Characterization of African swine fever virus IAP homologue expression in porcine macrophages infected with different virulence isolates

Genes modulating apoptosis are encoded by many viruses and have an important role in viral evasion mechanisms. Our objective was to characterize the expression of the IAP homologue gene of African swine fever virus (ASFV), 4-CL, during in vitro infection of porcine macrophages, the preferential target cell for viral replication. Expression was compared along parallel infections by two naturally occurring ASFV isolates of different virulence: highly virulent ASFV/L60 (L60) and low virulent non-hemadsorbing ASFV/NH/P68 (NHV). Efficiency of macrophage infection by both isolates was similar, as observed both by the percentage of infected cells in culture and by virus progeny production. Our results showed that transcription of 4-CL initiates very early after infection with both isolates, since specific mRNAs were observed and quantified at 1.5 h post-infection (p.i.). However, the protein was produced later, from 4 to 8 h p.i., around the same time when viral DNA replication is reported to occur. 4-CL protein was more abundant in L60 than NHV infected cells, at both 8 and 16 h p.i. The mRNA levels, however, did not correlate with those of protein expression. Overall our results suggest the existence of a post-transcriptional step in the regulation of 4-CL gene expression.