Vaccinia virus antigens on the plasma membrane of infected cells. I. Viral antigens transferred from infecting virus particles and synthesized after infection

The vaccinia virus A4OR gene product is a nonstructural, type II membrane glycoprotein that is expressed at the cell surface

Gene A40R from vaccinia virus (VV) strain Western Reserve has been characterized. The open reading frame (ORF) was predicted to encode a 159 amino acid, 18152 Da protein with amino acid similarity to C-type animal lectins and to the VV A34R protein, a component of extracellular enveloped virus (EEV). Northern blotting and S1 nuclease mapping showed that gene A40R is transcribed early during infection from a position 12 nucleotides upstream of the ORF, producing a transcript of approximately 600 nucleotides. Rabbit anti-sera were raised against bacterial fusion proteins containing parts of the A40R protein. These were used to identify an 18 kDa primary translation product and N- and O-glycosylated forms of 28, 35 and 38 kDa. The A40R proteins were detected early during infection, formed higher molecular mass complexes under non-reducing conditions and were present on the cell surface but absent from virions. The proteins partitioned with integral membrane proteins in Triton X-114. Canine pancreatic microsomal membranes protected in vitro-translated A40R from proteinase K digestion, suggesting the A40R protein has type II membrane topology. A mutant virus with the A40R gene disrupted after amino acid 50, so as to remove the entire lectin-like domain, and a revertant virus were constructed. Disruption of the A40R gene did not affect virus plaque size, in vitro growth rate and titre, EEV formation, or virus virulence in a murine intranasal model.

Flow cytometric analysis of African swine fever virus-induced plasma membrane proteins and their humoral immune response in infected pigs

African swine fever (ASF) virus-induced plasma membrane proteins may contribute to the protective immune response against the disease since they can be involved in the antibody-mediated lysis of infected cells. In this study we describe the regulation of ASF virus-induced plasma membrane protein expression and its antibody induction in pigs after viral infection by flow cytometric analysis. More than 80% of infected cells contained viral antigens on the surface membranes at 6 hr postinfection (hpi), and the relative amount of viral antigen expression was increased at 12 and 20 hpi. The kinetics of individual viral protein expression on cell surfaces was studied by a collection of monospecific antibodies directed against the six viral plasma membrane proteins p12, p15, p16, p23.5, p30, and p35. Most of these proteins were expressed at 6 hpi, with the exception of p35, which was first detected at 12 hpi. The percentage of cells expressing each antigen at different hpi was also determined. The immune response against virus-induced plasma membrane proteins in pigs infected with an attenuated ASF virus strain was studied. Antibodies against viral epitopes exposed on plasma membranes reached a plateau at 20 days postinfection (dpi). The relative amount of antibodies induced during infection with these specificities was not directly related to the antibody titer of the sera. Sera obtained at 20 and 40 dpi contained antibodies against most of the viral plasma membrane proteins and were most efficient in recognition of viral antigens exposed on the surface of infected cells at early times.

Poxvirus pathogenesis

Poxviruses are a highly successful family of pathogens, with variola virus, the causative agent of smallpox, being the most notable member. Poxviruses are unique among animal viruses in several respects. First, owing to the cytoplasmic site of virus replication, the virus encodes many enzymes required either for macromolecular precursor pool regulation or for biosynthetic processes. Second, these viruses have a very complex morphogenesis, which involves the de novo synthesis of virus-specific membranes and inclusion bodies. Third, and perhaps most surprising of all, the genomes of these viruses encode many proteins which interact with host processes at both the cellular and systemic levels. For example, a viral homolog of epidermal growth factor is active in vaccinia virus infections of cultured cells, rabbits, and mice. At least five virus proteins with homology to the serine protease inhibitor family have been identified and one, a 38-kDa protein encoded by cowpox virus, is thought to block a host pathway for generating a chemotactic substance. Finally, a protein which has homology with complement components interferes with the activation of the classical complement pathway. Poxviruses infect their hosts by all possible routes: through the skin by mechanical means (e.g., molluscum contagiosum infections of humans), via the respiratory tract (e.g., variola virus infections of humans), or by the oral route (e.g., ectromelia virus infection of the mouse). Poxvirus infections, in general, are acute, with no strong evidence for latent, persistent, or chronic infections. They can be localized or systemic. Ectromelia virus infection of the laboratory mouse can be systemic but inapparent with no mortality and little morbidity, or highly lethal with death in 10 days. On the other hand, molluscum contagiosum virus replicates only in the stratum spinosum of the human epidermis, with little or no involvement of the dermis, and does not spread systemically from the site of infection. The host response to infection is progressive and multifactorial. Early in the infection process, interferons, the alternative pathway of complement activation, inflammatory cells, and natural killer cells may contribute to slowing the spread of the infection. The cell-mediated response involving learned cytotoxic T lymphocytes and delayed-type hypersensitivity components appears to be the most important in recovery from infection. A significant role for specific antiviral antibody and antibody-dependent cell-mediated cytotoxicity has yet to be demonstrated in recovery from a primary infection, but these responses are thought to be important in preventing reinfection.

