SOD1/Rag2 Mice with Low Copy Number of SOD1 Gene as a New Long-Living Immunodeficient Model of ALS

The most recent research concerning amyotrophic lateral sclerosis (ALS) emphasizes the role of glia in disease development. Thus, one can suspect that the effective therapeutic strategy in treatment of ALS would be replacement of defective glia. One of the basic problems with human glial progenitors (hGRPs) replacement strategies is the time needed for the cells to become fully functional in vivo. The lifespan of most popular high copy number SOD1 mutant mice might be too short to acknowledge benefits of transplanted cells. We focused on developing immunodeficient rag2-/- model of ALS with lower number of transgene copies and longer lifespan. The obtained hSOD1/rag2 double mutant mice have been characterized. QPCR analysis revealed that copy number of hSOD1 transgene varied in our colony (4-8 copies). The difference in transgene copy number may be translated to significant impact on the lifespan. The death of long- and short-living hSOD1/rag2 mice is preceded by muscular weakness as early as one month before death. Importantly, based on magnetic resonance imaging we identified that mutant mice demonstrated abnormalities within the medullar motor nuclei. To conclude, we developed long-living double mutant hSOD1/rag2 mice, which could be a promising model for testing therapeutic utility of human stem cells.

Quantitative "Hot Spot" Imaging of Transplanted Stem Cells using Superparamagnetic Tracers and Magnetic Particle Imaging (MPI)

Magnetic labeling of stem cells enables their noninvasive detection by magnetic resonance imaging (MRI). In practical terms, most MRI studies have been limited to the visualization of local engraftment because other sources of endogenous hypointense contrast complicate the interpretation of systemic (whole-body) cell distribution. In addition, MRI cell tracking is inherently nonquantitative in nature. We report herein on the potential of magnetic particle imaging (MPI) as a novel tomographic technique for noninvasive “hot-spot” imaging and quantification of stem cells using superparamagnetic iron oxide (SPIO) tracers. Neural and mesenchymal stem cells, representing small and larger cell bodies, were labeled with 3 different SPIO tracer formulations, including 2 preparations (Feridex and Resovist) that have previously been used in clinical MRI cell-tracking studies. Magnetic particle spectroscopy measurements demonstrated a linear correlation between MPI signal and iron content for both free particles in homogeneous solution and for internalized and aggregated particles in labeled cells over a wide range of concentrations. The overall MPI signal ranged from 1 × 10⁻³ to 3 × 10⁻⁴ Am²/g Fe, which was equivalent to 2 × 10⁻¹⁴ to 1 × 10⁻¹⁵ Am² per cell, indicating that cell numbers can be quantified with MPI analogous to the use of radiotracers in nuclear medicine or fluorine tracers in ¹⁹F MRI. When SPIO-labeled cells were transplanted in the mouse brain, they could be readily detected by MPI at a detection threshold of about 5 × 10⁴ cells, with MPI/MRI overlays showing an excellent agreement between the hypointense MRI areas and MPI hot spots. The calculated tissue MPI signal ratio for 100 000 vs 50 000 implanted cells was 2.08. Hence, MPI can potentially be further developed for quantitative and easy-to-interpret, tracer-based noninvasive cell imaging, preferably with MRI as an adjunct anatomical imaging modality.

Survival of neural progenitors allografted into the CNS of immunocompetent recipients is highly dependent on transplantation site

