Schlaf G, Schieferdecker H L, Rothermel E, Jungermann K, Götze O
Abteilung für Immunologie, Georg-August-Universität Göttingen, Germany.
Lab Invest. 1999 Oct;79(10):1287-97.
The C5-anaphylatoxin (C5a) is a protein of 74 (human) or 77 (rat) amino acid residues, respectively, which is generated by limited proteolysis upon activation of the fifth component of complement. Its generation may be induced by both the classical and alternative pathways. C5a has been shown to indirectly increase glucose output from hepatocytes (HC) in perfused rat liver by inducing prostanoid release from Kupffer cells (KC) and hepatic stellate cells (HSC). A direct action of C5a on hepatocytes would require their expression of the specific C5a receptor (C5aR). In former studies using quantitative reverse transcription polymerase chain reaction (RT-PCR) it was shown that HC lack this receptor in contrast to KC, HSC and, probably, sinusoidal endothelial cells (SEC), all of which contained mRNA for the C5aR in decreasing amounts. Using a novel monoclonal antibody (mAb R63) against the rat receptor, expression of the rat receptor on the four cell types was investigated by FACS analysis, immunohistochemistry, and immunocytochemistry. The data obtained were confirmed by functional studies in which the Ca2+ response after stimulation of the isolated cells with recombinant rat C5a (rrC5a), the ligand for the receptor was recorded. The FACS and the immunocytochemical data presented here clearly indicate that rat HC do not express the C5aR, whereas KC have the highest expression level followed by HSC. SEC expressed the receptor only weakly. In line with these findings, a strong Ca2+ response was observed after stimulation of KC and HSC, and a weak one with SEC. However, no signal was obtained upon stimulation of HC. The results of this study support the indirect stimulation of glucose output from HC via prostanoid release from nonparenchymal liver cells and contradict the formerly proposed hypothesis of a direct action of C5 anaphylatoxin on hepatocytes.
C5过敏毒素（C5a）是一种分别由74个（人类）或77个（大鼠）氨基酸残基组成的蛋白质，它是在补体第五成分激活后通过有限的蛋白水解作用产生的。其产生可由经典途径和替代途径诱导。已表明C5a通过诱导库普弗细胞（KC）和肝星状细胞（HSC）释放类前列腺素，间接增加灌注大鼠肝脏中肝细胞（HC）的葡萄糖输出。C5a对肝细胞的直接作用需要其表达特异性C5a受体（C5aR）。在以前使用定量逆转录聚合酶链反应（RT-PCR）的研究中表明，与KC、HSC以及可能的窦状内皮细胞（SEC）相比，HC缺乏这种受体，所有这些细胞都含有数量递减的C5aR mRNA。使用一种针对大鼠受体的新型单克隆抗体（mAb R63），通过荧光激活细胞分选（FACS）分析、免疫组织化学和免疫细胞化学研究了大鼠受体在这四种细胞类型上的表达。通过功能研究证实了所获得的数据，在功能研究中记录了用重组大鼠C5a（rrC5a）（该受体的配体）刺激分离细胞后的Ca2+反应。此处呈现的FACS和免疫细胞化学数据清楚地表明，大鼠HC不表达C5aR，而KC的表达水平最高，其次是HSC。SEC仅微弱表达该受体。与这些发现一致，刺激KC和HSC后观察到强烈的Ca2+反应，刺激SEC后反应较弱。然而，刺激HC后未获得信号。本研究结果支持通过非实质肝细胞释放类前列腺素间接刺激HC的葡萄糖输出，与先前提出的C5过敏毒素对肝细胞直接作用的假设相矛盾。
