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ABL-MYC is a recombinant retrovirus that constitutively expresses the v-abl and c-myc oncogenes. When used to infect immunized mice this virus rapidly and efficiently induces plasmacytomas of which an unusually high percentage secrete antigen (Ag)-specific monoclonal antibodies. These findings suggested that ABL-MYC targets Ag-stimulated B cells for transformation and that infection of lymphoid cells in vitro might be a useful, alternative method for generating monoclonal, Ag-specific plasmacytomas (ASPCTs). Therefore, we used helper virus-free ABL-MYC to infect suspensions of cells from spleens and other lymphoid organs from mice that had been immunized with a variety of Ags and transplanted them into naive mice. The results show that ABL-MYC preferentially transforms splenocytes that are Ag-reactive. They also demonstrate that ASPCTs can be produced by in vitro infection of cell suspensions from the spleen, lymph nodes and Peyer's patches of mice that had been immunized intraperitoneally with sheep red blood cells, Escherichia coli core RNA polymerase or Epstein-Barr virus gp340 protein or immunized orally with live Giardia lamblia parasites. The ASPCTs usually consisted of one to three colnes, secreted antibodies that were quantitatively and qualitatively similar to those obtained from hybridomas, and could continue to secrete Ag-reactive antibody over eight transplant generations.

In an attempt to develop anti-AIDS drugs, the compound isatin beta-thiosemicarbazone has been subjected to systematic structural modifications. The resulting synthesized thiosemicarbazone derivatives (TSCDs) were examined for their ability to act as antiretrovirus agents in a model system--2M3/M cell system--consisting of B lymphocytes transformed by the v-abl oncogene and chronically infected with a retrovirus, the Moloney leukemia virus (M-MuLV). The efficacy of the synthesized TSCDs against retroviruses was determined by assaying the therapeutic index (TI) values of the compounds. The results enabled the classification of TSCD groups based on the relationship between chemical structure and antiretroviral activity. The compound N-allylisatin-beta':4'-diallylthiosemicarbazone showed the highest TI value and efficiently suppressed the chronic infection of M-MuLV in continuous long-term treatment.

The murine acquired immunodeficiency syndrome (MAIDS) caused by defective LP-BM5 murine leukemia virus (MuLV) is a disease that shows severe immunodeficiency with abnormal lymphoproliferation, and hypergammaglobulinemia in susceptible C57BL/6 (B6) mice. To examine the cellular mechanisms of development of MAIDS, we injected LP-BM5 MuLV intraperitoneally into B6 mice bearing the X chromosome-linked immunodeficiency (xid). xid mice lack functionally mature B cells including Ly-1 B cells (also known as B-1 cells). All B6 mice died by 20 wk after LP-BM5 MuLV inoculation. In marked contrast, xid mice have continued to survive without any sign of MAIDS-related symptoms till at least 20 wk after the inoculation. The delayed progression of MAIDS in xid mice appears to depend on xid mutation, according to our experiments using both sexes of (B6.xid x B6)F1 and (B6 x B6.xid)F1 mice. Furthermore, Ly-1 B cells, enriched by a FACS, were shown to integrate the defective genome and appeared to be a major virus-infected B cell population. Our data corroborate that Ly-1 B cells play an important role in the induction and progression of MAIDS.

B lymphoblast cells were immortalized by infection with a v-myc and v-raf/mil containing recombinant retrovirus. The immortalized B cells do not require exogenous growth factors or mitogens for growth. These cells express characteristic mature B cell phenotypic markers including IgM and IgD. Northern blot analysis detected mu and delta mRNA, and Southern blot analysis revealed rearrangements of Ig genes but not TCR genes in these cells. The immortalized B cells were found to respond to B cell mitogens by proliferation and IgM secretion, and to respond to IL-4 by an increase in la expression. Furthermore, they were found to differentiate to secrete IgM and to switch to IgG1 production following interaction with Staphylococcal enterotoxin B- activated Th2 cells. These cell lines are thus valuable tools for analyzing the molecular events involved in B lymphocyte growth and differentiation.

