SUPPRESSION OF TNF-ALPHA MESSENGER-RNA EXPRESSION IN LPS-PRIMED MACROPHAGES OCCURS AT THE LEVEL OF NUCLEAR FACTOR-KAPPA-B ACTIVATION, BUT NOT AT THE LEVEL OF PROTEIN-KINASE-C OR CD14 EXPRESSION

Previously, we reported that preexposure of proteose peptone-elicited murine peritoneal exudate macrophages (P-PEM) to a low dose of LPS sup pressed the expression of TNF-alpha mRNA, but not of IL-1 beta mRNA, i nduced by a second round of LPS exposure. To elucidate the mechanisms underlying this hyporesponsiveness to LPS, we focused on two molecules : nuclear factor (NF)-kappa B and CD14. Activation of NF-kappa B induc ed by a second round of LPS was suppressed in LPS-primed P-PEM much li ke the suppression of TNF-alpha mRNA expression. However, protein kina se C (PKC), a candidate as an activator of NF-kappa B, was not desensi tized by LPS priming. LPS-induced TNF-alpha production was not affecte d by depletion of PKC, and LPS could not induce translocation of PKC. CD14 expression showed no significant difference between control and p rimed P-PEM. In contrast with J774.1 cells and thioglycolate medium-el icited macrophages (T-PEM), P-PEM exhibited serum-independent TNF-alph a production, and a polyclonal Ab to murine CD14 had no inhibitory eff ect on the LPS-induced TNF-alpha production by P-PEM. These results su ggest that priming by LPS causes blockage at an early step, at least b efore the activation of NF-kappa B, in the LPS signal transduction pat hway, but not at the expression of CD14. Our results also suggest that , in P-PEM, in contrast to J774.1 cells and T-PEM, neither PKC nor CD1 4 is involved in the LPS-induced activation and suppression of TNF-alp ha gene expression.