Ultrastructural characteristics and morphogenesis of porcine reproductive and respiratory syndrome virus propagated in the highly permissive MARC-145 cell clone.

A Québec reference strain of PRRSV (IAF-KLOP) was successfully propagated in MARC-145 cells, a highly permissive cell clone to PRRSV derived from the MA-104 cell line. Purified extracellular virions appeared as pleomorphic but mostly spherical enveloped particles, 50-72 nm in diameter, with an isometric core about 25-30 nm. By indirect immunofluorescence, detection of viral antigens within the cytoplasm was possible as soon as 6 h.p.i. Nucleocapsids, budding at smooth endoplasmic reticulum (ER), and enveloped viral particles that tended to accumulate in the lumen of ER or Golgi vesicles, were the main features of the viral morphogenesis. The virus apparently was released by exocytosis.