Faure E, Equils O, Sieling P A, Thomas L, Zhang F X, Kirschning C J, Polentarutti N, Muzio M, Arditi M
Division of Pediatric Infectious Diseases, Ahmanson Department of Pediatrics, Steven Spielberg Pediatric Research Center, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California 90048, USA.
J Biol Chem. 2000 Apr 14;275(15):11058-63. doi: 10.1074/jbc.275.15.11058.
A missense mutation in the cytoplasmic domain of the Toll-like receptor-4 (TLR-4) has been identified as the defect responsible for lipopolysaccharide (LPS) hyporesponsiveness in C3H/HeJ mice. TLR-4 and TLR-2 have recently been implicated in LPS signaling in studies where these receptors were overexpressed in LPS non-responsive 293 human embryonic kidney cells. However, the signaling role of TLR-4 or TLR-2 in human cells with natural LPS response remains largely undefined. Here we show that human dermal microvessel endothelial cells (HMEC) and human umbilical vein endothelial cells express predominantly TLR-4 but very weak TLR-2 and respond vigorously to LPS but not to Mycobacterium tuberculosis 19-kDa lipoprotein. Transient transfection of non-signaling mutant forms of TLR-4 and anti-TLR-4 monoclonal antibody inhibited LPS-induced NF-kappaB activation in HMEC, while a monoclonal antibody against TLR-2 was ineffective. In contrast to LPS responsiveness, the ability of HMEC to respond to 19-kDa lipoprotein correlated with the expression of TLR-2. Transfection of TLR-2 into HMEC conferred responsiveness to 19-kDa lipoprotein. These data indicate that TLR-4 is the LPS signaling receptor in HMEC and that human endothelial cells (EC) express predominantly TLR-4 and weak TLR-2, which may explain why they do not respond to 19-kDa lipoprotein. The differential expression of TLRs on human EC may have important implications in the participation of vascular EC in innate immune defense mechanisms against various infectious pathogens, which may use different TLRs to signal.
Toll样受体4（TLR-4）胞质结构域中的一个错义突变已被确定为C3H/HeJ小鼠中脂多糖（LPS）低反应性的缺陷原因。最近在这些受体在LPS无反应性的293人胚肾细胞中过表达的研究中，TLR-4和TLR-2被认为与LPS信号传导有关。然而，TLR-4或TLR-2在具有天然LPS反应的人类细胞中的信号传导作用在很大程度上仍不明确。在这里我们表明，人真皮微血管内皮细胞（HMEC）和人脐静脉内皮细胞主要表达TLR-4，但TLR-2表达非常弱，并且对LPS有强烈反应，但对结核分枝杆菌19-kDa脂蛋白无反应。TLR-4的无信号突变形式的瞬时转染和抗TLR-4单克隆抗体抑制了HMEC中LPS诱导的核因子κB激活，而抗TLR-2单克隆抗体无效。与LPS反应性相反，HMEC对19-kDa脂蛋白的反应能力与TLR-2的表达相关。将TLR-2转染到HMEC中赋予了对19-kDa脂蛋白的反应性。这些数据表明，TLR-4是HMEC中的LPS信号受体，并且人内皮细胞（EC）主要表达TLR-4和弱TLR-2，这可能解释了它们为何对19-kDa脂蛋白无反应。TLR在人EC上的差异表达可能对血管EC参与针对各种感染性病原体的天然免疫防御机制具有重要意义，这些病原体可能使用不同的TLR来发出信号。
