OCCURRENCE AND ROLE OF AN EARLY ANTIGEN AND EVIDENCE FOR TRANSFORMINGABILITY OF PORCINE CIRCOVIRUS

By means of indirect immunofluorescence assay (IFA) using natural swin e immune serum and hyperimmune serum from rabbits infected with porcin e circovirus (PCV), a PCV antigen was detected present prior to the on set of viral and cellular DNA synthesis in nucleoli of cells of synchr onized and growth stimulated infected PS cell cultures grown for more than 12 h in the presence of hydroxyurea. The number of cells containi ng specifically fluorescing nucleoli increased with increasing time of growth in the presence of hydroxyurea. The concomitant increase in th e number of cells containing virus structural (VS) antigen in the nucl ei and the increase in the amount of replicative (RF) DNA and accompan ying 5 S DNA after release from the hydroxyurea block suggest that EA is involved in induction of PCV DNA replication. Primary pig kidney ce ll cultures persistently infected with PCV survived mock-infected cont rol cultures for 16 passages. They had lost contact inhibition and for med cell colonies in soft agar at a ratio of 0.1 to 0.4%. Cell lines d erived from agar colonies showed properties of transformed cells e.g. low requirement for serum growth factors, ability to overgrow a contin uous cell layer, anchorage independence of growth. In transformed cell s stimulated to growth and grown in the presence of hydroxyurea, non-s tructural viral antigen visible by IFA in nucleoli and VS antigen loca ted in the cytoplasm were expressed. Contrary to virus bound nuclear V S antigen in productive infection, accumulation of cytoplasmatic VS an tigen was independent of DNA synthesis and caused cell destruction, th us limiting growth of cell layers and colonies in soft agar.