Pugin J, Ulevitch R J, Tobias P S
Scripps Research Institute, Department of Immunology, La Jolla, CA 92037, USA.
Prog Clin Biol Res. 1995;392:369-73.
Optimal activation of endothelial cells by nanomolar quantities of endotoxin (lipopolysaccharide, LPS) requires the presence of plasma or serum. We and others have demonstrated that soluble CD14 (sCD14) and LPS binding protein (LBP) were the key plasma proteins mediating endothelial cell responses to LPS. The role of LBP is to transfer LPS to sCD14 and newly formed LPS-sCD14 will in turn activate endothelial cells via an as yet unknown surface receptor. This plasma-dependent pathway of endothelial cells activation is referred as to the direct pathway. However, endothelial cells are in constant contact with whole blood and not only with plasma. In experiments where whole blood was substituted for plasma, we showed that endothelial cells became sensitive to picomolar, rather than nanomolar quantities of LPS. The fact that endothelial cell responses were amplified by the presence of whole blood prompted us to search for the responsible blood cell(s) and mediator(s) for this effect. Blood cell fractionation experiments, experiments with blood from PNH patients and the use of anti-CD14 antibodies pointed to the monocyte as the blood cell responsible for the amplification effect. Moreover, the blood effect could be entirely reproduced by cells from a CD14-expressing cell line, such as calcitriol-differentiated HL-60 cells. Inhibitors to TNF and to IL-1 blocked LPS-induced activation of endothelial cells partially when added separately to whole blood, but abrogated endothelial cell responses when added together. Thus, the whole blood effect begins with LPS activation of monocytes via cell membrane CD14 and results in endothelial cell activation by the effects of TNF and IL-1. The monokine-mediated endothelial cell activation is referred as to the indirect pathway.
内皮细胞被纳摩尔量的内毒素（脂多糖，LPS）最佳激活需要血浆或血清的存在。我们和其他人已经证明，可溶性CD14（sCD14）和LPS结合蛋白（LBP）是介导内皮细胞对LPS反应的关键血浆蛋白。LBP的作用是将LPS转移至sCD14，新形成的LPS-sCD14进而通过一种未知的表面受体激活内皮细胞。这种内皮细胞激活的血浆依赖性途径被称为直接途径。然而，内皮细胞持续接触的是全血而非仅仅是血浆。在以全血替代血浆的实验中，我们发现内皮细胞对皮摩尔量而非纳摩尔量的LPS变得敏感。全血的存在放大了内皮细胞反应这一事实促使我们寻找造成这种效应的血细胞和介质。血细胞分级实验、对阵发性睡眠性血红蛋白尿症（PNH）患者血液的实验以及抗CD14抗体的使用表明单核细胞是造成放大效应的血细胞。此外，来自表达CD14的细胞系（如骨化三醇分化的HL-60细胞）的细胞能够完全重现血液效应。单独添加到全血中时，TNF和IL-1的抑制剂会部分阻断LPS诱导的内皮细胞激活，但一起添加时则消除内皮细胞反应。因此，全血效应始于LPS通过细胞膜CD14激活单核细胞，并通过TNF和IL-1的作用导致内皮细胞激活。这种单核因子介导的内皮细胞激活被称为间接途径。
