(A) Western blot analysis of monoclonal antibodies to recombinant N protein. Purified GST-N fusion protein was separated on the sodium dodecyl sulfate-10% polyacrylamide gel and transferred onto a nitrocellulose membrane. The strips were reacted with different anti-N protein monoclonal antibodies. Lanes 1 to 4: different monoclonal antibody clones (N1E8, N8E1, N10E4, and N10A4, respectively). (B and C) Western blot analysis of N protein in the culture filtrate of SARS-CoV. Culture filtrate from the Vero cells infected with SARS-CoV was concentrated and separated on the sodium dodecyl sulfate-10% polyacrylamide gel and transferred onto a nitrocellulose membrane. The strips were reacted with different anti-N protein monoclonal antibodies, control monoclonal antibodies and convalescent SARS patient sera, respectively. (B) Lanes 1 to 11, different monoclonal antibody clones (N1E8, N8E1, N10E4, N10A4, N14A3, N14E19, N14E7, N14E1, N14B6, N10E2, and N1A7, respectively); lanes 12 to 14, control monoclonal antibodies. (C) Lanes 1 to 12: 12 cases' sera; lane 13, normal serum control.