(A) Conditioned medium containing AP, AP-PGRN, AP-Grn D, or AP-Grn E were incubated with COS-7 cells transfected with PSAP fused to PDGFR. Cells were fixed and AP binding was visualized with AP substrates. Scale bar=100μm. (B) AP–PGRN binding to PSAP-PDGFR expressing COS-7 cells measured as a function of AP–PGRN concentration. (C-E) Scatchard plot of AP-PGRN (C), AP-GRN D (D) or AP-GRN E (E) binding to PSAP-PDGFR expressing COS-7 cells. KD, mean ± sem, n = 4.