Bacterial polysaccharides, endotoxins, and immunomodulation.

These studies show that at least some--though certainly not all--of the adjuvant effects of LPS and its derivatives can be attributed to its ability to eliminate the inhibitory effects of Ts which are activated during the course of a normal immune response. The ability of nontoxic MPL to act in this fashion suggests that it can be used as a safe and acceptable alternative to Freund's complete adjuvant to increase the immunogenicity of poorly immunogenic antigens. More important, the ability of MPL to eliminate the expression of Ts activity, without adversely influencing other T cell functions (e.g., Th, Ta, and Tc activity) makes its use as an adjuvant even more promising since it can then permit those T cell functions to be expressed in a much more efficient manner. Obviously, this would have great significance for the development of tumor immunity.