Specific binding of scFv-uPA fusion protein to cells expressing mouse PECAM. (A) FITC-streptavidin staining of REN/PECAM (left) versus control REN (right) cells after incubation with biotinylated anti-PECAM scFv-scuPA (original magnification × 40). (B) ELISA: binding of anti-PECAM scFv-uPA to REN/PECAM (•) versus REN (○) cells. (C) ELISA: inhibition of binding of fusion protein to REN/PECAM cells by parental anti-PECAM IgG mAb 390. Error bars indicate standard error of the mean (SEM).