Mouse anti-IsdA serum enhances aLf killing in an IsdA-dependent manner. Different concentrations of sera were added to killing assay mixtures. (A) Symbols: •, Newman plus 0.5 μM aLf (P < 0.01); ▪, Newman plus 0.5 μM aLf plus anti-IsdA (1:100 dilution of antibody; P < 4 × 10−5); □, Newman plus 0.5 μM aLf plus anti-IsdA (1:1,000 dilution of antibody; P < 2 × 10−5). (B) Symbols: ×, SRC105 plus 0.5 μM aLf; ▴, SRC105 plus 0.5 μM aLf plus anti-IsdA (1:100 dilution of antibody); ▵, SRC105 plus 0.5 μM aLf plus anti-IsdA (1:1,000 dilution of antibody). The data for all three mixtures overlap extensively. The values are the means of three independent experiments.