Murine AIDS (MAIDS) is caused by a defective retrovirus which encodes a gag fusion protein (Pr60gag). We previously reported that this virus induced an oligoclonal proliferation of infected cells and suggested that this cell expansion was an important event in the pathogenesis of MAIDS. To identify these target cells, we constructed novel defective viruses whose genomes could be detected with specific probes. Helper-free stocks of these viruses induced MAIDS. Using in situ hybridization and immunocytochemistry and Southern analysis, we found that most infected cells belong to the B-cell lineage. Transformation of these B cells appears to be the primary event responsible for the development of immunodeficiency. This animal model may be relevant to our understanding of AIDS, of the immunodeficiencies associated with B-cell lymphoproliferative disorders, and of the role of B-cell proliferation and transformation in the effects of superantigens, since Pr60gag appears to be a superantigen.

Heavy chain gene rearrangements were analyzed in 67 independently derived reticuloendotheliosis virus (REV-T) transformed avian lymphoid cell lines. The status of the heavy chain genes in these REV-T transformed cell lines was determined, in part, by the age of the chicken whose spleen cells were transformed. Cell lines derived by the in vitro transformation of splenic lymphocytes obtained from embryos did not contain heavy chain gene Ig rearrangements. By contrast, splenic lymphocytes transformed by REV-T obtained from birds 1 week or older generally exhibited heavy chain gene rearrangements. The REV-T transformed lymphoid cell lines with heavy chain rearrangements also had light chain gene rearrangements. The Ig gene rearrangements in REV-T transformed cells were functional. The majority of the cells which had heavy chain rearrangements expressed a 2.2-kb mu transcript and synthesized and secreted IgM. An REV-T transformant was also identified which produced IgG, suggesting that v-rel can transform a terminally differentiated cell. Irrespective of their Ig chain gene status the REV-T transformed cell lines expressed variable amounts of some but not all normal B cell-specific markers and failed to express T cell markers. All the cell lines analyzed expressed the B-L (Ia-like) antigen as well as a common leukocyte antigen. Based on the expression of these surface molecules, the transformants with or without Ig gene rearrangements all appear to be committed to the B cell pathway.

A lymphoblastoid cell line (B1) was isolated in culture following a brief exposure to 5-azacytidine from peripheral-blood mononuclear cells of a boar previously injected with cells (Shimozuma) producing porcine retrovirus (Tsukuba-1) and suffering a severe non-neoplastic syndrome at autopsy. B1 cell line and 5 of its sublines were propagated for more than 100 generations, retaining doubling times comprised between 16.8 and 27.5 hr and growing readily in agarose or agar (plating efficiency: 5 to 50%). Karyotype analyses showed that 4 sublines were nearly diploid, except for cells of L14, which displayed a monosomy affecting chromosome 18 pair. Two sublines (L35 and L45) were considered as being of T-cell lineage, since MSA, antigen was observed on the surface of approximately 30% of cells. Three sublines (L23, L14 and L52) were considered of B-cell lineage, since membrane immunoglobulins were observed on the cell surface. In addition, sublines L23 and L52 were actively secreting immunoglobulin of mu isotype. Retrovirus particles were evidenced in gradient-purified preparation of 200-fold-concentrated cell culture supernatants of the B1 cell line, L14, L35 and L52 sublines, using both a reverse transcriptase activity assay and electron microscopic observation. These cell lines can be used to select for porcine retrovirus variants with transforming potential for lymphocytes of B and T lineages.

A simple, efficient method has been developed for detecting retroviral RNAs expressed in cells. In this method, total RNAs or poly A+ RNAs extracted from various human cells are separated by electrophoresis and hybridized with synthetic oligonucleotides corresponding to the 3'-terminal 18 nucleotides of various tRNAs. Genomic and subgenomic RNAs of HTLV-I and HTLV-II in virus-infected cells and of xenotropic murine leukemia virus expressed in human lung cancer cells were easily detected with the tRNA(Pro)-derived oligonucleotide probe. This technique can be used to search for unidentified retroviruses expressed in human cancer cells and tissues.

