Antitumor Activity and Its Properties of Eubacterium lentum

In the present study, some basic effects of Eubacterium lentum (TYH‐11), isolated from normal intestinal flora, upon the immune system and various experimental tumor cell lines were investigated. E. lentum showed no direct cytotoxicity against Ehrlich ascites tumor, while Serratia marcescens (TY‐142) did show direct cytotoxicity. E. lentum presented striking antitumor activity which differed according to the injection route and time. This strain showed antitumor activity against 11 experimental tumor cell lines including Ehrlich ascites tumor, Meth‐A, etc., but not against EL4 or Lewis lung carcinoma. The antitumor activity in this strain was recognized to lie in the cell wall and granular fractions. The effect of this strain on the immune system was studied by using plaque formation and the footpad reaction. When mice received 5 injections of E. lentum, the plaque number increased to treble the control level. Spleen weight was also increased following administration of E. lentum. In normal and tumor‐bearing mice immunized with SRBC alone, the footpad reaction was increased significantly to the control level by administration of E. lentum.