The present invention relates to a new polynucleotide that encodes a polypeptide involved in cellular entrance of PRRSV, to a recombinant vector comprising said polynucleotide, to a cell capable of expressing said polypeptide, a method of producing said polypeptide as well as to cell culture and to a novel method of producing the PRRSV virus. The present invention further relates to a method of identifying compounds that affect the PRRSV receptor function of the polypeptide as well as to the use of the polypeptide or identified compounds in the manufacture of medicaments. The present inventors have succeeded in isolating a protein from PAM membranes that seems to play a crucial role in virus entry into the cell. The elucidated nucleotide sequence encoding the protein, as well as the amino acid sequence of the protein, were compared with sequences stored in sequence databases. Surprisingly the putative PRRSV receptor provided by the present invention showed a great deal of homology to certain proteins belonging to the Siglec family.