Cellular processes essential for African swine fever virus to infect and replicate in primary macrophages

The macrophage (Mø) is an essential immune cell for innate immunity. Such cells are targeted by African swine fever virus (ASFV). The early phases of infection with ASFV have been previously characterized in non-leukocyte cells such as Vero cells. Here, we report on several additional key parameters that ASFV utilizes during the infection of primary Mø. Related to virus infection, we established that receptor-mediated endocytosis of the virus by Mø is not the exclusive means of entry to infect the host cells. Analysis of the ensuing processes identified divalent cation-dependent activities to be particularly important, relating to the virus requirement for microtubule assembly needed for endocytic and endosomal processing. Actin-dependent endocytosis and endocytic flux involving microtubule activity are also implicated, pointing to entry via phagocytosis. Subsequently, the virus avoids terminal degradation by circumventing mature lysosome activities, including autophagosome-lysosome delivery. Nevertheless, the replicative cycle is apparently dependent on certain lysosomal functions, i.e. activities sensitive to propylamine are essential for the virus, whereas vinblastine- and leupeptin-sensitive functions only partially influence viral replication. The present work has identified cellular processes essential for ASFV to infect and replicate in the macrophage. These findings will improve our understanding of the cellular pathways employed by viruses infecting immune scavenger cells.