Chicken syncytial virus, a member of the reticuloendotheliosis virus family, induces B-cell lymphomas in chickens that arise by transcriptional activation of the chicken c-myc gene. In vitro transcription studies on cloned tumor DNA containing a deleted chicken syncytial virus provirus integrated upstream from, and in the same transcriptional orientation as, the chicken c-myc coding region were utilized to map possible transcriptional promoters and initiation sites. In vitro transcripts extending into c-myc sequences were initiated at two sites within the downstream long terminal repeat (LTR) closest to c-myc coding sequences. Both initiation sites have been precisely mapped by S1 nuclease and DNA sequencing methods. One site (I1) lies at the U3-R junction of the LTR, and the other site (I2) lies approximately 160 nucleotides upstream. Transcriptional control signals, including TATA- and CAAT-like sequences are present at appropriate distances upstream from the initiation sites. Both initiation sites are utilized to a similar extent. The upstream chicken syncytial virus LTR was also shown to be transcriptionally active in vitro. Two strong transcriptional initiation sites were also found in the LTR of spleen necrosis virus, a related member of the reticuloendotheliosis virus family; therefore, it seems likely that the existence of two transcriptional initiation sites is a common feature of the reticuloendotheliosis virus LTR, in contrast to other previously studied retroviral LTRs that exhibit one such site. The possible implications of these findings are discussed.

Bovine leukemia virus (BLV) is experimentally infectious for sheep. Virus production does not occur in the animals, but only after in vitro cultivation of infected lymphocytes in the presence of phytohemagglutinin. Lipopolysaccharide or dextran sulfate 500 had no effect. After panning separation, it was possible to demonstrate that, in peripheral blood lymphocytes, BLV was integrated in the B lymphocytes only and that BLV expression took place in a fraction of this population. The ovine leukemia may constitute a good experimental model for understanding the virus-induced leukemias of the BLV-human T cell leukemia virus group.

Mitogen treatment of murine (BALB/c) B-cells induces two different endogenous retroviruses involving two unlinked, presumably proviral, loci Bxv-1 and Bdv-1. To determine the usefulness of these loci as genetic markers for B-cell differentiation their expression was studied under conditions that interfered with B-cell proliferation and differentiation into IgM-secreting plaque-forming cells (p.f.c.). Maximum production of both viruses followed peak DNA synthesis by an interval of about 18 h. Treatments that blocked DNA synthesis or killed proliferating cells inhibited virus production. Addition of BUdR to mitogen-stimulated cultures selectively induced Bxv-1 while inhibiting the generation of p.f.c. Both effects require BUdR incorporation into the DNA of proliferating cells. 5-Azacytidine induced Bxv-1-dependent virus production without inhibiting terminal B-cell differentiation. Pretreatment of mitogen-stimulated B-cells with anti-mouse IgM serum decreased both virus production and generation of p.f.c., but had little effect on DNA synthesis. Experiments using a mitogenic F(ab')2 preparation of anti-IgM in the presence and absence of lymphokines also suggested that the generation of p.f.c. and Bxv-1-dependent virus production are linked phenomena. The data imply that Bxv-1- and Bdv-1-dependent virus production require DNA synthesis and cell proliferation and, at least for Bxv-1, B-cell differentiation. It is proposed that the induction of these loci reflects the involvement of neighbouring DNA sequences in B-cell proliferation or differentiation.

Type D retroviruses have recently been shown to induce a wasting syndrome with associated lymphadenopathy, thymic atrophy and transient decreased peripheral blood lymphocyte blastogenic responsiveness in juvenile macaque monkeys. The replication in vitro of D/New England virus was assessed in various lymphocyte subpopulations to determine the possible pathogenesis of the immune dysfunction induced by this virus. While D/New England did not replicate in cultured T lymphocytes or induce any demonstrable dysfunction of T cells in vitro, it did grow in the cells of the B lymphocyte lineage. D/New England growth occurred in vitro in African Burkitt's lymphoma and pre-B cell lines, but not in Epstein-Barr virus-transformed normal B lymphocytes. The infection of a restricted B lymphocyte population by this primate type D retrovirus may play a role in the aetiology of the immune abnormalities which it induces.

B-cell lines which showed predominantly surface IgA kappa immunoglobulins were established from each of seven adult T-cell leukemia (ATL) patients. ATL virus proviral DNA was found in five of the lines. Though the chromosomal analysis of the B-cell lines yielded normal results, fresh leukemic T-cells showed chromosome abnormalities.

