Stimulation of erythropoietic differentiation in BALB/c mice infected with Rauscher leukemia virus.

The function of phenylhydrazine (PHZ) hemolysis in ameliorating the anemia induced in mice by a slow-acting strain of Rauscher leukemia virus (RLV-A) was described. After cessation of treatment with PHZ, mid-stage RLV-A-infected, anemic mice responded with massive reticulocytoses and a rebound in hematocrit above control levels. RLV-infected mice, subjected to PHZ-induced hemolysis or phlebotomy, produced high levels of plasma erythropoietin (Ep); this suggested that Ep mediated the PHZ-induced differentiation. In addition, administration of exogenous Ep induced a wave of erythroid maturation in RLV-infected anemic mice, which indicated that virus-infected erythroid precursors could still respond to the hormone governing normal differentiation.     

Effects of Rauscher leukemia virus infection on BALB/c mouse embryos.

The effects of Rauscher leukemia virus (R-MuLV) infection on BALB/c mouse embryos were described. In mice infected with R-MuLV 12 days before mating, there were no embryos 8 days after possible conception, whereas in those infected either 8 days or 1 day before mating, pregnancy was established. The most striking effect of R-MuLV infection on the microscopic properties of the embryos was vast "apoptosis" in the mesoderm. The XC test with trypsinized embryo cells showed numerous polykaryons, which suggested that active leukemia virus was present in the embryonal tissue. Indirect immunofluorescence studies with specific rabbit antiserum to R-MuLV demonstrated the presence of virus antigens in the embryonal tissue. Vast immunofluorescence was also found in trophoblastic cells and embryonal membranes. We concluded that R-MuLV in BALB/c mice was transmitted from mother to embryo through the placenta and thereby caused excessive cell death, especially in the mesoderm.     

The influence of Rauscher leukemia virus (R-MuLV) on the differentiation of red blood cells in BALB/c mice

The influence of Rauscher Leukemia Virus infection of BALB/c mice on the differentiation of red blood cells has been investigated. Twenty-one days after infection, the total number of red blood cells in the spleen is increased 20 times in contrast to the bone marrow which is largely unaffected. The cellular composition of these hemopoietic organs has been analysed using a number of markers of erythroid maturation, i.e. heme and hemoglobin synthesis and the presence of globin messenger RNAs.These studies show that most of the blasts present in leukemic spleens are immature as judged by morphological criteria and do not contain globin mRNA, whereas the more mature blasts contain globin mRNA as determined autoradiographically by in situ hybridization to globin cDNA. The number of mature blasts, comprising about one-third of the immature ones, is both in absolute terms and per mg tissue higher than in control spleens.Pulse labelling with ⁵⁹Fe shows, that heme and hemoglobin synthesis takes place in leukemic spleens.The rate of heme synthesis in leukemic spleens, as judged by short-term incorporation of ⁵⁹Fe and ¹⁴C-glycine is intermediate between the values for spleens from anemic and control animals.After a pulse, labelled ⁵⁹Fe is first bound to non-hemoglobin proteins. After a chase, this protein-bound ⁵⁹Fe is transferred to hemoglobin as erythroid differentiation occurs in spleens of normal and anemic mice. However, this transfer of ⁵⁹Fe to hemoglobin does not occur in leukemic spleen cells during a pulse/chase in vivo.These results could mean that these immature blasts die or that the maturation is inhibited in the enlarged spleens, whereas only a minor portion differentiates in smaller basophilic erythroblasts, which mature into reticulocytes.     

Idiopathic mammary tumors in BALB/c mice.

A colony of BALB/c mice consisting of two sublines with a high incidence of mammary tumors was examined for the presence of a mammary tumor virus (MuMTV). The mammary tumor incidences in the two sublines were 18% and 35% at average tumor age 19-20 months. Over a period of 8 years, their milk at third to tenth lactations were monitored for the presence of MuMTV antigen,and the milk and tumors were examined for the presence of B particles. Neither antigen nor B particles were found. Milk and tumor extracts from the higher mammary tumor lines were also assayed for MuMTV bioactivity by intraperitoneal inoculation of weanling C57BL, BALB/c, and RIIIf females. No response was obtained, except possible in RIIIf. Both the MuMTV antigen incidence and the tumor incidence in inoculated RIIIf mice were somewhat elevated over controls. The question remains unanswered as to whether there is an active MuMTV in our colony of tumor-bearing BALB/c mice and, if there is, whether it is associated with B particles.     

