PRODUCTION, CHARACTERIZATION AND REACTIVITY OF MONOCLONAL-ANTIBODIES TO PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS

This report describes the preparation of six monoclonal antibodies (MA bs) raised against a British isolate of porcine reproductive and respi ratory syndrome virus (PRRSV), their characterization in terms of prot ein specificity and their reactivity with different PRRS viruses from Europe and the USA. Radioimmunoprecipitation and Western blotting stud ies of MAb reactivity with proteins from cell lysates of infected cell s and purified virus revealed that four of the six MAbs (WBE1 and WBE4 -6) precipitated a 15 kDa viral protein. Further studies using in vitr o translated products of the Lelystad virus genome showed that this pr otein was the product of ORF7, the putative nucleocapsid protein. The specificity of another MAb, WBE2, was found to be for a 45 kDa protein , determined to be the product of ORF3 and demonstrated to be present in purified virion preparations. The protein specificity of the sixth MAb, WBE3 could not be determined. Thirty-three PRRSV isolates from Eu rope and the USA were grown in alveolar macrophages and examined by im munoperoxidase staining, using the panel of six MAbs. Ah European isol ates were recognized by the four MAbs specific for the putative nucleo capsid, but the viruses showed different patterns of reactivity with W BE2 and WBE3. Furthermore, these two MAbs stained only a small proport ion of the cells infected with certain isolates, suggesting that a sin gle isolate may be antigenically heterogeneous. No MAbs bound to US is olates, indicating a consistent antigenic difference between the putat ive nucleocapsid of US and European isolates. Detergent extraction of cell lysate antigen abrogated the binding of WBE1-3, suggesting that t he epitopes are conformation dependent.