Electron microscope observation of cultured human leukemic B cell, T cell and null cell lines and reverse transcriptase assay of the culture supernatants were all negative for the presence of C-type virus. Bat cell line, which propagates primate C-type viruses well, was cocultivated with the human leukemic cell lines, in the hope of amplification of virus if present. Three weeks after mixed culture, the culture supernatants were again examined for reverse transcriptase activity and the cells were tested for syncytia formation by cocultivation with rat XC, human KC and RSb cell lines. All these tests, except for the positive control using a simian sarcoma virus, were negative, suggesting that no C-type was produced from these human leukemic cell lines.

We reported previously in vitro induction of endogenous C-type viruses from normal mouse spleen cells by lipopolysaccharide (LPS) as well as by combination treatment with concanabalin A and 5-bromo-2'-deoxyuridine (Con A/BrdU). To identify the cell types sensitive to virus induction and to study the relationship of mitogenicity to virus induction we have compared T cell populations (BALB/c thymus cells and cortisone-resistant thymus cells), B cell populations (nu/nu spleen cells and lymph node cells), adherent BALB/c peritoneal cells and mixed populations (BALB/c spleen cells, macrophage-depleted BALB/c spleen cells, and lymph node cells). LPS-induction occurred only in B cell-containing populations. In contrast, induction by Con A/BrdU depended on the presence of both T and B cells. In both instances, neither macrophages nor hemopoietic cells appeared to be a major source of virus. Treatment with anti-Ig serum and complement reduced virus induction by LPS/BrdU but not by Con A/BrdU suggesting that different cell populations produce virus after stimulation with these two different mitogens.

Neonatal infection of C57BL and BALB/c mice by cloned ecotropic and dualtropic mink cell focus-inducing (MCF) murine leukemia viruses (MuLV) induces a wide spectrum of different lymphomas of T, B, and non-T/non-B cell types. Oncogenic dualtropic MCF viruses and poorly oncogenic ecotropic MuLV act synergistically in lymphomagenesis. Within one mouse strain virus-induced T-cell lymphomas arise earlier than B-cell lymphomas after neonatal inoculation of a single-cloned MuLV. The host genetic constitution, notably the H-2 complex has a marked influence on lymphoma type. This H-2 influence can be explained by an H-2-linked difference in penetration of the thymus early in life by oncogenic thymotropic MuLV, which in turn is correlated with, but not necessarily due to the magnitude of the anti-MuLV antibody response.

Phytohemagglutinin (PHA) is known to increase the synthesis of bovine leukemia virus (BLV) particles and viral antigens in short-term culture of BLV-infected neoplastic and non-neoplastic lymphocytes. This stimulation of BLV expression has been shown to be due to enhanced transcription of the viral genome by a PHA-induced protein. We have investigated the binding of 125I-labelled PHA to BLV-infected bovine B lymphocytes and subsequent events that may lead to the stimulation of BLV-p25 synthesis. We found that PHA binding to the infected cells were rapid, but only a small fraction of the bound PHA is translocated to nucleus. However, bound PHA dissociated rapidly from the cell membrane, but not from the nucleus when PHA is removed from the culture medium. Furthermore, continuous presence of PHA was not essential for optimal stimulatory activity, instead a minimum incubation with PHA for 6 hr. followed by culturing the infected cells in its absence, was sufficient to exhibit maximal stimulatory activity. Our results raise the possibility that interaction of PHA with the plasma membrane probably triggers synthesis of a protein which in turn enhances the transcription of BLV genome in vitro.

Peripheral blood lymphocytes from 3 cows with persistent lymphocytosis were separated on nylon wool columns into nylon wool-adherent and nonadherent populations. The percentage of cells coated with surface immunoglobulin (B-cells) and the frequency of lymphocytic nuclear pockets in each sub-population were then determined. In each case the adherent population consisted predominantly of B-cells with an increased nuclear pocket frequency, whereas the nonadherent cells were 98.99% negative for surface immunoglobulin (non-B-cells) and contained essentially no nuclear pockets. These findings provided additional evidence that the B-subpopulation of cells was highly involved in bovine leukemia oncogenesis.

