FIG 7.

CO inhibits PRRSV intercellular spread. (A) Standard virus-neutralizing assay. Hyperimmune serum from a PRRSV-infected pig was serially diluted and incubated with the virus for 1 h at 37°C; the virus-antibody complex was then added to the MARC-145 cells. At 24 hpi, the cells were stained with 6D10, and fluorescence-positive cells were counted under the fluorescence microscope. The percentage of fluorescence-positive cells was calculated. (B) CO suppresses the intercellular spread of PRRSV. MARC-145 cells were infected with PRRSV at an MOI of 0.1. At 3 hpi, the negative serum, a 1:8 dilution of the hyperimmune serum, or a 1:8 dilution of the hyperimmune serum plus CORM-2 (150 μM) was added to the infected cells. At 24, 36, or 48 hpi, IFA was performed to detect the expression of N protein. (C) Virus titers of culture supernatants from the experiment described for panel B. The virus titer of culture supernatants was determined by TCID₅₀ assay. NS, negative-control serum from an uninfected pig; PS, hyperimmune serum from a PRRSV-infected pig.