Sheep erythrocytes provide metabolic triggers for tumour phagocytosis in polymorphonuclear neutrophils: a possible mechanism of tumour inhibition in mice.

Intraperitoneal (i.p.) injection of 7% Sheep Erythrocytes (SRBC) was found to inhibit growth of a transplanted tumour and exhibit a consequent increase in total survival compared to untreated tumour controls. In an attempt to probe into the mechanism(s) involved, functional aspects of Polymorphonuclear Neutrophils (PMNs) were investigated in terms of their 'metabolic (respiratory) burst' during tumour phagocytosis. Both NADPH-Oxidase mediated superoxide anion (O2-.) formation (NBT reduction) and Myeloperoxidase (MPO) mediated oxidisable halide incorporation (131I incorporation) were found to be highly stimulated by SRBC in normal (CS) and tumour bearing counterparts (TS). A little tumour mediated residual inhibition persists on the MPO system in PMNs of animals with tumour plus SRBC (TS) which, however, showed an obvious bonus effect over the tumour controls (TC). The results suggest a possible mechanism of tumour inhibition by SRBC in mice with the involvement of highly stimulated phagocytic metabolism in PMNs.