In the course of generating monoclonal antibodies to bovine thymus-dependent differentiation antigens, we were able to characterize an antibody, termed 8C11, that detects an antigen shared by a majority of thymocytes and peripheral T cells (in blood and thymus-dependent area of spleen and lymph-nodes), but undetectable on normal B cells. However, this antibody was reactive with B cells from cows infected with bovine leukemia virus (BLV). These BLV-infected B cells were found to express simultaneously high concentrations of both surface IgM and 8C11-detected antigen. The antigen recognized by this antibody was shown to be a 67.5 kDa molecule. Because similar findings have been made on mouse myelomas and on human chronic leukemia cells, where this antigen was considered to be the equivalent of mouse Ly-1 antigen and human Leu-1 or CD5 antigen, the T cell antigen detected on BLV-infected cells could be the bovine counterpart of the CD5 antigen. By another way, it has been found that the CD5 T cell antigen is also present on a minor subpopulation of B cells in the spleen but not in the blood. We suggest that in the bovine a similar B cell subpopulation should be the BLV target and expand as a consequence of viral insertion, leading to the persistent lymphocytosis observed on BLV-infected animals.

A strain of lymphadenopathy associated retrovirus ( LAV ) passaged in vitro was used to infect a lymphoblastoid cell line obtained by transformation with Epstein-Barr virus of B lymphocytes from a healthy donor. The virus produced from this line (B- LAV ) was also able to grow at a high rate in some other lymphoblastoid lines and in a Burkitt lymphoma line. This adapted strain retained the biochemical, ultrastructural, and antigenic characteristics of the original strain, as well as its tropism for normal T4+ lymphocytes. It is thus possible to grow LAV in large quantities that can be used for the preparation of diagnostic reagents. The interaction between such a human retrovirus and Epstein-Barr virus, a DNA virus, may have some implication for the pathology of the acquired immunodeficiency syndrome and related diseases.

To determine the phenotype of target cells for bovine leukemia virus (BLV) infection in sheep, we analyzed blood lymphocytes from BLV-infected clinically healthy and leukemic sheep by use of monoclonal antibodies. In clinically healthy and leukemic sheep that were BLV-infected, the blood concentration of T lymphocytes was within normal values, but the number of B lymphocytes was increased in several cases. In addition, the number of blood lymphocytes expressing the BLV antigen correlated well with that of B lymphocytes. Double immunofluorescence staining demonstrated that lymphocytes expressing BLV antigens bore B-cell but not T-cell surface markers. Moreover, neoplastic cells in the lymph nodes of leukemic sheep were stained immunohistochemically with an anti-B monoclonal antibody but not with any of anti-T monoclonal antibody tested, indicating that tumor cells are of B-lymphocyte origin. Collectively, these results show that BLV antigen-positive cells obtained from BLV-infected sheep that have no clinical signs and BLV-induced lymphosarcoma cells belong to the B-lymphocyte lineage.

Induction of endogenous retroviral proteins from spleen cells exposed to lipopolysaccharide (LPS) was studied in individual cells in relation to polyclonal B cell differentiation. After 4 days of culture with LPS, 30 to 40% of cells in many mouse strains stained for cytoplasmic mu heavy chains. A smaller number of lymphoid cells stained for cytoplasmic viral proteins, with a characteristic proportion for each strain, including 21% of lymphoid cells of AKR mice, 125 of DBA/2 cells, 7% of C57BL/6 cells, and 2% of BALB/c cells. More than 75% of retrovirus-positive cells were also mu-chain-positive in all strains. Cells from young (3- to 8-week-old) and old (43- to 46-week-old) mice of several strains showed similar proportions of retrovirus-positive cells typical for each strain, without differences at different ages. The induction of retrovirus proteins, as well as mu-chains, by LPS was markedly inhibited by goat anti-mu-chain antibody added to the culture medium (10 to 100 micrograms/ml). These data suggest that retrovirus induction may result from B cell differentiation.

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.

