CP1 strongly inhibits CH-1a infection and replication in Marc-145 cells. (A) Expression and purification of CP1 in P. pastoris. Lane 1 was the purified CP1 (3300 Da). Lane 2 was control. M was protein molecular weight marker. (B and D) Cells were infected with CH-1a (MOI =0.01) in the presence of different concentrations of CP1, YPD (control), or PBS for 36 h at 37°C. Cells were detected with IFA (B), and the viral yields were detected in the supernatants (D). (C) Cells were mock infected or infected with CH-1a (MOI =0.01) in the presence of CP1 (480 μg/ml) or YPD (control). A virus-produced CPE was observed with bright-field microscopy at 48, 72, and 96 hpi. (E) Potential cytotoxicity of CP1 against Marc-145 cells was detected with alamarBlue®. A series of concentrations of CP1 or YPD (control) was applied to 60%–70% confluent cells for 48 h, and then 10 μl of alamarBlue® was added for another 3 h. The data are the results of three independent experiments (means ± SE). Significant differences compared with the YPD-treated control group are denoted: *P <0.05, **P <0.01, or ***P <0.001.