Comparison of the natural humoral antitumor reactivity of different strains of mice.

Normal serum from C3Hf mice showed a complement-dependent cytotoxic reactivity against EL4 lymphoma cells, starting from 2 to 3 months of age, whereas normal serum from BALB/c and C57BL/6J mice became reactive only at a later age. The cytotoxins of normal sera of the 3 strains, as well as of a C57BL antiembryo antiserum studied in parallel, belong to the IgM class. When absorption were performed, using a variety of absorbing cells, marked differences were found among the sera, which according to their behavior could be divided in two groups: one group comprises the BALB/c and the C57BL sera, the other group the C3Hf serum from both young and old mice and the antiembryo antiserum. The reactivity of the 3 latter sera seems to be directed against specifities related to an ecotropic N-tropic virus, which on the contrary did not seem to be involved in the reactivity of BALB/c and C57BL sera. The C57BL antiembryo antiserum obtained by immunization with C3Hf embryos behaved differently from the C57BL normal serum and similarly to the C3Hf normal serum.