Snyder-Theilen feline sarcoma virus (ST-FeSV) codes for a protein kinase with specificity for tyrosine residues (Barbacid et al., Proc. Natl. Acad. Sci. U.S.A. 77:5158-5163, 1980), properties analogous to those of the transforming gene product of Abelson murine leukemia virus (Witte et al., Nature (London) 283:826-831, 1980). In the present report, ST-FeSV was demonstrated to transform murine hematopoietic cells under in vitro assay conditions which detect lymphoid cell transformation by Abelson murine leukemia virus. Bone marrow colony formation was shown to require ST-FeSV, follow single-hit kinetics, and require the presence of mercaptoethanol in the agar medium. ST-FeSV-induced colonies could be established in culture as continuous cell lines that demonstrated unrestricted self-renewal capacity and leukemogenicity in vivo. The hematopoietic blast cells transformed by ST-FeSV in culture appeared to be at an early stage of B cell differentiation. They possessed Lyb 2 surface antigens, were dependent on mercaptoethanol for growth, and contained only low levels of terminal deoxynucleotidyl transferase. Moreover, a large fraction of the lines synthesized immunoglobulin mu chain in the absence of light chains. Thus, the phenotype of ST-FeSV hematopoietic transformants was indistinguishable from that of the pre-B lymphoblast transformants induced by Abelson murine leukemia virus. These findings indicate that the in vitro functional similarities in the onc gene products of ST-FeSV and Abelson murine leukemia virus may reflect a common pathway by which they exert their oncogenic potential.

In order to determine which cell supports BLV replication in experimentally infected sheep, peripheral blood lymphocytes (PBL) were separated into purified B and T populations by a panning technique. Our data demonstrate that viral replication takes place only in B lymphocytes. However, PHA, a T cell mitogen, is necessary for BLV replication both in PBL and enriched surface immunoglobulin bearing cells, whereas B cell mitogens have no effect on viral replication. Altogether, these results suggest that BLV activation in enriched B lymphocytes is dependent on the presence of residual T cells, and occurs through a T cell interaction, probably mediated by a soluble factor. This possibility was confirmed by the fact that the conditioned medium from cultures of BLV-free sheep T lymphocytes greatly enhances viral production by infected B lymphocytes. Our data favor the hypothesis that BLV multiplication occurs through the regular activation mechanisms of the immune system.

We have established four cell lines in vitro from peripheral leukemic cells of four independent enzootic bovine leukosis (EBL) cattle. All cell lines exhibited differentiated B-cell characters. Two of them produced infectious bovine leukemia virus (BLV), but the others did not. Nonproducer cell lines contained single copies of defective BLV proviral genomes with the same integration profiles as the uncultured cells. On the other hand, numerous proviral copies were detected in producer cell lines. One of the producer cell lines, BL407, whose original uncultured cell contained complete and defective proviral genomes retained the original two copies and had increased only complete genomes in different integration sites after long term culture. These findings suggest that the monoclonal leukemic cells from EBL cases are preferentially established in vitro irrespective of their proviral structures, and the producer B-lymphoid cells amplify their proviral copies by reinfection with viruses re-expressed from the cells during in vitro cultivation.

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.

Type D retroviruses belong to viruses which often have a low titer in virus-reproducing cell-systems. In search of better conditions for virus propagation, Raji cells (an EBV-genome carrying human B-cell line) were infected with different isolates of type D retroviruses. as demonstrated by electron microscopy all of the viruses showed a very good and stable virus production during long term cultivation on Raji cells.

We have documented the effect of two nondefective helper viruses, reticuloendotheliosis virus A (REV-A) and chick syncytial virus (CSV) infection on bursal tissue. REV-A infection results in bursal atrophy, destroying both its structural and functional integrity. In contrast, the bursae in CSV-infected chicks, while reduced slightly in size, appear both structurally and functionally normal. REV-A-induced bursal atrophy is not a result of viral replication in the B-lymphocyte as (a) both viruses are capable of inducing, with equal efficiency, the formation of preneoplastic lesions containing proliferating B lymphocytes and (b) it appears that equivalent amounts of viral antigen are expressed in the bursae of chicks infected with either virus. We have examined the phenotype of tumors induced by the replication-defective virus REV-T when replicated by the two different helper viruses, REV-A and CSV. In REV-T(REV-A)-infected chicks, the majority of tumors that develop are negative for IgM expression. In contrast, the majority of tumors induced by REV-T(CSV) infection are IgM+. This finding is confirmed by recovery of IgM- cell lines from REV-T(REV-A)-infected chicks and IgM+ cell lines from REV-T(CSV)-infected chicks. In addition, repopulation studies show that bursal-derived cells that are IgM+ serve as target cells for REV-T(CSV)-induced lymphomas. This study demonstrates, therefore, that REV-T can induce IgM+, B cell lymphomas with high efficiency. We conclude that infections by the helper viruses, REV-A and CSV, differ dramatically in their effects on the composition of the population of cells that serve as targets for REV-T-induced neoplasia.

