Evolution and antiviral activity of a human protein of retroviral origin.

Endogenous retroviruses are abundant components of mammalian genomes descended from ancient germline infections. In several mammals, the envelope proteins encoded by these elements protect against exogenous viruses, but this activity has not been documented with endogenously expressed envelopes in humans. We report that the human genome harbors a large pool of envelope-derived sequences with the potential to restrict retroviral infection. To test this, we characterized an envelope-derived protein, Suppressyn. We found that Suppressyn is expressed in human preimplantation embryos and developing placenta using its ancestral retroviral promoter. Cell culture assays showed that Suppressyn, and its hominoid orthologs, could restrict infection by extant mammalian type D retroviruses. Our data support a generalizable model of retroviral envelope co-option for host immunity and genome defense.

Development of an ante-mortem diagnostic test for enzootic nasal tumor virus and detection of neutralizing antibodies in host serum.

Enzootic nasal adenocarcinoma (ENA) is a contagious neoplasm of the nasal mucosa of sheep and goats and is associated with enzootic nasal tumour virus (ENTV). As ENA is a common disease in North America and there are no vaccines against ENTV-1, diagnostic tests that can identify infected animals and assist with eradication and disease surveillance efforts are greatly needed. In this study, we endeavoured to develop a novel, non-invasive diagnostic tool that could be used not only to validate clinical signs of ENA but also to detect ENTV-1 infection prior to the onset of disease signs (i.e. pre-clinical diagnosis). Cytology, serology and reverse transcription (RT)-PCR-based diagnostic methods were investigated. Although the cytology-based assay was able to detect ENTV-1 infection in some animals, it had poor sensitivity and specificity and thus was not developed further as an ante-mortem diagnostic method. Three different assays, including ELISA, Western blotting and virus neutralization, were developed to detect the presence of ENTV-1-specific antibodies in sheep serum. Whilst a surprisingly large number of sheep mounted an antibody-mediated immune response against ENTV-1, and in some cases neutralizing, correlation with disease status was poor. In contrast, RT-PCR on RNA extracted from nasal swabs reliably detected exogenous ENTV-1 sequences, did not amplify endogenous ovine betaretroviral sequences, demonstrated high concordance with immunohistochemical staining for ENTV-1 envelope protein, and had perfect sensitivity and specificity. This report describes a practical and highly specific RT-PCR technique for the detection of clinical and pre-clinical ENA that may prove beneficial in future control or eradication programmes.

Detection of human mammary tumor virus proteins in human breast cancer cells.

Mouse mammary tumor virus (MMTV) has been proven to induce mammary cancer in mice. MMTV-like env gene sequences have been detected in one-third of the human breast tumors studied. The whole proviral structure with 95% homology to MMTV was found in two human breast tumors and was designated as human mammary tumor virus (HMTV). HMTV viral particles with betaretroviral features have been isolated. In addition, a retrovirus called human betaretrovirus (HBRV), homologous to the mentioned retroviruses, has been isolated from tissues of patients with primary biliary cirrhosis. In this report, the expression of HMTV envelope (Env) and capsid (Ca) was detected in 10 primary cultures of human breast cancer containing HMTV sequences (MSSM) by Western blot and fluorescence activated cell sorting (FACS), using a panel of antibodies against HMTV Env, HBRV Env and Ca and the MMTV Env Gp36 and Ca P27 proteins. By contrast, HMTV proteins did not react with antibody against the MMTV Env Gp52 protein. All the antibodies detected MMTV proteins with exception of two out of four monoclonal antibodies against HMTV Env. Approximately 13% of the MSSM cells showed HMTV protein expression by FACS analysis. This report shows the expression of HMTV proteins for the first time in human breast cancer cells using a panel of antibodies against HMTV, HBRV and MMTV proteins. This should be taken into consideration when MMTV antibodies are used to detect HMTV proteins in human tissues.

The endogenous langur type D retrovirus PO-1-Lu and its exogenous counterparts in macaque and langur monkeys.

