In chicken fibroblast DF1 cells infected with IBV an M.O.I. of 1, moderate up-regulation of both Bak (1.39–2.09 fold) and Mcl-1 (1.14–1.30 fold) at the transcriptional level were also observed by RT-PCR analysis at 8 and 16 hours post-infection (Fig. 1B). The gene discussed is MCL1; the disease is infection.