Protein cell receptors mediate the saturable interaction of African swine fever virus attachment protein p12 with the surface of permissive cells.

Previous studies have demonstrated that the entry of African swine fever virus (ASFV) into Vero cells and swine macrophages is mediated by saturable binding sites located on the plasma membrane. The ASFV protein p12 has been implicated in virus attachment to the host cell, but the cellular component responsible for the interaction with the virus is largely unknown. We have studied the binding of recombinant p12 and ASFV to different cell lines. Permissive cells were able to bind p12 in saturable and nonsaturable interactions, as reported for ASFV. Experiments of binding recombinant p12 have been used for the initial characterization of the specific receptors on Vero cells. The treatment of cell surfaces with different enzymes and lectins resulted in the inhibition of the p12 binding activity by several proteases, but not by glycosidases or lipase, suggesting that the receptor is composed of protein, with no carbohydrates or lipids involved in the virus attachment to the cellular membrane. The recovery of receptor activity after pronase treatment was completed in 6 h in culture medium containing tunicamycin, and could not be restored in the presence of cycloheximide, confirming that synthesis of new proteins, but not glycosylation, was required for the recovery of the receptor activity. These data support the idea that membrane protein(s) on the surface of permissive cells act as receptors for ASFV and that this specific interaction is, at least, one necessary step in a productive virus infection.