INVOLVEMENT OF MEMBRANE-BOUND VIRAL GLYCOPROTEINS IN ADHESION OF PSEUDORABIES VIRUS-INFECTED CELLS

Cell-associated spread of pseudorabies virus (PrV) plays an important role in the pathogenesis of the disease. Besides the already known dir ect cell-to-cell spread of the virus in monolayers, adhesion and subse quent fusion of suspended PrV infected cells to monolayers of uninfect ed cells are thought to occur. To study the adhesion of PrV-infected c ells, an in vitro model was developed in SK-6 cells. Specific adhesion of PrV-infected cells to an uninfected monolayer started 5 h after in fection of the cells and reached a maximum 6 h later. A correlation wa s found between the surface expression of PrV glycoproteins on the inf ected cells and the adhesion of these cells. PrV hyperimmune serum com pletely inhibited binding of the infected cells. To investigate which PrV envelope glycoproteins were responsible for the cell adhesion, the infected cells were incubated with antisera against glycoproteins gII , gIII, and gp50. Antiserum against either gII or gIII inhibited cell adhesion, and antisera against gII and gIII together had a cooperative effect. Antiserum against gp50 had no effect on binding when used alo ne but enhanced the inhibition induced by gII and gIII antisera. Hepar in and neomycin inhibited adhesion, showing that the receptor for adhe sion was a heparinlike substance. SK-6 cells infected with a gIII dele tion mutant of PrV exhibited a much lower adhesion. This binding was h eparin and neomycin independent and was not blocked by anti-gII serum. Nevertheless, it was completely inhibited with PrV hyperimmune serum and with anti-gp50 serum. This finding demonstrates that the ligand fo r adhesion of gIII--infected cells is glycoprotein gp50. These results strongly suggest that the mechanism for adhesion of a PrV-infected ce ll to an uninfected monolayer is similar to the mechanism of adsorptio n and penetration of a PrV virion to a host cell.