Lipopolysaccharide Activation Of Cells Research Articles

Activation of human and mouse Kupffer cells by lipopolysaccharide is mediated by CD14.

Upregulation of CD14 in Kupffer cells has been implicated in the pathogenesis of several forms of liver injury, including alcoholic liver disease. However, it remains unclear whether CD14 mediates lipopolysaccharide (LPS) signaling in this specialized liver macrophage population. In this series of experiments, we determined the role of CD14 in LPS activation of Kupffer cells by using several complementary approaches. First, we isolated Kupffer cells from human livers and studied the effects of anti-CD14 antibodies on LPS activation of these cells. Kupffer cells were incubated with increasing concentrations of LPS in the presence and absence of recombinant human LPS binding protein (LBP). With increasing concentrations of LPS, human Kupffer cell tumor necrosis factor-alpha (TNF-alpha) production (a marker for Kupffer cell activation) increased in a dose-dependent manner in the presence and absence of LBP. In the presence of anti-human CD14 antibodies, the production of TNF-alpha was significantly diminished. Second, we compared LPS activation of Kupffer cells isolated from wild-type and CD14 knockout mice. Kupffer cells from CD14 knockout mice produced significantly less TNF-alpha in response to the same amount of LPS. Together, these data strongly support a critical role for CD14 in Kupffer cell responses to LPS.

Kupffer cell activation by lipopolysaccharide in rats: role for lipopolysaccharide binding protein and toll-like receptor 4.

Lipopolysaccharide (LPS) binding protein (LBP) is a key serum factor that mediates LPS activation of mononuclear cells. In the presence of LBP, 1/1,000 the concentration of LPS is sufficient to activate peripheral blood monocytes. Previous studies with Kupffer cells have shown a variable effect of serum on LPS activation of these cells and led to the conclusion that, unlike extrahepatic mononuclear cells, Kupffer cells do not respond to LPS in an LBP-dependent fashion. Because there are multiple components in serum other than LBP that might affect LPS activation, these reports with serum are difficult to interpret. To investigate the specific role of LBP in LPS activation of Kupffer cells, we produced a functional recombinant rat LBP using a baculovirus expression system, which we used to selectively examine the role of LBP's on Kupffer-cell function. Isolated Kupffer cells exposed to increasing concentrations of LPS (0, 1, 10 ng/mL) showed a dose-dependent increase in TNF-alpha production, which was augmented and accelerated by the presence of LBP. The effects of LBP on Kupffer cell activation by LPS are dependent on a functional Toll-like receptor 4 (Tlr 4) because Kupffer cells from C3H/HeJ mice failed to respond to LPS in the presence of LBP. LBP plays an important role in mediating Kupffer cell activation by LPS, and these effects are dependent on the presence of functioning Tlr 4.

Pertussis toxin inhibition of B cell and macrophage responses to bacterial lipopolysaccharide.

Lipopolysaccharide, a component of the outer membrane of Gram-negative bacteria, activates B lymphocytes and macrophages. Pertussis toxin, which inactivates several members of the G protein family of signaling components, including Gi and transducin, was found to inhibit the lipopolysaccharide-induced responses of the WEHI-231 B lymphoma cell line and the P388D1 macrophage cell line. These results, combined with the demonstration that lipopolysaccharide inhibits adenylate cyclase activity in P388D1 cells, strongly argues that lipopolysaccharide activation of cells is mediated by a Gi-like receptor-effector coupling protein.