Sporadic bovine leukosis: a description of eight calves received at Animal Diseases Research Institute from 1974-1980

Eight calves with sporadic bovine leukosis are described. The common features were generalized lymphadenopathy, visceral involvement and raised total leukocyte and lymphocyte counts. Agar gel immunodiffusion tests for bovine leukemia virus antibodies were negative in eight animals and in all animals from three herds of origin. Lymphocytic nuclear pockets were found in the tissues of one calf but attempts to isolate bovine leukemia virus from two animals were unsuccessful.

[Detection of bovine leukemia virus in tissue cultures]

Syncytium formation was demonstrated in cocultivation of cow and sheep embryo kidney cells with peripheral blood lymphocytes from leukemic cattle. The beginning of this phenomenon was observed at 3--4, and maximum development at 6--8 days of cocultivation. Lymphocytes of 22 out of 24 leukemic animals were capable of inducing syncytium formation. Parallel examinations of cocultivated cells by the direct immunofluorescence procedure using fluorescent antibodies from sera of leukemic cows gave positive results in 23 our of 24 cases, whereas lymphocytes of 12 normal cows never induced either syncytium or specific antigens.

Detection of bovine leukemia virus by syncytium assay

When various indicator cells, including virus transformed and nontransformed cells, were cocultivated with bovine leukemia virus-producing cells, strong positive syncytia formation was found in transformed cells one day after cocultivation. The results of comparison of bovine leukemia virus antibody titers and the detection of bovine leukemia by the syncytium assay showed 89% of serologically positive cows were positive for bovine leukemia virus, whereas no reactors were found in serologically negative cows. However, the frequency of bovine leukemia virus detection differed according to the difference of incubation periods in the syncytium assay. Therefore, it is important to choose the appropriate indicator cell and culture conditions for the detection of bovine leukemia virus in the syncytium assay.

An infectivity assay for bovine leukemia virus using the immunoperoxidase technique

This report describes the development of a 7-day infectivity assay for bovine leukemia virus (BLV) which is based on the induction of the major internal virion antigen (a protein with a molecular weight of 25,000) in susceptible indicator monolayer cell cultures. In this assay, the antigen is detected in the indicator cells by the immunoperoxidase antibody technique using a specific rabbit antiserum to a BLV protein with a molecular weight of 25,000. The immunoperoxidase infectivity assay is specific, quantitative, reproducible, and more sensitive than the previously described syncytia induction assay. The immunoperoxidase infectivity assay can be applied to the detection of BLV-infected cells and provides a reliable method for the direct diagnosis of BLV infection in cattle.

Infectivity tests of secretions and excretions from cattle infected with bovine leukemia virus

Secretions and excretions from cattle with persistent bovine leukemia virus (BLV) infections were tested for BLV by inoculation into sheep. Development of antibody to the BLV glycoprotein antigen and reisolation of virus from peripheral blood leukocytes were the two criteria used to confirm infection in test sheep. The virus was detected in milk from 4 of 6 cows examined and in colostrum from 1 of 4 cows examined. The virus was not detected in semen from 8 bulls or in nasal secretions, saliva, and urine from 2 cows.

Natural mode of transmission of the bovine leukemia virus: role of bloodsucking insects

The development of bovine leukemia virus (BLV) infection was studied in 14 noninfected young adult cattle exposed to 25 to 30 BLV-infected cows in an area of approximately 0.5 ha. Of 7 cattle (group 1) exposed beginning in July and August (midsummer) of 1976, 4 were infected by October, and all 7 by November (4 months' exposure). Of 7 cattle (group 2) exposed from February 1977 (midwinter), all remained negative for 3 months, and only 1 was positive after 6 months. By October 1977, however, 4 cattle in this group were infected, indicating that contact transmission of BLV is prevalent during the summer months. This, and the fact that BLV-infected lymphocytes were recovered from tabanids allowed to feed on a BLV-positive cow, supports the idea that bloodsucking insects play a major role in the spread of BLV.

Direct syncytial assay for the quantitation of bovine leukemia virus

A direct in vitro tissue culture method is described for the quantitation of bovine leukemia virus, utlizing a feline S+L-- cell line.

