Antibody-induced endocytosis of viral glycoproteins and major histocompatibility complex class I on pseudorabies virus-infected monocytes.

Abstract

Purified porcine monocytes, the natural carrier cells of pseudorabies virus (PrV) in the pig, were inoculated in vitro with PrV. At different time-points post-inoculation (p.i.) (from 7 to 17 h p.i.), the cells were washed and incubated with fluorescein isothiocyanate-labelled porcine PrV-specific polyclonal antibodies (IgG) at 37 mC. At all time-points tested p.i., 1 h of antibody incubation induced passive patching and subsequent internalization of the plasma membrane-anchored viral glycoproteins in approximately 65 % of the infected monocytes. This endocytosis process is antibody-dependent, since biotinylated glycoproteins did not undergo spontaneous endocytosis. The process is fast and efficient, since only very low amounts of viral glycoproteins on the plasma membrane (7 h p.i.) and a minimal concentration of antibodies (0n04 mg IgG/ml) were needed to induce endocytosis. Experiments with PrV strains carrying deletions in the genes encoding the 11 different viral glycoproteins showed that viral glycoproteins gB and gD play a very important role in endocytosis (80 % reduction with deletion mutants, P 0n001), while the gE : gI Fc receptor complex, but not gE or gI alone, has a significant but lesser effect (45 % reduction, P 0n05). Double staining of viral glycoproteins and major histocompatibility complex class I (MHC I) showed a clear co-localization and co-endocytosis of MHC I with the viral glycoproteins, suggesting a possible role of the process in immune evasion of the virus.

Copatching and Lipid Raft Association of Different Viral Glycoproteins Expressed on the Surfaces of Pseudorabies Virus-Infected Cells

“…Earlier, we and others have shown that the interaction between PRV or HSV polyclonal serum antibodies and the viral proteins on the cell surface initiates intriguing, cell typedependent redistribution processes of the antibody-antigen complexes (8,10,39). Addition of polyclonal serum immunoglobulin G (IgG) to PRV-infected swine kidney (SK) cells or HSV-infected human embryonic lung fibroblasts (HEL cells) and human larynx epidermoid carcinoma (Hep-2) cells leads to aggregation of the viral cell surface proteins into patches, which subsequently polarize to one side of the cell to form a cap (10,39), sometimes followed by shedding of the caps (10).…”

“…Addition of polyclonal serum immunoglobulin G (IgG) to PRV-infected swine kidney (SK) cells or HSV-infected human embryonic lung fibroblasts (HEL cells) and human larynx epidermoid carcinoma (Hep-2) cells leads to aggregation of the viral cell surface proteins into patches, which subsequently polarize to one side of the cell to form a cap (10,39), sometimes followed by shedding of the caps (10). In PRV-infected blood monocytes, on the other hand, patches of viral cell surface proteins are rapidly internalized and do not cap (8). The exact function of these processes is not fully understood, although there are strong indications that they may be important for alphaherpesviruses to enhance virus survival in the face of an antibody response.…”

“…In both PRV-and HSV-infected cells, efficient capping has been shown to depend on the presence of viral protein gE, whereas internalization has been demonstrated to be initiated mainly by viral proteins gB and gD and to a lesser extent gE (8,10,39). Exactly how these viral proteins initiate the redistribution processes is not fully understood, but it has been shown that tyrosine-based amino acid motifs in the cytoplasmic tails of PRV gB and gE are of crucial importance for internalization and capping, respectively (7,9).…”

“…Interestingly, the addition of PRV-or HSV-specific serum antibodies does not result in exclusive capping or internalization of the viral proteins that initiate these processes but also results in that of the other viral cell surface proteins that are recognized by the immune serum (8,10,39). One explanation for this massive change in surface viral glycoprotein distribution initiated by single or a few viral proteins may be that (some of) the major viral envelope proteins that are present on the surfaces of PRV-or HSV-infected cells are somehow linked, allowing one or a few viral proteins to initiate lateral movement of many, if not all, of the viral proteins in the cell surface.…”

Cell biological and molecular characteristics of pseudorabies virus infections in cell cultures and in pigs with emphasis on the respiratory tract

“…Such attachment has already been described between PrVinfected monocytes and endothelial cells [67]. PrV-infected monocytes that have been exposed to virus-specific antibodies internalize their viral glycoproteins together with their MHCI molecules, leaving cells that are masked from efficient recognition and elimination by different components of the immune system [11,68]. These immune-masked monocytes have been shown to adhere specifically to endothelial cells by the cellular adhesion molecules wCD11R3 and CD18.…”