Newcastle disease virus infection of L cells

Modulation of splenic macrophages, and swine leukocyte antigen (SLA) and viral antigen expression following African swine fever virus (ASFV) inoculation

Expression of viral and major histocompatibility complex (MHC) antigens and localization of T cells and macrophages was studied in frozen tissue sections of spleens taken from normal pigs or from pigs inoculated with highly virulent Lisbon 60 (L60), or with moderately virulent Dominican Republic 1978 (DR-II), African swine fever virus (ASFV) isolates. Splenic sections from L60 inoculated pigs exhibited a large decrease in macrophage staining, whereas DR-II infected animals appeared more intensely stained in the macrophage sheath arteries. Class I and class II MHC expression was decreased in spleens from pigs infected with either isolate at 3 day post inoculation (DPI). This was reversed in DR-II inoculated pigs at 4 DPI. Splenic tissue sections from L60 inoculated pigs exhibited only a marginal increase in SLA expression at a later time, 6 DPI. We suggest that the recovery of SLA expression during infection of pigs with ASFV is associated with survival or replacement of macrophages in the spleen leading to an effective immune response against the virus.

Establishment and preliminary characterization of a cell line persistently infected with Newcastle disease virus

A murine osteosarcoma (OGS) cell line was permanently infected with Newcastle disease virus (NDV). The presence of NDV in the subsequent passages was demonstrated by haemadsorption and by immunofluorescence. Compared to the uninfected OGS line the persistently infected cells had a slightly reduced growth rate and they had a reduced sensitivity to several viruses, shown by several different methods. Interferon sensitivity was considerably reduced in the OGS-NDV cells, both the antiviral activity and the cell multiplication inhibitory activity.

Persistent viral infections as models for research in virus chemotherapy

The acute systemic virus infection is commonly used as an experimental model in chemotherapy research despite the fact that the chance for an effective chemotherapy of acute virus infections is small. In most acute infections, virus multiplication is well advanced before the disease is expressed and treatment will, in many cases, come too late. However, control by chemotherapy might be promising for persistent virus infections, where, owing to the slow progression of the disease, sufficient time for treatment is available. Although there are various ways in which viruses can persist in their hosts, comparative studies in vitro and in vivo reveal common features that shall be briefly reviewed. Animal models with persistent virus infections are usually difficult to experiment with because of the varying length of the incubation period brought about by the complex relationship among virus replication, immune reactions, and disease.

Virus-induced decrease of insulin receptors in cultured human cells

Viral infections may produce abnormalities in carbohydrate metabolism in normal subjects and profound changes in glucose homeostasis in insulin-dependent diabetics. Using an in vitro radio-receptor assay with 125I-labeled insulin and human-amnion (WISH) cells, the effect of viral infections on insulin receptors was examined. Both herpes simplex virus and vesicular stomatitis virus produced a 50% decrease in insulin binding. There was no evidence that this decrease was due to degradation of insulin. On quantitative analysis, this decrease in binding was found to be the result of a decrease in receptor concentration with no change in receptor affinity. The decrease in receptors occurred between 4 and 12 h, at the time viral antigens were being inserted into the plasma membrane of infected cells. Because the t 1/2 of insulin receptors in uninfected cells was between 14 and 24 h, the decrease in insulin receptors cannot be explained solely by virus-induced shut-off of macromolecular synthesis. Moreover, viruses such as encephalomyocarditis that do not insert new antigens into the plasma membrane, did not cause changes in the number of insulin receptors. The most likely explanation is that virus-induced changes in the plasma membrane altered or displaced insulin receptors. It is concluded that the insulin receptor assay is a sensitive and quantitative method for studying the effect of viral infections on cell membranes. These data also suggest that abnormalities in glucose metabolism associated with some viral infections may be due, in part, to changes in the concentration of insulin receptors.

Electron microscope study of cultured cells of the chorioallantoic membrane infected with representative paramyxoviruses

Chorioallantoic membrane (CAM) tissue cultures were found to be permissive for representative paramyxoviruses. The CAM cells can be used for plaque assay without the presence of trypsin. Ultrastructures of CAM cells infected with paramyxovirus Yucaipa (PMY), Sendai virus, and NDV were different. Nucleocapsids were readily seen in budding structures of cells infected with PMY, and in Sendai virus infected cells, large clusters of nucleocapsids were clearly evident in the cytoplasm. The site of glycoprotein cleavage does not have any effect on the nature of budding. It appears that a factor or factors in addition to the nature of the plasma membrane influences the morphology of cells infected with paramyxoviruses.

