Radioimmunoassay of mammalian type-C polypeptides. IV. Characterization of woolly monkey and gibbon viral antigens

Long-term infection and vertical transmission of a gammaretrovirus in a foreign host species

Increasing evidence has indicated natural transspecies transmission of gammaretroviruses; however, viral-host interactions after initial xeno-exposure remain poorly understood. Potential association of xenotropic murine leukemia virus-related virus (XMRV) in patients with prostate cancer and chronic fatigue syndrome has attracted broad interests in this topic. Although recent studies have indicated that XMRV is unlikely a human pathogen, further understanding of XMRV xenoinfection would allow in vivo modeling of the initial steps of gammaretroviral interspecies transmission, evolution and dissemination in a new host population. In this study, we monitored the long-term consequences of XMRV infection and its possible vertical transmission in a permissive foreign host, wild-derived Mus pahari mice. One year post-infection, XMRV-infected mice showed no notable pathological changes, while proviral DNA was detected in three out of eight mice. XMRV-infected mice remained seropositive throughout the study although the levels of gp70 Env- and p30 capsid-specific antibodies gradually decreased. When vertical XMRV transmission was assessed, no viremia, humoral immune responses nor endogenization were observed in nine offspring from infected mothers, yet one offspring was found PCR-positive for XMRV-specific sequences. Amplified viral sequences from the offspring showed several mutations, including one amino acid deletion in the receptor binding domain of Env SU. Our results therefore demonstrate long-term asymptomatic infection, low incidence of vertical transmission and limited evolution of XMRV upon transspecies infection of a permissive new host, Mus pahari.

Isolation and identification of lymphocytic and myelogenous leukemia-specific sequences in genomes of gibbon oncornaviruses

Five gibbon ape leukemia virus substrains (two from gibbons with lymphocytic leukemia and three from gibbons with myelogenous leukemia) were examined for unique genomic sequences specific for each form of leukemia. By using sequential adsorption procedures, the genome from each gibbon ape leukemia virus was fractionated into four sets of distinct nucleotide sequences. Based on their hybridization specificities toward DNAs of leukemic tissues, these sequences were designated as follows: (i) "COM," (ii) "LYM" or "MYE," (iii) "UNI," and (iv) "UND." The COM fraction represented sequences common to all of the viral genomes. The LYM fraction, which was isolated only from gibbon ape leukemia viruses associated with lymphocytic leukemia, represented genomic sequences associated with lymphocytic leukemia since the RNA hybridized at a 4- to 15-fold-higher rate to infected tissue DNA from lymphocytic leukemic gibbons than to infected tissue DNA from myelogenous leukemic gibbons. The MYE fraction, which was isolated only from gibbon ape leukemia viruses associated with myelogenous leukemia, represented genomic sequences associated with myelogenous leukemia since the RNA hybridized at a 5- to 15-fold-higher rate to infected tissue DNA from myelogenous leukemic gibbons than to infected tissue DNA from lymphocytic leukemic gibbons. The UNI fraction contained sequences unique to one virus substrain. The UND fraction contained sequences which varied depending upon the substrains involved in the adsorption procedures. These findings suggest that each gibbon ape leukemia virus examined in this study contains subgenomic sequences that are specifically identifiable only with the form of leukemia from which the virus was isolated.

Major structural proteins of type B, type C, and type D oncoviruses share interspecies antigenic determinants

Interspecies antigenic determinants have been used as markers to study the evolution of oncoviruses. By radioimmunologic techniques, it has been possible to detect crossreactivities among the major structural proteins of prototype viruses representing each of the three major Oncovirinae genera. Two different subsets of interspecies antigenic determinants were demonstrated. One encompasses known type B and type D viruses; the other is shared by type D and mammalian type C viruses. Such determinants were also demonstrated in certain as yet unclassified oncoviruses. These findings provide experimental evidence supporting the concept of an evolutionary relationship among the three major oncovirus genera.

Antigenic characterization of a new gibbon ape leukemia virus isolate: seroepidemiologic assessment of an outbreak of gibbon leukemia

A type-C virus recently isolated from a leukemic gibbon in a colony located on Hall's Island, Bermuda, was characterized with respect to the antigenic properties of its gag and env gene-coded proteins. This virus, designated GaLV-H, was found to be closely related immunologically to type-C viruses previously isolated from gibbons (GaLV-SF, GaLV-SEATO, GaLV-Br) and from woolly monkey (SSAV). However, GaLV-H was readily differentiated from these isolates in a radioimmunoassay for its env gene product, gp70. Seroepidemiology established that GaLV-H was horizontally transmitted among gibbons within the colony. There was no evidence of exposure leading to an immune response to the virus or viral antigenemia in humans working in association with these animals.

