Cellular membrane factors are the major determinants of porcine reproductive and respiratory syndrome virus tropism.

The mechanism that restricts porcine reproductive and respiratory syndrome virus (PRRSV) replication in a variety of cell-lines has been investigated in this study. Using a virus binding assay, it was found that PRRSV could not bind to most cell-lines tested. However, vero cells, which are non-permissive to PRRSV infection, were able to bind and internalize a virus almost as efficiently as the permissive cell-line MARC-145. In addition, MARC-145 and vero cells internalized PRRSV in an infectious form, indicating that virus entry occurred by receptor mediated endocytosis. Polyethylene glycol (PEG)-mediated fusion of virus with cells induced the production of infectious virus from vero and MARC-145, but not from the others cells tested. Infectious virus was also recovered from vero and several other non-permissive cell types after transfection of viral RNA, indicating that the viral genome is infectious per se. Thus, absence of PRRSV binding to cells might be one major determinant of PRRSV cell tropism. However, because vero cells restricted PRRSV replication following virus binding and internalization but prior to RNA replication, it is possible that multiple viral and cellular components might be involved in allowing PRRSV replication on cells.