In vitro Transformation of BALB/c 3T3 Cells by 1,1,2,2-Tetrachloroethane

1,1,2,2-Tetrachloroethane (1,1,2,2-TTCE) was shown to be capable of inducing in vitro transformation of BALB/c 3T3 cells (clone A-31) either in the presence or in the absence of S9 activating system using an amplification-transformation (level-II) assay by reseeding confluent cells from each treatment and allowing additional rounds of cell replication. In the absence of metabolic activation, the highest assayed dose (1000 μg/ml), exerting the highest toxicity, was the only transforming dose. Lower doses of 1,1,2,2-TTCE were capable of transforming BALB/c cells in the presence of S9 activating system, the dose of 500 μg/ml exerting the highest transforming activity. The number and size of transformed foci recognized in the level-II plates were a function of the number of cells reseeded in the amplification assay. Foci obtained in the presence of S9 activating systems were larger in size, more deeply basophilic, and exhibited denser multilayering of constituent cells than foci recognized in the absence of exogenous metabolic activation.     

In vitro transformation of BALB/c 3T3 cells by 1,1,2,2-tetrachloroethane

1,1,2,2-Tetrachloroethane (1,1,2,2-TTCE) was shown to be capable of inducing in vitro transformation of BALB/c 3T3 cells (clone A-31) either in the presence or in the absence of S9 activating system using an amplification-transformation (level-II) assay by reseeding confluent cells from each treatment and allowing additional rounds of cell replication. In the absence of metabolic activation, the highest assayed dose (1000 micrograms/ml), exerting the highest toxicity, was the only transforming dose. Lower doses of 1,1,2,2-TTCE were capable of transforming BALB/c cells in the presence of S9 activating system, the dose of 500 micrograms/ml exerting the highest transforming activity. The number and size of transformed foci recognized in the level-II plates were a function of the number of cells reseeded in the amplification assay. Foci obtained in the presence of S9 activating systems were larger in size, more deeply basophilic, and exhibited denser multilayering of constituent cells than foci recognized in the absence of exogenous metabolic activation.     

Lung carcinogenesis by procarbazine chlorate in BALB/c mice

A study of the carcinogenic action of procarbazine chloratein BALB/c/Cb/Se mice showed that this substance significantlyincreases the incidence of lung tumours in both sexes. The inducedtumors were alveolar-lining, papillary and alveolarpapillarytype carcinomas with a tendency to invade the bronchial wall.     

The stimulating effect of complete Freund's adjuvant on tumour induction by polyoma virus in mice and by Rous sarcoma virus in rats

Complete Freund's adjuvant was shown to greatly stimulate viral oncogenesis both in the case of polyoma virus in mice and in the case of Rous sarcoma virus in rats. Tumours appeared in 74% of CC57BR/Mv mice infected when newborn with polyoma virus — adjuvant emulsion, whereas control mice injected with virus alone failed to develop tumours. Rous virus (Carr-Zilber strain) and adjuvant when administered together as emulsions to Wistar rats (newborn or sucklings as well as 2.5-month-old animals) resulted in a 100% tumour incidence. In control animals treated with the virus alone when 0–4 days old, tumour incidence was no more than 30–40%; no tumours appeared in control animals which received virus alone when they were more than 2 weeks old. A significant stimulating effect of Freund's adjuvant was also revealed when the virus was inoculated into 4- to 15-day-old rats which received adjuvants as neonates. Thirty per cent of rats given virus — adjuvant emulsion produced measurable quantities of complement-fixing antibodies to soluble antigens of Rous sarcoma, while in animals given virus alone such antibodies were not demonstrable. It is suggested that the stimulating action of complete Freund's adjuvant on polyoma and Rous oncogenesis is based upon a mechanism similar to the classical “enhancement phenomenon”.     

BALB/c and CBA mice differ in the subtype of T cell involved in Moloney murine leukemia virus-induced lymphomas

Subsets of T cells can be recognized by presence or absence of terminal deoxynucleotidyl transferase (TdT) or 20 alpha-hydroxysteriod dehydrogenase (20 alpha SDH) activity. By use of these enzyme markers Moloney murine leukemia virus (M-MuLV)-induced lymphomas were shown to involve different T-cell subtypes. In the present paper we show that the genotype of the mouse has a strong influence on the subtype of T cell involved in lymphoma. BALB/c mice preferentially develop 20 alpha SDH-positive lymphomas, whereas CBA lymphomas often have the TdT phenotype. Comparison of the 20 alpha SDH activity of normal bone marrow cells showed that BALB/c mice have higher enzyme levels than CBA mice. The relative availability of a certain type of cell at a critical early step in leukemogenesis may thus influence lymphoma type.