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Radiation leukemia in C57BL/6 mice. I. Lack of serological evidence for the role of endogenous ecotropic viruses in pathogenesis.

The humoral immune response against endogenous ecotropic murine leukemia viruses (MuLV) was examined in irradiated and control C57BL/6 mice. Control mice developed antibodies against MuLV slowly throughout life. In contrast, within 2-3 mo after irradiation 90% of irradiated C57BL/6 mice had developed detectable antibodies against MuLV. The characteristics of this immune response, however, were identical in control and irradiated mice in terms of peak titers, specificity for endogenous ecotropic MuLV, and reactivity against the ecotropic viruses' glycoprotein (gp71). Moreover, the rate of appearance of antibodies against MuLV in irradiated mice and the peak titers were generally not affected by age at irradiation, dose of irradiation (two, three, or four treatments of 175 R), or bone marrow reconstitution. Although the ability of irradiation to accelerate the appearance of antibody in a population of C57BL/6 mice suggested activation of endogenous ecotropic MuLV, there was no apparent correlation between the appearance of this immune response or its persistence and the development of lymphoma. Thus, the incidence of lymphoma was comparable in mice that: (a) developed no immune response; (b) developed an immune response only transiently after irradiation; or (c) developed an immune response which persisted until death from lymphoma. Moreover, experimental conditions that alter the ability of irradiation to induce leukemia, such as age, dose, or bone marrow reconstitution did so without significantly altering either the rate of appearance of a humoral immune response to MuLV or its peak titers. The results, therefore, fail to demonstrate any seroepidemological relationship between endogenous ecotropic MuLV and radiation-induced leukemia.

AKR murine leukemia virus

Increased synthesis and expression of H-2 antigens on thymocytes as a result of radiation leukemia virus infection: a possible mechanism for H-2 linked control of virus-induced neoplasia.

Previous studies from this laboratory have mapped resistance and/or susceptibility to radiation-induced leukemia virus (RadLV)-induced neoplasia to the H-2D region. H-2 linked effects on virus replication can be detected subsequent to the initial virus infection, and clear-cut differences in numbers of virus infected thymus cells can be detected as early as 5 wk after RadLV inoculation. Rapid increases in cellular synthesis and cell surface expression of H-2 antigens are detectable immediately after virus inoculation. These changes have been studied by immunofluorescence, absorption, cell surface iodination followed by sodium dodecyl-sulfate-polyacrylamide gel electrophoresis, and two dimensional gel electrophoretic analysis of internally labeled lymphocyte proteins. Expression of H-2K molecules is significantly increased in cells of susceptible and resistant animals. However, significant increases in expression of H-2D antigens occurs only on thymus cells from resistant strains (H-2Dd). Transformed cells of resistant and susceptible H-2 haplotypes adapted to tissue culture lack detectable H-2 antigens as determined by serological absorption studies. It is argued that altered expression of H-2 antigens plays a very significant role in the mechanism of host defense to virus infection.

Animals

Detection of a TL(+) murine leukemia cell line that resists the cytotoxic effects of guinea pig complement and specific antiserum.

RADA-1 cells [H-2a thy-1b; thymus-leukemia (TL) 1, 2, 3], a radiation-induced murine leukemia cell line maintained by serial transfer in histocompatible recipients, resisted lysis by guinea pig complement (GPC) and TL 1, 3; TL 2; or TL 1, 2, 3 antiserum. The cells expressed TL antigenic specificities as determined by indirect fluorescent antibody methods, the direct isolation of TL antigens from the cells, and the capacity of the cells to reduce known titers of TL antisera. GPC was consumed to the same extent during the reaction of resistant cells and TL antisera as occurred in the reaction of sensitive cells (killed under similar conditions) and TL antisera. RADA-1 cells were not nonspecifically resistant to complement (C)-mediated lysis; they were killed in the presence of H-2a antiserum and GPC. The TL antisera contained antibodies for TL determinants. They stimulated the C-mediated lysis of ASL-1 cells (TL 1, 2, 3) and thymocytes from strain A mice (TL 1, 2, 3). The TL antigens of resistant RADA-1 cells underwent antigenic modulation, the reversible disappearance of TL antigens from the cells stimulated by specific antiserum. After the cells were treated with neuraminidase, they became susceptible to the cytotoxic effects of aliquots of the same TL antisera and GPC used previously.

