Potentiation of Lipopolysaccharide-Induced Chemokine and Adhesion Molecule Expression in Corneal Fibroblasts by Soluble CD14 or LPS-Binding Protein

In allergic asthma, inhalation of antigen provokes an early increase in microvascular permeability with protein extravasation and a delayed recruitment of inflammatory cells. We showed that similar concentrations of lipopolysaccharide (LPS) are present in bronchoalveolar lavage fluid (BALF) in 12 subjects without asthma (86.5 +/- 53.8 pg/ml) and 12 subjects with mild asthma (111 +/- 37.0 pg/ml). These LPS levels are insufficient to stimulate cytokine release without accessory molecules. BALF obtained 24 h after segmental ragweed antigen challenge in 11 asthmatics allergic to ragweed contained increased levels of two LPS accessory molecules compared with preantigen BALF, 158-fold more LPS-binding protein (LBP) 4.83 +/- 2.02 vs. 742 +/- 387 ng/ml; P < 0.03) and 31.6-fold more soluble CD14 (sCD14) (3.45 +/- 1.04 vs. 110 +/- 51.6 ng/ml; P < 0.02). Postantigen BALF enhanced binding of fluorescein-conjugated LPS to CD14-bearing THP-1 cells and supported LPS-induced non-CD14-bearing endothelial cell expression of intercellular adhesion molecule-1 and interleukin-6, indicating functional LBP and sCD14. We suggest that extravasation of LBP and sCD14 into the bronchoalveolar compartment after antigen inhalation may enhance the capacity of inhaled or aspirated LPS to activate an inflammatory cascade that may amplify the inflammatory response to inhaled antigen in some asthmatics.

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Soluble CD14 acts as a shuttle in the neutralization of lipopolysaccharide (LPS) by LPS-binding protein and reconstituted high density lipoprotein.

Journal of Experimental Medicine ◽

10.1084/jem.181.5.1743 ◽

1995 ◽

Vol 181 (5) ◽

pp. 1743-1754 ◽

Cited By ~ 164

Author(s):

M M Wurfel ◽

E Hailman ◽

S D Wright

Keyword(s):

High Density Lipoprotein ◽

Lipid Transfer Protein ◽

Binding Protein ◽

Direct Action ◽

Density Lipoprotein ◽

High Density ◽

Lipid Transfer ◽

Soluble Cd14 ◽

Transfer Protein ◽

Lps Binding

We have recently shown that lipopolysaccharide (LPS)-binding protein (LBP) is a lipid transfer protein that catalyzes two distinct reactions: movement of bacterial LPS (endotoxin) from LPS micelles to soluble CD14 (sCD14) and movement of LPS from micelles to reconstituted high density lipoprotein (R-HDL) particles. Here we show that LBP facilitates a third lipid transfer reaction: movement of LPS from LPS-sCD14 complexes to R-HDL particles. This action of LBP is catalytic, with one molecule of LBP enabling the movement of multiple LPS molecules into R-HDL. LBP-catalyzed movement of LPS from LPS-sCD14 complexes to R-HDL neutralizes the capacity of LPS to stimulate polymorphonuclear leukocytes. Our findings show that LPS may be transferred to R-HDL either by the direct action of LBP or by a two-step reaction in which LPS is first transferred to sCD14 and subsequently to R-HDL. We have observed that the two-step pathway of LPS transfer to R-HDL is strongly favored over direct transfer. Neutralization of LPS by LBP and R-HDL was accelerated more than 30-fold by addition of sCD14. Several observations suggest that sCD14 accelerates this reaction by serving as a shuttle for LPS: addition of LBP and sCD14 to LPS micelles resulted in LPS-sCD14 complexes that could diffuse through a 100-kD cutoff filter; LPS-sCD14 complexes appeared transiently during movement of LPS to R-HDL facilitated by purified LBP; and sCD14 could facilitate transfer of LPS to R-HDL without becoming part of the final LPS-R-HDL complex. Complexes of LPS and sCD14 were formed transiently when LPS was incubated in plasma, suggesting that these complexes may play a role as intermediates in the neutralization of LPS under physiological conditions. These findings detail a new activity for sCD14 and suggest a novel mechanism for lipid transfer by LBP.

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