Analysis of L. lactis strains expressing VP3. Proteins from log-phase growing cultures were fractionated and analyzed by Western blotting with 9.7 anti-VP3 monoclonal antibodies. spUsp45, signal peptide from the Usp45 preprotein; cwaM6, cell wall anchor domain from the M6 preprotein; PP, protoplast; CW, cell wall; SN, supernatant; IBDV, purified IBDV. The positions of full-length VP3 and molecular mass standards (kilodaltons) are indicated.