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Syngeneic mammary gland tumor (MMT-1) grew slower in non-factor C3H/f (MTV-L) mice than in wirus-positive C3H/He (MTV-S) mice. The immunization of mice with tumor (MMT-1), inoculated and later excised, revealed a higher immune reactivity in the mice of the non-factor substrain. In studying the dynamics of the cytotoxic activity of lymphocytes in regional lymph nodes cytotoxically active lymphocytes were found to appear in C3H/f mice on day 6 after the inoculation of tumor (MMT-1), while the areactive state of lymphocytes was observed in C3H/He mice on days 3 and 24 and in C3H/f mice on day 24 after the inoculation of tumor (MMT-1). Spleen lymphocytes in C3H/f mice had no cytotoxic effect on tumor cells.

Three cell cultures of C3H mouse strain--L, MMT1 and embryonic fibroblasts have different sensitivity to cytolytic action of allogeneic antiserum and to immune lymphocyte action. A sensitivity to cytolytic action of antiserum for these cultures is correlated with the amount of corresponding transplantation antigens. A sensitivity to cytolytic action of immune allogeneic lymphocytes is correlated with the amount of corresponding antigens as well as cell with properties determining the level of lymphocyte sorption on them.

Tumour cells were shown to secrete substances stimulating macrophage migration in vitro and also those depressing the cytopathogenic action of immune lymphocytes in vitro. Embryo fibroblasts (examined in paralled as nontumour cells) secreted as did tumour cells, substances stimulating the macrophage migration, but not substances capable of depressing the cytopathogenic action of immune lymphocytes. L-cells secreted substances inhibiting macrophage migration, but failed to secrete substances depressing the cytopathogenic action of immune lymphocytes.

Some tumors of no mammary tissue origin (sarcoma, hepatoma) grew more effectively in MTV-free mice (C3Hf) as compared with MTV-infected mice (C3H/He), whereas the tumors of mammary gland origin grew more rapidly in the latter ones. It has been shown that C3H/He mice develop a stronger specific immune reaction against hepatoma 22a cells than do C3H/f mice and that the animals of MTV-bearing subline exhibit a higher natural killer activity against these cells.

Immunogenicity of 11 3-methylcholanthrene-induced tumours has been tested in vitro, which was a necessary step in constructing a complex characteristic of cell resistance to the host immune reactions. Such a complex estimate is shown to be useful for predicting the extreme tumourigenicity variants in vivo.

Malignancy of 13 cell cultures cultivated in vitro was studied. 11 cultures were induced by subcutaneous injection of 20-methylcholanthrene to 3 lines of mice. The malignancy was studied by transplantability, growth rate and metastasis formation after subcutaneous injection of a various cell number into normal and sublethally irradiated syngenic mice. A convenient model for studying the significance of certain immunological properties of tumour cells in determination of the malignancy was obtained.

The expression of three phenotypic markers of transformation in vitro, i.e. serum dependence, contact inhibition and anchorage dependence of growth has been investigated using the lines of mouse cells obtained from spontaneously in vitro transformed embryonal fibroblasts (three stages of a continuous passage in vitro being considered) and from induced tumours. The results obtained indicate that in the cell lines arising spontaneously in the continuous passage in vitro the origin of the transformation features can be observed. Anchorage independence demonstrates not high (r = 0.69) but much better correlation with tumourigenicity than other studied markers.

Mouse tumour cell immune resistance in vitro and in vivo is compared. Cell lysis in the cytotoxic test was estimated in the first case, while the dynamics of elimination of the labelled 125I cells from the organism--in the second case. The lysis of cells in vitro and in vivo was found to correspond to 10 out of 11 studied cell lines of mouse tumours. However in spite of the similarity these methods are not identical, since there were cases when differences between certain cell lines were revealed in vitro but not in vivo, and vice versa.

The sensitivity of 3 primary and 13 continuous tumour cell cultures 11 of which were induced with 20-methylcholanthrene to natural killer cells and cytotoxic macrophages has been tested. It is shown that the sensitivity of target cells varies markedly to both types of effector cells and that the level of susceptibility correlates with transplantability of tumour cells but not with their growth rate in syngeneic animals. Cells with high or zero transplantable capacity proved to be resistant, while cells with intermediate transplantability were sensitive to nonspecific immunity effector cells.