Immunologic approaches toward detection of type C viral expression in man

Type C RNA viruses have been isolated from a large number of mammalian species. These agents may be horizontally transmitted as infectious cancer-inducing agents, or vertically transmitted from one generation to the next, often in an unexpressed form, within the host genome. To date, the translational products of three viral genes have been identified. With purified virus-coded proteins as probes, sensitive and highly specific radioimmunologic assays have been developed for the detection of antibodies and antigens related to the known type C viruses. These techniques have proved valuable in sero-epidemiologic studies of the horizontally transmitted oncogenic viruses of cats, cattle, and gibbons, and have been used to detect translational products of endogenous viruses in tissues of species from which complete virus has yet to be isolated. This review describes the application of radioimmunoassays in the search for immunologic evidence of type C virus expression in man.

A method for classification of 5' termini of retroviruses

A new method for the classification of retroviruses is presented. The scheme is based on the length and sequence of a DNA transcript of the 5' end of the genome. The method can be used to detect similarities between distantly related viruses as well as to discriminate between very closely related viruses. The method is applied to viruses isolated from mice, baboons, gibbons, a woolly monkey and chickens.

Purification and characterization of gibbon ape leukemia virus DNA polymerase

An RNA directed DNA polymerase was purified over 2500 fold from gibbon ape leukemia virus by successive column chromatography on Sephadex G100, DEAE cellulose, phosphocellulose and hydroxyapatite. The purified DNA polymerase has a molecular weight of 68 000, a pH optimum of 7.5, a Mn2+ optimum of 0.8 mM, and KCl optimum of 80 mM. The purified enzyme transcribes heteropolymeric regions of viral 60-70 S RNA isolated from avian myeloblastosis virus, Rauscher murine leukemia virus and simian sarcoma virus and it is inhibited by antiserum prepared against either gibbon ape leukemia virus or simian sarcoma virus DNA polymerases.

Expression of feline type-C virus in normal and tumor tissues of the domestic cat

Tumor and normal tissues from domestic cats were examined for FeLV and RD-114 specific nucleic acids and proteins. Virus-positive tissues showed a 100- to 200-fold higher level of FeLV and a 200- to 400-fold higher level of FeLV p30 than virus-negative tumors and normal cat tissues. In contrast, the levels of RD-114 viral RNA and p30 antigen were comparable in the majority of tumorous and normal tissues examined. When the DNA of these tissues was examined for FeLV-related sequences, the virus-positive tumors were found to contain extra copies of FeLV DNA. Virus-negative tumors contained DNA sequences homologous with FeLV but the copy number of these sequences could not be distinguished from normal tissues. The results indicate that in certain FeLV-induced type-C lymphoproliferative diseases, extra type-C sequences not present in normal tissues can be identified.

The endogenous origin and transmission of RNA viral genomes that code for cancer

In certain experimental animals, type-C virus genomes are universally prevalent. They are mostly but not exclusively transmitted genetically and produce tumors naturally as well as when transmitted experimentally. The spontaneous virus and tumor expressions are regulated and modified by genetic factors; and virus-specific virogenes used as vaccines prior to high-level natural expressions can suppress natural expressions of the virogenes. Application of this significant information to the prevention of cancer in mice now seems quite feasible; however its application to the control of human cancer is still dependent on the isolation of specific human type-C virus(es).

Transformation of horse skin cells by type-C sarcoma viruses

A horse skin cell line (E. Derm, NBL-6, CCL-57) was susceptible to focus formation by the Kirsten mouse sarcoma virus, feline sarcoma virus (ST stain) and the MSV pseudotypes with woolly monkey, gibbon monkey, RD-114, AT-124, baboon placenta and murine xenotropic (BALB/c 3T3 and C57L/JD) type-C viruses. Foci were detected within 5 days after infection and the transformed cells continued to produce infectious virus and group-specific antigen of their respective type-C leukemia viruses. The transformation efficiency of various type-C sarcoma viruses in horse cells was also very high.

