Immunolabeling for MHC class II or C3d on thawed Tokuyasu cryosections from Raji cells having been exposed to C3dg-gold10 for 120 minutes at 37°C.

(A, B) Class II molecules are labeled with mAb HLA-DR/CR43 (anti–β-chain) visualized by antimouse immunoglobulin coupled to 5-nm gold particles. Colocalization with internalized C3dg-gold10 (arrows) occurs in juxtanuclear endosomes; scale bar, 0.1 μm. (C) A certain amount of endocytosed C3dg-gold10 stains with rabbit antihuman C3d (visualized by antirabbit immunoglobulin coupled to 5-nm gold particles; arrowheads); scale bar, 0.2 μm. (D) C3dg-gold10 bound to cell surface protrusions readily stains with rabbit antihuman C3d (visualized as in Figure 3C); scale bar, 0.2 μm.