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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 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.