Allografts continue to be used in clinical neurotransplantation studies; hence, it is crucial to understand the mechanisms that govern allograft tolerance. We investigated the impact of transplantation site within the brain on graft survival. Mouse [Friend leukemia virus, strain B (FVB)] glial precursors, transfected with luciferase, were injected (3 × 10(5)) into the forceps minor (FM) or striatum (STR). Immunodeficient rag2(-/-) and immunocompetent BALB/c mice were used as recipients. Magnetic resonance imaging (MRI) confirmed that cells were precisely deposited at the selected coordinates. The graft viability was assessed noninvasively with bioluminescent imaging (BLI) for a period of 16 days. Regardless of implantation site, all grafts (n = 10) deposited in immunodeficient animals revealed excellent survival. In contrast, immunocompetent animals only accepted grafts at the STR site (n = 10), whereas all the FM grafts were rejected (n = 10). To investigate the factors that led to rejection of FM grafts, with acceptance of STR grafts, another group of animals (n = 19) was sacrificed during the prerejection period, on day 5. Near-infrared fluorescence imaging with IRDye 800CW-polyethylene glycol probe displayed similar blood-brain barrier disruption at both graft locations. The morphological distribution of FM grafts was cylindrical, parallel to the needle track, whereas cells transplanted into the STR accumulated along the border between the STR and the corpus callosum. There was significantly less infiltration by both innate and adaptive immune cells in the STR grafts, especially along the calloso-striatal border. With allograft survival being dependent on the transplantation site, the anatomical coordinates of the graft target should always be taken into account as it may determine the success or failure of therapy.

A comparison of dopaminergic cells from the human NTera2/D1 cell line transplanted into the hemiparkinsonian rat

Human NT cells derived from the NTera2/D1 cell line express a dopaminergic phenotype making them an attractive vehicle to supply dopamine to the depleted striatum of the Parkinsonian patient. In vitro, hNT neurons express tyrosine hydroxylase (TH), depending on the length of time they are exposed to retinoic acid. This study compared two populations of hNT neurons that exhibit a high yield of TH+ cells, MI-hNT and DA-hNT. The MI-hNT and DA-hNT neurons were intrastriatally transplanted into the 6-OHDA hemiparkinsonian rat. Amelioration in rotational behavior was measured and immunohistochemistry was performed to identify surviving hNT and TH+ hNT neurons. Results indicated that both MI-hNT and DA-hNT neurons can survive in the striatum, however, neither maintained their dopaminergic phenotype in vivo. Other strategies used in conjunction with hNT cell replacement are likely needed to enhance and maintain the dopamine expression in the grafted cells.

Intrathecal application of neuroectodermally converted stem cells into a mouse model of ALS: limited intraparenchymal migration and survival narrows therapeutic effects

Stem and progenitor cells provide a promising therapeutic strategy for amyotrophic lateral sclerosis (ALS). To comparatively evaluate the therapeutic potentials of human bone marrow-derived mesodermal stromal cells (hMSCs) and umbilical cord blood cells (hUBCs) in ALS, we transplanted hMSCs and hUBCs and their neuroectodermal derivatives (hMSC-NSCs and hUBC-NSCs) into the ALS mouse model over-expressing the G93A mutant of the human SOD1 gene. We used a standardized protocol similar to clinical studies by performing a power calculation to estimate sample size prior to transplantation, matching the treatment groups for gender and hSOD-G93A gene content, and applying a novel method for directly injecting 100,000 cells into the CSF (the cisterna magna). Ten days after transplantation we found many cells within the subarachnoidal space ranging from frontal basal cisterns back to the cisterna magna, but only a few cells around the spinal cord. hMSCs and hMSC-NSCs were also located within the Purkinje cell layer. Intrathecal cell application did not affect survival times of mice compared to controls. Consistently, time of disease onset and first pareses, death weight, and motor neuron count in lumbar spinal cord did not vary between treatment groups. Interestingly, transplantation of hMSCs led to an increase of pre-symptomatic motor performance compared to controls in female animals. The negative outcome of the present study is most likely due to insufficient cell numbers within the affected brain regions (mainly the spinal cord). Further experiments defining the optimal cell dose, time point and route of application and particularly strategies to improve the homing of transplanted cells towards the CNS region of interest are warranted to define the therapeutic potential of mesodermal stem cells for the treatment of ALS.

