The biological activity of a preparation of heat killed cells of Enterococcus faecalis, FK-23 which was isolated from the feces of a healthy human, was investigated in C3H/He mice. Intraperitoneal injection of the preparation caused an accumulation of neutrophils and macrophages in the peritoneal cavity of the mice 6 h later. As a parameter of the activation of macrophages, the effect of the FK-23 preparation on the production of tumor necrosis factor (TNF) was examined. The mice were given two consecutive intravenous injections of the preparation at a dose of 10μg/mouse and, 3 h later, of 300μg/mouse. The TNF level in the sera reached 99 U/ml in mice 2 h after the second injection. This preparation also stimulated peritoneal macrophages to produce TNF in vitro and increased the capacity of neutrophils to adhere to plastic plates and to release active oxygens, but did not induce blastogenic transformation of lymphocytes. These results suggest that the FK-23 preparation is a biological response modifier (BRM) with various activities on phagocytes similar to a streptococcal antitumor agent, OK432.
