Monoclonal antibody directed against a membranous protein of MARC-145 cells blocks infection by PRRSV.

Abstract

In its natural host, infection by the porcine reproductive and respiratory syndrome virus (PRRSV) is restricted to cells of the macrophage/monocyte lineage and testicular germ cells (Plagemann 1996; Sur et al., 1996). In vitro, only cell subclones derived from the established monkey kidney epithelial cell line MA-104, such as MARC-145 and CL2621, and primary cultures of porcine alveolar macrophages (PAMs) efficiently replicated the porcine arterivirus (Bautista et al., 1993). Factors implicated in this restricted tropism have not yet been elucidated, but PRRSV enters in PAMs and in MARC-145 cells through a mechanism of receptor-mediated endocytosis (Kreutz and Ackermann, 1996; Nauwynck et al., 1999). Recently, a 210 kDa protein has been proposed as a putative receptor for PRRSV on PAMs, since a MAb directed against this protein blocked virus infection of PAMs (Duan et al., 1998). However, this MAb failed to react with MARC-145 and porcine monocytes, suggesting that PRRSV may enter in these cells by interacting with other cellular proteins. MAbs to Gp4 and Gp5 enveloped glycoproteins of PRRSV neutralize viral infectivity, but the viral structural protein responsible for viral attachment is still to be identified (Meulenberg et al., 1997; Pirzadeh and Dea, 1997). In this study, the capacity of PRRSV to attach and infect different cell lines was first determined. Subsequently, two MAbs directed against a 60 to 66 kDa membranous protein of MARC-145 cells were found to interfere with viral infection, thus representing a putative receptor or co-receptor for PRRSV.