Isolation of a primate type-C virus from a lymphomatous baboon

A type-C RNA virus has been isolated from various tissues of a lymphomatous baboon (sp. P hamadryas). Virus isolations were made by co-cultivating baboon cells from the inguinal and mesenteric lymph nodes, testes, kidneys and spleen with cells of canine or human origin. The isolated virus grew in canine, bat, rhesus, and human cells but not in cells of mouse, rat, cat or rabbit origin. The baboon isolate resemble a type-C virus when infected cells were examined by thin section in the electron microscope. In addition, the virus was capable of providing helper function by rescuing and transmitting the Moloney and Kirsten sarcoma virus genome from non-productively transformed cells. Antibody directed against the RD114 virus reverse transcriptase was very effective in inhibiting the baboon virus polymerase while while anti-mouse and woolly type-C virus polymerase antibodies had no significant inhibitory activity. Further analysis by immunodiffusion and competitive radioimmune assay revealed a close immunological relationship between this virus, RD114 and another type-C virus isolated from the placenta of a different species of baboon. Finally, three different classes of interspecies antigenic determinants have been demonstrated in mammalian type-C virus isolated from the placenta of a different species of baboon. Finally, three different classes of interspecies antigenic determinants have been demonstrated in mammalian type-C viruses.

Type-C RNA virus gene expression in human tissue

Partially purified fractions of human tissues have been analyzed by competition radioimmunoassay for the presence of two of the principle structural components of type-C RNA viruses, the major core protein (p27 to p30) and the major envelope glycopeptides (gp69/71). Screening of tissues was carried out by use of a heterologous assay system of (125)I-labeled Rauscher murine virus p30 antigen and anti-RD 114 virus serum which was found to detect a class of interspecies determinants common to murine, feline, and primate viruses. A competitor with the same apparent affinity for antibody binding as that of purified viral core proteins was found in relatively high concentration in tissues from patients with systemic lupus erythematosus, in some neoplastic tissues, and also in normal human tissues. This competitor from a lupus spleen chromatographed on phosphocellulose and showed size fractionation during gel filtration similar to known p27 to p30 viral proteins. An immunologically reactive protein was also demonstrated by immunodiffusion and by immunoprecipitation of (125)I-labeled human protein with anti-RD 114 p28 serum. Analysis of these human competitor proteins with homologous assay systems of viral core proteins and corresponding antisera showed that all, including the normal tissue extracts, appear similar to core proteins of known viruses, especially the RD 114 and woolly monkey species. A hypothesis suggested by these data is that many, if not all, humans harbor at least part of the genome of one or more type-C viruses, the properties of which are similar to those of viruses from other mammalian species, particularly primates.

Radioimmunoassay for the major structural protein of hamster type C viruses

A radioimmunoassay for the major, group-specific antigen (p30) of hamster type C viruses was developed. The test detected approximately 5 ng of viral protein per ml and was highly specific for hamster viruses when used with homologous antibody. Comparison of three hamster viruses, two being mouse-hamster pseudotypes, in homologous and heterologous intraspecies assays, showed no evidence of type specificity for these proteins. The pseudotype viruses showed no evidence of mouse virus p30 antigenic determinants. An interspecies antigen assay employing (125)I-labeled hamster p30 and anti-feline p30 was completely inhibited by cat (feline leukemia virus), hamster, and rat viruses, to a slightly lesser degree by mouse viruses, and only poorly by RD 114 and Gibbon ape viruses. The Mason-Pfizer virus did not inhibit this assay. Hamster p30 was detected by radioimmunoassay in individual embryos from two LSH hamsters and in several adult tissues, excluding muscle at levels below that required for detection in complement-fixation tests.

Modified radioimmunoassay for murine sarcoma-leukemia virus group-specific antigen

Iodination of disrupted Moloney strain murine sarcoma-leukemia virus resulted in labeled group-specific (gs) protein which was subsequently purified on an isoelectrofocusing column. This iodinated purified gs antigen, prepared from a relatively small quantity of purified virus, was used in a radioimmunoassay. A radioimmunoassay inhibition method was developed so that antibody specific for mammalian C-type gs antigen could be measured in undiluted or low dilutions of test serum without altering the known reagents of the test. The gs antigen isolated from purified Moloney strain murine sarcoma-leukemia virus has an isoelectric point (pH 5.95) which is significantly lower than that reported for other murine leukemia viruses.

Detection of baboon type C viral sequences in various primate tissues by molecular hybridization

Nucleic acid sequences homologous to a single-stranded [(3)H]DNA transcript prepared from a baboon type C virus replicating in dog thymus cells can be readily detected in the cellular DNA of several Old World monkeys (baboon, patas, African green, and two species of macaques-rhesus and stumptail). These results demonstrate that primates other than the baboon also contain endogenous type C viral genes. With the hybridization conditions employed (S(1) nuclease, 65 C), no homologous sequences were detected in DNA from human or New World monkey tissues. Of various nonprimate tissues examined, only domestic cat cellular DNA was partially homologous to the baboon virus [(3)H]DNA transcript. In reciprocal experiments, [(3)H]DNA transcripts of RNAs from endogenous cat viruses (RD-114/CCC group) show a significant partial homology with cellular DNA from Old World primates (baboon, patas, and rhesus monkey). The partial homology between type-C-related information in the DNA of domestic cats and various Old World monkeys suggests the possibility of horizontal transmission between the progenitors of these animals at some point in evolution. No nucleic acid sequences homologous to [(3)H]DNA transcripts prepared from type C viruses isolated from tumor tissue of a woolly monkey and a gibbon ape could be detected in any primate tissue DNA examined; however, a partial nucleic acid homology was found between woolly monkey and gibbon ape type C viral [(3)H]DNA and normal mouse cellular DNA.

