To obtain the whole IgG described in this study, the BD BaculoGold System (BD Biosciences Pharmingen, San Diego, CA, USA) was used. Briefly, nucleotide sequences codifying heavy and light chains of PN-SIA28 Fab fragment were sub-cloned into the baculovirus expression vector pAc-k-Fc (PROGEN Biotechnik GmbH, Heidelberg, Germany). Sf solution containing the antibody was dialyzed against PBS and then concentrated using Amicon Ultra-15 Centrifugal Filter Devices (Millipore, Billerica, MA, USA). Antibody concentration was determined by SDS-PAGE gel and by spectrophotometric measurement at 280 nm.