Diphosphoryl lipid A derived from lipopolysaccharide (LPS) of Rhodopseudomonas sphaeroides inhibits activation of 70Z/3 cells by LPS.

Diphosphoryl lipid A derived from nontoxic lipopolysaccharide (LPS) of Rhodopseudomonas sphaeroides ATCC 17023 did not stimulate the murine pre-B cell line 70Z/3 to synthesize surface immunoglobulin or kappa mRNA. However, it effectively blocked Escherichia coli LPS-induced activation of 70Z/3 cells in a concentration-dependent manner. This inhibition was specific only to cells activated by LPS, since it did not inhibit activation of 70Z/3 cells by gamma interferon. Maximal inhibitory effect occurred when the antagonist was added within 2 h before adding the LPS. These results strongly suggested that R. sphaeroides diphosphoryl lipid A is competing with E. coli LPS for physiological lipid A receptors on the 70Z/3 cells.