A SERUM-MEDIATED MECHANISM FOR CONCOMITANT RESISTANCE SHARED BY IMMUNOGENIC AND NONIMMUNOGENIC MURINE TUMORS

Resistance of rumour-bearing mice to a second tumour challenge, that i s concomitant resistance, was evaluated in euthymic and nude mice usin g nine tumours with widely different degrees of immunogenicity. Two te mporally separate peaks of concomitant resistance were detected during tumour development. The first one was exhibited only by small immunog enic rumours; it was tumour specific and mediated by classical immunol ogical T-cell-dependent mechanisms. The second peak was shared by both immunogenic and nonimmunogenic large tumours; it was non-specific, th ymus independent and correlated with the activity of a serum factor (n either antibody nor complement) that inhibited the in vitro proliferat ion of tumour cells. This Factor was eluted from a Sephadex G-15 colum n at fractions corresponding to a molecular weight of approximately 10 00 Da and it was recovered from a high-performance liquid chromatograp hy column in one peak presenting maximum absorption at 215 and 266 nm. The data presented in this paper suggest for the first time, to our k nowledge, that in spite of the differences between immunogenic and non -immunogenic rumours, a common serum-mediated mechanism seems to under lie the concomitant resistance induced by both types of rumours at lat e stages of tumour development.