Cell-mediated immunity to mouse adenovirus infection. Blocking of macrophage migration inhibition and T cell-mediated cytolysis of infected cells by anti-S antigen or anti-alloantigen serum

Migration of peritoneal exudate cells (PEC), which were prepared from mice immunized against mouse adenovirus (M-Ad), was inhibited upon exposure to the antigenic extract of M-Ad-infected cells. This inhibition was shown to be blocked when infected cells or their extracts were pretreated with antiserum against M-Ad-induced cell surface (S) antigen(s) or with antisera against alloantigens of infected cells. Immune spleen cell-mediated cytolysis of M-Ad-infected cells was also blocked in the presence of anti-S, anti-alloantigen or anti-beta 2m serum. Immunofluorescent antibody staining of S antigen(s) was blocked when infected cells were pretreated with anti-alloantigen or anti-beta 2m serum, whereas it was not blocked when they were pretreated with anti-mouse immunoglobulin or anti-Thy-1.2 serum. Conversely, immunofluorescent antibody staining of alloantigens was blocked when infected cells were pretreated with anti-S serum. These findings indicate that S and alloantigens are associated with each other or at least located very close to each other.

Human histocompatibility determinants and virus antigens: effect of measles virus infection on HLA expression

Histocompatibility antigens on the surface of human lymphoblastoid cells were quantified by a microadsorption technique. During the course of measles virus infection, no quantitative or qualitations in surface HLA antigens were observed. In contrast, infection with poliovirus type 1 or vesicular stomatitis virus, or treatment with puromycin (50 microgram/ml) resulted in a significant decrease in surface HLA. These experiments suggest that an inhibition of host protein synthesis rather than the insertion of virus-specificied antigens into the membrane results in a net decrease in amounts of this cell surface antigen. The HLA antigens also appear to be both functionally and structurally distinct from measles virus surface antigens. Pretreatment of cells with HLA-directed antibody did not prevent the infection of these cells by measles virus, thus HLA antigens appear unrelated to the measles virus receptor site on the plasma membrane. Electron microscopic studies revealed that measles virus maturation occurs at membrane sites devoid of demonstrable HLA. Furthermore, HLA antigens could not be detected on the surfaces of mature infectious virions.

Inhibition of intracellular multiplication of adenovirus by interaction between infected and uninfected cells

The possibility that virus multiplication may be inhibited by interaction of infected cells with uninfected cells was tested by experiments, using human adenovirus type 12 (Ad12). Permissive human cells (human embryonic kidney-HEK,KB or HeLa) were infected and seeded on uninfected or infected "nonpermissive" cell (human embryonic lung=HEL) monolayers, and virus yields or proportions of viral antigen-synthesizing cells were compared with each other. Both the virus yields and the proportions of viral antigen-positive cells were not reduced significantly when seeded on infected HEL cells, while they seeded on uninfected HEL cells both of them were reduced remarkably, compared with the yield and the proportion of controls seeded on glass. Similar results were obtained regardless of the type of permissive cells, HEK, KB, or HeLa. Similar reduction of the yield was observed when seeded on HEL cells infected with Ad12 inactivated by heat or by antiserum, and partial reduction was observed when seeded on HEL cells infected with UV-inactivated Ad12, depending on the extent of UV dosis. These experiments showed that intracellular virus multiplication may be inhibited by interaction of infected cells with uninfected cells, and this may be due to the difference in the cell surface structure.

Interactions of vesicular stomatitis virus with murine cell surface antigens

The process of maturation of vesicular stomatitis virus (VSV) results in the loss of 70% of the H-2k antigenic activity from L-cell plasma membranes. This phenomenon is also demonstrated during VSV infection of cells of the H-2d haplotype. Using the method of inhibition of immune cytolysis, VSV-infected L5178Y tissue culture cells and VSV-infected METH A fibrosarcoma cells grown in vivo show a loss of H-2d activity of 73 and 76%, respectively. Using monospecific antisera, it is seen that VSV infection results in a significant loss of antigenic activity of the gene products of both the H-2D and H-2K regions in cells of the H-2d and H-2k haplotypes. In hybrid cells expressing H-2k as well as H-2b, VSV infection results in the decrease of both H-2 antigenic activities to the same extent. VSV purified from L cells shows considerable H-2k activity, but the reaction of this virus with anti-H-2k serum does not prevent a normal subsequent infection with this virus. VSV may associate with H-2 antigen in the culture medium, but the results of mixing VSV with uninfected H-2-containing homogenates suggest that this association occurs only when the host cell and the cell homogenate share the same H-2 haplotype. Velocity sedimentation of VSV, which would remove contaminating cellular membrane fragments, does not separate H-2 activity from VSV. H-2 activity is also stably associated with VSV throughout sequential sucrose gradient centrifugation steps. It is possible that H-2 antigen is a structural component of VSV grown in murine cells.

Persistent infection of tissue culture cells by RNA viruses

In this paper, the characteristics of cultured cells persistently infected with RNA viruses, other than leuko viruses are described. The roles that the host cell, interferon, virus mutants and defective interfering particles may play in the establishment and maintenance of persistent infection are discussed. It is proposed that the interaction of viruses with certain types of host cells can lead to persistent infection. The differences in virus-host interactions may be attributable to differences in membrane properties of various cells. Defective interfering particles may play a role in the establishment of persistent infections in cells which normally undergo lytic virus development. Mutant types of virus appear to be prominent in the virus released from persistently infected cells, but the role that various mutants play in the maintenance of persistent infections remains unclear.