CLQ SYNTHESIS BY TISSUE MONONUCLEAR PHAGOCYTES FROM NORMAL AND FROM DAMAGED RAT-LIVER - UP-REGULATION BY DEXAMETHASONE, DOWN-REGULATION BY INTERFERON-GAMMA, AND LIPOPOLYSACCHARIDE

The subcomponent of complement C1, C1q, mediates complement activation via the classical pathway, and therefore may play an important role i n the inflammatory processes in which complement activation is involve d, The aim of our study was to investigate C1q synthesis by macrophage s of normal and of acutely damaged livers, The localization of C1q in liver tissue was studied by immunohistochemistry. Rat liver tissue mac rophages were isolated from normal as well as from acutely damaged (ca rbon tetrachloride model) liver, and were separated into small, monocy te-like phagocytes and large, mature tissue macrophages, as revealed b y immunocytochemistry, C1q gene expression was studied by endogeneous labeling of newly synthesized proteins, immunoprecipitation, and sodiu m dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and b y reverse-transcription polymerase chain reaction (RT-PCR) of C1qB mes senger RNA (mRNA). Semiquantitative analysis was performed by Northern blotting of total RNA and hybridization with the radioactively labele d RT-PCR product. C1 esterase inhibitor synthesis was studied in paral lel. For comparison, C1q and C1-inhibitor synthesis were also investig ated in blood monocytes and peritoneal macrophages. C1q was weakly det ectable in sinusoidal cells of the normal liver, C1qB mRNA, as well as constitutive synthesis and secretion of C1q, was clearly detected in freshly isolated and cultured Kupffer cells from normal rat liver, In comparison, newly recruited ''inflammatory'' macrophages from damaged rat liver synthesized considerably lower amounts of the protein, simil ar to what was found in the monocyte-like macrophages of normal liver and in peritoneal macrophages. Monocyte C1qB mRNA was not detected eve n by RT-PCR, and remained undetectable during the time in culture, Sim ilar behavior was observed for C1-inhibitor synthesis, Treatment of th e cultures with interferon gamma (IFN-gamma) or lipopolysaccharide (LP S) strongly decreased, whereas treatment with dexamethasone strongly i ncreased C1q gene expression in the macrophage populations, and induce d C1qB mRNA in cultured monocytes, as revealed by RT-PCR, Kupffer cell s of normal liver may produce considerable amounts of C1q, whereas the inflammatory macrophages of the acutely damaged liver may not be so i mportant for the synthesis of C1q.