Special Issue "Viral Evasion or Suppression of Host Immunity".

Viruses have evolved to survive in hosts, presumably by devising meticulous strategies to elude or suppress host immunity [...].

Postentry restriction of Mason-Pfizer monkey virus in mouse cells.

UNLABELLED: Mason-Pfizer monkey virus (M-PMV) is a prototypical betaretrovirus responsible for simian AIDS (SAIDS) in rhesus macaques. It has been shown previously that mouse cells are resistant to infection by HIV-1 and other primate lentiviruses. However, the susceptibility of mouse cells to primate retroviruses such as M-PMV remains unexplored. In the present study, using single-round green fluorescent protein (GFP) reporter viruses, we showed that various mouse cell lines are unable to support the early stages of M-PMV replication. The block to infection occurs postentry and is independent of the viral envelope. Using quantitative real-time PCR, we showed that the block to infection occurs after reverse transcription but before formation of circular DNA or proviral DNA. Finally, we showed that the M-PMV block in mouse cells is not attributable to the previously characterized mouse restriction factor Fv1. Overall, these findings suggest that mouse cells exhibit a previously uncharacterized block to M-PMV infection. IMPORTANCE: Here we document a novel postentry restriction to M-PMV infection in mouse cells. The block occurs after reverse transcription but before the formation of circular or proviral DNA and is independent of the previous characterized mouse restriction factor Fv1.

Antibodies to retroviruses in recent onset psychosis and multi-episode schizophrenia.

BACKGROUND: Immunological abnormalities involving the upregulation of endogenous retroviruses have been associated with schizophrenia in small studies. METHODS: Blood samples from 666 individuals (163 with recent onset psychosis, 268 with multi-episode schizophrenia, and 235 controls) were assayed for IgG antibodies to murine leukemia virus (MuLV), Mason-Pfizer monkey virus (MPMV), and feline immunodeficiency virus (FIV) by enzyme immunoassay utilizing whole virus and viral components. Antibody levels in the psychiatric groups were compared to controls by multivariate linear regression. Odds ratios associated with increased antibody levels were calculated based on values ≥ 75th percentile of the controls. Samples were also tested for antibodies to viral proteins by Western blotting and for DNA from infectious retroviruses by real time PCR. Homology between the target virus and the prototype human genome was determined using sequence analysis methods. RESULTS: Compared with controls, individuals with recent onset of psychosis had increased levels of antibodies to MPMV and MuLV (both p<.001 adjusted for covariates), and increased antibody levels for defined portions of the MPMV and MuLV gag, pol and env proteins. The specificity of these antibodies was confirmed by Western blotting. Individuals with multi-episode schizophrenia did not show elevated antibody levels to any of the retroviruses measured. Infectious retroviruses were not detected in the blood of any participants. Homology analyses indicated that there are multiple regions of the human genome homologous with MPMV and MuLV proteins, the highest being with the MuLV gag protein. CONCLUSIONS: Antibodies to retroviral proteins are elevated in individuals with recent onset psychosis but not in individuals with multi-episode schizophrenia. The immunopathological consequences of this antibody response should be the subject of additional studies.

Vesicular stomatitis virus-simian retrovirus type 2 vaccine protects macaques from detectable infection and B-cell destruction.

Natural infection with simian retrovirus (SRV) has long been recognized in rhesus macaques (RMs) and may result in an AIDS-like disease. Importantly, SRV infections persist as a problem in recently imported macaques. Therefore, there is a clear need to control SRV spread in macaque colonies. We developed a recombinant vesicular stomatitis virus (VSV)-SRV vaccine consisting of replication-competent hybrid VSVs that express SRV gag and env in separate vectors. The goal of this study was to assess the immunogenicity and protective efficacy of the VSV-SRV serotype 2 vaccine prime-boost approach in RMs. The VSV-SRV vector (expressing either SRV gag or env) vaccines were intranasally administered in 4 RMs, followed by a boost 1 month after the first vaccination. Four RMs served as controls and received the VSV vector alone. Two months after the boost, all animals were intravenously challenged with SRV-2 and monitored for 90 days. After the SRV-2 challenge, all four controls became infected, and viral loads (VLs) ranged from 10(6) to 10(8) SRV RNA copies/ml of plasma. Two animals in the control group developed simian AIDS within 7 to 8 weeks postinfection and were euthanized. Anemia and weight loss were observed in the remaining controls. During acute infection, severe B-cell depletion and no significant changes in T-cell population were observed in the control group. Control RMs with greater preservation of B cells and lower VLs survived longer. SRV-2 was undetectable in vaccinated animals, which remained healthy, with no clinical or biological signs of infection and preservation of B cells. Our study showed that the VSV-SRV vaccine is a strong approach for preventing clinically relevant type D retrovirus infection and disease in RMs, with protection of 4/4 RMs from SRV infection and prevention of B-cell destruction. B-cell protection was the strongest correlate of the long-term survival of all vaccinated and control RMs.

