Scanning electron microscopic studies on the surface structure of activated macrophages and on their interaction with tumor cells.

Experiments on peritoneal macrophages obtained from Corynebacterium parvum (C. parvum)-treated or untreated normal mice were performed in order to quantitate the cytotoxic activities and surface morphological modifications. The cytotoxic activities of activated macrophages were significantly higher than those or normal macrophages. There were prominent differences in surface morphology between C. parvum-activated and normal macrophages as seen by scanning electron microscopy. The activated macrophages were larger and exhibited higher surface membrane activities than normal macrophages. In interaction between macrophages and tumor cells, both activated and normal macrophages were observed to come into contact with target tumor cells during the first 24 hr. The surfaces of tumor cells entirely lost their microvilli and showed pores. Tumor cells finally died after interaction with activated macrophages for 48 hr. In contrast, no significant alterations were observed on the surfaces of tumor cells incubated with normal macrophages. In conclusion, it seems that the cytotoxic activities of macrophages correlate with the extent of macrophage activation, and the activation correlates with the surface membrane alterations.