Effect of neutrons alone or combined with diethylnitrosamine on tumor induction in the livers of infant C57BL mice

The possible combined effects of the initiator diethylnitrosamine (DEN)+neutrons on the induction of foci, adenomas and carcinomas in the livers of C57BL/Cnb mice were evaluated. Four groups of infant mice were treated as follows: DEN alone, neutrons alone, DEN followed by neutrons and neutrons followed by DEN. Ten mice in each group were killed at 10-week intervals over 70 weeks. The following parameters were measured: body weight, liver weight, number and size of superficial macroscopic liver lesions, and number and total surface area of the different types of microscopic liver lesions. The rate of appearance of foci increased significantly at different times when a dose of 0.125 Gy of neutrons was administered 7 days before or after a dose of 1.25 micrograms of DEN. No significant differences were observed in the total surface area of foci and/or adenomas and carcinomas when increasing doses of neutrons were given 7 days before or after the administration of 1.25 and 2.5 micrograms of DEN.

Effect of X rays alone or combined with diethylnitrosamine on tumor induction in infant mouse liver

The possible combined effects of the initiator diethylnitrosamine (DEN) with X rays on cancer induction in C57BL/Cnb mouse liver were evaluated. Four groups of infant mice were treated as follows: with DEN alone, with X rays alone, with DEN + X rays, and with X rays + DEN. Mice in each group were killed at 10-week intervals over 70 weeks. The following parameters were measured: body weight, liver weight, number and size of macroscopic liver lesions, and number and total surface of the different types of microscopic liver lesions. The number of induced liver foci and carcinomas was found to depend essentially on the dose of DEN. X irradiation did not produce any combined effect on the induction of foci and carcinomas when given 7 days before or after DEN administration.

Unexplained fever and chronic fatigue: abnormal circadian temperature pattern

OBJECTIVES

Standard clinical and biological investigations can be used to determine the origin of persistent and moderate fever in a large number of otherwise asymptomatic patients. However, in a small proportion of cases, isolated fever and fatigue persist despite the absence of detectable organic malfunction. This study was conducted to investigate the circadian thermic pattern in patients with apparently unexplainable fever and chronic fatigue and in those with fever of recognized origin.

METHODS

We recorded central temperature continuously for 24 hours in patients with moderate fever of both unexplained and recognized origin, and in a control group of healthy volunteers. A Fourier series was used for harmonic analysis.

RESULTS

Thermic patterns specific to the three groups were identified by statistical and factorial analysis. The patients with fever of unknown origin and chronic fatigue were clearly characterized in terms of the phase, amplitude of the first (fundamental) harmonic and minimum circadian temperature.

CONCLUSION

The abnormal central temperature pattern in these patients may prove to be an important step in the management of febrile patients.

Protamine allergy reactions during cardiac catheterization and cardiac surgery: risk in patients taking protamine-insulin preparations

Protamine insulin use may immunologically sensitize patients to protamine, leading to anaphylactoid reactions upon subsequent exposure to protamine sulfate during cardiac catheterization or cardiovascular surgery. The risk of such reactions in protamine insulin-dependent patients is uncertain. One catheterization study reported a 50-fold greater risk while a second showed no increased risk! To clarify the risk, the records of 7,750 cardiac catheterization procedures between 1984 and 1987 were analyzed for presence of NPH or PZI insulin use, protamine administration, and any complications or adverse reactions. Protamine was administered in 3,341/7,750 procedures (43%), including 171 in diabetics receiving NPH insulin. Adverse reactions to protamine occurred in 2/3, 170 noninsulin patients, 0.06%, and adverse reactions due to probable NPH insulin sensitization occurred in 1/171, 0.6%, of NPH diabetics, p = .034. Meta-analysis of risk showed an odds ratio of 7.96 for the NPH diabetic patients, and combining these results with the other large series in the literature (269 NPH diabetics total) showed an odds ratio of 4.19 compared to a non-NPH insulin group. Meta-analysis of the surgical literature showed the risk in surgical patients to be 2.1% in NPH patients versus 0.12% with no NPH, with an odds ratio of 15.52. The greater incidence in surgical patients may be due to protamine sensitization at prior catheterization and to the larger dose of protamine administered to surgical patients.

