Induction of TNF-alpha and MnSOD by endotoxin: role of membrane CD14 and Toll-like receptor-4

Endotoxin (LPS) is a potent inducer of tumor necrosis factor-alpha (TNF-alp ha) and manganese superoxide dismutase (MnSOD). Recent evidence suggests th at LPS induction of TNF-alpha and MnSOD mRNAs is mediated through distinct intracellular signal transduction pathways. Membrane CD14 (mCD14) and Toll- like receptor-4 (TLR4) mediate LPS induction of TNF-alpha in macrophages. I n the current study, we evaluated the role of mCD14 and TLR4 in LPS inducti on of MnSOD using peritoneal macrophages from CD14 knockout (CD14-KO) mice and mice with the Tlr4 gene point mutation (C3H/HeJ) or deletion (C57BL/10S cCr). We studied mCD14-dependent (1 and 10 ng/ml) and mCD14-independent (1, 000 ng/ml) concentrations of LPS. Compared with control (BALB/c) macrophage s, LPS at 1 and 10 ng/ml failed to induce TNF-alpha or MnSOD mRNA in CD14-K O macrophages. However, LPS at 1,000 ng/ml induced TNF-alpha and MnSOD mRNA s equally in macrophages from CD14-KO and control mice. LPS (1, 10, or 1,00 0 ng/ml) failed to induce TNF-alpha or MnSOD mRNA and failed to activate nu clear factor-kappaB in C3H/HeJ or C57BL/10ScCr macrophages. Measurements of TNF-alpha and MnSOD enzyme activity paralleled TNF-alpha and MnSOD mRNA le vels. These data demonstrate that, like TNF-alpha, induction of MnSOD by LP S is mediated by mCD14 and TLR4 in murine macrophages.