Quantitative Comparison of Milk-released C3H and RIII Mammary Tumor Viruses in Infected BALB/c Hosts

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 F85, 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.

Stability of Characters of Mammary Tumors in Balb/cfRIII Mice

The biological and morphological characteristics of mammary tumors in BALB/c mice infected with RIII mammary tumor virus (MTV) by foster nursing have substantially kept stable and unchanged after 20 years, 53 inbred generations and transfer of the strain from Perugia to Pisa. This suggests that the causal MTV keeps unaltered in time its biological properties.

Pathogenesis and characteristics of spontaneously metastasizing mammary carcinomas and the general principle of metastasis

Chemical mammary carcinogenesis in immunologically attennuated W/Fu female rats, subjected to specific and nonspecific immunostimulations, yielded many spontaneously metastasizing adenocarcinomas with varying degrees of glandular differentiation, and growth rates. The pathogenesis of these tumors suggested that while carcinogens transform target cells, the host immune system endows them with metastatic potential. The metastatic pathways were recognizable as hematogenous, lymphogenous, or hematogenous-lymphogenous combined, according to the capacity of the tumor cells to intravasate the lymphatic and/or vascular channel and traverse the pulmonary artery. The same metastatic pattern can be reproduced with cells from any of the organs involved, indicating that it is inherent in all cells within a given tumor, rather than being determined by the organs they colonize. The biological, biochemical and immunological characteristics of these tumors resemble human breast cancer thus becoming an effective tool in the formulation of the general principle of metastasis by malignant solid tumors.

Natural infection of Swiss mice with mouse mammary tumor virus (MMTV): viral expression in milk and transmission of infection

Quantitative determinations of gp52, the main envelope glycoprotein, and p28, the main core protein, of MMTV, have been performed in about 1000 individual samples of milk of breeding females from our colony of MMTV-infected Swiss mice, a line characterized by a moderate incidence of mammary tumors. A computer analysis of the results showed: 1-- an important individual variation, ranging from 0 to 120 micrograms per ml of milk for p28, and from 0 to 320 micrograms per ml of milk for gp52; 2-- a variation of the release of both antigens during a single lactation, with a maximum on the 7--8th day of nursing; 3-- an increase of the release of both antigens with parity up to the 6th lactation, followed by a marked decrease during later lactations; 4-- a higher degree of infection in the offspring of 2nd and 3rd litters. The possible dependence of viral expression and transmission of infection upon factors such as cyclic activity of the mammary gland and progressive immunization of mice against MMTV is analyzed. The status of our laboratory line of MMTV infected Swiss mice is discussed in comparison with high and low tumor incidence strains.