Diphosphoryl lipid A from Rhodobacter sphaeroides transiently activates NF-kappa B but inhibits lipopolysaccharide induction of kappa light chain and Oct-2 in the B-cell lymphoma line 70Z/3.

Lipopolysaccharide (LPS) is implicated in much of the pathophysiology associated with gram-negative septic shock. One approach to this serious clinical problem is to develop new drugs that antagonize the action of toxic LPS. A model system to study LPS action and test for potential antagonists is readily provided by LPS regulation of the kappa gene in the murine B-cell line 70Z/3. Rhodobacter sphaeroides diphosphoryl lipid A (RsDPLA) effectively blocked toxic LPS induction of kappa light-chain immunoglobulin expression in 70Z/3 cells. Induction of kappa expression by LPS is dependent on the activation of at least two transcription factors, Oct-2 and NF-kappa B. RsDPLA completely repressed the long-term activation of NF-kappa B observed after 24 h of Salmonella typhosa LPS treatment and antagonized activation of oct-2 mRNA expression. However, RsDPLA was not an inert competitor of LPS. RsDPLA alone strongly activated NF-kappa B binding activity by 30 min but not beyond 9 h of treatment. It also induced a small increase in oct-2 mRNA levels. RsDPLA is not simply a weak agonist; we found no graded increase in kappa expression with increasing RsDPLA concentrations up to 50 micrograms/ml. The NF-kappa B complexes activated by RsDPLA and S. typhosa LPS were both composed of the p50-p65 heterodimer. These results suggest that the physiological LPS receptor(s) on B cells transmits qualitatively different signals depending on the nature of the binding ligand and that the fatty acyl groups of LPS play an important role in activating signal transduction.