Augmentation of spontaneous cytotoxicity of human lymphocytes by RU 41.740, a glucoprotein extract of Klebsiella pneumoniae.

RU 41.740 (Biostim) is an extract of Klebsiella pneumoniae with immunomodulating properties. This substance was observed to augment spontaneous cytotoxicity of human blood lymphocytes provided that monocytes were present during Biostim treatment. Maximal augmentation was observed after 2 h of incubation. The F1 fraction, a glucoprotein which comprises approximately 20% of Biostim, and LPS from Klebsiella pneumoniae were also observed to augment spontaneous cytotoxicity of lymphocytes. Biostim treatment of K562 cells, which were used as target cells for killing, did not change their sensitivity to the lytic action of spontaneously cytotoxic cells.