Figure 3. HCT116 cells produce human Cp in vitro and in tumor xenografts. (A) WB with antibodies to human Cp. Lane M, molecular weight marker (prestained proteins, Fermentas, code SM0671). Lane 1, culture medium in which HCT116 cells were grown; lane 2, human serum (positive control); lane 3, bovine serum (negative control). The two WB panes are sections of a single blot. (B) Oxidase activity in human (H), rat (R), and murine (M) sera, o-dianisidine stain of a non-denaturing 8% PAGE, 1 μl of serum per lane; WB of the same samples with antibodies to human (C) and rat (D) Cp, 0.5 μl of serum per lane. Immune complexes were detected using a goat anti-rabbit IgG-conjugated peroxidase/α-naphthol assay. (E) Human Cp content as measured by dot-spot hybridization with [¹²⁵I]-mAB-hCp. One, human serum; 2, serum of HCT116-bearing nude mice (n = 6).