T-B cell cooperation for bovine leukemia virus expression in ovine lymphocytes

Bovine leukemia virus (BLV) replication in B lymphocytes from experimentally infected sheep depends on three conditions. First, viral production is detected only when the infected animals exhibit blood lymphocytosis. Second, it requires in vitro cultivation but is never observed in vivo. Third, enhancement of virus expression after phytohemaglutinin (PHA) or concavalin A stimulation is observed in lymphocyte cultures for all infected animals, whereas specifically B cell mitogens are inefficient. The PHA effect is linked to the presence of T lymphocytes. In addition, the conditioned medium prepared from PHA-stimulated normal lymphocytes greatly enhances BLV production. Altogether, these results establish that T lymphocytes, through a lymphokine production, are important and may be essential for BLV growth in B lymphocytes.     

Methylation pattern of the bovine leukemia provirus genome in bovine leukemic cells

All the known genes of the bovine leukemia proviral genome were found to be heavily methylated in both fresh and short-term-cultured leukemic cells, the latter of which expressed viral antigens. However, the pXBL region appeared to be mostly demethylated or at least hypomethylated in both cells, indicating that there is a non-uniform methylation pattern of the proviral genome.     

Tumor-associated antigen in bovine and ovine lymphosarcoma.

Specific tumor-associated antigens were found on the membrane and in the cytoplasm of lymph node cells and peripheral blood lymphocytes (PBL) from cattle and sheep with lymphosarcoma by immunofluorescence tests. Materials from 15 cattle with the adult form of lymphosarcoma were examined. Cytoplasmic antigen was detected in fixed tumor cells from all 15 cases and in PBL from 9 cases tested. Membrane antigen was detected in living cells from 10 of the cases tested. In 3 calf-type cases, cytoplasmic antigen was found in a few (1 to 3%) of the tumor cells, while 1% of the cells from 2 thymic cases had cytoplasmic tumor antigen. In 15 cattle infected with bovine leukemia virus (BLV) but with no evidence of tumor, PBL from 3 cattle had the tumor-associated antigen in the cytoplasm. Negative results were obtained with similar tests done with 9 normal cattle that had no detectable BLV or BLV antibody. Cells from tumors induced with BLV in 5 sheep also had cytoplasmic antigen and membrane tumor-associated antigen. Tumor-associated antigen was found in PBL from 1 or 7 BLV-infected sheep with no clinical evidence of tumor. Similar tests were negative on 4 normal sheep.     

Murine leukaemia virus expression in the AKR following thymectomy.

Thymectomy effectively prevents the development of spontaneous lymphoma in the AKR but how this effect is achieved remains to be determined. One possible mechanism, namely suppression of genomic expression of the oncogenic murine leukaemia virus now seems unlikely since levels of the group specific MuLV antigen were in comparision with their sham operated controls unaltered in both neonatally and adult thymectomized AKR.     

Integration of retroviral DNA into the genome of the infected cell

Retroviruses replicate through an intermediate known as a provirus, a DNA copy of the viral genome that is covalently integrated into the host genome. The formation of the integrated provirus ensures the persistence of the viral genome in the infected cell and its transmission to daughter cells. Integration is thus central to the ability of retroviruses to make permanent genetic changes in the host cell through transfer of active oncogenes or through insertional activation of endogenous proto-oncogenes. Our current understanding of the integration reaction will be reviewed below.     

Infectious feline leukaemia virus is erythrosuppressive in vitro

The direct effect of the feline leukaemia virus (FeLV) on erythroid colony formation in vitro was investigated. Bone marrow mononuclear cells (BMMC) from FeLV-na?ve, specific-pathogen-free (SPF), adult cats were inoculated with FeLVs of characterized strains and biologically cloned subgroups and the subsequent development of colony forming units-erythroid (CFUE) and burst forming units-erythroid (BFUE) and colony forming units-granulocyte-macrophage (CFUGM) was monitored. Exposure to the anaemia-causing Kawakami-Theilen strain of FeLV (FeLV-KT), a phenotypic mixture of subgroups A, B, and C, caused constant depression of day 2 CFUE (to 47% of sham-inoculated controls), day 4 CFUE (41% of controls), and day 10 BFUE (38% of controls). CFUGM were unaffected. The lymphoma-causing Rickard strain of FeLV (FeLV-R-TL) caused sporadic depression of CFUE and BFUE. In contrast, neither FeLV-R passaged through feline embryonic kidney fibroblasts (FeLV-R-CRFK) nor biologically cloned, subgroup-specific, FeLVs of fibroblast origin, caused decrements in CFUE or BFUE, suggesting that fibroblast passage attenuated the direct erythrosuppressive effect of FeLV. Suppression of CFUE and BFUE by lymphoma cell-origin FeLV was dependent on infectious virus and was associated with FeLV replication by the cultured myelomonocytic precursor cells. Attenuation of infectivity by heat or u.v. restored CFUE and BFUE development. Examination of the relationship between viral infectivity (VI), viral protein concentration, and CFUE suppression showed that the infectious FeLV was 20-fold more effective than u.v.-inactivated FeLV as an inhibitor of erythrogenesis in vitro.     

Cross-neutralization of ovine and bovine C-type leukemia virus-induced syncytia formation.

Ovine leukemia virus (OLV) could not be distinguished from bovine leukemia virus (BLV) morphologically. Both C-type RNA tumor virus-producing cells induced syncytia when cocultivated with several indicator cells including XC and KC cells. Syncytia formation could be blocked by antibodies against OLV and BLV, indicating that fusion was virus mediated. Furthermore, antibodies against OLV and BLV exhibited reciprocal syncytial blocking properties, suggesting that OLV and BLV were closely related viruses.     

