Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/1996
Publication Date: N/A
Citation: Interpretive Summary: Porcine reproductive and respiratory syndrome virus (PRRSV) is a new virus that recently emerged in the United States. The virus causes reproductive failure in pregnant sows and a flu-like syndrome in animals of all ages. Currently, the disease caused by this virus is a major concern for the pork industry. It has been difficult to isolate and characterize the virus, mainly because it does not replicate in most types of cells grown in laboratories. Our lab has been studying the interaction of this virus with cells in culture and the mechanism that it uses to enter and replicate in these cells. Thus, by recognizing the mechanism of virus infection of cells grown in the laboratory, we hope to improve our understanding of the mechanism by which the virus causes disease in the animal. In this report we identified some requirements of virus infection and means of blocking virus entry into the cells so that it can no longer replicate and destroy the cells.
Technical Abstract: The entry pathway of porcine reproductive and respiratory syndrome virus (PRRSV) entry into MARC-145 cells was investigated. The effect of lysosomotropic drugs, which raise the pH of intracellular vesicles, on PRRSV entry was assessed by measuring viral RNA replication and production of infectious virus. The production of infectious virus particles by chloroquine treated cells was reduced with increasing concentrations of this drug. In addition, the amount of viral RNA detected under the same conditions was reduced. Chloroquine and ammonium chloride inhibited virus replication when added to the cells prior to, at infection or soon after infection, with little or no effect when added at 30 min p.i. The effect of chloroquine on PRRSV replication was reversible under acidic conditions of the media, indicating that a low pH was required during virus entry. Electron microscopic data of the early stages of virus and cell interaction showed virus particles at the cell's surface or within small vesicles which were circumscribed by a clathrin-like zone. The effect of cytochalasin B and phenylarsine oxide, which inhibit endocytosis, was determined by fluorescent antibody staining of infected cells. The number of PRRSV-infected cells was decreased in the presence of cytochalasin B and phenylarsine oxide. Thus, we concluded that PRRSV entry might occur through a microfilament-dependent endocytic mechanism in which a low pH is necessary for proper virus uncoating.