ELISA results using concentrated media containing VCP from vaccinia virus-infected cells (A–D) or purified recombinant VCP (E–H). To determine specific vs. non-specific binding of VCP, microtiter wells were coated with C3b (open triangles and solid lines) or BSA and blocked with the following BSA preparations (solid triangles and dashed lines): BSA-7906 (A & E), BSA-2934 (B & F), BSA-3059 (C & G), or BSA-9430 (D & H). Data for BSA-7638 is not shown, but it gives identical results as BSA-3059, -A7906, and -A9430.