The involvement of granulocytes in spontaneous regression of Walker 256 carcinoma

We described before that oxidative burst of granulocytes is cytotoxic for melanoma B16F10 and for Walker 256 carcinoma (W256). Therefore, we assumed that granulocytes could also be important mechanism of the host defence against tumour. In current study we report massive granulocyte infiltration at the site of W256 transplanted in the hind limb of Sprague–Dawley associated with spontaneous tumour regression observed for 22/25 rats (87%). Peripheral blood granulocytes of these animals were highly cytotoxic for W256 cells cultured in vitro. After the tumour disappearance the inflammatory oxidative burst of the granulocytes ended. Distraction of granulocytes from the tumour by s.c. Sephadex injection decreased the incidence of the W256 regression to only 7/25 animals (30%). These results suggest that innate immunity based on immune competent granulocytes may be the cause of well known phenomenon of spontaneous regression of W256 carcinoma.