The molecular biology of radiation-induced carcinogenesis: thymic lymphoma, myeloid leukaemia and osteosarcoma

In mice, external X- or gamma-irradiation may induce thymic lymphomas or myeloid leukaemias, while bone-seeking alpha-emitters may induce osteosarcomas and, to a lesser extent, acute myeloid leukaemia. The present paper aims to review briefly some of the experimental data with respect to the molecular mechanisms underlying these radiation-induced carcinogenic processes. Thymic lymphomagenesis proceeds through an indirect mechanism. Recombinant proviruses often occur in the tumour cell DNA, favouring the idea that they might be involved. However, there are indications that they might mediate tumour growth rather than induction. It is plausible that activation of ras oncogenes by somatic point mutations might play a role in the carcinogenic process, although at a yet undetermined stage. Myeloid leukaemogenesis is characterized by a very early, putative initiating event, consisting of non-random rearrangements and/or deletions of chromosome 2. These may be related to deletions in the developmentally important homeobox gene clusters and to rearrangements of the sequences flanking the IL-1 beta gene. Either a gene of the homeobox family or IL-1 beta might be considered as potentially involved in the induction process. Osteosarcomagenesis in mice is often associated with the expression of proviruses, and the tumours often contain somatically acquired proviruses. These viruses may contribute to tumour development by affecting various growth-suppressor genes. Viruses isolated from bone tumours, although non-sarcomagenic, induce osteopetrosis, osteomas and lymphomas upon infection of newborn mice. Osteogenic tumours frequently display amplification of a region on mouse chromosome 15, which encompasses c-myc and Mlvi-1 sequences. Enhanced transcription of various oncogenes is found in individual tumours, but no specificity for osteosarcomas has been identified. In vitro systems of skeletoblast differentiation are being developed to study tumour induction in vitro.

Failure to detect immune deficiency in rats after prenatal or early postnatal irradiation

We have looked for medium-term sequelae in the immune system of rats that had been X-irradiated (0-2 Gy whole-body irradiation) during prenatal or early postnatal life. At an age of 8 weeks the histology of the spleen was normal, and so was the distribution of B and T lymphocytes. The serum immunoglobulin levels were not significantly altered, even when the different isotypes were considered. At an age of 10 weeks, the rats were immunized with a T-dependent or a T-independent dinitrophenylated-carrier antigen. Normal levels of specific antibodies were generated in all groups of animals injected with the T-independent antigen. The T-dependent response, in contrast, was higher in animals irradiated between day 6 and day 20 of gestation (but not in rats irradiated early after birth). This increase, however, was significant only for the IgM and IgG1 responses of some irradiated groups. Thus no medium-term immunodeficiency could be documented with the methods used. The alteration in a T-dependent response, however, points to a radiosensitive T regulatory mechanism.

Evidence of recombinant ecotropic provirus integration in thymic lymphomas induced by direct or indirect radiation effects

Several investigators described the occurrence of ecotropic recombinant proviruses in the DNA of in-vivo or in-vitro propagated radio-induced lymphomas, but such proviruses were never detected in primary tumors. To assess their biological significance in the tumorigenic process, we reinvestigated the presence of new proviruses chiefly in primary radio-induced tumors and in models of radioleukemogenesis which could give additional support for their role. Such models included thymic lymphomas originating after (i) graft of non-irradiated thymuses in thymectomized irradiated mice and (ii) the injection of a B-ecotropic retrovirus (T1223/B) in association with a subleukemogenic dose of irradiation. We report for the first time that new ecotropic proviral sequences are encountered in a significant number (30%) of primary lymphomas induced directly by irradiation or indirectly in non-irradiated thymuses grafted in irradiated hosts. The existence of a 3.5-kbp Kpn1 restriction fragment with ecotropic sequences in the digested DNA of these tumor cells indicates that these new sequences belong to an ecotropic provirus recombinant in the gag-pol region. We observed that most of the primary radio-induced tumors in which novel recombinant provirus could be detected, displayed the integration at a single or at a few sites, demonstrating their clonality with respect to viral integration. The same was observed in thymic lymphomas arising after T1223/B virus injection and irradiation and in in-vivo or in-vitro propagated tumors. Altogether, these data bring the first evidence of the integration of ecotropic recombinant proviral genomes in a significant number of primary radiation induced thymic lymphomas and of their possible role in view of their frequent occurrence in grafted thymomas.

