Mice 269 kidneys. (A) Mouse 269 no. 3, kidney, light microscopy, HES staining (original magnification × 200): glomeruli without abnormalities, tubular casts are large with fracture lines, tubular lumen are enlarged. (B) Mouse 269 no. 8, kidney, immunofluorescence microscopy, antihuman κ conjugate (original magnification × 500): numerous reabsorptive granules in the cytoplasm of proximal tubular cells with a pattern different from that noted in Fig 3 upper right quadrant. (C) Immunofluorescence microscopy, antihuman κ LC conjugate: strong staining of a cast in 1 tubular lumen. Note fracture lines in cast. Tubular basement membranes are unstained. Staining for human λ LC and mouse Igs were negative. (D) Electron microscopy (original magnification × 10,000): osmiophilic myeloma cast without crystalline substructure.