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PubMedDate not supplied

Characteristics of lymphomas in the BALB/cfRIII mouse strain.

The occurrence of 392 lymphomas in 1607 BALB/cfRIII mice from F0 to F45 is analyzed. Lymphoma incidence increased rapidly in the first 5 generations, reached a high plateau from F6 to F20 and then decreased slowly until it disappeared altogether. After F35, only sporadic cases of lymphoma have been observed. The morphologic characteristics of 350 of these lymphomas observed from F0 to F20 are described. Three main types of lymphomas have been recognized on the basis of gross morphology, histology and age: a) early, lymphocytic, with thymic involvement; b) early, lymphocytic, without thymic involvement; and c) late, histiocytic, without thymic involvement. The first 2 types are virus-induced and thymus-dependent, and the third type is both virus and thymus independent. Lymphomas without thymic involvement and histiocytic lymphomas increased with the generations. The source of causative virus, the interference with mammary tumors, and the possible cell types of origin of lymphomas are discussed.

Age Factors↗
PubMed1981

Carcinogenicity of dichlorvos.

Dichlorvos, 2,2-dichlorovinyl dimethyl phosphate, an organophosphate insecticide, is widely used for the control of agricultural, industrial, and domestic pests (Fig. 1) [1]. Dichlorvos is administered orally as an anthelmintic to swine, horses, cats, and dogs. It is applied by dermal application to cattle, goats, sheep, swine, and chickens to control fleas, flies, and mites. Cucumbers, radishes, lettuce, and tomatoes are treated with dichlorvos in greenhouses. Aerosols and strips are used for the control of ants, bedbugs, ticks, cockroaches, flies, mosquitoes, silverfish, spiders, and wasps. Exposure to dichlorvos is by the inhalation of sprays or vapors from impregnated resins, by skin contact, or orally as a residue in food. The predominant mode of toxicity of dichlorvos is inhibition of cholinesterase. This review includes, to the best of our knowledge, every study on the carcinogenicity of dichlorvos in animals. The studies reviewed are: NCI Dichlorvos Rat Study, Tunstall Laboratory Dichlorvos Rat Study, Kettering Laboratory Dichlorvos Rat Study, Kettering Laboratory Dichlorvos Dog Study, Shell Chemical Company Dichlorvos Swine Study, and NCI Dichlorvos Mouse Study. The conclusions from the NCI Dichlorvos Rat Study and the NCI Dichlorvos Mouse Study are based on my examination and diagnosis of the histological sections. Statistical tests of significance were obtained with Fisher's exact test, and tests for positive linear trend and departure from linear trend.

Adenoma↗
PubMed1979

Macrophages in experimental and human brain tumors. Part 1: Studies of the macrophage content of experimental rat brain tumors of varying immunogenicity.

Although the presence of lymphoreticular cells within tumors has been recognized for over 100 years, it is only within the last decade that the concept has arisen that standard histological examination techniques may lead to an underestimation of the true extent of tumor infiltration by lymphoreticular cells, and particularly by macrophages. The macrophage content of certain systemic tumors has been correlated with their immunogenicity and growth characteristics. Since the central nervous system is to some extent an "immunologically privileged site" and contains within it specialized reticuloendothelial cells called microglia, the authors determined the macrophage content of three rodent brain-tumor cell lines, and attempted to correlate this macrophage content with their immunogenicity and growth characteristics. Their findings indicate a direct correlation between the immunogenicity and macrophage content of these three neural tumor cell lines.

Animals↗
PubMed1975

Alterations in ribonuclease activities in the plasma, spleen, and thymus of tumor-bearing mice.