Animals

Effect of BNU treatment on leukaemogenesis in lethally irradiated AKR mice restored with bone-marrow and spleen cells.

The leukaemogenic effect of N-butyl-N-nitrosourea (BNU) was studied in normal and thymectomized AKR mice which were lethally irradiated and restored with either bone-marrow (BM) or spleen cells from (AKR X AKR/T1ALD)F1 donors. In some instances T1ALD thymic cells were added to the restorative inoculum. It was possible to determine the origin of the leukemic cells by the metacentric marker chromosomes of T1ALD. The T- or B-cell characteristics were further ascertained by the cytotoxicity test for theta antigen and the EAC rosette test. All leukaemias whether thymic (TLS) or extra-thymic (ETL), developed from donor bone-marrow or spleen cells and never from the injected thymic cells. In non-thymectomized animals BNU increased the percentage of TLS and shortened their latency. Most of TLS which occurred after BNU treatment of BM-restored mice were theta-negative whereas the majority of TLS which occurred in controls and in spleen-restored animals were theta-positive. This suggests that during their maturation process BM-derived T precursors transit through a theta-negative compartment. This compartment does not reach a similar size during the maturation process of the spleen-derived precursors. Adding thymic cells to the restorative inoculum enhanced leukaemogenesis and suppressed theta-negative TLS in BM-restored mice. Thymectomized mice, restored either by BM or spleen, had a low incidence of ETL which was not significantly increased by BNU treatment except in the case of mice restored with spleen cells. The leukaemic cells of one ETL were theta-positive whereas all the other leukaemias had no detectable T or B marker. The percentage of ETL was higher in thymectomized mice treated with BNU alone than in those previously subjected to irradiation and restoration. These results strongly suggest that a theta-negative T precursor could be involved in extra-thymic leukaemogenesis but the possible involvement of a B precursor cannot be rule out unless experiments are carried out with specific markers of T- and B-cell sub-classes.

Animals

Mortality from leukaemia and cancer in shipyard nuclear workers.

A review of death certificates in New Hampshire, Maine, and Massachusetts for 1959-77 yielded a total of 1722 deaths among former workers at the Portsmouth Naval Shipyard where nuclear submarines are repaired and refuelled. Next of kin were contacted for 592. All deaths under age 80 were classified as being in former nuclear or non-nuclear workers depending on information supplied by next of kin. With U.S. age-specific proportional cancer mortality for White males as a standard, the observed/expected ratio of leukaemia deaths was 5.62 (6 observed, 1.1 expected) among the 146 former nuclear workers. For all cancer deaths, this ratio was 1.78. Among non-nuclear workers there was no statistically significant increase in proportional mortality from either leukaemia or from all cancers. The excess proportional leukaemia and cancer mortality among nuclear workers exceeds predictions based on previous data of radiation effects in man.

Aged

Definition of a unique cell surface antigen of mouse leukemia RL male 1 by cell-mediated cytotoxicity.

BALB/c x-ray-induced leukemia RL male 1 is strongly immunogenic for (BALB/c x C57BL/6)F1 mice. Transplants of RL male 1 regressed after initial growth, and after tumor regression mice could resist repeated inocula of 10(7) RL male 1 cells. Spleen cells from immunized mice after in vitro stimulation with RL male 1 were cytotoxic for RL male 1 cells in 3-hr 51Cr assays. Pretreatment of immune spleen cells with Thy-1, Lyt-2, or Lyt-3 antisera and complement eliminated cytotoxic activity, indicating that effector cells for RL male 1 lysis are T cells. Tests with other target cells showed little or no cytotoxicity. Analysis of the specificity of T-cell killing of RL male 1 by competitive inhibition assays with unlabeled cells indicated that only RL male 1 could inhibit killing; other BALB/c tumors (13 x-ray or murine leukemia virus-induced leukemias and three myelomas) failed to inhibit lysis of RL male 1. A range of alloantisera and heteroantisera were tested for their capacity to block lytic activity in the absence of added complement. H-2d antisera and Lyt-2 and -3 antisera blocked lysis, the latter at the level of the effector cell. Antisera to other cell surface alloantigens, murine leukemia virus-related antigens, and immunoglobulins did not block RL male 1 lysis. Thus, T cells from mice immunized against RL male 1 recognize an individually distinct or unique antigen that does not appear to be related to any of the serologically defined cell surface determinants of RL male 1. In its restriction to a single leukemia, the RL male 1 antigen resembles the individually distinct antigens of chemically induced tumors and other tumor types of rodents.

