We generated recombinant PSG1-Fc, which contains the same PSG1 domains as PSG1-FLAG but has a different tag at the C-terminus. The FLAG, V5, and His tags of PSG1-FLAG were replaced by the Fc tag, which consists of the mutated human IgG hinge domains, CH2 and CH3, from the pFuse-hIgG1e3-Fc1 vector. The recombinant protein has an approximate molecular mass of 70 kDa (Fig. 1, lane 2) . The FLAG-Fc protein (Fig. 1, lane 3) secreted from CHO was used as the control protein, as described in Materials and Methods.