Effect of X-rays alone or combined with diethylnitrosamine on cancer induction in mouse liver

The possible combined effects of the initiator diethylnitrosamine (DEN) with X-rays on cancer induction in infant C57BL/Cnb mice were evaluated. Preliminary data show that a dose of X-rays administered 7 days before a single injection of DEN was more effective in inducing liver nodules than when administered 7 days after DEN administration.

Nucleotide sequence of a radiation leukemia virus genome

The complete nucleotide sequence of an infectious molecular clone of a radiation murine leukemia proviral DNA RadLV/VL3(T+L+) has been determined. The sequence of the RNA genome is 8318 nucleotides long and contains three large open reading frames encoding the gag, pol, and env gene products. With the exception of a xenotropiclike R peptide and the LTR which bears structural similarities to a xenotropic LTR, displaying typical enhancerlike sequences, the remaining sequences are strikingly similar to the endogenous, ecotropic Akv murine leukemia virus. Therefore, it could be postulated that the leukemogenic properties of RadLV/VL3(T+L+) were generated by a recombination event between a xenotropic virus and an Akv-like ecotropic virus.

Expression of protooncogenes in murine osteosarcomas

The expression of 7 protooncogenes (c-sis, c-abl, c-mos, c-bas, c-Ki-ras, c-fos, c-myc) was examined in transplants and established cell lines from spontaneous and radiation-induced murine osteosarcomas. The transplant tumors were compared with different tissues, particularly skeletal tissue (sternum), and the osteosarcoma cell lines with fibroblast lines from the same mouse strains. C-sis was expressed above the level of controls in 2 osteosarcomas (TV, Os5). Three osteosarcomas showed over-expression of c-abl (TVK, DOS, Os5), c-bas (DOS, Os5 and V893) and c-fos (TVK, DOS, Os5), and 4 osteosarcomas showed over-expression of c-Ki-ras (TVK, DOS, Os5, Os16) and c-myc (TVK, DOS, TV, Os5). C-mos expression was not observed under the conditions used. One cell line (Os5) showed an altered transcript (1 kb transcript of c-fos). Apart from the relatively frequent increase in expression of the c-myc and c-ras-family, there was no indication that any particular protooncogene or combination of protooncogenes was associated with murine osteosarcomas.

Retroviruses in radiation-induced lymphomas

The nucleotide sequence of RadLV/VL3 (T+L+), the thymotropic and leukemogenic entity of the in-vitro propagated radiation leukemia virus complex (RadLV/VL3), is that of a recombinant retrovirus. The gag, pol and most of the env gene are very similar to the homologous regions of Akv MuLV. The 3' end of the env gene and the LTR appear to have derived from a xenotropic MuLV. However, the LTR has acquired a feature shared by other lymphomagenic MuLVs. This feature consists in sequence rearrangements resulting in the generation of presumed enhancer elements. RadLV/VL3(T+L+)-specific proviral sequences were found adjacent to the c-myc gene in several virus-induced thymic lymphomas of the rat, suggesting that the enhancer elements might play a role in lymphomagenesis. However, we found that the presence of a provirus at a specific DNA site can lead to an in-vitro growth advantage and to clonal cell selection independently of a lymphomagenic process. We conclude from this observation that clonal appearance of an integrated provirus in cultured radiogenic lymphoma cells does not necessarily reflect a viral induction of radiation-induced leukemogenesis.