PO-1-Lu, the endogenous type D retrovirus of langurs (Trachypithecus obscurus) has previously been considered a progenitor to the prototype type D retrovirus, Mason Pfizer monkey virus (M-PMV/SRV-3), that became established in macaque monkeys (Macaca spp.) following a zoonosis. This study reevaluates this hypothesis to include other exogenous SRVs. New sequence information from the gp70(SU)-encoding region of PO-1-Lu shows striking similarity to the newly identified exogenous langur retrovirus, SRV-6, recently isolated from the Hanuman Langur (Semnopithecus entellus). An unrooted, bootstrapped neighbor-joining tree derived from env gene nucleotide sequences shows PO-1-Lu and SRV-6 appear more closely related genetically to SRV-2 than SRV-1 or SRV-3 (M-PMV). This is also reflected in our observations that the M-PMV envelope glycoprotein precursor gPr86(Env) and gp70(SU) were antigenically distinct from PO-1-Lu, although the gp22(TM) glycoproteins were antigenically cross-reactive. The potential that SRV-6 represents an exogenous form of PO-1-Lu that has arisen following a recent zoonosis is discussed.

Sheep pulmonary adenomatosis: characterization of two pathological forms associated with jaagsiekte retrovirus.

Pathological and immunohistochemical studies were performed on the lungs of 10 sheep with lesions of "classical" sheep pulmonary adenomatosis (SPA) and six sheep with "atypical" lung tumours. Lung tumour samples and other tissues from the same 16 animals were tested for the presence of jaagsiekte retrovirus (JSRV) by a polymerase chain reaction (PCR) that amplified a portion of the U3 long terminal repeat. The differences in the gross appearance of the classical and atypical forms paralleled the histopathological differences. The latter mainly concerned the stroma of the tumours which in the atypical cases was more heavily infiltrated by inflammatory cells and connective tissue fibres. JSRV major capsid protein was detected immunohistochemically in the epithelial transformed cells of both classical and atypical tumours, but the immune reactivity was slightly milder in atypical SPA. Proviral U3 sequences of JSRV were detected by specific PCR in all the tumour samples. Furthermore, the sequences of amplimers obtained from the two different pathological forms of the tumour were very similar. However, the dissemination of JSRV to other organs was greater in sheep with classical SPA than in those with atypical SPA. The pathological and virological features of these two forms of tumour are compared in an attempt to clarify whether classical and atypical SPA are two separate diseases or different expressions of a single disease spectrum.

Lack of a specific immune response against a recombinant capsid protein of Jaagsiekte sheep retrovirus in sheep and goats naturally affected by enzootic nasal tumour or sheep pulmonary adenomatosis.

Enzootic nasal tumour (ENT) and sheep pulmonary adenomatosis (SPA) are two contagious adenocarcinomas of the respiratory tract of sheep and goats. Both diseases are associated with related, but distinct, type-D-retroviruses (ENTV and JSRV respectively). No evidence of circulating antibodies has been described in animals affected by either ENT or SPA using antigens from natural sources. We evaluated the usefulness of a recombinant JSRV capsid protein (JSRV-CA) as antigen to study the antibody responses of animals naturally affected by ENT or SPA, using immunoblotting. Positive reactions were detected in the sera of both affected and unaffected sheep and goats. The reactivity was abolished completely by absorption with the GST fusion partner but not by JSRV-CA, suggesting that it was not specific. The results support prior observations indicating that sheep and goats infected by JSRV and ENTV do not develop specific humoral responses to these retroviruses.

Seroprevalence of specific viral infections in confiscated orangutans (Pongo pygmaeus).

A serological survey of confiscated orangutans was conducted to determine the prevalence of specific viral infections cross reacting with human viruses. Antibodies specific for human hepatitis A (HAV) and B (HBV) viruses, herpes simplex viruses (HSV), and human T-lymphotropic virus (HTLV types I and II), as well as for the simian type D retroviruses (SRV types 1 to 3) and simian immunodeficiency virus (SIV) were tested in samples from 143 orangutans. Results revealed a high prevalence of potential pathogens. The most prevalent viral infection found was HBV (59.4% prevalence) of which 89.4% of infected individuals seroconverted to the non-infectious state and 10.6% remained as chronic carriers. Antibodies to HAV, HSV, HTLV-1, and SRV were also detected but at a lower prevalence. There was no evidence of lentiviral infections in this group of animals. The results confirm the importance of quarantine and the need for diagnostic differentiation of virus infections to determine if they are of human origin or unique orangutan viruses.