Characterization of virus replication in splenocytes. (A) Virus titration of culture supernatants from virus-infected splenocytes using plaque formation test in CEF. (B) Analysis of viral M gene transcription profiles using qRT-PCR. The transcription levels of viral M gene were normalized to those of β-actin gene in the corresponding sample. Asterisk (*) indicates significant difference at p < 0.05 (n = 3) between experimental groups.