Eight lymphoblastoid cell lines were established from the peripheral blood of individual African green monkeys (AGM). The AGM-2206 line grew out spontaneously. The others - AGM-6, 7, 8, 10, 12, 13, and 16 - were obtained after infection of peripheral AGM lymphocytes with cell-free culture supernatant of AGM-2206. All lines contained, and were probably transformed by, AGM-EBV. Moreover, they expressed immunoglobulins but lacked the Leu l T-cell marker. Thus they were B cells. Since a high percentage of AGMs are naturally infected with a virus similar to adult T-cell leukemia virus (ATLV), we examined these cell lines for ATLV. With immunofluorescence tests we detected ATLV-related antigens (ATLA) in three of the eight cell lines. EBV membrane antigen was present in three out of four. The highest percentage (40%) of ATLA-positive cells was found in the AGM-13 line. After metabolic labelling of these cells, ATLV-specific polypeptides p24, p19, p15, and p10 were detected. Hybridization experiments showed that both AGM-2206 and AGM-13 cell lines contained ATLV-proviral DNA. Electron micrographs of AGM-13 revealed a few type-C particles morphologically similar to the MT-2 virus. By cocultivation this AGM virus was able to infect and immortalize human peripheral blood lymphocytes. One such human cell line, NA-13, expressed polypeptides closely related to ATLV core antigens but a 68,000 mol.wt. glycopolypeptide was serologically distinct from MT-2 ATLV gp68.

Bovine leukemia virus-infected sheep were demonstrated to possess a plasma factor that specifically suppresses in vitro virus expression in lymphocyte cultures. This blocking activity is observed even after phytohemagglutinin (PHA) stimulation and is independent of cellular proliferation. Such a factor may play a critical role in the regulation of BLV expression.

A human type C retrovirus, designated HTLV, previously was isolated from or identified in some patients with leukemias and lymphomas of mature T lymphocytes. HTLV is genetically and serologically distinct from any known animal retroviruses. The absence of HTLV proviral sequences in DNA from normal humans showed that HTLV is not a ubiquitous endogenous (germ-line transmitted) virus of humans. Antibodies to HTLV core proteins have been identified in some people with T-cell neoplasias and are particularly prevalent in Japanese with adult T-cell leukemia, suggesting that HTLV is acquired horizontally. However, it was possible that HTLV is transmitted through the germ line of some (possibly rare) families and is then expressed in the HTLV- positive malignancies. An opportunity to study this question was provided by the development of several T-cell lines and a B-cell provided by the development of several T-cell lines and a B-cell line from one HTLV-positive patient with a cutaneous T-cell lymphoma. Here we report that HTLV proteins or nucleic acids (or both) are found in three independently derived T-cell lines, all shown by HLA typing to have originated from the patient. In contrast, the B-cell line, the identity of which was also ascertained by HLA typing, contained no detectable HTLV protein, RNA, or proviral DNA. Because the sensitivity of the latter assay is more than sufficient to detect one proviral equivalent per haploid genome, the results indicate that HTLV was not transmitted to this patient through the germ line but rather was acquired by infection.

Bovine peripheral blood lymphocytes from a cow with persistent lymphocytosis were separated on nylon wool columns into nylon-adherent and nonadherent populations. Nylon-adherent cells were highly enriched for surface immunoglobulin (SIg) bearing B lymphocytes (95.5%) and nonadherent cells for SIg negative non-B cells, presumably T lymphocytes (96.3%). The B lymphocytes were found to be the major producers for bovine leukemia virus. A total of 39% of the B-enriched cells, surviving after 72 hours in culture, produced bovine leukemia virus as compared with 0.5% of the non-B cells.