2 antibodies for 72 h before viability was measured by MTS assay. Results are shown as “mean ± SEM” of “EGFR binding [RFI]” (A), “inhibition of EGF binding [%]” (B) and “cell viability [%]” (C) of five different experiments. Significant differences (p ≤ 0.001) between EGFR-specific and non-specific (control IgA2) antibodies are indicated by *, between mutant and wild type IgA2 by #.