Early immunopathology events in simian retrovirus, type 2 infections prior to the onset of disease.

Immunopathology during early simian retrovirus type 2 (SRV-2) infection is poorly characterized. Here, viral dynamics, immune response and disease progression in transiently- or persistently-infected cynomolgus macaques are assessed. Viral nucleic acids were detected in selected lymphoid tissues of both persistently- and transiently-infected macaques, even after viral clearance from the periphery. Immunohistochemical staining of lymphoid tissues revealed alterations in a number of immune cell populations in both transiently- and persistently-infected macaques. The precise pattern depended upon the infection status of the macaque and the marker studied. Gross immunopathological changes in lymphoid tissues were similar between SRV infection and those observed for other simian retroviruses SIV and STLV, suggesting a common immunopathological response to infection with these agents.

The Mhc class II DRB genotype of Macaca fascicularis does not influence infection by simian retrovirus type 2.

Simian retrovirus type 2 (SRV-2) is a natural pathogen of Macaca fascicularis. Although SRV-2 may be endemic in macaque colonies, it is not necessarily detected in all individuals suggesting differential susceptibility to SRV-2; factors contributing to this susceptibility are not fully understood. We have investigated the role of host genetic origin on virus susceptibility. We have shown that high levels of anti-SRV-2 antibodies correlate with failure to establish persistent virus infection, thus we targeted our genetic analysis of virus susceptibility with an investigation of the role of the polymorphic macaque major histocompatibility complex (MHC) class II locus. DRB genotypes, both novel and previously characterised, were identified in individuals and family groups. A discordance with SRV-2 infection status suggests that an Mhc II DRB genotype is not overtly associated with the outcome of viral infection.

Identification of postentry restrictions to Mason-Pfizer monkey virus infection in New World monkey cells.

TRIM5alpha has been shown to be a major postentry determinant of the host range for gammaretroviruses and lentiviruses and, more recently, spumaviruses. However, the restrictive potential of TRIM5alpha against other retroviruses has been largely unexplored. We sought to determine whether or not Mason-Pfizer monkey virus (M-PMV), a prototype betaretrovirus isolated from rhesus macaques, was sensitive to restriction by TRIM5alpha. Cell lines from both Old World and New World primate species were screened for their susceptibility to infection by vesicular stomatitis virus G protein pseudotyped M-PMV. All of the cell lines tested that were established from Old World primates were found to be susceptible to M-PMV infection. However, fibroblasts established from three New World monkey species specifically resisted infection by this virus. Exogenously expressing TRIM5alpha from either tamarin or squirrel monkeys in permissive cell lines resulted in a block to M-PMV infection. Restriction in the resistant cell line of spider monkey origin was determined to occur at a postentry stage. However, spider monkey TRIM5alpha expression in permissive cells failed to restrict M-PMV infection, and interference with endogenous TRIM5alpha in the spider monkey fibroblasts failed to relieve the block to infectivity. Our results demonstrate that TRIM5alpha specificity extends to betaretroviruses and suggest that New World monkeys have evolved additional mechanisms to restrict the infection of at least one primate betaretrovirus.

Persistence and dissemination of simian retrovirus type 2 DNA in relation to viremia, seroresponse, and experimental transmissibility in Macaca fascicularis.

