The effect of Biostim (RU 41.740) on natural killer activity in different mouse organs

The effect of Biostim, a mixture of two glycoproteins extracted from K. pneumoniae, on NK activity in lung, blood and spleen was investigated in mice. Marked increases in NK-cytotoxicity for YAC-1 targets were found after single or repeated administrations of this compound by the i.p. or the oral route in the absence of increases of serum IFN. The highest increases in NK activity were found in lymphoid cells recovered from the lung, active treatments with Biostim significantly increasing the proportion of both target-binding cells and lytic conjugate-forming NK cells. In addition to increasing the rate of clearance from lung and spleen of in vivo-injected radiolabelled YAC-1 cells, short (3 h) exposures to Biostim in vitro augmented the NK-cytotoxicity of murine and human cells. By showing that NK cells can also be a target of Biostim, these results can contribute to a better understanding of the mode of action of this immunomodulator.