Immunotherapy of the rat 13762SC mammary adenocarcinoma by vaccinia virus augmentation of tumor immunity

We studied whether vaccinia virus (VV) functioned as an immunogenic carrier in augmenting anti-tumor immunity in rats bearing a syngeneic metastatic tumor. The primary tumor was induced by injecting 10(6) 13762SC mammary adenocarcinoma cells subcutaneously into the right hind footpad of Fischer 344 rats. A concomitant anti-tumor response is induced by the tumor as demonstrated by the inhibited growth of a second tumor challenge given in the contralateral footpad 3-15 days later. Attempts were made to increase the concomitant immunity by injecting tumor-bearing animals intramuscularly with irradiated, VV-infected or uninfected 13762SC cells without adjuvant. Provided the immunotherapy was done within 5 days of the tumor challenge, administration of 10(6)-10(7) irradiated, VV-infected 13762SC cells resulted in significantly slower tumor growth, or led to complete tumor regression, compared to control animals given no treatment. In contrast, tumor growth in animals given only VV or given irradiated, uninfected 13762SC cells, alone or mixed with VV, was the same as that in control animals. Kinetics of early primary tumor growth were predictive of a longer-term anti-tumor effect. Rechallenge of 13762SC tumor-cured animals with either the homologous or with a heterologous syngeneic mammary adenocarcinoma showed the animals to be specifically 13762SC tumor-resistant, since only rats challenged with the heterologous mammary adenocarcinoma developed progressive tumors. We interpret these results to mean that early immunotherapy with irradiated, VV-infected 13762SC cells enhances an on-going anti-tumor immune response sufficiently to cause rejection of the primary tumor and any metastases that have occurred. We also believe that later immunotherapy with irradiated, VV-infected cells has no effect due to tumor-induced immunosuppression becoming paramount.

The immune response to vaccinia virus infection in mice: analysis of the role of antibody

Immune response to primary intraperitoneal infection with vaccinia virus (strain IHD-J) was studied in C3H/Hej mice. Antibodies reactive with virus structural proteins were detected 6 days and neutralizing antibodies 8 days after infection. Although serum antibodies from infected mice bound to vaccinia virus infected cells, these antibodies were ineffective in complement mediated lysis of infected cells and were only moderately active in experiments with antibody dependent cellular cytotoxicity (ADCC). Immunoblotting analysis showed that serum antibody reacted with a number of structural proteins of both intracellular and extracellular forms of vaccinia virus. Immunoprecipitation results showed antibody binding of nonstructural proteins and glycoproteins. Correlation of the kinetics of NK and CTL activities in infected mice with neutralizing antibodies indicated that the cellular functions clearly precede the appearance of serum neutralizing antibody. The resolution of primary infection in mice thus appears to be mediated by functions of cellular immunity while resistance to reinfection may be dependent on circulating neutralizing antibody.

A 14,000-Mr envelope protein of vaccinia virus is involved in cell fusion and forms covalently linked trimers

A monoclonal antibody, MAbC3, that reacts with a 14,000-molecular-weight envelope protein (14K protein) of vaccinia virus completely inhibited virus-induced cell fusion during infection. Immunoblot and immunofluorescence studies revealed that the 14K protein was synthesized at about 6 to 7 h postinfection and transported from the cytoplasm to the cell surface. Synthesis and transport of the 14K protein during infection occurred in the presence of rifampin, an inhibitor of virus maturation. One- and two-dimensional gel electrophoretic analyses demonstrated that the 14K protein forms largely trimers (42K) that are covalently linked by disulfide bonds. The facts that MAbC3 prevents virus uncoating and blocks virus-induced cell fusion but does not prevent virus attachment to cells and the 14K envelope protein forms trimers all suggest that this protein plays major role in virus penetration.

Vaccinia virus proteins on the plasma membranes of infected cells. IV. Studies employing L cells infected with ultraviolet-irradiated vaccinia virions

As measured by in vitro, 51Cr-release assays, the expression on plasma membranes of two, immediate-early, vaccinia virus-specified cell-surface antigens, with mol wt of 25K-27K and 16K-17K, could be directly correlated with the susceptibility of target cells to lysis by vaccinia virus-specific cytotoxic T cells.

