Glycosylation of minor envelope glycoproteins of porcine reproductive and respiratory syndrome virus in infectious virus recovery, receptor interaction, and immune response

The role of N-glycosylation of the three minor envelope glycoproteins (GP2, GP3, and GP4) of porcine reproductive and respiratory syndrome virus (PRRSV) on infectious virus production, interactions with the receptor CD163, and neutralizing antibody production in infected pigs was examined. By mutation of the glycosylation sites in these proteins, the studies show that glycan addition at N184 of GP2, N42, N50 and N131 of GP3 is necessary for infectious virus production. Although single-site mutants of GP4 led to infectious virus production, mutation of any two sites in GP4 was lethal. Furthermore, the glycosylation of GP2 and GP4 was important for efficient interaction with CD163. Unlike PRRSVs encoding hypoglycosylated form of GP5 that induced significantly higher levels of neutralizing antibodies in infected piglets, PRRSVs encoding hypoglycosylated forms of GP2, GP3 or GP4 did not. These studies reveal the importance of glycosylation of these minor GPs in the biology of PRRSV.