Endemic simian retrovirus (SRV) infection can cause fatal simian AIDS in Macaca fascicularis, but many individuals survive with few clinical signs. To further clarify the parameters of SRV pathogenesis, we investigated the persistence of viral DNA forms in relation to active viremia, antibody response, and transmissibility of infection. In M. fascicularis from endemically SRV-2-infected colonies, viral DNA was present in both linear and unintegrated long terminal repeat circular forms in peripheral blood mononuclear cells of all viremic and many nonviremic animals. Long-term followup of three individuals with distinct infection patterns demonstrated persistence of linear and circular forms of viral DNA in peripheral blood mononuclear cells and tissues, irrespective of viremia or antibody status, but reactivation of latent infections was not observed. The role of viral DNA in transmission and early pathogenesis of SRV-2 was investigated by inoculation of SRV-2 DNA-positive blood into groups of naïve M. fascicularis from either a viremic or nonviremic donor and subsequent analysis of the virological and serological status of the recipients. Transmission of SRV and development of anti-SRV antibodies were only observed in recipients of blood from the viremic donor; transfer of SRV provirus and unintegrated circular DNA in blood from the nonviremic donor did not lead to infection of the recipients. These results indicate that a proportion of M. fascicularis are able to effectively control the replication and infectivity of SRV despite long-term persistence of viral DNA forms in infected lymphocytes.

The envelope of Mason-Pfizer monkey virus has immunosuppressive properties.

We have demonstrated previously that the envelope protein of a murine retrovirus, Moloney murine leukaemia virus, has immunosuppressive properties in vivo. This property was manifested by the ability of the protein, when expressed by tumour cells normally rejected by engrafted mice, to allow the env-expressing cells to escape immune rejection and to proliferate. Here, it is shown that this property is not restricted to the envelope of a murine retrovirus, but is also shared by the envelope encoded by a primate retrovirus, Mason-Pfizer monkey virus.

Serum antibodies reactive with non-human primate retroviruses identified in acute onset schizophrenia.

Schizophrenia is a pervasive neuropsychiatric disease of uncertain etiology. Previous studies have postulated that retroviruses may contribute to the etiology of some cases of schizophrenia. We examined the possible relationship between retroviral infection and schizophrenia by measuring antibodies to a number of different primate retroviruses in the sera of individuals undergoing their first hospitalization for this disease. Sera from patients with first onset schizophrenia and matched healthy controls were analyzed by immunoblot and enzyme linked immunosorbent assays using purified retrovirus antigens to identify and quantify antibodies reactive with retrovirus proteins. A significantly increased incidence of antibodies reactive to gag encoded proteins of Mason-Pfizer monkey virus (MPMV), baboon endogenous virus (BaEV) and simian retrovirus type 5 (SRV-5) was observed in the sera of schizophrenia patients compared to controls. The reactivity of the cases and controls displayed the greatest differences in terms of antibodies to the proteins of Mason-Pfizer monkey virus. Employing an algorithm of enzyme linked immunosorbent assay reactivity followed by immunoblot confirmation, we found that MPMV antibodies in 28.9% of the individuals with first episode schizophrenia patients as compared to 3.7% of the unaffected controls (P<0.009, Fisher's Exact Test). These studies are consistent with the occurrence of retrovirus replication in some individuals who are undergoing their first episode of schizophrenia.

Markers of type D retroviruses in children with Burkitt's-type lymphoma.

Antibodies to gag-coded proteins of type D retroviruses have been detected in children with lymphadenopathy [1]. We tested 41 HIV noninfected children with lymphoproliferative diseases (27 cases of Burkitt's-type lymphoma, six cases of Hodgkin's disease, four cases of T-cell lymphoma, three cases of lymphoblastic lymphoma and one case of large-cell anaplastic lymphoma) for the presence of type D retroviral serological and genetical markers. Twenty-five healthy donors were tested as a control. DNA samples from peripheral blood lymphocytes were analyzed by the polymerase chain reaction (PCR) and Southern blotting for the presence of type D retroviral related sequences. MPMV pro-pol specific sequences have been detected in 18 out of 27 children with Burkitt's-type lymphoma. By means of Western blotting, six patients positive in PCR/Southern blotting analysis were also found to contain Mason-Pfizer monkey virus (MPMV) specific antibodies, in their sera. All children with other lymphoproliferative diseases as well as healthy donors were negative in PCR/Southern blotting and Western blotting analysis. These data suggest the possible association of type D retroviral markers with Burkitt's-type lymphoma of children.