Immunological properties of two polypeptides of Mason-Pfizer monkey virus

Two polypeptides were isolated from the Mason-Pfizer monkey virus (MP-MV). The polypeptides, designated MP-MV p26 and MP-MV p15, were 26,000 and 15,000 molecular weight, respectively, based on gel filtration chromatography in the presence of 6 M guanidine hydrochloride. Radioimmunoassays developed for MP-MV p26 and p15 were, respectively, 10 and 100 times more sensitive than immunodiffusion and 1 and 10 times more sensitive than micro-complement fixation for the detection of MP-MV. Antigens of other reverse transcriptase-containing RNA viruses did not cross-react in either MP-MV radioimmunoassay. Further, antisera against these other viruses did not react with the radioiodine-labeled MP-MV polypeptides. The MP-MV radioimmunoassays should be useful in studying the natural occurrence of this virus and its relationship to primate tumors.

Primate and murine type-C viral nucleic acid association kinetics: analysis of model systems and natural tissues

Hybridization studies employing single-stranded (3)H-DNA transcripts of type-C viruses isolated from a woolly monkey or gibbon ape failed to detect nucleic acid sequences homologous to these viruses in the DNA from a variety of uninfected primate species. The possible significance of these results for the epidemiology of type-C viruses in primates is discussed.

Specificity of the DNA product of RNA-dependent DNA polymerase in type C viruses. II. Quantitative analysis

A number of mammalian Type C viruses were analyzed for relatedness by the technique of DNA.RNA hybridization. Viral DNAs were prepared in single-stranded form from complexes with 70S viral RNA formed during endogenous polymerase reactions. Extent of hybridization was assayed with the single-strand nuclease (S-1) from Aspergillus oryzae. Results obtained indicated a high degree of viral specificity, with significant cross-reactions being observed only with viruses obtained from within a species, as in the case of mouse and cat viruses, or in the special case of woolly monkey-gibbon comparisons. Comparisons of RD-114 virus, recently determined to be of feline origin, and conventional feline Type C viruses (FeLV), revealed minimal relatedness, especially when feline virus was grown on human cells, thus indicating the possibility of coexistence of greatly disparate Type C viruses within one species. A rat-specific virus, recovered from tumors induced by murine sarcoma virus, was found to contain genetic material common to both the original mouse virus and viruses indigenous to the rat, even though only rat-specific proteins have been detected during infection by this virus.

Mason-Pfizer virus characterization: a similar virus in a human amniotic cell line

Mason-Pfizer monkey virus (MP-MV) is a RNA virus with an RNA-instructed DNA polymerase first isolated from a rhesus monkey mammary adenocarcinoma in 1970. Until recently, there have been no other isolates. A continuous human amnion cell line, AO, was found to be producing a virus indistinguishable or closely related to the Mason-Pfizer virus as measured by morphological, immunological, and biochemical methods. By thin-section electron microscopy, the extracellular virus particle in AO line is 115 to 130 nm in diameter and has a preformed nucleoid (80 to 90 nm) before budding, properties which are also characteristic of MP-MV. Two proteins of the virus from the AO line were studied. By immunodiffusion, sera which react specifically with MP-MV give a line of identity with virus from the AO line. The AO viral RNA-instructed DNA polymerase purified by phosphocellulose chromatography was specifically inhibited by anti-MP-MV polymerase sera, and the AO cells contained both DNA and RNA sequences related to MP-MV (3)H-DNA. Viruses thus far indistinguishable from MP-MV have also recently been found by others in different human lines, raising again the question of the species of origin of MP-MV. Because the virus in the AO cells cannot be differentiated from MP-MV, we attempted to determine the origin of MP-MV virus by measuring DNA sequences related to MP-MV (3)H-DNA in uninfected human and rhesus monkey cells. The quantity of MP-MV-like DNA sequences in uninfected primate tissues was found to be much lower than the amount of DNA sequences of murine type-B or type-C viruses in uninfected murine tissues. Thus, it was not possible to determine whether the virus produced by AO cells or MP-MV was of human or monkey origin, or both.