Kupffer cells of normal liver may produce consid-
The subcomponent of complement C1, C1q, mediates complement activation via the classical pathway, and therefore erable amounts of C1q, whereas the inflammatory macrophages of the acutely damaged liver may not be so important may play an important role in the inflammatory processes in which complement activation is involved. The aim of our for the synthesis of C1q. (HEPATOLOGY 1997;26:98-106.) study was to investigate C1q synthesis by macrophages of normal and of acutely damaged livers. The localization of C1q
The complement system represents one of the links bein liver tissue was studied by immunohistochemistry. Rat tween the innate and specific immune system and comprises liver tissue macrophages were isolated from normal as well a number of serum proteins that, once the complement casas from acutely damaged (carbon tetrachloride model) liver, cade is driven on, are successively activated and generate and were separated into small, monocyte-like phagocytes and biologically highly active C3b that further initiates generation large, mature tissue macrophages, as revealed by immunocyof the terminal membrane attack complex with the aim of tochemistry. C1q gene expression was studied by endogecellular lysis. 1 Different mechanisms of activation have been neous labeling of newly synthesized proteins, immunoprecipidescribed that are supervised by regulatory complement protation, and sodium dodecyl sulfate-polyacrylamide gel teins. The classical pathway of complement activation 2 is electrophoresis (SDS-PAGE), and by reverse-transcription known to be initiated by binding of immune complexes to polymerase chain reaction (RT-PCR) of C1qB messenger RNA the C1 subcomponent, C1q, thereby enabling coupling and (mRNA). Semiquantitative analysis was performed by Northsubsequent activation of the serine proteases, C1r and C1s, ern blotting of total RNA and hybridization with the radioacresulting in the generation of active C1, the first component tively labeled RT-PCR product. C1 esterase inhibitor synof complement. C1q as the first subcomponent of complethesis was studied in parallel. For comparison, C1q and ment thus holds one of the key roles in the function of the C1-inhibitor synthesis were also investigated in blood monocomplement system. cytes and peritoneal macrophages. C1q was weakly detectable C1q is assembled from 18 polypeptide chains of three in sinusoidal cells of the normal liver. C1qB mRNA, as well different types, called the A-, B-, and C-chains, with molecuas constitutive synthesis and secretion of C1q, was clearly lar weights of 29, 27, and 23 kd, respectively. A triplet comdetected in freshly isolated and cultured Kupffer cells from posed of one chain of each type forms one of six individual normal rat liver. In comparison, newly recruited ''inflammasegments each acquiring a collagen-like, triple helical structory'' macrophages from damaged rat liver synthesized considture in the amino terminal region and a globular structure erably lower amounts of the protein, similar to what was in the carboxy terminal region that is capable of binding found in the monocyte-like macrophages of normal liver and immune complexes. C1q binds to the Cg2 domain of immuin peritoneal macrophages. Monocyte C1qB mRNA was not noglobulin (Ig)G and Cm3 domain of IgM in the state of detected even by RT-PCR, and remained undetectable during antigen-coupling. It also binds directly to surfaces of bacteria the time in culture. Similar behavior was observed for C1or viruses, and, once fixed, activates C1r and C1s to generate inhibitor synthesis. Treatment of the cultures with interferon C1. The serpin C1 inhibitor negatively controls the assembly gamma (IFN-g) or lipopolysaccharide (LPS) strongly deof functionally active C1 by inactivation of C1r and C1s, creased, whereas treatment with dexamethasone strongly inleaving nonassembled C1q, which is now able to bind to C1q creased C1q gene expression in the macrophage populations, receptors 3 shown to be present on the cell surface of various and induced C1qB mRNA in cultured monocytes, as revealed cell types like mononuclear phagocytes, epithelial cells, fibroblasts, platelets, and T cells. 4-7 Furthermore, C1q was also shown to be surface membrane-bound on macrophages. It Abbreviations: Ig, immunoglobulin; mRNA, messenger RNA; IFN-g, interferon gamma; LPS, lipopolysaccharide; SDS, sodium dodecyl sulfate; PAGE, polyacrylamide was suggested that C1q could serve as an Fc-receptor, 8,9 facilgel electrophoresis; cDNA, complementary DNA; RT, reverse transcriptase; PCR, polyitating endocytosis of membrane-or antigen-bound immunomerase chain reaction.
globulins, but others did not confirm this hypothesis. 10 From the Zentrum Innere Medizin, Abteilung Gastroenterologie und Endokrinolo-Synthesis of C1q has been shown in different cell types gie, Georg-August-Universita ¨t Go ¨ttingen, Go ¨ttingen, Germany.