Sulfation is required for elastic fiber formation. Indirect immunofluorescence for matrix proteins deposited by untreated (A, C, E, and G) and chlorate-treated (B, D, F, and H) FBCs demonstrates that sulfation is required for the assembly of elastic fibers by these cells. (A and B) MAGP-1; (C and D) fibrillin; (E and F) tropoelastin; (G and H) fibronectin.