Identification of antigenic determinants by polyclonal and hybridoma antibodies induced during the course of infection by vaccinia virus

In order to extend the understanding of determinants involved in the humoral response in the infected host, mice were subjected to an immunization regimen using both active and uv-killed vaccinia virus. The spectrum of antibody specificity in hyperimmune sera was followed by Western blotting. Comparable studies involving Western blotting and immunofluorescence were conducted with a panel of monoclonal antibodies derived from hybridomas selected from similarly immunized animals. Hyperimmune sera contained circulating antibodies primarily against three polypeptides of 28K, 35K, and 62K. These antigens were shown to be located both at the surface and within the virion. The repertoire of monoclonal antibodies included some that reacted with the 28K and 35K antigens and others that recognized a 32K core complex component or a nonvirion cell surface component, corresponding to the viral hemagglutinin. Within the panel of monoclonal antibodies was a large group which reacted with a 32K antigen found in the IHD-J virion but absent from the IHD-W strain. This finding correlates with the absence of a 32K polypeptide from the IHD-W particle. Overall, the current findings reveal the absence of any particular correlation between the incidence of polyclonal antibodies in the circulation of the immune host and the frequency of selected hybridomas against vaccinia antigens. Application of this type of immunological analysis should provide useful data concerning the detection and mapping of the antigens and their epitopes which are significant for humoral immunity.

Vaccinia virus proteins on the plasma membrane of infected cells. III. Infection of peritoneal macrophages

Primary macrophage cultures were prepared from the peritoneal exudate cell population harvested from mice challenged intraperitoneally with saline, thioglycollate, or vaccinia virus. Vaccinia virus was adsorbed and penetrated into primary macrophages and L-cells with similar kinetics. As evidenced by the expression of some "early" virus-specified proteins, partial uncoating and activation of the virion-associated DNA-dependent RNA polymerase occurred in the infected macrophages. Subsequently, the viral replication cycle in macrophages was aborted; with time after infection, viral DNA and virion proteins initially associated with infected cells could be detected in an acid-soluble form in the medium harvested from infected macrophage cultures. The results suggest that at the time that the final stages of virus uncoating should have occurred, intracellular subviral particles were, instead, degraded in the infected, primary macrophages. Viral DNA synthesis could not be measured in vaccinia virus-infected macrophages, no "late" virus functions were expressed, and progeny virions were not assembled. As measured by the binding of antiviral-antibody-125I-protein A complexes to the surface of vaccinia virus-infected cells, the expression of virus-specified antigens on the surfaces of infected macrophages was significantly reduced and never exceeded that measured at 2 hr after infection on the surfaces of infected L-cells. The expression of virus-specified polypeptides with mol mass of 48-50, 45-46, 36-37, and 25 kDa on the plasma membranes of vaccinia virus-infected, thioglycollate-elicited macrophages, rendered the infected macrophages susceptible to lysis by vaccinia virus-specific cytotoxic T-cells.

Vaccinia virus proteins on the plasma membranes of infected cells. II. Expression of viral antigens and killing of infected cells by vaccinia virus-specific cytotoxic T cells

Evidence is presented that virion-derived antigens as well as viral antigens expressed on cell surfaces after infection, may participate in the formation of "target-antigen complexes" (TACs) which render vaccinia virus-infected cells susceptible to recognition and killing by syngeneic, vaccinia virus-specific cytotoxic T cells (VV-CTLs). By employing L cells infected with trypsin-treated and untreated virions, evidence was obtained that proteins with molecular weights of 32K and 37K may be among the virion-derived antigens which participate in TAC formation. Following virus infection, a sequential expression of virus-specified antigens on the plasma membrane of infected cells could be detected. At 1 hr p.i., polypeptides with molecular weights of 48K-50K and 36K-37K were present on infected cell surfaces; by 2 hr p.i., polypeptides with molecular weights of 48K-50K, 42K-44K, 36K-37K, 29K-30K, and 16K-17K were detected on plasma membranes. As measured by in vitro, 51Cr-release assays, vaccinia virus-infected L cells were completely susceptible to lysis by VV-CTLs (greater than or equal to 50% measured specific lysis) when (a) "early" but not late viral functions were expressed as measured with virus-infected cells which had been treated with hydroxyurea (5 X 10(-3) M) to block DNA replication or (b) when active protein synthesis was allowed to proceed for 90 min postadsorption and the infected cells were then treated with cycloheximide (100 micrograms/ml) to block further protein synthesis. Under these experimental conditions, polypeptides with molecular weights of 58K, 48K-50K, 42K, 36K-37K, 34K, 32K-33K, 27K-29K, and 16K-17K were expressed on the plasma membranes of vaccinia virus-infected cells but not uninfected cells. Whether each of the virion-derived and (or) virus-encoded polypeptides can associate with Class I, major histocompatibility antigens on the surfaces of virus-infected cells to form a primary or cross-reacting TAC recognized by VV-CTLs remains to be investigated.