Further studies on CELO virus: Its relationship to the adenovirus group

Summary CELO virus is resistant to trypsin at 37° C; it is not stabilized by 1M MgCl₂ at 50° C. The multiplication of CELO is inhibited by iododeoxyuridine, a drug which selectively inhibits DNA viruses. In growth studies, it was found that the titer of the cell-associated virus is more than 100 times higher than the extra-cellular one.Some electron microscopic pictures are presented, showing the reaction of the nuclear components to viral multiplication, the occurrence of ring-like bodies, small irregular bodies, and the release of virus in the extracellular space.All here described properties of CELO are common to adenoviruses, a further evidence that CELO should be classified in the adenovirus group.Part of these observations has been presented at the XVII World Veterinary Congress, Hannover, August 1963.The electron microscopic work was carried out at the Centro di Microscopia Elettronica, University of Padova.     

Chick embryo lethal orphan (CELO) virus: some physical and immunological properties

Chick embryo lethal orphan (CELO) virus was partially purified by equilibrium centrifugation in CsCl density gradients. The virus was found to band at 1.32 g/cm³, and this band was found to contain the peak infectivity titres of virus. Electron microscopy of partially purified CELO virus revealed icosahedral particles of 60–80 nm diameter, and with a capsid of 252 capsomeres. The thermal denaturation temperature (T_m) of CELO virus DNA indicated a base composition of 46% guanine-cytosine. CELO virus CF antigens, separated from virus particles during purification of the virus, had the same sedimentation properties in preformed linear sucrose gradients as did the CF antigen of adenovirus 7.     

Characterisation of two highly oncogenic strains of Marek's disease virus

The RB-1B and ALA-8 strains of Marek's disease (MD) virus, which were isolated from chickens with MD and which had been vaccinated with the herpesvirus of turkeys (HVT), were evaluated for their oncogenic potential in genetically susceptible (P-line) and resistant (N-line, PDRC) chickens. RB-1B and ALA-8 were both highly oncogenic, causing a high incidence of MD in both susceptible and resistant birds. Vaccination of P-line birds with SB-1 or HVT did not protect satisfactorily against RB-1B. However, a bivalent vaccine consisting of SB-1 and HVT enhanced protection significantly. HVT alone, and the bivalent vaccine, protected PDRC and N-line chickens well against RB-1B, but SB-1 was less protective in PDRC birds. HVT protected equally well against challenge with ALA-8 and the standard JM-10 strain. Differences in the pathogenesis of viral infection could not be detected among ALA-8, RB-1B and JM-10 between 4-7 days post-infection (d.p.i.). However, after d.p.i. 12 RB-1B caused significantly higher levels of viral internal antigen and virus isolation rates than did JM-10 in the same genetic strain. Prior vaccination prevented the expression of ALA-8 at 5 and 20 d.p.i., but not that of RB-1B. Pathogenetic events such as expression of VIA or level of virus infection appeared to be directly related to the level of protection observed in challenged birds.     

Sialidase activity of oncogenic cells transformed by herpes simplex virus

Sialidase in normal nononcogenic hamster embryo fibroblasts was not active toward added disialo- and trisialoganglioside, but all transformed lines of hamster embryo fibroblasts studied had sialidase active toward added ganglioside substrate. The levels of exogenous sialidase activity suggested a parallel trend in the amount of this activity and the degree of oncogenicity of the transformed cells. Exogenous sialidase activity in a weakly oncogenic cell line was found to increase after passage of the cells into hamsters and isolation and cell culture of the resulting tumors which gave rise to a cell line of relatively high oncogenicity.     

Effect of histone on oncogenic properties of Moloney's murine sarcoma virus

Summary The effect of total histone on oncogenicity of Moloney murine sarcoma virus was studied. Combined intramuscular inoculation of histone and virus was shown to enhance the carcinogenesis markedly: it inhibited spontaneous regression of tumors, produced progressive growth of tumors followed by death of mice, shortened the latent period of tumor formation, produced metastases in surviving animals. A topical effect of histone is suggested, even though it is not excluded that formation of metastases may be associated with its immunodepressive effect.     