7 continuous cell lines with different degrees of malignancy were obtained from cultures of embryo fibroblasts of 4 strains of mice. Three of them were selected in vivo for enhanced malignancy. A study of regularities of changes in immunologic and some cytologic characteristics of these cells in the processes of transformation and malignization has been started. The data are presented that in these processes the density of H-2 antigens in embryo fibroblasts many vary significantly in both directions. These alterations are stochastic and do not depend on transformation or malignization of cells. It is also shown that the sensitivity of the cells under study to the complement lytic action may significantly vary, and does not always correlate with the density of antigens which are the targets of the complement lytic action.

Malignant LS cells obtained from benign L cells by selection retained their immunogenicity in syngeneic recipients. Nevertheless, such selection resulted in a partial change in their antigenic structure, which was manifested by the fact that only partial cross reactivity existed between L and LS cells on the level of both humoral and cellular immunity. The preliminary inoculation of L cells induced statistically significant lymphocytic reaction in the animals against LS cells, sufficient to protect 30% of mice inoculated with these cells.

LS cells, the malignant subline of benign L cells, were obtained from L cells by selection carried out by means of their cultivation in the abdominal cavity of allogenic mice. When inoculated subcutaneously in a dose of 1 x 10(6) into the back, LS cells took and progressively grew in 70% of syngeneic animals. The preliminary immunization with L cells protected 30% of mice inoculated subsequently with L cells.

Cytotoxic antibodies against mouse mammary tumour cells, L-cells and hepatoma 22a cells have been found in the serum of C3H/f and C3H/He mice over 8 months of age. Analogues antibodies were found in the serum of young and old BALB/c mice, but not in C57BL/6 mice. The cytotoxic activity of antimammary tumour cell serum has been completely abolished by its depletion by renal tissue of syngeneic and allogeneic animals.

The intensity of the immune response of cells in mice to strong transplantation antigens of the H-2 complex can depend on the histological type of cells taken for immunization. Splenic cells of C3H mice immunized the cells of BALB/c line better that cells of the non-lymphoid origin taken from the same donor. A reverse situation was observed in case of immunization by the same cells of the lines C57Bl/6 and A/He. It was shown by the analysis of the lines of the first generation derived from the crosses between the 3 lines studied and also by the analysis of these characters in mice born from the backcross, that these characters do not exhibit a simple Mendelian segregation.

The previous report contained the information on obtaining in vitro continuous cell lines of embryonic fibroblasts of mice of 4 genotypes, including C3H. In this paper, data on the degree of lysis of some derivatives of FC3H3 cells by natural killers and macrophages are given. It was shown that normal cells were not lysed by these effectors unlike cells which overcame Hayflick's limit and got minimum malignancy in vitro. However, it was established that the in vivo selection of cells for high tumorigenicity resulted in the formation of tumor cells resistant to lymphocytes--natural killers and macrophages.

The malignant subline of L cells did not differ from the initial benign subline in such immunological parameters as immunogenicity, ability for modigying immunological reactions by their metabolic products, sensitivity to the lyzing action of the complement, ability for surface adsorption of lymphocytes. The cells of the malignant subline were somewhat less sensitive to the lyzing action of T lymphocytes than the cells of the initial subline.

Complement-dependent cytotoxic antibodies against the cells of mammary tumor MMTI appeared in the blood of C3H/He and C3Hf mice at the terminal stage of tumor growth; at the same time the mice of the above-mentioned substrains showed no difference in the degree of reaction. The level of natural cytotoxic antibodies against MMTI tumor cells detected in old C3H/He and C3Hf mice significantly exceeded their level in young mice affected with tumor; however, MMTI tumor cells grew equally fast in both old and young animals. The sera of mice affected with tumor had a weak cytolytic activity against the cells of hepatoma 22a and did not affect L cells and embryonal fibroblasts. The sera were partially exhasted by spleen and renal tissues, as well as the cells of spontaneous mammary tumor obtained from syngeneic animals and were not exhausted by allogenic cells infected with Rauscher murine leukemia virus.