Morphogenesis of bovine leukemia virus

Cellular distribution of bovine leukemia virus proteins gp51SU, Pr72(env), and Pr66(gag-pro) in persistently infected cells

Monoclonal antibodies (mAbs) against bovine leukemia virus (BLV) mature proteins and precursors were used to map the localization of these proteins in persistently infected non-lymphocytic cell lines using immunofluorescence assay (IFA) and immuno-electron microscopy. IFA staining was observed in the basolateral surface of live FLK-BLV cells. When using a mAb against Pr66(gag-pro), mottled pinpoint fluorescence was seen in the cell surface of polarized cells, but no reaction was observed in cells undergoing mitosis. However, a mAb against Pr72(env) stained only mitotic cells and cellular fragments. Additionally, in these dividing cells, this envelope (Env) precursor polyprotein was not evenly distributed but concentrated predominantly in only one daughter cell. To the best of our knowledge, this observation has not been reported previously, either for BLV or for other retroviruses. The results of immunogold electron microscopy confirmed the specificity of the mAbs in the intracellular level. In infected cells, Pr72(env) and gp51SU were seen in proximity at the plasma membrane in incipient budding sites. Additionally, the mAb against Pr72(env) also reacted with Env precursor polyproteins in the mitochondria of BLV-bat(2) ultrathin sections. These mAbs may be used as a tool for mapping virus excretion sites in the cell surface of naturally or in vitro infected cells in the different stages of the cell cycle.

Evaluation of virus excretion by cells persistently infected with the bovine leukaemia virus (BLV) using monoclonal antibodies

BACKGROUND

bovine leukaemia virus (BLV) is the causative agent of enzootic bovine leukaemia. Studies in vitro usually require the use of infected cell lines, mostly to produce antigen. Two of the most widely used cell lines are FLK-BLV and BLV-bat2.

OBJECTIVE

the dynamics of the excretion of BLV proteins and whole virus by the persistently BLV-infected cell lines mentioned above was studied using an indirect ELISA in combination with eight monoclonal antibodies (mAbs) and cow and rabbit serum.

STUDY DESIGN

tissue culture flasks were seeded with different concentrations of cells (13000-67000 cells per cm2, corresponding to 1-5 million cells per 75 cm2 flask) and were studied for 20 days. Samples (1.5 ml) were removed every 24 h and the presence of BLV proteins was determined using an indirect ELISA assay in which the antigen reaction with the monoclonal antibodies was evidenced by peroxidase labeled anti-mouse immunoglobulins.

RESULTS

cell line FLK-BLV produced a complete monolayer as early as 4 days after passage, 3 days earlier than BLV-bat2. Using mAbs, the amount of viral proteins in the supernatant showed a cyclic pattern, with two evident peaks at days ca. 8 and 16. These peaks occurred even in the absence of passage or medium change, which causes depletion of essential nutrients and acidity. In comparison to polyclonal serum, mAbs gave more clear and defined values and are useful for determining the dynamics of viral production.

CONCLUSION

when aiming for high viral yield, BLV should be harvested between days 6 and 8 after passage, when viral shedding is at its maximum. These results are very useful for preparing antigen for monoclonal antibody production, or for techniques such as ELISA or Western blot.

In vitro infection of cells of the monocytic/macrophage lineage with bovine leukaemia virus

The oncogenic retrovirus bovine leukaemia virus (BLV) primarily infects B cells. Most infected animals remain asymptomatic for long periods of time before an increase in circulating B cells or localized tumours can be observed. This long clinical latency period may be explained by cells of the monocyte/macrophage lineage (M/M) becoming infected and acting as a reservoir for the virus, as shown for other retroviruses (human immunodeficiency virus-1, feline immunodeficiency virus). M/M cells in different stages of differentiation (HL-60, THP-1, U-937, J774, BGM, PM2, primary macrophages of sheep and cows) were cultured with BLV produced by permanently infected donor cells (FLKBLV and BLV-bat(2)). Donor cells were inhibited from multiplying by either irradiation or treatment with mitomycin C. In other experiments, supernatant from donor cells containing virus was used. In co-culture with the donor cells, the less differentiated monocytic cells showed severe cellular changes such as differentiation, vacuolization, cell lysis and membrane blebbing; apoptosis was a frequent phenomenon. Budding and extracellular viruses were also observed. The more differentiated macrophage cells, although they showed less signs of infection by microscopy, had a complete BLV protein profile, as seen by Western blotting; bands corresponding to p24CA (Gag) and its precursors were clearly seen. In addition, gp51SU was identified by syncytia formation assays. It is concluded that M/M cells may be infected by BLV, the consequences of the infection differing according to the type of cell.

Electron microscopical and biochemical investigations on retra viruses in spleen tissue in malignancy

Simultaneous biochemical and electron microscopical investigations on surgically removed spleens yielded evidence for the presence of reverse transcriptase containing (Retra) virus in two patients with hematological malignancies with spleen involvement. In three other patients with hematological diseases and in one control patient, the spleens were negative in both assays. The results of these combined studies support the view, that retraviruses are present in human malignancies.

Induction of C-type virus in cell lines derived from calf form bovine lymphosarcoma

For attempt to detect an etiological agent, cultures from bovine lymphosarcoma cases (adult form (ALS), calf form (CLS), and thymic form (TLS) were maintained in vitro for over a 18 month period. In two cultures from ALS, bovine leukemia virus (BLV) antigen was constantly detected. On the other hand, BLV antigen remained negative in cultures from two CLS and one TLS cases up to 40 passages. The RNA dependent DNA polymerase activities in these cultures were also negative. Treatment of a culture from CLS (3178) originated from liver tumor with 5'-iodo-2'-deoxyuridine (IdU) and dexamethasone (DXM) resulted in production of an agent serologically and morphologically similar to BLV and in alteration of cell morphology. No virus was detected in culture from TLS after treatment with IdU and DXM.

Induction of oncornavirus-like particles in cell line of canine mammary carcinoma

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