Dynein is a minus-end-directed microtubule-associated motor protein involved in cargo transport in the cytoplasm. African swine fever virus (ASFV), a large DNA virus, hijacks the microtubule motor complex cellular transport machinery during virus infection of the cell through direct binding of virus protein p54 to the light chain of cytoplasmic dynein (LC8). Interaction of p54 and LC8 occurs both in vitro and in cells, and the two proteins colocalize at the microtubular organizing center during viral infection. p50/dynamitin, a dominant-negative inhibitor of dynein-dynactin function, impeded ASFV infection, suggesting an essential role for dynein during virus infection. A 13-amino-acid domain of p54 was sufficient for binding to LC8, an SQT motif within this domain being critical for this binding. Direct binding of a viral structural protein to LC8, a small molecule of the dynein motor complex, could constitute a molecular mechanism for microtubulemediated virus transport.

We have analyzed the production of tumor necrosis factor alpha (TNF-α) induced by in vitro infection with African swine fever (ASF) virus (ASFV) and the systemic and local release of this inflammatory cytokine upon in vivo infection. An early increase in TNF-α mRNA expression was detected in ASFV-infected alveolar macrophages, and high levels of TNF-α protein were detected by ELISA in culture supernatants from these cells. When animals were experimentally infected with a virulent isolate (E-75), enhanced TNF-α expression in mainly affected organs correlated with viral protein expression. Finally, elevated levels of TNF-α were detected in serum, corresponding to the onset of clinical signs. TNF-α has been reported to be critically involved in the pathogenesis of major clinical events in ASF, such as intravascular coagulation, tissue injury, apoptosis, and shock. In the present study, TNF-α containing supernatants from ASFV-infected cultures induced apoptosis in uninfected lymphocytes; this effect was partially abrogated by preincubation with an anti-TNF-α specific antibody. These results suggest a relevant role for TNF-α in the pathogenesis of ASF.