The streptococcal preparation, OK.432, with predominant
host-mediated mode of action, was studied. By giving OK-432 to mice intraperitoneally prior to transplantation of Ehrlich carcinoma, a host-mediated action to increase life-span was clearly confirmed. Pretreatment with OK-432 was also effective against the development of Rauscher leukemia. The host-mediated action of OK-432 varied with the interval between its pretreatment and the inoculation of tumor cells. The effect was most marked when the transplant was performed immediatedly after the pretreatment, and became less marked when the transplant was made one week and two weeks after pretreatment. The host-mediated action can be observed even with a single dose of pretreatment, and becomes more potent as pretreatment was given repeatedly. The host-mediated action was weakened by concomitant pretreatment with cyclophosphamide or roentgen irradiation, and the mechanisms of such action was supposed to be associated with the function of the reticulo-endothelial system.</p