Attenuation of avian reticuloendotheliosis virus: Loss of the defective transforming component during serial passage of oncogenic virus in fibroblasts

Oncogenic preparations of avian reticuloendotheliosis virus, consisting of REV and its associated helper virus REV-A, were found to lose transforming activity during serial passage in fibroblast cultures. Electrophoretic analyses of virion RNA suggested that this loss of transforming activity results from loss of REV from the virus population. Attenuation of viral oncogenicity was not observed during passage in hematopoietic cell cultures. The different effects of virus passage in fibroblasts and hematopoietic cells are discussed.     

Alterations in nucleic acid metabolism induced by infection with an oncogenic virus

Summary Polyoma virus multiplies inin vitro cultures of mouse embryo fibroblasts, and the replicating cycle is accompanied by an increase in the incorporation of labelled precursors into the nucleic acids of the host cells particularly of DNA. From polyoma-infected mouse cells a virus-specific DNA can be isolated which, after purification by chromatography, retains its infectivity forin vitro cultures and oncogenic properties for suckling rodents. Fractionation on a column of methylated albumin allows separation of such virus type DNA from cellular DNA.Rat embryo cells infected with the oncogenic virus do not replicate the particles or form viral antigen, but undergo a malignant transformation. In this case no evident quantitative change or characteristic qualitative alteration in nucleic acids metabolism of the host cells was observed. Though these data do not offer absolute proof that the alternative pathways induced by polyoma virus, i. e., multiplication of viral particles and malignant transformation, involve two different metabolic pictures in the host cell, they suggest this possibility.     

Evidence for the multiple oncogenic potential of cloned leukemia virus: in vitro and in vitro studies with avian erythroblastosis virus.

Avian erythroblastosis virus (AEV) strains R and ES4 were found to consist of a defective transforming virus and a helper virus in excess. Helper viruses of each strain induced the formation of plaques and were clone-purified by isolating the virus from a single plaque. Pseudotypes of AEV, consisting of cloned AEV and cloned helper virus, could be rescued after helper virus superinfection of nonproducer fibroblasts transformed by infection with only the transforming virus. These pseudotypes were able to transform erythroblasts as well as fibroblasts in in vitro assays. Injection of AEV-transformed nonproducer fibroblasts into 1-week-old chicks led to the formation of fibrosarcomas. Erythroblastosis was obtained after the inoculation of all AEV-pseudotypes tested.The helper viruses naturally associated with AEV-R and AEV-ES4 did not transform cultured cells but induced a slight cytopathic effect. In vivo studies demonstrated that they cause anemia and that they are probably responsible for the anemia-inducing capacity of AEV stocks.     

A low oncogenic variant of friend murine leukemia virus with strong immunosuppressive properties

Summary Friend leukemia complex (FLC) is known to induce immunosuppression but the use of FLC in studies of immune cells function is disadvantageous since the immunosuppression always is accompanied by an acute erythroleukemia. To obtain immunosuppressive variants of FLC with reduced leukemogenic potential, we isolated T-helper cells from FLC infected mice, and passed lysates of the cells to recipient uninfected mice. A group of these mice developed a condition distinct from the disease induced by FLC. A viral stock prepared from these mice, designated Fd-MIV for friend derived murine immunodefiency virus, induced a profound suppression of the primary antibody response without acute transformation in adult NMRI mice. Terminally a wasting disease with weight loss, atrophy of the thymus and lymph nodes and renal disease was observed in some mice. Analysis of viral DNA and RNA from infected NIH 3T3 cells showed that Fd-MIV contained at least two viral components, a 8.4 kb friend murine leukemia virus (F-MuLV) and a 7.4kb mink cell focus (MCF) / xenotropic virus related genome. The 7.4 kb genome was not detected in Fd-MIV infected, immunocompromised mice indicating that the 8.4kb genome might be responsible for the disease.     

Genes for fowl adenovirus CELO penton base and core polypeptides

Summary A 3.5-kilobase DNA fragment of the fowl adenovirus type 1 (CELO), located between map units 31.1 and 39.4 has been determined. The sequence contains the probable CELO equivalents of the IIIa protein, penton base, pVII and pV core protein genes of human adenovirus (HAV). The CELO penton base and major core protein (analog HAV pVII) were found to consist of 514 (56.8 kDa) and 72 amino acids (8.4 kDa), respectively.