Oncogene involvement in radiation- and virus-induced mouse osteosarcomas

Internal irradiation of mice using bone seeking radionuclides results in the activation of endogenous retroviruses and in the subsequent development of bone tumors. Genomic DNA from an osteosarcoma cell line, derived from an 90Sr-induced bone tumor, was cotransfected with the plasmid pSV2-neo into NIH/3T3 cells and G418-resistant transfectants gave rise to colonies in soft agar. Southern blot analysis of these first cycle transformants revealed the presence of extra copies of c-ras. We have analysed the arrangement of ecotropic murine leukemia proviral sequences in seven 90Sr-induced bone tumors and one osteosarcoma cell line of CF1-mice. Integration of ecotropic and/or ecotropic recombinant proviruses seems to be involved in rearrangements of 3' provirus cellular junction fragments occurring in all tumor DNAs analysed, but no indication for site-specific integration was found. We also determined the primary structure of FBR-MuSV, a transforming retrovirus able to induce bone tumors in newborn mice. FBR-MuSV contains sequences from all four exons of the murine c-fos gene, but lacks sequences encoding the first 24 and the last 98 amino acids of the c-fos gene product. The coding region of FBR-MuSV has also undergone two small in frame deletions. Thus, the v-fosFBR-MuSV retains 236 amino acids of the 380 amino acids of the murine c-fos product. In FBR-MuSV-transformed cells two fos-containing mRNAs have been detected: a 3.3-kb full-size genomic RNA and a 2.2-kb subgenomic mRNA as revealed by both fos- and MuLV-hybridization probes.

Nucleotide sequence of the envelope gene of radiation leukemia virus

The nucleotide sequence and the predicted amino acid sequence of the envelope gene (env) of RadLV/VL3 (T+L+) has been determined. RadLV/VL3 (T+L+) is a highly thymotropic (T+) and leukemogenic (L+) murine recombinant retrovirus continuously produced at high titer by BL/VL3 cells, a line established in culture from a radiation leukemia virus (RadLV)-induced C57BL/Ka mouse thymic lymphoma. The envelope gene is strikingly similar (92% homologous) to that encoded by the ecotropic Akv-MuLV. Among the differences, 134 scattered, although unevenly distributed point mutations (6.4%), two 9-bp deletions as well as a 6-bp insertion were observed (which result in 49 amino acid changes in the env gene of RadLV/VL3 (T+L+)).

Integrity of glycoprotein complex sugars is required for homing but not for several other membrane-mediated functions

In order to correlate the biochemistry of cell surface carbohydrates with cell function, we have treated cells with swainsonine and followed the biochemical and functional modifications induced by this compound. After treatment with swainsonine, surface glycoproteins had a lower apparent molecular weight and a higher isoelectric point. This is compatible with the replacement of complex carbohydrates by hybrid or high-mannose carbohydrates. Several functional tests were unaffected. However, swainsonine-treated cells displayed an altered pattern of in vivo homing, suggesting that carbohydrates play a role in this process.

Surface proteins of radiation-induced and radiation leukemia virus-induced thymic lymphosarcomas in mice

Thymic lymphosarcomas (TLS) were induced in C57BL mice by X-rays or by Radiation Leukemia Virus (RadLV) and their surface glycoproteins (gps) compared after cell-surface radioiodination and polyacrylamide gel electrophoresis (SDS-PAGE). All lymphocytic antigens tested (T200, 170/100, Thy-1) and proteins with apparent molecular weight (Mr) around 120,000 and 100,000 were present on all tumours, as well as retrovirus--encoded proteins but considerable variation in the Mr of several serologically-related proteins was observed. Therefore, the TLS in C57BL mice form a heterogeneous group, suggesting that T cells can be transformed at different stages of maturation. The possibility that transformation allows or even triggers differentiation is also entertained.

Common proviral integration sites in C57BL mouse lymphomas induced by radiation leukemia virus and absence of novel virus-related sequences in radiogenic lymphoma DNA