Animals

Radiation leukemia in C57BL/6 mice. II. Lack of ecotropic virus expression in the majority of lymphomas.

The expression of endogenous ecotropic viruses in radiation-induced thymomas of C57BL/6 mice was examined. Competition radioimmunoassays for AKR MuLV gp71, p30, and p12 were used for viral antigen expression. 3 of 40 lymphomas had readily detectable ecotropic gp71 at levels of 95-689 ng/mg protein; the remainder of the tumors had no detectable gp71 (less than 1.0 ng/mg protein). 30 thymomas were characterized by the presence of MuLV p30 at levels of 1-10 ng/mg protein, levels that were comparable to those found in thymus extracts from age-matched, nonirradiated control. 10 tumors were characterized by having p30 levels of 10-30 ng/mg protein. In one tumor significant levels of AKR MuLV p12 were detectable. Since B-tropic and N-tropic viruses from C57BL/6 mice have glycoproteins (gp71) indistinguishable from AKR MuLV gp71 and the N-tropic virus had a p12 serologically identical to AKR MuLV p12, these results demonstrate that overt endogenous B-tropic virus was detectable in 2 of 40 thymomas and endogenous N-tropic virus was detectable in 1 of 40 thymomas. The lack of overt expression of gp71 or p12 was also confirmed by cytotoxicity assays using monospecific antisera to these viral proteins. Radiation-induced lymphomas were also examined for the presence of reverse transcriptase after chromatography of tissue extracts on poly G-Sepharose. One tumor, which was characterized by the lack of gp71, also had no detectable reverse transcriptase; whereas one tumor with gp71 was characterized by readily detectable levels of reverse transcriptase in cellular extracts. The presence of viral RNA was examined using AKR cDNA. Low levels of RNA capable of hybridizing with AKR cDNA were found in age-matched, nonirradiated mice; these hybrids had Tm's of 72 degrees C, while hybrids with AKR MuLV 70S RNA had Tm's of 80 degrees C. In 1 of 12 thymomas the concentration of hybridizable RNA and the Tm of the hybrids were identical to control values. In 9 of 12 thymomas the concentration of hybridizable sequences increased approximately three-to fivefold and the Tm of these hybrids varied from 73 to 75 degrees C. In 1 of 12 thymomas the concentration of hybridizable sequences increased over 100-fold, hybridized completely with AKR MuLV cDNA, and the hybrids had Tm's of 79 degrees C. This thymoma was also characterized by the presence of the AKR MuLV type of gp71 and p12. One tumor was characterized by a 10-to 100-fold increase in hybridizable sequences, which only partially hybridized with AKR MuLV cDNA, and hybrids had a Tm of 73 degrees C. This tumor was characterized by the presence of AKR MuLV gp71 but not AKR MuLV p12. The results taken together demonstrate that overt endogenous ecotropic virus expression is only rarely detectable in radiation-induced thymomas of C57BL/6 mice.

AKR murine leukemia virus

Characterization of an RNA-directed DNA-polymerase from a cell line derived from a radiation-induced lymphoma in mice.

An RNA-directed DNA polymerase was purified from a cell line derived from a radiation-induced lymphoma in NIH Swiss mice which produced non-infectious type C virus particles. The enzyme was isolated from a high speed particulate fraction which bands at a density of 1.16--1.19 g/ml in a sucrose gradient, and purified by successive chromatography on DEAE-cellulose, phosphocellulose and hydroxyapatite. The purified DNA polymerase has a molecular weight of 68 000, a pH optimum of 7.5, a KCl optimum of 50 mM, and a Mn2+ optimum of 0.25 mM. It prefers (dT)15 . (A)n to (dT)15 . (dA)n as the primer template and transcribes the poly(C) strand of (dG)15 .(C)n and (dG)15 . (OMeC)n. It transcribes heteropolymeric regions of avian myeloblastosis virus 70 S RNA, and is inhibited by antiserum to Rauscher murine leukemia virus DNA polymerase. Comparison of the properties of DNA polymerase purified from radiation-induced lymphoma cells with the DNA polymerase purified from non-defective murine type C RNA tumor viruses shows that the mouse lymphoma enzyme is both biochemically and immunologically related to murine leukemia virus DNA polymerases.