Interaction between feline leukaemia virus subgroups in the pathogenesis of erythroid hypoplasia

The interaction of feline leukaemia virus (FeLV) of subgroups A and C in the pathogenesis of erythroid hypoplasia in cats was studied. Weanling kittens infected with FeLV-A became permanently viraemic but remained haematologically normal over a period of 36 weeks. Similar kittens inoculated with FeLV-C, which produces erythroid hypoplasia when administered to newborn kittens, neither became viraemic nor developed the disease. However, weanling kittens inoculated with a mixture of FeLV-A and C became viraemic, first with FeLV-A and then additionally with FeLV-C, and the emergence of FeLV-C into the blood coincided with the advent of erythroid hypoplasia. When FeLV-C was inoculated into five older cats which had been viraemic with FeLV-A for several months previously, it appeared in the plasma of three of the cats and erythroid hypoplasia was diagnosed in two of these, 16-20 weeks after infection with FeLV-C. These results show that FeLV-A enhances the growth of FeLV-C in cats and overcomes their age-related resistance to FeLV-C. Also, the appearance of FeLV-C in the plasma of cats viraemic with FeLV-A indicates that erythroid hypoplasia will subsequently occur rapidly. These findings are relevant to the origin of FeLV-C isolates and their occurrence in nature.     

Integration and expression of the oncornavirus type D genome in transplantable cells]

The authors investigated five cell cultures producing oncornaviruses type D by the method of molecular hybridization of viral nucleic acids with cell nucleic acids. It was shown that nuclear DNA of the cell lines under study contained scores and hundreds of viral RNA genome-equivalents, while cytoplasmatic RNA contained hundreds and thousands of viral genomes. Viruses produced by the cultures involved are found to be identical or highly similar to nucleotid sequences of their nucleic acids.     

Azacitidine induces demethylation of the Epstein-Barr virus genome in tumors.

PURPOSE: To determine whether therapy with a DNA methyltransferase inhibitor is effective in achieving demethylation and gene re-expression in tumor DNA in patients. METHODS: Biopsy specimens were obtained from patients with Epstein-Barr virus-associated tumors, enrolled on a clinical trial of 5-azacitidine, within 72 hours of the conclusion of the last infusion of the first cycle of therapy, and compared to pretreatment specimens. Methylation-specific polymerase chain reaction, bisulfite genomic sequencing, and immunohistochemistry were used to assess demethylation and gene re-expression. RESULTS: Substantial degrees of demethylation were detected in all latent and lytic Epstein-Barr virus promoters examined. Immunohistochemistry suggested activation of a previously silent viral antigen expression in one instance. CONCLUSION: Pharmacologic reversal of dense CpG methylation in tumor tissue can be achieved in patients.     

Sero-epidemiological analysis of the risk of virus infections for childhood leukaemia

Virus infections have been thought to be involved in the development of childhood leukaemia. In order to address this issue we determined, in a case-control study, the prevalence of antibodies to viruses infecting blood or bone-marrow cells [Epstein-Barr virus (EBV), human herpes virus type 6 (HHV-6), parvovirus B19] as well as to the human virus known for its tumour-suppressive properties, the adeno-associated virus type 2 (AAV-2), in the sera of 121 children with leukaemia in Germany, and in 197 control individuals, hospitalized for other reasons, and matched for age and gender to the cases. In addition, we developed a questionnaire to be answered by the children's parents, in order to gain information on previous infections of the children as well as to calculate for factors which may influence serological findings. Comparative determination of the prevalence of antibodies against AAV-2, B-19 or HHV-6 revealed no significant differences in cases and controls. However, antibodies to EBV were more frequently found in children with leukaemia younger than 6 years of age (age at the time of diagnosis of leukaemia) than in controls. Apparently, infection with AAV-2 has no protective effect in childhood leukaemia, in contrast to results observed for other malignancies. Similarly, and in accordance with results on leukaemia in adults, we found no indication of a protective effect of infection with the parvovirus B-19. The data suggest that EBV, which is known to be involved in various lymphomas, may play a role in the development of childhood leukaemia in young children. © 1996 Wiley-Liss, Inc.     

The influence of sex upon the development of friend virus leukaemia

The morbidity and mortality in Parkes mice of both sexes following the injection of various doses of Friend leukaemia virus have been studied. Individual mice were tested for the presence of viraemia and for neutralizing and tumour-specific cytotoxic antibodies. The principal findings were: (1) more rapid death among the female than the male mice; (2) the fact that, among the mice with splenomegaly, those with viraemia are usually male while those with neutralizing or cytotoxic antibodies are usually female; (3) the presence of circulating cytotoxic antibody in many mice with splenomegaly. It is hypothesized that female mice with Friend virus leukaemia are considerably superior to males in antibody-producing capacity and that the former owe their more rapid death to tissue damage caused by an immunological response to the virus or cellular neo-antigen.     

Antiapoptotic activity of bovine papilloma virus

Transformed fibroblasts have been recently shown to be sensitive for induction of apoptosis by TGF-beta-treated neighbouring untransformed cells. Cells transformed by a variety of different transformation principles were regularly sensitive for intercellular induction of apoptosis, but fibroblasts transformed by bovine papillomavirus (BPV) represented a striking exception. In contrast to chemically transformed C127 cells, BPV-transformed C127 cells showed resistance against intercellular induction of apoptosis. In addition, BPV-transformed cells were resistant against induction of apoptosis by ROS in glutathione depleted cells. The antiapoptotic function of papillomaviruses may be of central importance for papillomavirus-induced tumor formation as it can protect transformed cells from intercellular control of oncogenesis.