Potentiation of tumour growth by endotoxin in serum from syngeneic tumour-bearing mice.

The subcutaneous growth of 2 antigenically distinct syngeneic methylcholanthrene-induced murine fibrosarcomas, designated H1 and H7, were significantly augmented by the concomitant administration of E. coli endotoxin (LPS). Amounts as little as 0.2 micrograms i.p. potentiated tumour growth. The weakly antigenic tumour, H1, was more susceptible to provocation by LPS than the more strongly antigenic H7. Maximum provocation of H1 tumour growth occurred when LPS was injected 1 day before the administration of 5000 tumour cells. In contrast, significant anti-tumour resistance resulted if LPS was administered 6 days before the inoculation of tumour cells. Preliminary evidence indicates that low doses of LPS can facilitate the "sneaking through" phenomenon. Enhancement of tumour growth could not be demonstrated with sera or plasma from tumour-bearing mice, unless the samples were contaminated with endotoxin. The results illustrate the importance of excluding endotoxin from solutions used in studies of experimental tumours.