Animals

[Modified Giemsa technique for the study of characteristic chromosomes of leukemic C57Bl mice].

G-banded karyotypes have been studied in C57Bl control mice and in animals developing leukemia after i.p. injection of acellular extract of spleen or lymph nodes from isologous animals showing radiation induced leukemia. No visible differences could be detected with respect to the number, size and position of the G-bands between the two groups of animals. From the present observations and from previous work with conventional staining methods, it can be concluded that the development of such leukemia does not involve the presence of chromosome abnormalities.

Animals

Establishment, characterization and virus expression of cell lines derived from radiation- and virus-induced lymphomas of C57BL/Ka mice.

Permanent cell lines have been established in vitro from lymphoid tumors induced in C57BH/Ka mice by fractionated X-irradiation or by inoculation of the radiation leukemia virus (RadOV). The cultured cells are lymphoblastic, replicate rapidly in vitro, and are tumorigenic in vivo. The cell surface markers Thy 1, Ly 1, Ly 2,3 and GIX are expressed by the lymphoid tumor cells in the mouse and persist in the corresponding cell lines; expression of the H-2 and TL antigens is greatly reduced during in vitro passage, but is restored on in vivo transplantation. The cell lines derived from RadLV-induced tumors (BL/VL lines) produce a virus population (RadLV/LTC) with the thymotropic and leukemogenic attributes of RadLV. Those derived from radiation-induced, virus-negative lymphomas (BL/RL lines) are initially devoid of MuLV expression, but frequently become spontaneous virus producers during in vitro cultivation.

Animals

Second malignancies complicating Hodgkin's disease in remission.

The incidence of second tumours occurring in the course of Hodgkin's disease has been investigated in a series of 452 patients treated with standard chemotherapy or radiotherapy, combination chemotherapy alone, intensive radiotherapy alone, or both intensive radiotherapy and combination chemotherapy administered in sequence. 16 tumours were noted. When analysed according to mode of treatment, 6 cases occurred in a group of 62 patients who received both modalities. When analysed for age, sex, and man-years of follow-up, this group appears to have 14-5 times the risk of developing a second tumour. However, that subgroup which had a complete remission after intensive radiotherapy followed by a relapse of disease, prior to receiving combination chemotherapy, had the highest risk with 18-5 times greater incidence of second tumour than expected. It is noteworthy that, of the 16 second tumours, 2 were acute myeloid leukaemia; in both cases a similar chromosomal abnormality (45 chromosomes, C-group deletion) was noted. The mechanism of oncogenesis may represent a combination of the immunosuppressive effects and cellular effects of those forms of treatment.

Adolescent

Temperature-dependent rosette formation by mouse lymphoma cells as a result of viral hemadsorption.

Cells from several mouse lymphomas formed rosettes with nonsensitized foreign erythrocytes through C-type virus particles clustered on the cell surface in serum-free medium held at 4 degrees C. This type of rosetting was found most typically in a lymphoma induced by Rauscher leukemia virus in tissue culture (RD-12), but it also occurred in 23 of 61 spontaneous thymic lymphomas in AKR mice. Chemically or X-ray-induced leukemias and spontaneous reticulum cell sarcomas did not form rosettes. The nature of the rosette formation may be interpreted as viral hemadsorption, with a possible relationship to hemagglutination by murine leukemia viruses. The receptor on virus particles was trypsin sensitive and showed high affinity to serum inhibitors (RIF). Serum rosette-inhibiting activity was assessed by a quantitative rosette inhibition test; rosette inhibition proved widely distributed among species. Physicochemical properties of serum RIF and their function both in vivo and in vitro were described. Rosette formation with similar temperature requirements, previously reported in a mouse lymphoma carrying membrane-bound heterophile cold hemagglutinin, was readily distinguished from viral hemadsorption by its insensitivity to mouse serum RIF.

Animals