A) Comparison of binding of respective soluble scFv against H1N1pdm and sH1N1 particles by ELISA. To compare the binding ability of soluble scFv against purified H1N1pdm NP, ELISA was performed against each immobilized antigen in duplicate. N.C. represents negative control (soluble scFv against rabies virus phosphoprotein). P. C. indicates positive control (serum of H1N1pdm-infected ferret). Values are mean ± SE; N = 2. B) Identification of the target protein of scFv No. 29 by immunoprecipitation and SDS-PAGE. The lysates of H1N1pdm/sH1N1-infected and mock-infected MDCK cells were immunoprecipitated with soluble scFv No. 29 followed by SDS-PAGE analysis and silver staining. Lysate origins include H1N1pdm-infected cells (P), sH1N1-infected cells (S), and mock-infected cells (Mo). C1 and C2 indicate negative control reactions; only the lysate of mock-infected cells (C1) and the soluble scFv fluid (C2) were subjected to magnetic beads before following the same procedure as described for the other samples. ‘MW’ indicates a protein molecular weight marker. Filled arrow corresponds to the 56 kDa protein, presumably NP. Empty arrow denotes soluble scFvs. Other bands were considered to be non-specific binding of unrelated proteins.