An acetylated derivative prepared from Salmonella typhosa O-901 endotoxin has been found to retain the ability to stimulate non-specific host resistance to a variety of bacterial infections. Relative to the parent endotoxin, the derivative has been reduced in the gross in its pyrogenicity to rabbits and lethality to mice. With the use of this chemically modified preparation under a variety of conditions, the direct dissociation of the toxic properties of endotoxin from its protective capacity appears evident.
In young male mice, the endotoxin and its derivative produced a leucocytosis but no leucopenia. However, no direct correlation could be found with the level of the peripheral white blood cells and resistance to infection with Escherichia coli. Furthermore, under the conditions employed, passive transfer of early resistance to infection by serum or plasma was not detectable.