Apoptosis in porcine macrophages infected in vitro with African swine fever virus (ASFV) strains with different virulence.

African swine fever virus (ASFV) replicates in porcine macrophages. Since modulation of cell death by ASFV strains of different virulence is poorly understood, we studied the development of apoptosis in porcine macrophage cultures during in vitro infection with the high- and low-virulence isolates ASFV/L60 (L60) and ASFV/NH/P68 (NHV), respectively. In cultures inoculated with each isolate, similar numbers of cells hosting infection showed morphological signs of apoptosis, which were visible from a relatively early time of infection (8 h), although a significant proportion of the infected cell populations remained non-apoptotic until 18 h. L60 inhibited caspase-3 activation by 18 h after infection and induced less DNA internucleosomic fragmentation at 8 h than NHV. However, at the late infection time, apoptosis levels were similar in both infections and occurred, at least partially, independently of caspases, suggesting the existence of yet unknown alternative pathways committing ASFV host cells to apoptotic death.