DISSOCIATION OF LIPOPOLYSACCHARIDE (LPS)-INDUCIBLE GENE-EXPRESSION INMURINE MACROPHAGES PRETREATED WITH SMOOTH LPS VERSUS MONOPHOSPHORYL LIPID-A

Lipopolysaccharide (LPS) and the nontoxic derivative of lipid A, monop hosphoryl lipid A (MPL), were employed to assess the relationship betw een expression of LPS-inducible inflammatory genes and the induction o f tolerance to LPS in murine macrophages. Both LPS and MPL induced exp ression (as assessed by increased steady-state mRNA levels) of a panel of seven ''early'' inflammatory genes including the tumor necrosis fa ctor alpha (TNF-alpha), interleukin-1beta, type 2 TNF receptor (TNFR-2 ), IP-10, D3, D8, and D2 genes (the last four represent LPS-inducible early genes whose functions remain unknown). In addition, LPS and MPL were both capable of inducing tolerance to LPS. The two stimuli differ ed in the relative concentration required to induce various outcome me asures, with LPS being 100- to 1,000-fold more potent on a mass concen tration basis. Characterization of the tolerant state identified three distinct categories of responsiveness. Two genes (IP-10 and D8) exhib ited strong desensitization in macrophages pretreated with tolerance-i nducing concentrations of either LPS or MPL. In macrophages rendered t olerant by pretreatment with LPS or MPL, a second group of inducible m RNAs (TNF-alpha, interleukin-1beta, and D3) showed moderate suppressio n of response to secondary stimulation by LPS. The third category of i nducible genes (TNFR-2 and D2) showed increased expression in macropha ges pretreated with tolerance-inducing concentrations of either LPS or MPL. All of the LPS-inducible genes examined exhibited modest superin duction with less than tolerance-inducing concentrations of either sti mulus, suggesting a priming effect of these adjuvants at low concentra tion. The differential behavior of the members of this panel of endoto xin-responsive genes thus offers insight into molecular events associa ted with acquisition of transient tolerance to LPS.