Pattern of Fab Staining of Osteosarcoma Cells and TissueFurther analysis of Fab reactivity was addressed by comparing the ability of the antibody fragments to bind to monolayers of osteosarcoma cells and normal fibroblasts by cell surface ELISA. Figure 4 shows the confirmation that the purified Fabs recognized a protein present in both kinds of cells (tumor and normal human fibroblast).