Schematic diagram of the chimeric and scFv anti-Id–IL-2 fusion proteins. Solid and shaded areas represent light-chain and heavy-chain variable regions from an anti-Id mAb, S5A8. Open areas represent human γ1 and κ constant regions. Checkered regions represent the mature IL-2 sequence. (B) SDS-PAGE of S5A8 (lanes 1 and 5), chS5A8 (lanes 2 and 6), chS5A8–IL-2 (lanes 3 and 7), and scFvS5A8–IL-2 (lanes 4 and 8) under nonreducing (lanes 1 through 4) or reducing (lanes 5 through 8) conditions. The MW is determined by marker proteins. (C) Immunoblot analysis of the various anti-Id Abs. S5A8 (lanes 1 and 5), chS5A8 (lanes 2 and 6), chS5A8–IL-2 (lanes 3 and 7), and scFvS5A8–IL-2 (lanes 4 and 8) under nonreducing (lanes 1 through 4) or reducing (lanes 5 through 8) conditions were subjected to SDS-PAGE followed by electroblotting to nitrocellulose. Nitrocellulose strips were reacted with 38C13 Id (lanes 1 through 4) or rat antimouse IL-2 (lanes 5 through 8) and detected with horseradish peroxidase-conjugated second-step reagents.