Role of colony-stimulating activity in antitumor activity of Lactobacillus casei in mice

Wide-ranging differences were observed between the antitumor activities of 23 lactobacilli (13 species; 23 strains) and their capacities to elevate the level of serum colony-stimulating activity (CSA) by intraperitoneal administration in mice, and a good correlation existed between the two activities. The mechanism of enhanced production of CSA by administration of Lactobacillus casei YIT 9018 (LC 9018), one of the bacteria that had the strongest activities, and the role of CSA in antitumor activity of LC 9018 were studied. Colony-stimulating activity in the washing fluid from the peritoneal cavity of mice that had been administered LC 9018 intraperitoneally was elevated at 3 to 24 h after the injection, and CSA was also detected at elevated levels in the serum of the mice 6 to 12 h after injection. The cells responsible for the production of CSA after stimulation with LC 9018 seem to be the resident macrophages at the site of administration, because the resident macrophages of mice lavaged 1 h after an intraperitoneal administration of LC 9018 released CSA when they were cultured in vitro. Moreover, resident peritoneal macrophages of normal mice cultured with LC 9018 in vitro also produced CSA. Similar results were obtained with athymic nude mice, and the CSA-inducing activity of LC 9018 was diminished in the mice pretreated with carrageenan, which is selectively toxic to mature macrophages. Bone marrow cells matured to macrophages and polymorphonuclear cells by culture with the CSA induced by LC 9018 for 7 days. These matured macrophages showed strong antitumor activity both in vivo and in vitro. These results suggest that CSA plays important roles in the antitumor activity of LC 9018: it enhances not only the multiplication of committed precursor cells for macrophages and polymorphonuclear cells, but also the functional maturation of the precursor cells for macrophages which serve as potent effectors for tumor cells.