Detection of bovine leukemia virus in B-lymphocytes by the syncytia induction assay

Bovine peripheral blood lymphocytes (PBL's) from 3 cows and 1 steer infected with bovine leukemia virus (BLV) were separated by fractionation through nylon wool columns into nylon-adherent and nonadherent cell populations. Nylon-adherent cells were enriched in B-lymphocytes, as determined by the presence of surface membrane immunoglobulins (slg), whereas nylon-nonadherent cells or "non-B-lymphocytes" contained few slg-bearing cells. PBL's and separated B- and non-B-lymphocyte populations were assayed for the presence of BLV by the induction of syncytia in bovine embryonic spleen cells. PBL's and B-lymphocyte populations both produced many syncytia, whereas non-B-lymphocytes yielded few or no syncytia. The specificity of syncytia formation by anti-BLV serum. PBL's from 2 control animals were negative for syncytia induction. This study presents further evidence that B-lymphocytes are the target cells for BLV infection.

Bovine lymphosarcoma in twin calves

Lymphosarcoma in twin female calves, apparently the first to be observed in Canada, is reported here. Peripheral blood and cultured mononuclear cells of one of the calves showed aneuploidy of the chromosomes. No hematological or serological evidence of bovine leukemia virus infection was observed in the other members of the herd. Bovine leukemia virus infection of the leukemic cells could not be detected by electron microscopy or by tissue culture procedures. There is a need to clarify the relationship of the calf form of the disease to the adult form of enzootic bovine leukosis.

Cellular basis of persistent lymphocytosis in cattle infected with bovine leukemia virus

Peripheral blood lymphocytes from 14 cattle infected with the bovine leukemia virus (BLV) and 14 BLV-free cattle were examined by the membrane immunofluorescent antibody technique to detect surface immunoglobulin (S-Ig) and by the erythrocyte-antibody-complement (EAC) rosette test for the detection of complement receptors. Direct comparisons of the percentages of S-Ig-bearing cells and EAC rosette-forming cells in both infected and BLV-free animals showed no evidence for the presence of a substantial population bearing one surface marker but not the other. The data showed that cells with surface markers characteristic of B lymphocytes are responsible for most of the increase in peripheral blood lymphocytes which may accompany BLV infection. The release of infectious BLV and the spontaneous uptake of thymidine by short-term cultured peripheral blood lymphocytes from BLV-infected cattle were also studied. The results indicate that both of these activities are function of B lymphocytes.

Isolation and characterisation of oncornavirus from primary cultures of tissues from cattle with leukemia

The purpose of this investigation was to search for oncornavirus in primary cell cultures obtained from leukemic cattle organs and lymphocytes and to study their molecular-biological properties and role in the etiology of cattle leukemia. The investigation was carried out on 25 primary trypsinized cell culutres of lymph nodes, spleens, kidneys and lymphocytes from cattle with acute and chronic leukemia. It was demonstrated that all cell cultures from leukemic cattle (in contrast to cell cultures from healthy cattle) released oncornavirus into the culture medium. The virus possesses the main properties of oncornaviruses: it has a virion of C-type structure with a density of 1.16--1.18g/ml in a 20--60 per cent sucrose gradient, which may be induced by 5-bromodeoxyuridine, inhibited by Actino-mycin D, has reverse transcriptase activity, contains 60S RNA, that is annealed in the reaction of molecular hybridization with DNA of lymph nodes of cattle with leukemia. The propagation of the isolated oncornavirus in continuous cell lines of calf kidney culture was demonstrated. Experimental inoculation of purified oncornavirus was carried out on 60 baby calves and 15 lambs from leukosis free herds or flocks. Several of the calves later showed evidence of virus infection.

Inhibition of bovine leukemia virus release by antiviral antibodies

Peripheral blood lymphocytes from bovine leukemia virus (BLV) infected cattle were grown in vitro with serums from BLV-infected and uninfected cattle, sheep and rabbits. Only serums from infected animals which had antibody to gp 45/55, the major glycoprotein antigen, inhibited the release of virus from the cells. Although viral antigens could be detected in the cells themselves, none were detected in the supernatants of cultures grown with these serums. Normal serums and serums with antibody only to p23, the internal BLV antigen, did not inhibit virus release. To identify the factor responsible for virus release inhibition, 2 inhibitory serums were absorbed with either gp 44/55, p23 or tissue culture cells from BLV-infected and uninfected cells lines. The results indicated that antibody to gp 45/55 is the factor responsible for virus release inhibition.