Development and application of an antibody ELISA for the marker protein of ovine pulmonary carcinoma.

Ovine pulmonary carcinoma (OPC) is a contagious pulmonary neoplasia with a suspected retroviral etiology. The major core protein (P27) of the putative OPC virus cross-reacts with antibodies to P27 of the Mason-Pfizer monkey virus (MPMV), a type-D retrovirus. This serological reactivity serves as the only accepted biological marker for OPC. In order to make a useful reagent for the detection of the OPC marker for serodiagnosis and epidemiological studies, the MPMV-P27 coding region was cloned and expressed in Escherichia coli. Gel purified recombinant MPMV-P27 protein was used to develop an immunoassay. This recombinant enzyme-linked immunosorbent assay (ELISA) was then used to screen 223 sera from US sheep and 176 sera from Italian sheep. In this study, we found: (1) a high prevalence of infection with the putative OPC retrovirus in sheep with chronic pneumonia; (2) a subclinical infection with OPC virus may be more common in US sheep than indicated by the rare recorded occurrence of pulmonary carcinoma; (3) an apparent association between ovine lentivirus (OLV) and OPC infection.

The (YXXL/I)2 signalling motif found in the cytoplasmic segments of the bovine leukaemia virus envelope protein and Epstein-Barr virus latent membrane protein 2A can elicit early and late lymphocyte activation events.

The cytoplasmic domains of the transducing subunits associated with B and T cell antigen receptors contain a common amino acid motif consisting of two precisely spaced Tyr-X-X-Leu/Ile sequences (where X corresponds to a variable residue). Expression of a single copy of this motif suffices to initiate B or T cell activation. The bovine leukaemia virus (BLV) is a B cell lymphotropic retrovirus which causes a non-neoplasic proliferation of B cells. The cytoplasmic domain of the BLV transmembrane envelope glycoprotein, gp30, possesses two overlapping copies of the Tyr-X-X-Leu/Ile-containing motif which could participate in the induction of B cell activation. Similarly, the N-terminal cytoplasmic domain of the latent membrane protein 2A (LMP2A) of the Epstein-Barr virus (EBV) contains a single copy of the Tyr-X-X-Leu/Ile-containing motif which could play a critical role in B cell transformation. To determine whether these two virus-encoded cytoplasmic domains are endowed with signalling functions, we constructed chimeric proteins by replacing the cytoplasmic tail of CD8-alpha with that of either BLV gp30 or EBV LMP2A. We show here that, once separately expressed in B or T cell lines, these chimeras are capable of triggering both calcium responses and cytokine production when cross-linked with an antibody to CD8-alpha. Furthermore, using site-directed mutagenesis, we demonstrated unequivocally that this signalling function may be accounted for by the Tyr-X-X-Leu/Ile motifs they contain.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies to gag gene coded polypeptides of type D retroviruses in healthy people from Guinea-Bissau.

Antibodies to proteins of Mason-Pfizer monkey virus (M-PMV) were screened in sera from 61 healthy donors living in Guinea-Bissau (4 HIV-1 and HIV-2 antibody positive HIV = human immunodeficiency virus), from 19 healthy French European blood donors, and from 9 French patients with induced immunodeficiency prior to bone marrow transplantation (all HIV-1 antibody negative). In 30 (49%) of the African sera tested, antibodies reacting against p27 and/or p14 were detected by western blot. Some of these cases were confirmed to be positive using radioimmuno precipitation assay. Only one serum from a French blood donor was detected by western blot to be slightly positive against p27 M-PMV. Thirty-two sera screened for M-PMV were also tested for squirrel monkey retrovirus by western blot. In eight (25%) sera antibodies at least against p36 were detected. Among squirrel monkey retrovirus positive sera, three were also positive with p27 M-PMV. The other five were found to be M-PMV negative.