Expression of GM-CSF by rHuN4-GM-CSF. Cells were infected at a multiplicity of infection (MOI) of 1 with viruses and incubated for 24 hours before analysis. (A) The virus-infected MARC-145 cells were fixed and tested by IFA to determine the expression of PRRSV N protein and porcine GM-CSF. Original Magnification 200×. (B) Western blot detection of GM-CSF in the supernatant fraction (sup) or cell lysates (cell lys) of MARC-145 cells infected with viruses.