Six transplantable murine tumor models were evaluated for changes in RNase activity. This study was conducted with spleen and thymus homogenates, as well as with plasma collected from tumor-bearing mice. Nuclease activity directed against the synthetic substrates, polyadenylic acid, polyuridylic acid, and polycytidylic acid, was measured and the data obtained for tumor-bearing animals were compared to their normal counterparts. Elevated activity against polyuridylic acid was observed in the plasma of all tumor-bearing mice. Although not as all inclusive, RNase levels in both the spleen and thymus were generally altered as well. The observance of unilateral changes in nuclease activity directed against the synthetic substrates demonstrated that, in most cases, two or more enzymes were being detected. The assay may have some eventual value in the monitoring of cancer

Adenocarcinoma↗
PubMed2000

[Possible clinical application of immunochemotherapy experimented in animals].

The author has been investigating the value of combination chemotherapy in order to augment the effects of immunotherapy (biotherapy) for experimental tumors in animals. The accumulated evidence from experimental immunochemotherapy is briefly reviewed in this paper; for example, low-dose chemotherapy not only reduced tumor burden but also brought about immunological effects such as restoration of anti-tumor immune responses. The paper also contains a summary of the immune escape mechanisms frequently observed in tumor-bearing hosts. Clinically, immunotherapy is generally applied to cancer patients in order to overcome the immune escape mechanisms and restore the immune responses to tumor cells. It is hard to expect, however, that the various strategies of cancer immunotherapy which show strong immunological effects in immunocompetent hosts would overcome the immune escape mechanisms in tumor-bearing hosts. The combined use of chemotherapy enhanced the effects of immunotherapy in the experiments. The author suggests that low-dose chemotherapy can augment the immune responses to tumor cells by overcoming the immune escape mechanisms in tumor-bearing hosts. Other findings presented are that the activity of immunosuppressor T cells or the production of an immuno-suppressive cytokine, TGF-beta, by tumor cells could be selectively inhibited by low-dose chemotherapy. On the basis of such evidence in animal experiments, the author presents his proposals for clinical cancer treatments.

Animals↗
PubMed1975

Immunosuppression in primary liver and colon tumor induction with N-hydroxy-N-2-fluorenylacetamide and azoxymethane.

The question was examined as to whether immunosuppression in a rat model system would affect the carcinogenic processes leading to tumors in the liver and the large bowel. The protocols were designed to detect an increased incidence or a shorter latent period stemming from a change in immune status. Groups of rats were given injections prior to initiation of the carcinogen regimen and continuously thereafter with a purified gamma fraction of antilymphocytic serum (ALG). Appropriate controls received the gamma fraction of normal rabbit serum or 0.9% NaCl solution. Permanence of skin allografts showed that ALG was an effective immunosuppressive treatment. For liver cancer induction, rats were fed 120 ppm N-hydroxy-N-2-fluorenylacetamide in the diet for 16 weeks, then were continued on control diet. The animals given ALG developed liver tumors at a rate similar to that of controls. For cancer of the large bowel, rats received a single s.c. dose of 7.5 mg azoxymethane per kg per week for 16 weeks and were then held on control diet. With an identical ALG treatment, there were fewer intestinal tumors in the early part of the treatment, because of the important early development of liver angiosarcoma, not seen in control rats given injections of 0.9% NaCl solution. At a later time, the incidence of intestinal cancer was similar in rats on ALG or on 0.9% NaCl solution. Thus, immunosuppression had little effect on the rate of liver tumor formation with a liver carcinogen. Also, ALG led to the precocious development of liver angiosarcomas, but failed to affect intestinal cancer induction in animals given azoxymethane.

2-Acetylaminofluorene↗
PubMed1976

Tumorigenic activity of lead chromate.

Lead chromate was investigated for its carcinogenic potential in both rats and mice. Results show that this compound is a very potent carcinogen in rats when administered i.m. Sixty-four % of the animals treated developed malignant tumors at the injection site. Three renal carcinomas were also found after i.m. treatment with lead chromate. Since lead powder is a comparatively weak carcinogen in rats, whether given p.o. or i.m., it is suggested that the combination of lead and chromium (also weak carcinogen) accounts for the high carcinogenic activity of lead chromate in rats. Swiss albino female mice could not tolerate the same high dose level as did the rats; at the lower dose administered to the mice, no tumors were detected.

Animals↗