Three C57BL/Ka mice were inoculated with RadLV/VL3, a thymotropic and leukemogenic virus population released by the permanent BL/VL3 cell line, which was derived from a C57BL/Ka lymphoma induced by radiation leukemia virus (RadLV). The neoplastic thymus and bone marrow cells from these mice were grown until the cultures became permanently established, and their DNAs were examined for the presence of virus-related sequences by restriction enzyme analysis. All six cell lines displayed identical EcoRI and BamHI restriction fragments, not found in control C57BL/Ka DNA and accounting for the presence of more than one novel provirus. The primary and secondary tumors were thus clonal and, even though they were obtained from different animals, possessed identical integration sites. The BL/VL3 cell line also displayed the clonal appearance of novel proviral sequences, partly identical, with respect to location and BamHI restriction pattern, to those found in the RadL/VL3-induced tumor cell lines. Neither radiation-induced tumors, nor cloned cell lines derived therefrom, whether producing leukemogenic virus (BL/RL12-P) or not (BL/RL12-NP), displayed the presence of novel virus-related sequences when compared with control tissues. Our results strongly suggest not only that, as described in the case of avian leukosis virus-induced tumors of the chicken, RadLV-induced leukemogenesis might be a consequence of cellular gene activation by promotor insertion, but also that more than one integration site might be involved. Radiation-induced tumorigenesis might be initiated by a comparable mechanism, not requiring the participation of a virus.

[Biology, serology and biochemistry of leucemogenic viruses derived from a radiation-induced tumor of C57BL mice]

Two distinct rat propagates of a radiation leukemia virus (RadLV-Rs) from the C57BL mouse respectively induced characteristic leukemogenic effects. These were found to be related with the infection titers of the isolates, but not with either their antigenic specificities or their viral and proviral genome sequences.

Radioimmunoassay determination of two main cross-reacting viral antigens during radiation and Rauscher induced leukemias

The two main proteins p 30 and gp 70 from the Rauscher leukemia virus (RLV) have been isolated, labeled with 125I and used in radioimmune competition assays to estimate the amount of cross-reacting antigens produced during the evolution of various leukemias. The Rauscher leukemia in Balb/c mice, the radiation induced leukemia (RadLV) in C57Bl mice and two types derived therefrom by serial passages in mice (RadLV-RS) and in rats (RadLV-rat) were studied. Whereas the p 30 from RLV or RadLV (rat) viruses showed complete identity, the cross-reaction of their gp 70 proteins wasonly partial. The main findings in the tissues were the following: 1. The concentration of p 30 and gp 70 antigens increased much more during the RadLV-rat leukemia than in irradiated or RadLV (RS) treated mice. 2. In the serum, the ratio p 30/gp 70 was in general higher than one in the Rauscher leukemic mice and less than one in all types of RadLV leukemias. 3. In the spleen, RLV and RadLV (RS) infected mice had higher levels of p 30 than of gp 70. The reverse occurred in irradiated mice and in leukemic rats. Finally, the catabolic degradation of labeled RLV gp 70 was similar in normal and leukemic mice.

Characterization by molecular hybridization of two viral populations derived from a radiation leukemia virus

Two leukemogenic viral populations were derived from a radiation leukemia virus of the C57BL mouse. One (FB), in which only B-tropic virus could be detected, was obtained in vivo by serial passage of cell-free extract in newborn rats. The second (3C), a complex containing at least B-tropic and xenotropic viruses, was produced in vitro by a permanent cell line (13-3C) established from the spleen of a virus-infected C57BL mouse. In molecular hybridization experiments, the 70S RNA of Gross leukemia virus hybridized 96 and 78% of FB and 3C radioactive complementary DNA's, respectively, with a relatively high thermal stability of the duplexes formed. In contrast, the 70S RNA of Rauscher leukemia virus hybridized 23 and 20% of the FB and 3C DNA probes, respectively, with a low thermal stability. The rat-grown FB virions exhibited 50% genome homology with the viruses produced in vitro on the 13-3C cells. Finally, hybridizing the FB and 3C probes with normal or leukemic mouse spleen DNA's resulted in 89 to 100% homology. The rat-grown virions did not appear to contain detectable rat cellular DNA sequences, while about 20 complete copies of their nucleotide sequences were detected in covalent linkage with FB-infected rat spleen DNA. These findings strongly support the endogenous murine origin of the investigated virions.

L cell virus: infectivity for type N and B mouse embryo cells

The efficiency of focus formation of four L cell virus populations was significantly higher on type N mouse embryo fibroblast cultures than on type B cells. [5-3H]uridine-incorporating material sedimenting at a density of 1.158/g/cm3 was observed in the supernatant fluids of type N and B cultures infected with the four viral populations.